Bobcat 743B Left Reverse Drive Problem

[TBP]

Hi,
I have a drive issue with a Bobcat 743B with over 5000 hrs.
The issue is there is not much drive on the left stick in reverse.
On soft ground on occasions the left wheels will kick in and drive especially if I return the right stick to neutral.
Also it will skid steer right with more power than left.
Not sure what to check or look at I'm new to Bobcats and there drive system.
Thanks

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[SSdoxie]

There is a combination high pressure relief directional check valve in the pumps for each direction and each drive side. If one is stuck open, you will get this symptom. On the pump locate the 2 drive hoses feeding to the left motor (note: 1 hose will be on left side of pump, other on the right side). Just above each hose connection is a large hex plug, remove the plugs and take the relief valves out and put them in opposite side. If 1 is stuck, problem will move the no drive forward in that side.

Another possibility; there is 1 seal in the distributor of the drive motor that could fail in such manner to allow pressure to by-pass in one direction but seal fine the opposite. If seal in both motors fail or get weak, there would be loss of drive forward on 1 side and reverse on the other.

 

[TBP]

I swapped the 2 reverse valves on the pump that wasn't the problem will move on to the drive motors.
Can the drive motors be swapped to do a test?
Thanks for the info.

 

[TBP]

Another possibility; there is 1 seal in the distributor of the drive motor that could fail in such manner to allow pressure to by-pass in one direction but seal fine the opposite. If seal in both motors fail or get weak, there would be loss of drive forward on 1 side and reverse on the other.

SSdoxie I swapped the drive motors and now it lacks drive forward on the right side so I think I have found my problem.
Do you know if this is an expensive fix?
Thanks for your help

 

[SSdoxie]

If the drive is weak in only 1 direction, the critical/expensive hard parts should be OK. Doing a little deeper research on this motor, I see it uses a Shuttle Valve to direct low pressure oil to case drain. Look at the back of the end cap, there will be a Allen Hex plug to remove. Inside is a set of springs, a spool, and coned seats that the springs push against and the spool is supposed to slide back and forth with change of oil pressure. If this spool sticks it allows high pressure drive oil to escape to tank. I have has some luck (with other Eaton motors using this system) in taking the spool out and polishing it with fine grit Emery Cloth.
Note: There are 2 Allen Screw caps in the end cap of the motor. 1 goes in the side of the end cap, this one has a 65 psi spring and poppet to maintain back-pressure on the case drain to prevent motor from Free-wheeling. The other cap (the Shuttle Valve cap) is on the very end.

A quick test to see if the shuttle valve is stuck: Remove the small case drain hose and put a steel cap on the fitting so oil cannot flow out of case drain then test drive. If drive power is restored, it is the Shuttle Valve sticking. DO NOT operate for any length of time or it could cause severe damage to drive motor and/or pump.

 

[TBP]

A quick test to see if the shuttle valve is stuck: Remove the small case drain hose and put a steel cap on the fitting so oil cannot flow out of case drain then test drive. If drive power is restored, it is the Shuttle Valve sticking. DO NOT operate for any length of time or it could cause severe damage to drive motor and/or pump.

I will give this test a try and see how I go.

Look at the back of the end cap, there will be a Allen Hex plug to remove. 1 goes in the side of the end cap, this one has a 65 psi spring and poppet to maintain back-pressure on the case drain to prevent motor from Free-wheeling. The other cap (the Shuttle Valve cap) is on the very end.

Do I have to dismantle the motor to get to these Allen Hex plugs in the end cap?

I have the same Bobcat part number 6657024 for the drive motors as trull007 did when you helped him with 743 B drive motor failure?

 

[TBP]

A quick test to see if the shuttle valve is stuck: Remove the small case drain hose and put a steel cap on the fitting so oil cannot flow out of case drain then test drive. If drive power is restored, it is the Shuttle Valve sticking. DO NOT operate for any length of time or it could cause severe damage to drive motor and/or pump.

SSdoxie I tried this test today and didnt notice any difference.
But Im wondering if I did it right.
I removed the small hose from the drive motor and put a plug on the fitting to cap it off.
I didnt cap off the hose to the pump just zip tied a bag over the end of the hose to catch any drips (had about 1 litre in the bag much to my surprise when I finished).
Is this the correct way to test?
Thanks

 

[SSdoxie]

Test sounds correct. Seems like problem is internal in motor.

 

[Lwells]

743b feathers to the right when both sticks are forward the main issue is when I am trying to load bucket I veers to the right like there is more power on the left drive motor
If bring the right stick back the left side will kick in but it jerks to the left
Is this a valve sticking?
I read the issue about left reverse and it seems like the same issue but in forward
I checked the right drive motor to look for a large hex plug and did not see one do I need to look at the main hydraulic pump

 

[SSdoxie]

743b feathers to the right when both sticks are forward the main issue is when I am trying to load bucket I veers to the right like there is more power on the left drive motor
If bring the right stick back the left side will kick in but it jerks to the left
Is this a valve sticking?
I read the issue about left reverse and it seems like the same issue but in forward
I checked the right drive motor to look for a large hex plug and did not see one do I need to look at the main hydraulic pump

It could be something sticky or catching in relief/replenishing check valve but it sounds more like steering linkage is loose. Check all rubber bushings and especially the arm that clamps on to the pump shaft. This arm was cast aluminum when 743 was built and were common repair items on machines with some age.