Mahindra HST problem

[SooperYooper]

Mahindra 3540 Hydrostatic. When I press forward or reverse pedal I get a several second delay before the tractor starts moving. I've been banging my head against this for a few days and would appreciate some input.

- Sudden change, not a gradual worsening
- When tractor starts moving, it is not a jerking motion. Its just a slow ramping up. Does not change with RPM.
- No unexpected noises.
- Identical problem in forward and reverse.
- Loader performance is normal.
- Once tractor starts moving, it seem to operate fine under load.
- Changed fluid and filters. Cleaned HST suction strainer. Nothing out of the ordinary noted.
- Checked charge pressure at oil cooler and got ~300psi, which is within spec.
- Backhoe had been on for 6months. Problem started day after taking it off.

Does anyone have a suggestion on what to check next? After ruling out the simple things I expected to see a low charge pressure. Since that pressure is fine, the service documentation suggests this implies damage to the HST itself. I'm really really really hoping I'm missing another possibility.

Any help would be greatly appreciated. Thanks!!

 

[Mike O]

Make sure your remote hydraulic setting is set to neutral.

 

[oldnslo]

Does your back hoe require activating one of the rear remotes to operate or does it have dedicated quick disconnects for supplying oil?

If dedicated quick disconnects did you install the jumper hose required when hoe is removed?

 

[SooperYooper]

Thanks for the suggestions! There are rear remotes that need to be activated for the backhoe. The lever is in the neutral position.

I can't think of a reason the backhoe would be involved, but I did think it was worth mentioning that it happened a day after removing it. I attach and remove the hoe a few times each year.

 

[Racer4]

Maybe put the hoe back on and see if the issue goes away.

 

[oldnslo]

Does that model tractor have electronic control for the HST vs mechanical? If yes wondering if possible a wire or connector was somehow compromised during removal of the hoe. Since same in both forward and reverse points towards a common element.

 

[JTKub]

Sorry if I missed it, but will the machine get up to full/normal ground speed in F or R eventually? Is everything moving normally with the F/R pedals and pedal dampener (if so equipped)?

Does it do this right after cold start, or only once warmed up?

If the loader and hydraulics work at normal full strength, you wouldn't think there's anything going on hydraulically.

 

[SooperYooper]

Sorry if I missed it, but will the machine get up to full/normal ground speed in F or R eventually? Is everything moving normally with the F/R pedals and pedal dampener (if so equipped)?

Does it do this right after cold start, or only once warmed up?

If the loader and hydraulics work at normal full strength, you wouldn't think there's anything going on hydraulically.

It does get up to full speed eventually. I've eliminated the pedal linkage as a possibility by bypassing it all and engaging the HST right at the shaft coming out of the case.

 

[oldnslo]

Does it seem to have full power- torque to the wheels when it starts moving?

 

[RjCorazza]

Not likely, but is it possible that the rims are spinning at the tire bead?

 

[SooperYooper]

Does it seem to have full power- torque to the wheels when it starts moving?

I would say no. It goes something like this: Press pedal all the way down, 2 seconds later it barely starts to move, ramps up to full speed over the next 5 seconds.

I was starting to think about a stuck relief valve inside the HST until I saw the charge pressure was fine.

 

[SooperYooper]

Not likely, but is it possible that the rims are spinning at the tire bead

Thats definitely not happening, but thats basically what it feels like. Like you're spinning tires on ice and they slowly gain traction.