Lazy track problem

[David Boreham]

It seems that I'm a proper member of this group now because not only to I have a min-ex, but now I have a hydraulic problem

Would be grateful for some fault isolation advice. My Volvo ECR38 has one track that is not working quite right. I've done some Internet research and gathered the following info:

1. The problem doesn't seem to be related to oil temperature. It happens right from cold, and when hot.
2. The problem only affects one direction. The other direction seems fine.
3. The problem occurs on both high and low speed.
4. I've eliminated simple "mat stuck under the pedal" causes by removing the mat, cleaning dirt from around the pedal, checking there's no rocks wedged under it, etc.
5. Engine RPM drops when power is demanded of the lazy track, as if it is supplying power, regardless of whether it turns strongly or not.
6. Trying various things with the tracks off the ground, I get the impression that the bad track will run properly, but it sort of takes fiddling with the pedal/lever. For example if you ease it slowly in the "bad" direction, the track seems to leap into action and run strongly for a few seconds, but if you keep pushing the lever further forward it seems to lose momentum and slow down. Once it gets slow it never speeds up again until you stop it, or perhaps run it a bit backwards which seems to "wake it up" again.
7. The "good" side lever feels a bit different from the "bad side" -- but not in exactly a way that would account for the difference in behavior directly -- e.g. it isn't that the bad side just can't be pushed full travel. But it just feels different like the mechanical mechanism underneath, valve spring rate and what not is not the same. Unfortunately I don't have a good machine to compare.

Otherwise the machine seems fine. Hydraulic fluid is clean, full, all other cylinders work ok. It has ~1000hrs and is 9 years old.

Would be grateful for some pointers on where to look to diagnose this further. I have the service manual. It is silent on this, unless I've missed that section in the 500 pages...

 

[Cmark]

Not familiar with this particular machine, but a couple of questions;
Does it have two-speed travel? What you describe sounds like the motor turning in fast mode, then hydraulic pressure builds and it drops into slow mode (as it should)
Following on from that, have you checked your final drive oils? It could be the final drive seizing up.
If that all checks out, you should test main relief pressure with the travel motors stalled. Check both sides, both directions and note down the figures.

 

[David Boreham]

Not familiar with this particular machine, but a couple of questions;
Does it have two-speed travel? What you describe sounds like the motor turning in fast mode, then hydraulic pressure builds and it drops into slow mode (as it should)
Following on from that, have you checked your final drive oils? It could be the final drive seizing up.
If that all checks out, you should test main relief pressure with the travel motors stalled. Check both sides, both directions and note down the figures.

Thanks for the pointers. It has two speeds however the bad side is "bad" at both speeds. That is in slow speed it still runs slower than the other side. I believe the drive oil is ok as it was checked recently although not by me personally. The bad side runs just fine in one direction.

 

[Cmark]

Okay. So I suggest start with checking relief pressures as I described. Comparing the pressure on the bad side with a good one will give you a starting point for your troubleshooting.

 

[uffex]

Good day David
Please see the attached from your description it will either be as Cmark suggests or a sticking overspeed spool, take the easiest first be aware fluid will run from the open port.
Kind regards
Uffex

 

[David Boreham]

Good day David
Please see the attached from your description it will either be as Cmark suggests or a sticking overspeed spool, take the easiest first be aware fluid will run from the open port.
Kind regards
Uffex

Thanks, I'll see if I can perform that test, although due to day job pressure I may get an expert to look at it.

One more question : parts catalog shows (I'm assuming I can't post a screen shot here for legal reasons..) a cable from the travel lever to the main valve assembly. Is there any possibility the problem is in that cable (e.g. it is binding due to loss of lubricant)? I think in one travel direction it pulls the cable while the other pushes the cable. It's the "push" direction that's not functioning correctly.

 

[uffex]

Hi David
My suggestion would be measure the spool movement and compare with the good side, sure that could make the track move slowly but I would be surprised if normal wear has caused loss of drive. What you describe as the issue loss of RPM when you use the lazy side sounds as if the pump is responding to flow demand. It is always a little problematic making diagnostics over the web but it appears you are being thorough with the investigation. Pressure testing the main lines should show up the fault and to be honest it takes away a lot of the guess work which can be expensive.
Kind regards
Uffex

 

[David Boreham]

Ok, I see : the fact that RPM drops the same as with the good side/direction implies that fluid flow is normal and the linkage from the lever to the control valve via the cable is operational, so the problem is probably somewhere beyond that point, in the drive motor.

 

[uffex]

Good day David
The spool moves in an equal amount in each direction with a little assistance makes it possible to check that out and yes you have interpreted my conclusions correctly. Switching the shock valves is reasonably easy leave each on the last thread before the switch as you are opening the line to tank and the fluid will drain - check the rings are in tact as you make the switch or supervise.
Kind regards
Uffex

 

[David Boreham]

Hi thanks, sorry I'm a bit slow on this but I think you're saying to swap the hoses between ports on the drive motor such that it should run backwards. Then see if the fault stays on the same direction (implying a problem inside the drive motor) , or switches direction (implying a problem not in the drive motor). Did I get that right?

 

[uffex]

Hi David
That is one test you can make to identify if the issue belongs with motor or upstream in the valve chest.
Kind regards
Uffex

 

[David Boreham]

It's been a while (just over a year it seems) but I can now answer my own question:

A guy from the local Volvo dealer came out to look at my ECR38 (primarily to set relief pressures on the new thumb's circuit). I asked him to look at the lazy drive problem while he was on-site. He isolated the fault to the linkage/cable between the pedal and the valve, by disconnecting the cable at the valve end and operating the valve directly with a screwdriver/pliers. Under those conditions the lazy motor worked just fine. He concluded there was some issue with the linkage attachment to the cable such that it didn't quite "hold" in one direction. When the lever is pushed in the opposite direction, that force is enough to make the cable catch on the linkage for a while. Then push it the other way and the cable slowly works its way loose somehow, or perhaps stretches. We never fully diagnosed the fault, but after adjusting the cable position at the pedal (like on a bicycle brake) the problem seems cured for now.