Hydraulic Drive Problem

[wgraves]

Hi Everyone,

I am having a hydraulic drive problem on my 1991 Toyota 2SDK7 skid steer and I'm hoping there are some hydraulic experts on here that can help.

The skid steer is steered using the levers. Everything works fine when the unit is cold, but once it warms up, whenever you put it under even moderate load, the right lever just "gives out" and there is no drive on the right side. If you go back to neutral and start again you're good until you put moderate load on it again.

I was originally thinking pressure relief valves. There are four. I swapped them around assuming the issue would more to the left side if that was the case. Nope, still on the right side. I have changed all oils and filters as well.

Any ideas?

Thanks,

Wes

 

[ed12345]

Hi Everyone,

I am having a hydraulic drive problem on my 1991 Toyota 2SDK7 skid steer and I'm hoping there are some hydraulic experts on here that can help.

The skid steer is steered using the levers. Everything works fine when the unit is cold, but once it warms up, whenever you put it under even moderate load, the right lever just "gives out" and there is no drive on the right side. If you go back to neutral and start again you're good until you put moderate load on it again.

I was originally thinking pressure relief valves. There are four. I swapped them around assuming the issue would more to the left side if that was the case. Nope, still on the right side. I have changed all oils and filters as well.

Any ideas?

Thanks,

Wes

Not familiar with the specific skid stear

Is the hydrostatic drive unit one combined unit on each side or are the motors separate from the pumps

If separate try swapping the right side motors to the left and see what happens. Will tell you if it’s a motor issue or the pump/control valve side

 

[Brendon-KS]

Welcome to YT, Wes.

One question is does the loss of drive always follow a back-and-forth transition? In other words, did you just back up when you went to go forward and when the drive went out or vice versa? I'm thinking about the loop flush valve in the motor - I've seen those not shuttle properly which can cause venting oil out of the high side of the loop, something that should never happen and would cause a loss of drive .

Being that you've already verified the relief valves aren't the issue there's not a whole lot in the pump itself that would always cause issues on a single side, especially for a direct displacement control pump that isn't stroked using servos. Things like charge oil supply and pressure, case pressure, etc are for the most part overaching between the two sections and if the problem is always on the right side it would have me looking closely at the motor.

 

[wgraves]

Welcome to YT, Wes.

One question is does the loss of drive always follow a back-and-forth transition? In other words, did you just back up when you went to go forward and when the drive went out or vice versa? I'm thinking about the loop flush valve in the motor - I've seen those not shuttle properly which can cause venting oil out of the high side of the loop, something that should never happen and would cause a loss of drive .

Being that you've already verified the relief valves aren't the issue there's not a whole lot in the pump itself that would always cause issues on a single side, especially for a direct displacement control pump that isn't stroked using servos. Things like charge oil supply and pressure, case pressure, etc are for the most part overaching between the two sections and if the problem is always on the right side it would have me looking closely at the motor.

No it doesn't. You can be moving forward and then start to go up a hill. If the hill is too steep then it will eventually give out on the right side. It only does it in forward, not reverse.

 

[wgraves]

Not familiar with the specific skid stear

Is the hydrostatic drive unit one combined unit on each side or are the motors separate from the pumps

If separate try swapping the right side motors to the left and see what happens. Will tell you if it’s a motor issue or the pump/control valve side

I've attached a picture of the pump. I know next to nothing about these pumps, but it looks like they are separate.

 

[Brendon-KS]

No it doesn't. You can be moving forward and then start to go up a hill. If the hill is too steep then it will eventually give out on the right side. It only does it in forward, not reverse.

A flow meter plumbed into the case drain of the right side wheel motor would be helpful, ideally situated where you can view it during operation. If the case flow jumps way up when the motor stalls out it would be a sign that you have a problem there. If the case flow is reasonably low (1 gpm in neutral, maybe 4 gpm while moving with the loop flush valve open) it would point more to the pump. Most of us don't have hydraulic flow meters setting around but maybe you have a local hydraulic shop that could rent you one.

 

[rrman61]

A flow meter plumbed into the case drain of the right side wheel motor would be helpful, ideally situated where you can view it during operation. If the case flow jumps way up when the motor stalls out it would be a sign that you have a problem there. If the case flow is reasonably low (1 gpm in neutral, maybe 4 gpm while moving with the loop flush valve open) it would point more to the pump. Most of us don't have hydraulic flow meters setting around but maybe you have a local hydraulic shop that could rent you one.

Welcome to YT, Wes.

One question is does the loss of drive always follow a back-and-forth transition? In other words, did you just back up when you went to go forward and when the drive went out or vice versa? I'm thinking about the loop flush valve in the motor - I've seen those not shuttle properly which can cause venting oil out of the high side of the loop, something that should never happen and would cause a loss of drive .

Being that you've already verified the relief valves aren't the issue there's not a whole lot in the pump itself that would always cause issues on a single side, especially for a direct displacement control pump that isn't stroked using servos. Things like charge oil supply and pressure, case pressure, etc are for the most part overaching between the two sections and if the problem is always on the right side it would have me looking closely at the motor.

I agree it could be a weak motor but if the hydraulic oil is getting too hot that can magnify the problem.check your cooling fan and hydraulic radiator too

 

[Roger in Iowa]

No it doesn't. You can be moving forward and then start to go up a hill. If the hill is too steep then it will eventually give out on the right side. It only does it in forward, not reverse.

You can still go up the hill in reverse with no problem? If so, the pump and motor are okay. You have a bad valve, either charge or relief for forward direction.

 

[wgraves]

Ok, thanks everyone. I have some ideas to try now and I'll let you know how things turn out.