140 farmall year 1968 starter turns engine very slow

Replaced battery cleaned all ground terminals nothing changed

A starter can have bad bushings that cause the moving parts to drag on the stationary parts. Battery cables can be corroded internally. Engines can be
partially stuck, or difficult to turn. Ground terminals are 50% of the circuit. The leads to the starter switch, and those connections are also in the
circuit, and must be clean. Slow turning is going to make heat.
My first option would be to pull start it. (only if you and your helper are experienced, and know how to be safe. The tractor must be able to be
rolled in neutral, and stopped with the brakes. It also must be able to be rolled with it in any gear and the clutch pushed down.
If it runs, I would check for non ground side connections. Then if still slow, I would remove the starter and have it checked. If the battery cables
are made with copper the size of a standard round pencil or thicker, they should be OK, if less, they are too small. 2-O gauge is correct. Jim

Adding to Jim's advice to isolate the problem:

Crank the engine for 5 - 10 seconds. Then IMMEDIATELY feel the starter cables and switch looking for rise in temperature. Pay particular attention to the ground connection, the battery clamps and the cables under the insulation near the clamps/terminals - corrosion may hidden beneath the insulation. Any noticable warmth indicates high resistance and that the cable should be replaced

If cables remain cool then the problem then suspect the starter itself (dragging, bad brushes/commutator/field winding) or a stiff engine.

On the Super A - its predecessor - I've had to file the slots in the rocker switch to get better contact between the rocker point and the copper button on the outside of the starter housing. Those two surfaces inside the rocker housing should be as clean and non-pitted as possible. I don't think its possible to check condition from the outside. Must disassemble.

Hello Cedward welcome to YT! No offense to Matt but what he proposed about the contact button etc. likely
does not apply to your tractor. Being a 1968 I believe your tractor is a 12 volt system and the parts book I have
linked references Tractor serial number 26801 and later being so equipped. The 6 volt system Matt is referring
to uses a rod to activate a mechanical switch on the starter. I am pretty certain your tractor uses a solenoid
switch power to the starter. If your starter is the type shown in the link you can easily check the condition of the
brushes. There are 2 long bolts that hold the back bearing plate no. 1 on the starter. Make a small mark with a
marker on the side of the round starter case near the top bolt. Remove the bolts, carefully slide the end plate
away from the starter case. If it seems to bind and is connected to the starter with wires you will have to stop
and reassemble the starter because it is a different style. If it slides right off be careful there may be a washer in
there on the shaft don’t lose it. Check the bushing in the end plate for excess wear or extreme lack of lubrication.
With the bearing plate off you will be able to see the 4 brushes ..no. 5.. in the diagram. They are dark brown with
a copper tint. The screw heads that hold them on should have at least an 1/8” of space between them and the
commutator surface of the armature they contact. As they wear they get closer and eventually hit the
commutator making the brush lose contact. If that looks good put a dab ..size or 2 BBs..of chassis grease in the
end plate bushing and reassemble. Unfortunately doing this does not check the drive end bushing of the starter.
Good luck! I am going to add the parts diagram can be a little fuzzy but if you click it, it will open clearer as a
picture, also the brush locations are not shown real clearly.
Farmall 140 starter diagram

(quoted from post at 06:49:10 08/29/20) Replaced battery cleaned all ground terminals nothing changed

Click to expand...

You only cleaned half of the connections, then.

Do your battery cables have those repair terminals on them? If so disassemble those too, cut the cable, strip fresh copper, and reinstall. OR replace the cables entirely.

Just a word of caution: I touched a loose battery connection after cranking and it was HOT HOT HOT! I found the problem, but it was painful. Big blister on right hand. So be careful. Dave