410 Backhoe reverser clutches slipping

[unimog_jason]

I have an old 410 I bought last summer.

In the warm weather, forward and reverse would engage without issue, I was able to put the tractor in high first without any noticable slippage. When the cold weather arrived, the machine had a hard time pulling itself around in low first. Revese engaged without a problem and locked up during the cold.

I removed #27 and put the test gauge in there today and I was seeing 40 psi in neutral, almost nothing when in forward and reverse. When I shut the engine off, the pressure gauge will hold pressure for 5 seconds before bleeding down. If I so much as breathe on the clutch pedal the pressure will start to drop. Just put my foot on it, it will drop a couple psi. If I press down any further, it goes to zero.

The oil temperature would have been close to 0C and the high pressure pump destroked.

At this point I'm looking for guidance on where to go next. Should I warm up the oil since it is a little thick? Should I pull the transmission relief valve and inspect? Pull the clutch control valve off and reseal?

Based on everything I've read, I should see around 140 psi at this test point if everything is working correctly and no oil will flow to the clutch packs.

With the pressure drop I'm seeing when I engage the forward and revese clutch packs, I suspect I have some faulty seals that will need to be addressed, but I'd like to see about improving my supply pressure before tearing into the machine too deeply.

Thanks in advance.

 

[Tx Jim]

When you checked hyd pressure was hyd oil at operating temp? How long since hyd filters were changed? How long since suction screen(key 30) was checked or cleaned?

 

[unimog_jason]

The oil was cold when I did the pressure test, but it's supposed to be fairly warm today, so I'm thinking I'll try again in the afternoon and let it warm up a bit first.

I was told by the former owner that the oil and filters had been changed recently, I see evidence to support that claim and the oil is very clean.

I'm still thinking I'll pull the filter cans off to take a peek inside and see if anything looks off. I'm hesitant to pull the screen out since I'd have to dump all that clean oil, but if I have to, I will.

Everything on the high pressure side works well in my opinion, so I think the oil supply to the main pump is ok.

 

[Tx Jim]

An another option to draining hyd oil to inspect suction screen is place nozzle on hose of an operating shop vacuum into hyd oil filler hole so as to create a vacuum long enough to R&R screen retaining plug. YMMV I think you have a failed seal/sealing ring in reverser.

 

[unimog_jason]

Interesting idea on the shop vac, might have to give it a shot and take a peek at it.

 

[Zebrafive]

Cold oil could cause the transmission filter relief valve to open, bypassing fluid and pressure. So retest with oil at operating temp.
Internal tube(s) to reverser control valve may have broke, or blown an O-ring(s).
There are shims to adjust pressure, but you're so low, it sounds like something leaking inside.

 

[unimog_jason]

Finally back trying to figure this problem out.

After the diff lock mess, I put everything back together, checked the strainer, relief valve and filters.

I replaced both filters, removed the relief valve and verified it was functioning and washed the small amount of debris off the strainer.

I refilled with oil and checked my pressures again.

On the low pressure supply side of the high pressure pump I'm seeing 50 psi regardless of engine speed. At the shuttle valve test port I'm seeing 30 psi in neutral, 0 when in gear.

I didn't measure the force of the spring in the relief valve, but it wasn't stuck open, it had reasonable resistance and closed all the way so I'm guessing it's not the reason for my low pressure.

I bought the service manual for this machine and based on the oil flow diagram, the oil comes out of the low pressure / high volume pump, passes through the transmission filter and relief valve before the flow is split between the main pump and the shuttle control. There is a relief valve in the other filter assembly, but that appears to be filtering the return oil so I don't think that valve is doing anything in this case.

My best guess at this point is that my low oil pressure might be the result of a tired low pressure pump.

Before ripping the engine and reverser out of the tractor, I'm thinking I may pull the shuttle valve apart to verify that I don't have any serious issues in there. One thing I do note is that if I touch the clutch pedal lightly, I'll drop all oil pressure at the shuttle test port. Based on what I read in the service manual, the pedal should provide much finer control over the pressure than what I'm seeing.

The difference in pressure between the shuttle test port and the main pump test port has me wondering too. Based on what I seeing in the diagram, I should have the same pressure at both test ports. I'm wondering if this is possible connected to the touchy clutch pedal? Maybe I have an internal leak inside the shuttle valve?

If anyone has any other ideas, I'm all ears at this point.

Jason

 

[Zebrafive]

Check the pressure regulating valve of the reverser control valve. It uses shims to set the pressure. It sends excess oil to the oil cooler. Your tech manual should tell what pressure should be. I am thinking 150psi?

 

[unimog_jason]

That's where I'm heading next I think, chase down the simple stuff before hauling the reverser out.

I was looking at the hydraulic flow diagram again and I found a tee that connects the low pressure pump output to the main pump and the return filter. My assumption is that if the main pump isn't calling for supply, the excess is routed through the filter for extra filtration before returning to tank.

Inside of that return filter housing there is another relief valve plus a surge valve. I'll pull them out and see if anything interesting falls out.

 

[Tx Jim]

I don't have access to a JD utility tractor tech manual of that era BUT I agree with Zebrafive that reverser operating pressures should be in the 150 psi range not 50 psi.