FMTV Air Hydraulic Unit Repair

[Lmtv772]

I bet you're getting really good at this NDT.

 

[Lmtv772]

I want to point out:
-when you do this job it's very important to throughly clean all the parts (even though you'll find an utter mess), and it's very important to put the parts together exactly the way you've found them (or how they came apart).
- the seal of the u shaped plunger goes in one way and you have to make 100% sure it's seated right.
- the big piston has a plunger inside as well. Test that it actually produces pressure. Or you'll put the thing back together and it still won't work. Good luck!

 

[dalej]

Someone had said that if you can see white smoke coming from the unit, you need to rebuild or replace something. Can anyone expand on this statement? When I raise my cab or anything else with the hydraulic pump, I count around 2 pumps per second from the air/hydraulic pump. Does that sound like a normal count? I do see white smoke sometimes but not always.

 

[Suprman]

Not smoke. You are blowing hyd fluid out the air vent it just comes out atomized in puffs. The air hyd unit needs to be rebuilt the main pump seal is bad. Compressed air used to run the pump is leaking past the seal and into the hyd reservoir.

 

[dalej]

Thanks, but what about the pump count? does a couple of pumps per second sound normal.

 

[Suprman]

Its not super fast but should make enough hyd pressure to raise the cab slow but steady. If it needs a seal it wont work right it will fight itself a bit.

 

[tennmogger]

Had a curious failure a couple of days ago. Plan was to lower my spare, leave it behind, and drive to a buddy's house to pick up another spare. Let the spare lift do all the work that way. The lowering went like clockwork (yes, about 2 puffs per second), disconnected the spare, and lifted the empty lift into transport position.

Got to the other site and tried to lower the lift. It would not move more than a couple of inches. No longer getting 2 puffs per second, more like one good puff, a feeble puff, then nothing. Yes. plenty of air in the tank but the engine was started anyway. Checked fluid level, topped it up, and still the lift would not work. So, we loaded the spare with a forklift.

Got back home and intended to fix the pump, but, it worked perfectly!! Down, up, up down, with and without the spare. So I installed the spare and lifted it into transport position. Done.

So now I do not trust it!! What do you guys think went wrong?

Bob

 

[Suprman]

Seal is going bad. There is a manual pump to the right. You can use a breaker bar to pump it.

 

[dalej]

So, we loaded the spare with a forklift. Bob

Man, I just throw the spare in the bed of the truck by hand.

Well, I'm going to put a new seal in my pump but wanted to get the right parts. Here is photos of all that I can see:



Is this in fact a SPX or the brand that is talk about in this thread? If so, is the part number listed at the start i.e. the U-cup the right one. I used photoshop to lay new letters and numbers over the box for clarity.

 

[tennmogger]

Seal is going bad. There is a manual pump to the right. You can use a breaker bar to pump it.

I should have mentioned the fact that the manual pump would not move the lift arm either, with the arm stopping at the same place it stopped with the air pump. Continued manual pumping would not move the piston of the lift.

Concurrently with the spare lift failure, the cab would lift just fine with both the air-over-hydraulic and the manual pump. It was just the spare lift arm that would not work.

 

[Lmtv772]

what happened when turn the cab lift raise/lower knob a few time and try again?
As a matter of fact, try moving all of the knobs and keep them all in the center when you are done, minus the cab raise/lower knob.
Might be that something obstructing in the sector manifold

 

[dalej]

Well, I'm going to put a new seal in my pump but wanted to get the right parts. Here is photos of all that I can see:

View attachment 585421 View attachment 585422

Is this in fact a SPX or the brand that is talk about in this thread? If so, is the part number listed at the start i.e. the U-cup the right one. I used photoshop to lay new letters and numbers over the box for clarity.[/QUOTE]

I talked to Terry at SPX Power Team, their tech number is 800.477.8326. He said that my 2 pumps per second during a cab lift is good but if there is some oil being slobbered out, I should replace the U-Cup and a couple of seals. He gave me the part numbers that I need for a SPX Power Team #58477 based on the last 5 numbers on the top of my unit. The U-Cup part: #14121 as stated above. and the 2 seals also used are part: #17429. Here is an exploded view of where the seals will be replaced.

 

[Lmtv772]

Well, I'm going to put a new seal in my pump but wanted to get the right parts. Here is photos of all that I can see:

View attachment 585421 View attachment 585422

Is this in fact a SPX or the brand that is talk about in this thread? If so, is the part number listed at the start i.e. the U-cup the right one. I used photoshop to lay new letters and numbers over the box for clarity.

I talked to Terry at SPX Power Team, their tech number is 800-477-8326. He said that my 2 pumps per second during operation is good but if there is some oil being blown out, I should replace the U-Cup and a couple of seals. He gave me the part numbers that I need for a SPX Power Team # 58477 based on the last 5 numbers on the top of my unirt. The U-Cup is part: 14121 and the seals are part: 17429. Here is a exploded view of where the parts will be replaced.

17429 usually is ok 14121 is the one that gets destroyed by the fluid and falls apart.
you can order 2 for $22 from he supplier listed. Make sure you put the pump together exactly in the way you took it apart.

 

[dalej]

Thanks for all the information on this thread! I'll be posting photos when the replacement part are installed, it won't be for a while since mine really isn't that bad.

Forgot to mention that Terry at SPX said. It is recommended that a in-line lubricator be installed. I thought that I would replace my compression air fitting at the unit with a Push-Loc air connector so I can add a few drops of lubricant once in a while to help with the wear of the seals.

 

[dalej]

I replaced the compression fitting with a Push-Loc fitting. It is real easy to undo and reconnect for adding a few drops of oil to lubricate the U-Cup seal and others

.

 

[mkcoen]

Someone had said that if you can see white smoke coming from the unit, you need to rebuild or replace something. Can anyone expand on this statement? When I raise my cab or anything else with the hydraulic pump, I count around 2 pumps per second from the air/hydraulic pump. Does that sound like a normal count? I do see white smoke sometimes but not always.

Reviewing the PS Magazine put out by they Army they had one posting that said if you saw mist coming out then rebuild it. They came back about a year later and said the manufacturer said, no that's normal venting and as long as you weren't losing fluid the unit was fine. I'm not sure which edition these were in as I was downloading about 15 years worth of them and stopped to review any article that had to do with FMTVs. It was somewhere between Jan '99 and Dec '14 so that was about 180 issues.

 

[Suprman]

It has been my experience with multiple trucks that when the pump seal is failing the unit will blow hydraulic fluid out the vent in clearly visible puffs. Good pump units will not have any visible puffing when standing at the hyd control. The pumps seem to have a high failure rate in general.

 

[Lmtv772]

A friend works as a mechanic and their lifts use the same air/ hydraulic pumps to lift the front or rear of a vehicle on the lift. Might be a good place to find a replacement

 

[Waltjg]

.

 

[mkcoen]

Crud. Looks like I need to rebuild mine. Lowering the cab trying to get the cab lock pin to retract and all I'm seeing are clouds of mist coming out of the unit.