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The Little A-Cs - Chapter 7

This book was written exclusively for Yesterday's Tractors Magazine. It is not published in any physical form but only available on this site. No part of this text may be used in any form other than as provided electronically from www.yesterdaystractors.com without express written consent of Yesterday's Tractors. Copyright 1996-1998.

View the table of contents.

7. Similarities and Differences

If you are like me, one of the most fascinating parts of owning and working on older tractors is to know the possible configurations within a given line and the interchangibility that comes with this knowledge. From a purist point of view, the only original tractor is a tractor that has the same castings and components that it left the factory with. For other restorers, it is sufficient to have the type of parts that came with the original but not necessarily the ones that were on it. For the majority, it is sufficient to have functional components that typify the tractor model. Of course there are always those that don't care about these issues and just want the machine to work. For them a 1975 Nissan muffler may just have the right fit and look. This section should provide a few items of interest for all of these folks.


The engine is the heart of any tractor and these are no exception. Looking at the horsepower to displacement numbers quickly tells you that the engine is not stressed even in the final form at 1650 RPM. This contributes to the fact that only in the last few years are they needing rebuilds. Even comparing the horsepower of similar tractors of the time shows a difference in the amount of horsepower exacted from similar sized engines. This engine could get by with this due to the relatively light weight of the machine and and long wheelbase for the weight. It could put more power on the ground by making better use of the engine and front end weight. Though major components are not interchangable, one sees similarities even in the later Power Crater versions used on the D-series.

The engine stayed basically the same from 1938 to 1957 with the bore and RPM changing the performance characteristics. Since the stroke and outside diameter of the sleeves remains constant through the series, the engine block is interchangable throughout this series as are most components such as the crankshaft, camshaft and rods. The exception is the 1937 since it was not manufactured by AC. Non-interchangable (either due to lack of originality or actual non-fitting) parts are as follows:

Engine Block - Certain B-125 stationary engines used a fuel pump. These blocks have the cutout required for mounting.  Though unnecessary to use the fuel pump on the tractor, certain stationary applications may require it rendering a non-fuel-pump block incompatible. From an original restoration standpoint, casting marks should be carefully analyzed when switching blocks.

Lifter Assembly & Valve Cover - There were 2 distinct versions produced that if replaced, require the replacement of both components. The difference is simply that the early valve cover bolts on with 2 nuts while the later cover bolts on with 4 nuts. The Lifter assembly must have the correct number of studs to match the valve cover.  Originality buffs will need to locate the 2 stud and nut cover and assembly for tractors from 1938 to 1942.  For restoration of machines beyond 1942, these components must be of the 4 stud and nut type.

Water Pump - later water pumps have an extra drilled & tapped plug that allowed hookup to the later D series (and non-diesel I Series). The later unit was provided originally on the CA and the late B but is non-original when used on 40s vintage machines (still it will work). The water pump gasket and shaft kits work on both.  True restorations on 1938 to mid-1950 must use the non-bypass version.

Thermostat Housing - Three different castings were made. The issue here is simply originality. The earliest unit is the tallest and does not hold a thermostat. The latest unit has bypass line that can connect to the water pump via a hose and fitting. If an early water pump is used in conjunction with this housing, the hose fitting hole must be plugged. The most common housing is the medium sized housing with out the bypass hole/plug.

Oil Sump Pickup - Early versions used a tubular screen in the bottom of the oil pan. Later models used a round pickup as seen in most 50s and 60s automobiles. The early version was thin cast metal and is frequently  unsalvagable. The round version is a 3rd party component and may be located on other American engines of the time.

Governor - Both shaft and weights were produced in 3 incarnations. It is safest to purchase the assembly when replacing.

Exhaust Manifold & Muffler - Three exhaust manifold configurations were manufactured causing minor difficulties when installing a new muffler. Additionally, if the tractor is set up for running on "tractor fuel" (a form of stove oil), the more common manifold will not allow the preheating of the intake tract as is necessary for combustion. The configurations are identified by the presence or absence of the heating chamber covering the intake tract. When the sheet metal shield is placed over this type of manifold, the intake is sufficiently heated to allow proper combustion of the low octane fuels. Without the heat shield this manifold operates normally as a gas manifold. This manifold has a single mounting point for the muffler and thus is predominantly used with the underhood muffler or straight pipe. The other two manifolds are gas only with the only difference being that the earlier version has a single muffler mount point and the later version has two mounting holes. The upright pipe of the 1951 and later machines required the two bolt configuration to hold the muffler. The upright pipe can still be used on earlier versions by using a straight pipe through the hood and clamping a correct diameter upright above the hood. In this case, one would not use the original equipment style upright pipe.

The engine blocks have many various numbers cast in them depending on the year (aside from the stamped engine number and AM part number). A 1943 vintage machine has the manufacture date cast while examination of other years failed to find this. This date was located toward the right front underneath where the manifold bolts on.


The CA is the unusual machine in the transmission area. It was equipped with a large 4 speed which shared many of its components with the later D Series tractors rather than the 3 speed-equipped Bs and Cs. Bs, Cs, and IBs share all components of the transmission but when you are salvaging parts remember to always replace gears in pairs to keep the transmission quiet and to insure that you aren't hit by a production change. The clutch-to-transmission shaft did undergo a production change from a normal U-joint style connection to a less expensive collar & pin arrangement. We presume that this was done to reduce cost and simplify repairs (the collar would never need repairs). This did not effect the transmission shaft itself. 

Final Drives

The final drives of the B & IB were identical using the same gear ratios, bearings, seals and shafts. The differences were as follows. The IB's were rotated forward to lower and shorten the machine. The C's case was cast wider (due to the 2 row goal) to accomodate the longer pinion axle, and the lower axle used a more standard inner hub assembly with lug bolts rather than the single bolt used to attach the B and IB hub. Lastly there were 4 different bull-to-pinion gear ratios with one of the higher ratios being the most common. The lowest ratios were provided during the early production where steel wheels were optional and standard (during World War II).

The finals on the CA were altogether different. Rather than being perfectly vertical like the others, the power was transmitted at an angle rearward similar to the D-series. The finals are larger and heavier in general. The right final had a clutch in the middle of the pinion axle to allow the driver to stop forward motion without effecting the use of the PTO. To explain it is just as if your car broke an axle on one side causing both wheels to stop turning due to the differential turning the side with the least resistance (ie the broken one). This was a simple and effective method of implementing live pto without a complete redesign to the power train. When coupled with the 4 speed transmission, the low bull-to-pinion ratio provided a greater speed range on both ends.

From the differential, pinion shafts were use to transfer power to the outboard pinion and bull gear arrangement. The pinion shaft had an oil tube surrounding it. I have yet to find one intact when opening the finals. The bearings at the differential and pinion gear have shims that allow restoration of the original factory clearance. These shims are removed to take up slack induced by wear. This can eliminate the noise so commonly heard eminating from the rear end while underway.

The rear bearings and seals remained the same thoughout all the models and are readily
available off-the-shelf components.

Rims, Wheels & Eccentrics

The rims of the B, C, & IB were similar though the early production B used a 7 inch rim and the clamps used a larger diameter eccentric bolt,  a different eccentric body, and the rims had a section of angle iron welded on to fit into the eccentric body. This made the Hub, rim and eccentrics incompatible. These were used into 1940. The later B, the C, and the IB employed eccentrics that would press out on a rise that extended inward around the rim. Some rims had this rise in only 4 position while most had it around its entire inner diameter. Retrofitted rims were used by owners that were similer to the Cub, MH Pony, MH Pacer, and several orphan brands like the Earthmaster. These rims had 4 square loops and matched up to the bolt holes on any of the hubs. These would never be original equipment but from a working standpoint are excellent.  AC offered 4 different widths for the standard 24 inch wheels including 7, 8, 9, and 10 inch. There were unusual diameter rims offered for 2 rare variants (the Asparagus and the "28 inch tractor"). These are seldom seen and have no aftermarket manufacturer sources. The Asparagus used a 38 inch rim implemented by steel brackets welded to the rim that joined up to the bolt holes normally used for the clamps. The last rear configuration was the steel wheel models that were common during Wartime production. There were different wheels for the B and C that closely resembled the wheels used on the rubber tired version. Rubber tire retrofits have long since made these quite rare.

For those unfamiliar with eccentrics on tractor rims. The eccentric was a bolt that had a non-concentric surface that allowed it to tighten as it was turned. In other words, you could slip the rim on easily while the flat side was outward, then when the bolt was rotated to the inside, the hub would be locked against the rim. The IB, B, and C used 2 eccentrics on each wheel and 2
standard bolts and clamps. The CA had 4 eccentrics to lock it down.

Three different wheel to hub assemblies are found are found on the B, IB, and C. The most common are a near flat single bolt wheel on the B and a conical lugged wheel on the C. The third was very nearly a composite of the 2 and is more unusual. It had the appearance of the single bolt style but the wheel was held on with lug bolts. The lug nut adaptor bolted to the standard single bolt axle. It was produced to allow a slight increase in width for the B by being able to turn the wheel around at the hub.  The Conical wheel used on the C is also found on some late production Bs and british versions. This wheel allowed a wide 3 1/2 inches of wheel spacing adjustibility.

The CA used a 24" power adjust wheel (PAW). This was an AC original but was copied on many other brands from then on. The PAW had spiral rails welded to the rim. The eccentrics put pressure on these rails when in operation. When adjustment was needed, the eccentrics were loosened allowing the rim to spin freely on the eccentrics. The engine was then used to turn the inner wheel (by turning the axles with 1st or reverse depending on the direction desired) on the rails which in turn would pull the tire and rim in or out. Due to the 24" size, the PAW rims are difficult to find and expensive when you do. Most PAWs manufactured today are 28" and will not fit on the CA. The wheels, eccentrics, and rims on the D-series look identical but are 26 inch and will not interchange.

Steering & Front Wheels

Steering differences were pronounced between all models and years. Redesigns and production changes provided 6 different models from 2 different manufacturers. Generally the compatibility is found between the C and CA and the B and IB. The C and CA used a front and rear steering gear which reversed the direction that the rear steering gear needed to go for left and right. The drag link on the C and CA connected to the gears built into the front pedestal and radiator support. Thus the C and CA had a heavy cast pedestal and radiator support. This allowed the use of both dual and single wheel tricycle configurations in addition to the standard adjustable wide front. No fixed width wide front was ever manufactured for these units. The areas where incompatibilities appear for these models are the early C models where a short rear steering arm and compensating drag link were used and the late production CAs where a different torque tube was used. The late CAs have different external mounting brackets for stabilizing the rear steering gear arm. The front pedestal on the CA is interchangable with the C but holes must be cut in the grill for the cultivator mounting bosses.

The B had three different configurations of adjustable wide fronts and the fixed width arched axle. The fixed width axle is by far the most common with the square-tube-stock adjustable being the next most common. Few examples remain of the other adjustable configuration as production ended in 1939, but they were arched with adjustment being provide at the spindle as opposed to the normal method where a portion of the axle beam adjusts. The rear steering arm is aimed down on the B and connects to the drag link via a ball socket. The C and CA used a nut and bushing to connect the drag link with their ball & socket being a part of the drag link.  The B axles had the steering arm directly connected to the front left spindle and a tie rod to turn the right wheel. The front also used a cast ball as an integral part of the front steering arm. Generally these differences make the B steering completely incompatible with the C and CA.

Due to the lowered nature of the IB, it had a fixed width but narrow front axle beam and very short spindle tubes. The steering gear is compatible with the B but many other steering components will not interchange.

Steering wheels, shafts, and tubes are interchangable across the line with the exception of the IB. It uses a short tube and shaft that is mounted at a more radical angle. This was to compensate for the shortening of the Torque Tube. When locating a replacement steering wheel, the MH Pony and Pacer used the same 3rd party produced wheel. This was manufactured by Sheller.

Five front rim configurations were found on these tractors. The most common were the 5 lug integral wheel and rim. These are commonly available even today from aftermarket sources. They mount to the bearing-carrying hub that bolts to the front spindle axle. These were used on most B, IB, C, CA, and all dual wheel tricycle models. The single wheel tricycle version is rare and non-interchangable with any of the other models. It mounts by a single axle that extends out both sides of the wheel and hub bolting to the forks extending down from the pedestal.

The remainder of the rim configurations use the single bolt mounting directly to the spindle axle shaft. The predominant wheel in this category is the 2 piece wheel and rim that uses clamps to hold the 2 together. The others were the steel wheel version and an unusual integral rim, wheel and hub that did not use lug bolts.

Torque Tube

The torque tube had many variants. The B had 4 configurations that included the version with the starter boss, the one without, and the industrial which was shorter and had a starter boss, and the final configuration that matched the CA. This tube was probably used to allow mounting of late CA midmount implements and simplify the parts inventory. The short tube became the IB component when it was seperated from the B serial number series. The C had additional bosses added to hold the steering arm support bracket. The CA added again more threaded bosses for implement mounting.

Sheet Metal


The grills came in 5 styles plus a chaff screen applique which could be placed over the normal expanded metal to further protect the radiator from straw and chaff. The 37 B looked the same as the rest but used different mounting holes and was reinforced to make up for the fact that it did not use as heavy a mounting bracket. The mounts for the 37 were different as a result of the different engine, the later AC engine used front mounts on the vertical face of the engine while the earlier engine had its mounting bolts on the lower horizontal face. The B and IB retained the grill appearance even though they were a different item. These grills completely encompassed the bottom of the radiator support due to the fact that no steering components were involved. With the advent of the Cs front cast housing and integral steering gear, came the need to have a significant cutout on the left lower portion of the grills side. The CA was identical to the C grill but had 2 additional holes cut in front to allow access to the new cultivator mounting holes that were cast in that machines radiator support. In general, these 4 variants must be considered non-interchangable though their appearance is identical to the casual observer. The last grill was used on auxiliary power unit applications such as balers and combines where straw and chaff could clog the radiator. These units had tight screening plus Frequently the primary grill screen is damaged beyond use. This can be replaced by using 1/2 x 1/4 expanded / extruded metal cut to the appropriate size and wire feed welded in place.


The hoods had minor variations due to muffler options and fuel type. The 4 possible muffler/exhaust pipe options account for the size of the hole used to allow the protrusion. The CA and late B had a larger hole that allowed the smaller diameter upright pipe to fit directly on to the manifold. If a larger diameter muffler is used the hole must be widened or an extension pipe used to bridge between the manifold and the muffler.  The most common hood uses a small hole to allow exit of the straight pipe or the output of the underhood muffler. 

The dual fuel models had additional holes cut for the mounting studs and fill hole of the gasoline (starting fuel) tank.  These were placed on the right side of the hood.

The B-125 and 60H stationary versions of the BE, CE, and CR engines had a hood that will work on the tractor version with one exception. There was an extra hole at the rear of the hood to accomodate the stationary versions gas tank filler cap. This should be filled with a sheet metal plate to restore originality.

The 37 B had the exhaust manifold on the opposite side.

Tool Box

The Tool box provides the support for the tank and covers the steering tube and rear gearbox. It is known as a tool box due to the door on the side that allows access to the unused space it provides. While all machines had the Tool box, there were differences due to the electrical option, model, and the  tank mounting. 

(The original 1937 B and later non-electric starting Bs and Cs had a tool box that extended to the steering post. The 1937 had rubber strips that covered the sheet metal edges and eliminated any vibration. This was dropped on the 1938 and above. Early B and C tool boxes provided the bolt holes to line up to tank mounts on the bottom rear of the tank. This was changed on the later models by using a strap from the top rear of the tank that connected to an angle iron welded to the rear face of the tool box. While either can be adapted to the other, it would be difficult and dangerous to adapt the new tool box to the older tank (it would require welding the strap on the tank and likely killing oneself). If the older tank is used, you must use the older mounting method.

The non-electric start Bs and Cs had a clip to hold the starting crank when not in use.

The electric start models (B, C, and all CAs) had the rear portion of the tool box cut off to make room for the battery box but were otherwise identical. These shortened versions were made for both the older and newer tank style.

The IB Tool box is smaller and does not have the door due to its reduced torque tube length. .

Battery Box

The battery box underwent few changes during the years. The lid was removable after which  one side would come off allowing complete accessibility to the battery.  On the IB there was insufficient room for the battery box in its normal position due to the shortened torque tube. As a result, the mounting was moved to the side to allow it to bolt to the wheel guard mounting plate.

Wood insulators were used on the top and the bottom of the battery with top insulator containing 3 holes for the battery caps. On the IB an extra wood block was inserted in the side to shim the battery due to the boxes slightly larger width. 

Reasonably good reproductions are available new from a couple of different suppliers. The sheet metal is thinner but not to the level of other replacement boxes such as those made for the Farmall Cub.

Instrument & Control Box

The instrumentation is pretty austere. Immediately viewable from the drivers seat is the Ammeter. The box that holds it also contains the magneto kill switch or ignition switch, depending on which type of spark generator the machine has, and the light and charge level switch if the machine was equipped with electrics. The CA had an additional oil gauge to allow monitoring of the draft control known as the power booster. This gauge would should how much hydraulic oil pressure was being applied to your implement lift arms. Since the control box had no room for more gauges, this one was attached to the upper surface of the steering shaft cover tube. Also left out of the instrument box was the oil pressure gauge which was mounted directly to the oil filter bracket. Viewing this gauge while running requires a good lean out the the right, not something you want to do in when working in an orchard but normally easy enough.


The tank was formed from 2 pieces of pressed steel. See the discussion under Tool box to find information about the rear mount. The front mount was simply a casting that allowed the tank to sit atop it with holes to accomodate the bolting down of a strap that would hold it, the hood, and the woven padding snugly in place.

The gas cap was very unique and should be preserved if possible. No reproduction is presently manufactured. It has a relatively flat metal cover and a "wing" that protrudes rearward to allow the use of the thumb when removing it. This same style cap was employed on the radiator.

Wheel Guards (fenders)

The fenders on most tractors of this era were called wheel guards rather than fenders. I would suppose this is due to the fact that they did not completely cover the tops of the tire and were rather a piece of sheet metal seperating the operator from the tire.  Most people call them fenders today anyway. 

There were three styles used.  The B and CA both used a guard that folds out at the top by about three inches from the vertical surface at the bottom.  The C fender was more upright, with the top surface protruding only about an inch. This guard was probably an attempt to avoid the tire rubbing when set to the narrowest width (the wheel cone turned inward and the rim bolted to the inside).  C guards are more difficult to locate and should be preserved if possible. The B fender will fit due to the seat mount and angle stock used to hold it on being the same on both. The later B and CA guards had a hole for light mounting and even optionally used the mid-50s bullet style AC light with red bezel. These are beautiful lights and if appropriate for the model are a crowning touch atop the right guard.

The IB used the same fenders that employed on the styled WC and WD. These are large fenders for the little IB and look like complete surround-style fenders on the small 24 inch tires. When used on the 28 inch tires of the WC and WD they were more like guards.

Operator Platform

The B and C had no operator platform per se. One of the great difficulties of these machines is getting on and off.  One places a foot on the tube stock that mounts the fender, seat and hitch angle iron mount, and steps up. Then a quick contortion allows a spin and slide into the seat (which is fortunately wide) while clearing the steering wheel with the right foot. The IB is the same but has floor boards and is closer to the ground which make it a bit easier.  Also, stepping on from the back is possible and preferable with the IB.

When the CA was released it had a bonafide platform in back. While not a place to stand while operating (none of these are stand-up-and-drive tractors), it is a help when getting on. The platform is of heavy sheet metal and finally make these machines look "finished" due to its covering the skeletal appearance of the rear end.  It does complicate some maintenance by requiring its removal for access to certain bolts and nuts.


As expected, the electrical system is quite simple. Tractors of that time period had no cabs thus had no options for heat and radio, even a horn would have been considered superfluous. Many farmers felt that even a starter or lights were gimicks and gadgets for a tractor.  Even nowadays, I appreciate the simplicity and low maintenance of the crank starter.  It is usually much easier to start an impulse-coupler equipped magneto tractor after sitting all winter than to get the battery back in shape and use the electric starter.

The most basic option was the non-electric which simply had the magneto and a kill switch. The kill switch would ground the magneto and stop spark generation (rewiring this one is easy). The electric starter and light options increased the complexity but were still trivial when compared to todays Chevrolet that has no less than 2 miles of wire snaking through every nook and cranny (and requires Mr Goodwrench to figure it all out). 

The magneto systems were equipped with an impulse-coupler which would wind as you slowly crank and fire a significantly hotter spark at low RPM. When I first began in the tractor business, I assumed that crank starting involved "spinning" the engine to cause it to fire similar to a Fordson or Model T. I had no idea that this little invention would allow you to slowly move the engine an 1/8th of a turn and have it spring to life.  You can pretty much determine if your impulse coupler is functional by an audible click every half turn of the crank. The impulse coupler is buried inside the Fairbanks Morse FMJ magneto or Wico X.  Though I have never tried it, the FMX magneto is reported to work for this series of tractor. 

Beginning in the 1950s the magneto was replaced on the B and CA with a normal battery ignition. Gone were the days of easy springtime crank starts and simplicity. This system used a Delco-Remy distributor, coil and different distributor drive than the magneto systems. The coil bolts to the rear of the distributor drive housing.  Obviously, the battery became an integral part of this system and some charge would be needed for the machine to start (short of pulling the tractor around with your car to start it).

All electrics-equipped units were shipped as 6 volt positive ground, that is to say, the positive battery pole is connected to ground and the negative pole was snaked through the tool box to the starter.  The tube that supports the steering column was the place where the ground wire was to connect to the tractor. Since most people are familiar with negative ground battery hookups,  most machines have been switched to negative ground. Though it is not difficult, there are a couple of items to think of when making the switch back. This is covered in Chapter 9 as is the general requirements for switching to 12 volt.

Until the last few years of production the generator was a 3 brush with cutout relay. The charging was controlled by the operator with the use of the 3 position light switch. The first position is just above a trickle charge. The second position would raise charging to 2 to 3 amps and the lights were turned on. The third position would bump up the charging amperage over 12 amps and turned the lights off.  Due to the constant high-charge characteristic of the third position, running for long periods of time in the third position, would result in overcharging and damage to the battery.  These generators were made by both Delco-Remy and Autolite throughout the production. They are easy to rebuild or replace as rebuilts are common. 

The non-third brush generator used on late production machines (B and CA) employed a standard regulator similar to what you find on any 50s vintage automobile. Charging was then automatically controlled on a demand basis. These were Delco-Remy units.

Starter motors used were compatible throughout the series with the exception of the stationary engines. These used a slightly different housing for the starter drive. The drive housing is the correct length but has the lock hole drilled at a different position making it impossible to keep the starter in place. When the cast housing is swapped with your original, the stationary engine starter may also be used. 

The correct starter switch must be used when changing from an Autolite to a Delco-Remy starter and vice versa. These are non-interchangable due to the width of the starter mounting screw holes. The Delco-Remy piece is readily available from most tractor parts dealers. The Autolite part is still available through Agco-Allis.

The common headlight used was a round back 5 inch Guide Tractor Light. These are non-sealed beam lights using a bulb and seperate bezel.  A direct replacement for this light assembly is not available though 4 1/2 inch round backs do work. The replacements have too shallow a rear shell to look completely original. Originals may be obtained in salvage yards off the WC, WD, and most letter series Farmalls (A, B, C, H, and M). Late production models may have had the pointed shell as introduced on the D-14 and D-17 in 1957. These are also available on many of the letter series Farmalls and the Cub.

The rear road light used was a non-descript round light that mounted under the seat at an angle facing downward. The rear lens was clear allowing it to double as a work light while the top rim had an opening and red lens to serve as a safety road light. The  black bullet style light used in late production was very unique and difficult to replace. This light mounted on the right rear wheel guard.  The red bezel for this light is still available but the housings are not.  The IB had a small bullet style light similar to the running lights found as side markers on trailers and flatbed trucks. The appearance is very close to those sold today by auto parts stores.

On many stationary and auxuilary engine versions, an oil pressure switch and water temperature switch system was integrated with the magneto grounding switch to allow automatic shutdown if engine oil pressure was lost or water temperature exceeded normal.  This switch was dropped in later production. If your tractor does have this system, it is likely that a previous owner used a B-125 stationary engine for parts. 


The non-hydraulic B and C drawbars were simplistic cast bars that connected either to the front side of the final drive housings facing forward or the rear side of the final drive housing facing rearward. The drawbar had several seven holes to allow pulling from not only the centerline but offset to the left or right.  An triangular extention plate was available to bolt onto the drawbar to provide the ASAE mandated distance from the PTO shaft. This allow standardized hook up when using the PTO with 3rd party manufactured implements requiring driveshafts such as manure spreaders.  The B and C used different width drawbars to allow for the fact that the final drives were farther apart on the C.  A limited-swing swinging drawbar was available for the B and C that bolted to the standard drawbar.

Late production Bs, could be fitted with a snap coupler bell. When so equipped, different mounting brackets and a different drawbar were employed.  I have no information on this system nor examples to document.  When so equipped, the snap coupler would allow for easier hitching and compatibility with the many CA implements but would not provide the benefits of the CA Power Booster draft control. 

The CA fixed drawbar came in 2 varieties depending on whether the machine was equipped with the snap coupler bell or not.  The early non-snap coupler versions connected to the hitch mounting bracket that bolted to the bottom of the transmission and differential castings. This used additional support brackets that connected to the final drive housings and seat mount angle iron brackets. This stout arrangement was replaced when the snap-coupler bell was added to the tractor with an arrangment that was similar to that used on the WD, WD-45 and later D-14 drawbar. These employed an boxed extension that bolted on to the rear differential case. The actual drawbar hooked in to the snap coupler bell and rested on the above mentioned bracket. This arrangement was much simpler to remove when switching back to the normal snap coupler  hitching.

The IB used a plate with brackets that connected to the fender mounts. The plate had a cast assembly bolted to it with a movable hook to accept a pintle style hitch on a trailer. The hook could be opened by pulling a rope.

Power Take Off

Not all machines were equipped with a PTO rear case. The hydraulics were dependant on having the PTO case due to the location of the cam drive shaft being located in that case. As a result non-PTO machines could not have hydraulics. On machines without PTO, a sheet metal cover was bolted to the rear of the differential case. Most IBs were shipped in this manner due to the lack of need for PTO on industrial machines though when hydraulics were required the machine would have PTO.  Machines without PTO can be converted easily by bolting on a unit from a salvage yard.  Though the CA could be ordered without hydraulics, the PTO case was standard equipment.

PTO equipped systems were initially sold with 1 1/8 inch shafts as was the norm until the early 50s. The early B could be shipped with a PTO shaft that did not have the cams necessary to drive the hydraulics until 1940. After this time, the 1 1/8 shaft had the cam drive.  The 1 1/8 shaft was replaced with a 1 3/8s shaft on the CA and B in the early 50s. The CA shaft used 4 cams versus the 2 needed for the other models piston pump. These shafts are not directly interchangable.

Early non-hydraulic B and C PTO cases were a different casting from the hydraulic version. The later non-hydraulic versions had a plate to cover the hole where the pump would have gone. The CA case used a similar plate. CA PTO cases were non-interchangable with B and C styles though are shared with the early D-10 and D-12 cases. 

The belt pulley shaft housing was integral with the PTO case exiting at a right angle on the left side of the case.  The early belt pulleys were cast iron while the later units, starting in 1939, were of pressed steel.  The cast iron pulley is a valuable and sought-after component.

There were two types of safety PTO covers provided. The early machines had a tube that could be bolted on to the PTO seal plate that completely covered the shaft when not in use. I have never seen one of these, presumably because once removed, it was difficult enough to put on that it would never be used again. The later cover remained in place without interference of belt or shaft and had the ASAE specified shaft cover mounting cut-out. This was essential a large right angle plate with a hole cut for the PTO shaft and holes to mount on the PTO seal plate.


All hydraulic pumps used on this series were of the high pressure piston pump variety with matching one-way high pressure rams.  While these pumps were more complex than the vane and gear pumps used on many other machines, the piston style pump was far more reliable and long lasting than the other pumps. This is graphically illustrated on the Ford NAA where prior to the end of the production year the vane pump was switched to a piston pump and the dealer notes are insistent that maintenance on the pump requires replacement with the piston model.  Since the piston pump is more expensive to build this must say something about piston pumps.  The switch to gear pumps was only expedited by the move to low pressure systems and the fact that it was much cheaper to replace.  Though there are more components to the piston pump they are not difficult to work on and most of the time a small amount of effort will restore these to functioning condition without replacement of any components. 

Function of the pump began by engaging (pulling up) the rod that actuated the PTO.  The PTO shaft had cams to push the pumps in and out generating flow, spring loaded ball valves allowed one way flow, and a shaft that directed the flow turned to open and close various orifaces thus determining which valves would be activated. A final relief valve was provided to allow pop-off when pressure reached a predetermined point. The predetermined point was determined by the distance the relief valve was pressed into the casing.  Pretty simple huh?  On the CA, adjustment of the valves was controllable by screw in and out controls changing the speed of rise and fall. The B and C pump had only a hold position control.

As mentioned earlier, the CA employed a larger pump and in fact the same unit that was used on the WD. This pump had four pistons versus the two used on the B, C and IB. Though most parts for these pumps are not available, they are seldom needed and if the salvage yard cannot provide help, rebuilts are available.

The B and C could be equipped with one or two small rams. If the two ram version was provided a three-way switch was mounted under the right side of the seat rails that allow the independant actuation of right, left, or both rams. When used with the switch, the hoses are connected to the top outlet of the pump. If the tractor was equipped with a single ram, the side oriface of the pump is connected and the pump actuation control is the only control used. The CA and late B used a larger diameter ram with a longer throw. All rams were single acting meaning that they were pressured up and gravity combined with release of a valve would push the fluid back into the PTO oil sump thus lowering the implement or load.

Since these are high pressure rams, they are not replaceable with the common low-pressure rams found nowadays. Rams that would be appropriate for custom applications would be found on the WD, WD-45, AC remotes, and any loader rams up to the AC #14 and #17 loaders. Care must be taken when employing large volume rams since the PTO case will be drained when attempting to fill these. Hooking up a seperate sump is difficult to say the least when the pump is integral to the case as it is with these tractors.

The CA was equipped with a draft control system known as the Power Booster. It had the capability of adding a portion of the weight of a mounted implement to rear end of the tractor at times when wheel spin was eminent.  The system would sense the extent of pull rearwards of the implement. When it reached a preset (adjustable for conditions) pull, the rams would actuate lifting the implement. The greater the pull the more the rams would lift providing better traction. When pull lessened, as would occur when soil condition changed, the rams would begin to lessen the lift.  The result was that the tractor would adapt to the various conditions found in a field and improve time and fuel consumption (needless to say eliminate the continuous need to watch your plow and adjust it). 

The CA also had a transport valve which allowed plug-in hookup of a remote implement ram. An example of the use of such a ram would be to control rear wheels on a disc when transporting or turning at the headland.  This would allow the CA to work a high-capacity implement than could normally be mounted.


The B and C used a bench seat that many considered to be the first consideration ever provided to comfort for the farmer.  The 28" x 15" x 6" (the 6 is assumed as I have never found an original in good enough shape to measure) foam and spring pad was quite luxurious even by todays standards.  The frame for this seat was different depending on whether the tractor was equipped with foot brakes or not. The frame on the hand brake version was constructed simply of 1 1/2 inch angle iron while the foot brake version used a 4 1/2 inch tall side plate.  The seat back was attached to 2 rounded bar stock pieces that bolted under the seat.  On the 1937 and some 1938 units, the back was wooden while most of the machines used a pressed steel back.

The IB had a standard pan seat with spring steel backrest commonly seen on the WC and WF.  This was mounted on a frame surrounding the transmission and differential case. Of the 2 models made, the most common was the later unit using wrapped spring steel cantilevered rearward.  The early version had a coil spring directly under the seat.

The CA seat was a large pan similar to those found on the WD and later D series only slightly narrower. This seat was supported by a shock absorber system as had become the norm with other manufacturers for some years.  The shock absorber connected to the PTO case.  This arrangement was continued into the D-series (D-10 and D-12) machines.


As an option, the B, C, and IB could be equipped foot brake controls. These were located on  the right. They could be used individually or together. Brake locks were provided that used an eccentric plate that could be flipped into position when the brakes were depressed.  The CA was similar.

The clutch was located on the left and had curious bar that allowed the clutch to be placed in the disengaged position for starting.  You depress the clutch and flip the bar which lodges against the forward wheel guard mount. This reduces drag on the engine for easy starting.

The PTO engagement lever is located to the right of the transmission case. In the down position it is disengaged.  When pulled up, the PTO, Belt Pulley and hydraulic pump are all engaged.

The hydraulic control is located under the seat to right. It is active once the PTO is engaged. In the forward position, implements are down and fluid freely returns to the PTO case.  When pulled all the way up, the fluid is permitted to pass to the rams and the implement lifts. When released, it is spring loaded to return to the middle or hold position.

The shift lever is self-explanatory.  No shift ball was provided when these machines were originally sold but the shift ball available through Agco Allis for the D-14 is a perfect fit. For those using the tractor as a work machine, this is a welcome upgrade and can even pop on and off without damage for shows.

Prev Page  Table of Contents   Next Page
1. Introduction
2. What are they?
3. History in Brief
4. Competing Tractors
5. Appearance
6. Identifying Numbers
7. Similarities and Differences
8. Cosmetics: What did they really look like?
9. Tips, Tricks and Maintenance
10. Using the Little Allis'
11. Tune-up Data, Quantities, and Specifications

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