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David Brown 990 Selectamatic 3PH

M

mooboy

Member
I have purchased a 1971 David Brown 990 with loader. The loader works good so I have reason to believe the hydraulic pump is working. However, the 3 point hitch will not raise/lower. I know I need to change the hydraulic fluid because it is milky. I have new shifter boots to install to keep water out in the future. So I have a few questions:

1. Need to know what position to have all the switches and knobs in for 3PH to work. Previous owner said he thought that might be all that was wrong with it. I've, tried every combination I know of with no success.

2. Assuming a valve is stuck in the valve chest, where is the chest located and how do I get into it?

3. Have heard of flushing the transmission sump with diesel fuel to clean things out. Good idea or bad?

4. Should I change the fluid/filter before attempting working in the valve chest?

Any suggestions about order in which to troubleshoot would be greatly appreciated.
 
If your loader works fine, the 3 point probably wont as the valves will be set for exernal. The raise/ lower lever will be clipped right back into select and the selectamatic valve will be set in TCU/external. By your left heel will be a selector valve with 4 positions L (linkage) L/1 1 & 2. Early tractors had taps. It will most likley be set on 1 or 2 IF the loader supply is taken from that valve. Set the valve to L, the Selectamatic valve then has to be in Hieght (position) or Depth (draft) position on the dial to the rear of the main raise / lower lever. Pull the raise / lower lever on the quadrant right back against the spring in to select BEFORE and while you turn the selector dial to depth or hieght. Also IF the tractor is fitted with a dump valve just behind the main lever for raise / lower make sure it is DOWN.

IF the loader supply is taken from the selectamatic valve on your right, then you will most likley have a blocked By-pass or hold valve, these are to your right under an oval plate, you may have a dump valve fitted into the hold valve, or not, they were an option.. These valves can stick. they are capped by a scew plug (slotted for a screw driver) If they are stuck they can be got out by whittleing a piece of wood to knock into the valve and turning and pulling. One of the valves has a fine filter and from memory there is a small ball bearing in there as well. With the valves removed, turn the engine with the starter with the engine stop in STOP, this will flush them with oil and remove any rubbish in there, also disassemble the valves and clean out with Diesel fuel and blow through.

The main filter is underneath and there is also a magnetic filer in with it. If your oil is milky best to do that before looking at the By-pass and hold valves because any loose debris from the filter goes straight to them.
 
(quoted from post at 02:40:02 11/23/11)

IF the loader supply is taken from the selectamatic valve on your right, then you will most likley have a blocked By-pass or hold valve, these are to your right under an oval plate, you may have a dump valve fitted into the hold valve, or not, they were an option.. These valves can stick. they are capped by a scew plug (slotted for a screw driver) If they are stuck they can be got out by whittleing a piece of wood to knock into the valve and turning and pulling. One of the valves has a fine filter and from memory there is a small ball bearing in there as well. With the valves removed, turn the engine with the starter with the engine stop in STOP, this will flush them with oil and remove any rubbish in there, also disassemble the valves and clean out with Diesel fuel and blow through.
Click to expand...

Lots of good advice here. without knowing how the loader is plumbed it is anyone's guess of where exactly to look for the problem. 3/4 way valve, power through, remotes, many ways to do it. Pictures would help us.

I don't flush with diesel, it can be as hard to get out as water, it is nearly as expensive as oil. a 990 only holds 5-6 gallons of oil. a bucket of cheap hy-tran is $35 at TSC. 15-40 motor oil is best if you have a cheap source.

The valves in the selectamatic unit can stick so badly that the wooden stick trick will not work. I just did one on a 1494 that took a big hammer and a punch(while out on a workbench). There are 9 valves in the box most of which can stick in their bores, each will give different symptoms. Some polishing with 1500 paper and a good cleaning of debris is probably the worst case scenario.

It is a big job to pull the selectamatic valve box. Pull sensing unit, drop lower links, rockshaft, quadrant, parking brake handle, and lots of little fiddly bits. Cabbed tractors are much worse.
 
If you get into that valve systen under the kidney shaped cover, the one you stick a pencil into to get the valve out- clean around that really well first. It's an awkward area to work in and you don't need to put dirt in the system, and make SURE you have a small bucket or something to put your parts in. Don't just lay them out in the open, bad things happen, trust me!

That little screen can get plugged by a tiny bit of dirt and the lift won't work right.

You might also take a look at the the David Brown Tractor Club website, THey have a good forum and those guys know their stuff. Another thing to try and get is some of the DB shop manuals that cover the hydraulic system. I got a mess of stuff off the internet and a manual off Ebay that help an awful lot. The tractor itself is very well designed, but the Brits do things just a little different than we might. Once you get into to it it's rather simple but some of it is almost backwards of the way Case or Deere might do things.
 

Thanks for all replies. I will be changing the oil and filter soon, won't flush with diesel. I have attached some pictures. The loader is run off one of the remotes on the Cessna valve. I have to tie the Cessna valve handle in the forward position for the loader to work. I assume the Cessna valve needs to be in the neutral position for the 3PH to work? There is a 3 way valve, a quadrant, a rotating knob below quadrant on the right side. One the left side is a two position rotating knob. That is all I know about. So what position to a place the controls in for the 3PH to work?

4027.jpg

4028.jpg
 
Cessna/remote needs to be in the neutral/center for the 3pt to work.

You have a 3/4 way? It would be under your battery charger? If so it needs to be in the "L" position.

The knob on the front by your right heel just controls how fast the linkage drops.

Your selectamatic dial is currently in "height" which is fine unless you are plowing.


My money is on a stuck bypass or hold valve.
 
(quoted from post at 17:54:23 11/23/11) Cessna/remote needs to be in the neutral/center for the 3pt to work.

You have a 3/4 way? It would be under your battery charger? If so it needs to be in the "L" position.

The knob on the front by your right heel just controls how fast the linkage drops.

Your selectamatic dial is currently in "height" which is fine unless you are plowing.


My money is on a stuck bypass or hold valve.
Click to expand...

What is a 3/4 way valve and where do I look for it? When you say battery charger do you mean the generator? What is the two position rotating knob in the bottom picture?
 

Your 3 way valve would be behind your left ankle when seated, approximately under the battery charger in the last picture. These are uncommon here in the US, I have only seen them where there was a factory loader. It diverts the oil from the 3 point hitch ram to your loader, log splitter or anyplace else you need it, you use your quadrant to turn the flow off and on. Just one of the many "different" features of a Selectamatic.

The knob/lever in your last picture, on the left rockshaft housing it the latch lever. If you turn it counterclockwise 90 degrees it will lock the 3 point arms in the full up position. There is a cam built into the back of it that allows a pawl to mechanically lock the arms up.
 
Your 3 way valve would be behind your left ankle when seated, approximately under the battery charger in the last picture. These are uncommon here in the US, I have only seen them where there was a factory loader. It diverts the oil from the 3 point hitch ram to your loader, log splitter or anyplace else you need it, you use your quadrant to turn the flow off and on. Just one of the many "different" features of a Selectamatic.

The knob/lever in your last picture, on the left rockshaft housing it the latch lever. If you turn it counterclockwise 90 degrees it will lock the 3 point arms in the full up position. There is a cam built into the back of it that allows a pawl to mechanically lock the arms up.
 
Looks like I don't have a 3-way valve. Per the picture below, do I have a cover plate where the 3-way valve would be? What job does it do? It has a plug in one end of the cover plate and I wonder if pressurized fluid is behind it. If so could I tap there with an isolation valve to run the loader?

4051.jpg
 
(quoted from post at 09:47:38 11/25/11) Looks like I don't have a 3-way valve. Per the picture below, do I have a cover plate where the 3-way valve would be? What job does it do? It has a plug in one end of the cover plate and I wonder if pressurized fluid is behind it. If so could I tap there with an isolation valve to run the loader?

4051.jpg
Click to expand...

A 3 way would bolt up where that cover plate is. If you installed one, and got your 3 point hitch working, you could draw your loader hydraulics from there. A 3 way is a diversion/isolation type valve.

Fluid is only pressurized there when the 3 point hitch is trying to lift. The piston for the 3 pt is directly behind that cover.
 
Today I changed the transmission fluid. What came out looked like a vanilla milkshake. I did the best I could to get all the old fluid out of the loader cylinders too. I did not have a new paper element filer so I washed the old one out with kerosene and put it back in. The suction strainer is missing. Since I have never seen one of these strainers other than in the IT manual, was wondering if the center portion of the strainer is solid. Seems to me that is the only way the paper filter would do anything otherwise fluid goes right up the center of the paper filter into the pump suction tube without any filtration. Does that sound right?

It did not take long for the fluid to get milky again. It was not as bad as what I drained out. Guess it will take several flushes to get rid of the milky look. The loader operates more crisply. 3PH still does not work.
 
(quoted from post at 21:54:50 11/25/11) The suction strainer is missing. Since I have never seen one of these strainers other than in the IT manual, was wondering if the center portion of the strainer is solid. Seems to me that is the only way the paper filter would do anything otherwise fluid goes right up the center of the paper filter into the pump suction tube without any filtration. Does that sound right?
Click to expand...

The core of the strainer is a spring loaded valve that opens(bypasses) when the paper one gets plugged. In a perfectly operating system the yellow dash light will come on when it opens indicating the need for a filter change.

The part number for the filter you need is k920522, they are about $25 aftermarket. Without having the strainer/valve it would be wasted money.

The first place to look on your 3pt is under the cover behind your quadrant. 2 large Phillips head screws hold it down. Then 2 slotted head caps under that. The valves likely causing your issue are under these caps.
 
Soon I am going to take the kidney shaped cover off that is located behind the quadrant. When I remove the slotted covers, the valve innards aren't likely to spring out are they? Is there just two valves with the slotted covers? Does it matter which one I work on first and how do I tell them apart? I assume the stuck spool will have a hollow center that a wooden dowel could be driven into to extract it? How do you tell if it is stuck or not? Please excuse my ignorance, I've never seen beneath that cover.
 
(quoted from post at 21:00:47 11/27/11) Soon I am going to take the kidney shaped cover off that is located behind the quadrant. When I remove the slotted covers, the valve innards aren't likely to spring out are they? Is there just two valves with the slotted covers? Does it matter which one I work on first and how do I tell them apart? I assume the stuck spool will have a hollow center that a wooden dowel could be driven into to extract it? How do you tell if it is stuck or not? Please excuse my ignorance, I've never seen beneath that cover.
Click to expand...

The springs are directly behind the slotted caps. as you unscrew them you will release most of the spring tension. Just 2 caps there. Both are just over 3/8" ID, a 1/2" dowel with some taper is ideal. Doesn't matter which you check first. If it moves/comes out freely then it probably isn't your problem, and you can move on to the next one. Just do one at a time to avoid any unneeded confusion.

The only word of caution is be careful not to drop any of the parts down inside the housing.
 
I took off the cover but did not find any slotted caps. I have attached a picture. Is my tractor missing parts? The tractor is running in the picture and oil is coming out somewhere at the bottom left of the enclosure. I did not try to take anything apart since I did not see slotted caps.

4297.jpg
 
Wrong cover.

The one you want is about 2" across. has two #3 Phillips head screws holding it down.

It is on top, not on the back, about 8" forward of the cover you have off.
 
Okay, I found the valves and was able to get them out. I was careful not to loose anything when removing valves, but comparing what I removed vs. the picture in the IT manual, I am missing some parts. For instance, the hold valve is missing the ball retainer and ball. There was also a spring in the center of the hold valve plunger that the IT manual does not show. The IT manual shows that the bypass valve plunger is supposed to have two springs in it but there was only one, so I wonder if the one I found in the hold valve does not belong there. Am I on the right track?
 
(quoted from post at 21:30:03 12/04/11) Okay, I found the valves and was able to get them out. I was careful not to loose anything when removing valves, but comparing what I removed vs. the picture in the IT manual, I am missing some parts. For instance, the hold valve is missing the ball retainer and ball. There was also a spring in the center of the hold valve plunger that the IT manual does not show. The IT manual shows that the bypass valve plunger is supposed to have two springs in it but there was only one, so I wonder if the one I found in the hold valve does not belong there. Am I on the right track?
Click to expand...

I&T is frequently wrong. recently I used one of their schematics to replace the lines on a steering system, just to find that when I turned right, the wheels went left.

The 3 point valve seem to have evolve over time, and not all the valves have the same fillings. I have had several without the ball and retainer. They worked find.

The Hold and Bypass both have one spring each , equal in size. I suspect second one you see in the bypass picture is actually a set screw with a hole drilled in it. under which you will find a screen.

Did the hold and bypass valves move freely, or are they sticky in their bores? Any shiny spots on the outside where they have been rubbing?
 
Okay, I understand that IT manuals are not always correct and different year tractors had different valve internals. I did not find a ball and retainer in either valve. I did find an orifice plate in bypass valve and perhaps the remnants of a screen.

When removing the bypass valve, I thought I felt it break free when inserting the wooden stick. I used penetrating oil and it did not take long to get both valves out. Both valve cartridges have shiny wear spots and a few pits. Was planning to smooth the bores and cartridges by wet sanding. When done should I reassemble and try it? Or should i go to the dealer and see if I can get mesh filter, ball and retainer, etc.?
 
Polish the outsides of the valves lightly with some 1500 grit paper/emory. Yes 15 hundred. This is a steel on steel seal like you would have in an injector pump. I wouldn't try to do anything with the bores with the valve body still in the tractor, the grit you make has no where to go and will cause other problems.

Put back together with what parts you have. It should work OK.

The bypass being stuck explains the symptoms you have.
 
Finally got back to working on the DB 990. I did polish up the valve parts and reassembled. Now the 3PH slowly rises to fully raised position and position of quadrant lever has no effect. What is the fitting above cover on the left axle housing (picture below). I had to replace it with a grease fitting was getting fluid out of the original fitting was wondering if it was a failed bleed screw. Anyways fluid pressure is always behind it which I think explains why the 3PH raises whenever the tractor is running. What to try next?
4940.jpg
 
If it raises you are getting somewhere. Now to determine if the "full up" issue is mechanical in the linkage, or a hydraulic issue in one of the other Selectamatic valves.

Tractor running... Selectamatic in "height"(center position on dial)IF you push in the clutch fully after raising the arms, do the arms lower properly using the quadrant(it will be slow unless you have weight on them)? Is the engine sound different with the clutch in than clutch out(like a load on the engine with the clutch out?).



The fitting in question is a bleed screw in the plumbing that goes to the lift cylinder.
 
I didn't have two people present to help me do the test you requested. But when I get off the tractor when it is running and quadrant in the down position, I can make the lift arms lower when I stand on them. Also, the rate of lift arm rise is related to engine speed, faster engine making them rise faster. Hitch might not make it to fully raised position with engine idling.

Next chance I get will find a weight to hang on the hitch and do the test you requested.
 
(quoted from post at 22:57:56 01/01/12) the rate of lift arm rise is related to engine speed, faster engine making them rise faster.
Click to expand...

Rate of lift is always related to engine speed. You only have a 6 gallon pump at max RPMs. maybe 2 at idle.
 
The lift arms will raise even with the quadrant lever rotated fully forward. Mashing clutch in has no effect on sound of engine. Had my wife sit on the tractor and depress clutch pedal. I stood on lift arms and they would not lower. Engine was at part throttle for this test. What to try next? Thanks for your help with this problem RG.
 
It must be linkage. When the clutch is in you have disconnected power to the hydraulic pump.

The cover below the quadrant lever near where your right heel would be that has the rate of lowering knob on it....Take it off, just 4 screws. You will see a nut screwed onto a threaded rod that moves when you move the quadrant lever. How many threads are sticking out past the nut?
 
Maybe 6 or 7 threads are showing, see photograph below. One more thing, when the clutch is depressed the PTO will not engage without grinding. That may be unrelated to disengaging hydraulic pump?
5004.jpg
 

Back that nut off till 1 thread or so is showing. There is a procedure for setting this, but not that I can type out. if nothing is bent broken or missing, 1 thread will be close enough. I have set many of these and at most have 2 or 3 threads showing.

Your PTO/hydraulic clutch plate might be stuck to the flywheel, which will cause the grinding and be a symptom to diagnose around which doesn't stop the hydraulic pressure when the clutch is pushed in.
 
I did back the nut out till one thread was showing. It still does not work right. I can stand on the lift arms with tractor running and in neutral. Once engine reaches about half throttle lift arms will raise, does not matter what position quadrant lever is in (acts the same in all positions). If I reduce the engine to idle while standing on the lift arms they will go down. Anything else to try?
 
I got nothing else easy to look at. You need to get your hands on a service manual and go through it step by step.

The engine speed shouldn't have an effect on its function, just its speed.
 
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