FMTV Air Hydraulic Unit Repair

[NDT]

This is the unit that provides the hydraulic power to raise the cab. Mine functioned (barely), but was slobbering hydraulic oil all over the place, and had to be refilled all the time. Today I tore into it. Sure enough, the shaft seal on the plunger was shot, allowing high pressure oil to enter the air chamber and be expelled through the air vent. After digging around in the TMs, turns out this power pack is made by respected hydraulic tool manufacturer SPX Fluid Power, and the packing is called a "U-cup" p/n 14121. For once the "off the shelf" aspect of the FMTV worked out here, and the pump is a part of SPX's line of portable power packs, and the part is available online from MROsupply.com and others.

After action report: Finally got the HPU working again. Mistakes made: Didn't mark the hoses, put them on backwards, wouldn't pump. Didn't seal the air line, some bug made it's nest deep down in the line, plugging it and making me think the HPU wasn't working. And the best of all, I put the U-cup in backwards, and it didn't seal, spraying oil everywhere again. You would think this was my first rodeo.

 

[gimpyrobb]

I have a couple things from SPX and have always gotten great info(even blueprints) form them when I emailed for information. As long as you include the serial number, they are a great source of information.

 

[Oxyacetylene]

That is great info. I have been thinking, maybe we need to start a list of part numbers and sources for the various things on these trucks.

 

[Duckworthe]

Thanks for the post and info. Mine was and still is having the same issue as yours. Mine does work manually though. I ordered the U-cup and installed that little sucker, (somewhat of a pain to get it down into place) and after going through the whole unit it still wont work except manually. Still wants to blow out the vent. Any ideas ,besides putting on a new unit. Everything inside was in perfect condition except that the U-cup was deteriorated. Thanks.

 

[NDT]

Thanks for the post and info. Mine was and still is having the same issue as yours. Mine does work manually though. I ordered the U-cup and installed that little sucker, (somewhat of a pain to get it down into place) and after going through the whole unit it still wont work except manually. Still wants to blow out the vent. Any ideas ,besides putting on a new unit. Everything inside was in perfect condition except that the U-cup was deteriorated. Thanks.

Are you SURE you put the u cup in the right way. The open part of the u should face the hydraulic oil so the pressure expands it.

 

[Duckworthe]

As per the drawings and talking to SPX, who by the way are great. The way it goes in is opposite the way that it seems it would. Basically the lip and goes into the housing first and you have to use a small screw driver to gently work the lip down into the bore. If you put it in backwards, it goes right in and yes it wont seal. Maybe I messed it up putting it in? It blows air out of the vent but no fluid, and it doesn't have the power to raise the cab.

 

[Duckworthe]

Actually, going back up to the pics above of the U-cup. The side of the seal that you see is what goes into the bore first.

 

[Duckworthe]

View attachment 64574 SPX.pdf

Also, Here is a drawing from SPX and progress on my truck.

 

[NDT]

Did you possibly connect the hoses backwards? I did that and the pump runs, but of course no movement.

 

[Duckworthe]

I put them back where they were prior. But they could have been on wrong from before I got it (since it never worked).

 

[Blackmagic94]

Great post

 

[Blackmagic94]

Just ordered a pair for 22 shipped from the provided vendor by the OP, thanks

 

[Lmtv772]

Just ordered a pair for 22 shipped from the provided vendor by the OP, thanks

Did you take yours apart , yet?

 

[Duckworthe]

I haven't dug back into mine yet. Been busy building my camper box for the truck.

 

[tburk49760]

Don't tease us... Show some pics... Please.

 

[wehring]

Just rebuilt mine and it is leaking again after only a week. Would like to get some OEM replacement o-rings. Anyone have a source?

justin wehring
979 997 3112

 

[Suprman]

The parts tm has the full breakdown of the unit. I am pretty sure you can order any part of it from an spx dealer. I have a few cores I want to rebuild as spares I wonder if a major rebuild kit is available.
Will

 

[Duckworthe]

I contacted SPX and i believe they said they don't have a total kit for it. Because it was a special sized piston kit for this truck use. So they don't have a one source kit available. but can buy it piece by piece. I need to get back on mine soon. The camper build is taking my time right now. I will get some pics up soon. My truck is looking amazing and running like a top. just need to swap out the gears for the MRAP units.

 

[Lmtv772]

So I've ordered the parts for $22 from the supplier mentioned by the OP. MROsupply.com is an absolute nightmare as far as their customer support is concerned. But I got my parts in the end. So it's not that bad. I'd suggest contacting SPX directly. Their part # is 14121 for the seal and the phone # is (815)873-3715

 

[NDT]

Coincidence you punched up this thread lmtv772. I think these parts get drop shipped from SPX.

Guess what I had to disassemble the HPU for the nth time. I left the decontaminator bracket off when I repaired this thing and rainwater made it past the exhaust muffler and hydrolocked the air cylinder. It would not pump.