FMTV Air Hydraulic Unit Repair

Lmtv772

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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.
It's not too hard to do. Gotta have a clean work area and don't put the new gasket in backwards
 

mkcoen

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I should have known when just taking the guard off the pump was such a chore that this was going to be a nightmare.

For those doing this for the first time the pump is under a fair amount of spring pressure. After taking the four bolts holding the pump housing loose it shot across my work area scattering pieces everywhere. I'm hoping the only things that came loose were the small spring, the big spring and the plunger. If there was anything else I can't find it.
 
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I just purchased the repair parts for the pump yesterday from E&R Industrial Sales in Indianapolis. 317.228.0106. All I had to do was give them the part numbers posted above and they are being drop shipped from SPX.

As background, I called SPX about a month ago asking about the parts. They verified that they had them in stock but would not sell directly to me because I did not have an account with them. At that time they referred me to Fastenal. I'll have to say that Fastenal wanted nothing to do with me ordering these parts, because I did not have an "account" with them. After several phone calls someone called me and said they would order them but a month passed and I never heard from them again. Yesterday I called SPX and got the same story, "we don't sell direct but we have them in stock, you will have to go through one of our distributors", so again I asked for a recommendation. First word out of their mouth was Fastenal, and I quickly asked for another reference. They asked where I was located and I told them so they gave me a local distributor. There were 2 or 3 to choose from. I call the first one on my list which I stated above. Within 30 minutes E&R had a quote for me in my email box. I called them back, gave them a credit card number and the parts are on their way. Simple and great customer service. Total cost was $41.00 including sales tax.
 

mkcoen

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Finally just took the pump over to Keith_J's house and he was able to get the spring clamp off (I'd been fighting it for about 30 min) pulled the nut (which after everything else being metric it was a 1" SAE), got the old cup out which now was flat at the end instead of having a lip, pressed the new one in with a vise and then made the final adjustment to seat the lip.
 

mkcoen

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So much for "it's simple, no big deal." This is the washer that goes around the plunger. I'm lousy at reading engineer drawings, is this 202613?

image.jpg
 

mkcoen

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I just purchased the repair parts for the pump yesterday from E&R Industrial Sales in Indianapolis. 317.228.0106. All I had to do was give them the part numbers posted above and they are being drop shipped from SPX.
The outfit NDT mentioned in the original post MROSupply.com is also an easy option. I just went in to find that washer (they actually call it a bumper), typed in the part number off the drawing and it pulled it right up. They do have a minimum number purchase - the u-cups were 2 and so are the bumpers - but they also have free shipping.
 

TNriverjet

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I can tell I will be referencing many of these posts in the future. This is a very useful thread. Thanks mkcoen for all your documentation and efforts.
 

mkcoen

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Here's a tip if you're doing this yourself. Get some 1/4"x20 6" long bolts to help reassemble things. You can lightly compress the spring and start the longer bolts then alternate tightening each one down until you get close enough to put 2 of the pump bolts back in. Continue tightening all 4 until the canister is seated then just take the 2 longer bolts out and replace with the pump bolts. Trying to compress the spring enough to get the pump bolts started first can send pieces flying in all directions.

IMG_4251.jpgIMG_4252.jpg
 

Duckworthe

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So, back when this post started i used it to repair my pump. However it never seemed to be quite right. So i took it out and had a guy who repairs floor jacks look at it. After about 3 days he said he finally got to it. He told me that everything inside looked very good condition, but what he noted that the seats where the check balls seat were a little corroded. He had some tools that cleaned the seats and they loked very clean and smooth again. He tested it on his bench and it seemed good. I took it home and put it back together with fingers crossed. So it worked perfectly. It worked better then i ever expected! So, along with the ucup and any obvious broken or worn pieces. And the check your balls and seats! Lol
 

EdMontana

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Finally will have some time to replace my power unit seal, any special hydraulic fluid to be used on this pump?
 
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Finally will have some time to replace my power unit seal, any special hydraulic fluid to be used on this pump?
It's just regular MIL-PRF-5606 hydraulic fluid. Very common on aircraft. It's not expensive or hard to get. I believe others on the forum have used jack fluid, power steering fluid, industrial hydraulic fluid.... It's a simple system, so I don't think it is very sensitive. I'm using 5606.

http://www.skygeek.com/phillips-1045377-xc-5606a-aviation-hydraulic-fluid-1-gal.html
 

EdMontana

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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.
Finally started work on my pump, just found a rubber washer at end of a plunger broken as well....I wish I knew that washer there, would have ordered with the seal
 
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mkcoen

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So much for "it's simple, no big deal." This is the washer that goes around the plunger. I'm lousy at reading engineer drawings, is this 202613?

View attachment 625020
Finally started work on my pump, just found a rubber washer at end of a plunger broken as well....I wish I knew that washer there, would have ordered with the seal
Just one page back and you would have seen it.
 

EdMontana

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Just one page back and you would have seen it.
auaauaaua


Yeah, problem is....page 5 did not existed when I ordered the parts


For those that will do this pump work, save yourself time and just order the bellow parts at once.

P/N 14121 - U CUP (one)
P/N 17429 - WASHER BACKUP (two) they are the big O rings
P/N 202613 - BUMPER (one) that's the polymer washer

www.mrosupply.com (at moment, you need call to order as the online ordering I was told, is not working, at end says cannot ship to your location)
 
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sjohn116

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MROsupply online ordering is working just fine right now, website is a little buggy with the minimum order number of each item and not matching up with what you want. I ended up ordering double the amount of everything I needed, totaling $101, about 10 days from order to delivery. Now I have spares for future wear/use/SS member(s) in need.
 

sjohn116

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A few quick questions for those who have already rebuilt their air over hydraulic pumps...I bought a used unit, arrived complete, and immediately took it apart with the intention of rebuilding one unit, swapping it out for the unit currently on the truck, and not having to worry about the truck being out of commission for a bit while I do the rebuild. I, like mkcoen, prefer to swap out parts/units rather than remove, rebuild, and then put back on, especially when the unit needing repair can be a chore in and of itself.

1). used unit has quite a bit of rust on all the cast parts inside the case....allen head bolts, casting pump body, etc. based on the dipstick length, and lines marking FULL/Empty, it appears that the casing has a lot of dead space full of air when working under normal conditions. Did anyone take any addition steps to address their rusts issues while rebuilding the pump (wire brush rust off, clean extensively with solvents, treatment, etc)?

2). all of the various O-rings that are revealed during the process... replaced or re-used, and if you replaced, did you go to local NAPA or parts supplier and just match them up? (I have the four pieces (three part numbers) talked about above, sourced from MRO, just wondering about the additional misc pieces). My o-rings are still pliable, but you can see they are partly deformed from years of use/pressure.

3). Three gaskets to hold 1) inlet/outlet block to top cover, 2) pump assembly to underside of top cover, and 3) cover to reservoir... cut your own or ....?

Those are my questions for now, I have an additional question about a small copper o-ring that fell out during initial disassembly, about the port with a spring that doesnt appear to go to anything (old gaskets didnt have a hole lining up with the port, appeared to terminate into the gasket underneath the top cover), but its really hard for me to describe without posting a picture, which I'm having a hard time uploading right now. I'll get the picture posted and then see if you can explain to me what is going on.

Thanks in advance, mkcoen and NDT...no pressure. :)
 

Smike740

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I rebuilt mine a few months ago, my unit didn't have significant rust on the castings. If they did i would have used a wire wheel to clean them up. I reused the orings without issue, i replaced the gaskets since i had purchased them already. The unit now works properly. Regarding the copper ring, i don't recall any that were external to the pump so i can't advise where it may have come from, perhaps looking at the parts manual may identify the location.
 
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