Cab and spare hydraulics problems M1078 LMTV

[Fireball1]

Cab and spare hydraulics act like there is a restriction in the valve body on all lift and lower functions. Acts like it builds pressure but the return through the valve body to the air-hydraulic pump is blocked in the valve body. The valve assembly is the one from Parker-Hanifin. The vehicle manufacture date 8/96. The manifold p/n is HFC32598.
I have the hydraulic schematic and will probably end up tearing the valve apart piece by piece to fine the restriction.
Any help or advice appreciated. Thanks

 

[NDT]

Is your air-hydraulic power pack pumping like crazy or really struggling?

 

[Suprman]

The parts tm show a full breakdown of the valve body. There could be a check valve in there. The air hyd lift pumps are a high failure item though.

 

[Fireball1]

Starts pumping normal, then almost stalls out. Acts like return isn't working. Get very little return from return line to air pump.

 

[Fireball1]

Had valve all apart today. Found no foreign material, no plugged orifices and no obviously damaged o-rings. Does cylinder have to have residual pressure to unlock? If so is that pressure generated by the orifices in the cylinder shown on the print? What unlocks the check balls in the cylinder? Are the orifices and checks considered pressure operated check valves or counterbalance valves?

 

[Fireball1]

Found 2 ball and spring check valves, 2 identical cartridge direct acting check valves and 1 longer check valve that appears to be a pilot operated check valve. On the hydraulic schematic they are all shown as ball type checks. Does any one have a pictorial of the passages in the valve body ? All I have found is the schematic in the back of TM 9-2320-365-20-4, I don't have a phantom view of the internals or if there are any fixed orifices (non removable) in the valve body.

 

[NDT]

Confirming, the pump stalls out when attempting to lift BOTH the cab and spare tire mount? If it's just the cab, can you see the safety indicator extend on the cab latch? If not the latch could be stuck, preventing the cylinder from raising the cab.

 

[Suprman]

Did you make sure you are not just low on fluid?

 

[Fireball1]

Fluid checks OK.

 

[MaiNiaK]

I almost asked yesterday if he had checked the fluid, but didn't want it to be taken badly.

Mine was recently doing the same thing. (I thought my cab latch was stuck) Turned out to be a quart low on fluid. (Those dip sticks are a hard read without proper lighting)

 

[Fireball1]

Well got the cab to come down. Think I have a problem with the pilot operated pressure relief valve in the valve body. Had some air in the system bled it but had to work the function knob back and forth and then with the pump running it decided to trip the pressure operated check for the cylinder or counterbalance valve which ever it is and go ahead and cycle. Had the same thing happen with the spare carrier. Still have some problem but have some other work before I can to get back on it. Thanks for all the help from all of you.

 

[aleigh]

I have this same problem on all my circuits, leading me to believe it's something in the manifold. Cab is stuck up right now. I've got the manifold off and I'm basically at the point of rebuilding it, I had leaky valves anyways. Did you ever get into your manifold and learn more about the problem?

Where did you find the hydro schematic? I'd like to see it. I have been backwards and forwards over the TMs and haven't run across it, or else I'm blind.

 

[Suprman]

Parts tm shows a good breakdown. There are filters in the valves.

 

[aleigh]

Sorry - I took it to mean he had a functional (block) schematic of the system. Like what valves are connected to what in what order, and where the check valves are, etc. Not the physical layout.

 

[Suprman]

The troubleshooting TMs have flowcharts. One of the repair TMs should have a schematic of the hyd system. I don't think there is anything that shows how it all flows in one easy diagram. Follow the feed and return from the pump to the valve body. Make sure those lines are clear. If the return line is clogged it would jam up everything.

 

[LostInTheWorld]

I think this is about the best the TM has. This is probably too small to read, but take a look starting at page 1,205 of TM 9-2320-365-20-3

 

[aleigh]

There are details and pics over on the other thread, http://www.steelsoldiers.com/showthread.php?155350-Coolant-Took-A-Vacation but basically I took my manifold apart and the checkvalves had some minor looking rust and a rough feel to them.

 

[Suprman]

Maybe some water got into the system. The check valves are an spx part.

 

[aleigh]

You sure? My check valves say Parker right on them, and it's a Parker-style part number in the TM.

 

[Suprman]

Parts tm should have the current spx part number. I'm pretty sure Parker discontinued the stuff. The parts can be found online with the spx numbers.