Critical FMTV PM not covered in TMs

DSD277

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Breakers go by amps only. I only had 5 breakers when I received my truck. I had no luck finding them back then, so I used good old ATO fuses :-D. It actually works out good. As I went through systems one by one, I figure a fuse would blow immediately, where as a 'unknown' CB could be defective and either not trip, or not set. I never had any of the fuses blow, and they are still there today. Why change what works?:mrgreen:
 

Radiogeek99

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I have a leaky latch as well, but it is coming from around the indicator pin. There is a small seal in the cover, has anyone found the number for this seal? The TM only shows the entire latch, not a breakdown of the individual parts.
 

Awesomeness

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I have a leaky latch as well, but it is coming from around the indicator pin. There is a small seal in the cover, has anyone found the number for this seal? The TM only shows the entire latch, not a breakdown of the individual parts.
The small seal in the cover is just a dust guard, not a seal. There are two actual seals in the whole assembly, which hold back hydraulic fluid.
1.) The big o-ring on the piston, which can be replaced as described above. (Was it #221?).
2.) A small o-ring in the main body of the latch (the part that bolts down), that seals against the thicker end of the piston when it's all assembled (the side that latches, not the indicator side). I just replaced this over the weekend. The OD of the thick side of the piston is 0.625" (5/8"). I'm not sure exactly what size o-ring I used, because the only place that was open at the time didn't have a-la-carte o-rings... I bought a sampler pack of viton o-rings, that were actually metric, and one worked well - it slid over the thicker nose of the piston fine, and was around 1/8" thick.
http://www.autozone.com/fuel-delive...el-line-seal-ring/238617/?_requestid=10086150
 

tennmogger

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The indicator pin seal is secondary and you really do not want to have it sealed too well. I found out the hard way. The real seal is inside on the main piston that does all the work, of which the indicator pin is part. Replace the o-ring on the main piston and don't worry about the wiper/seal around the indicator pin.

So how did my first repair go wrong? My first 'fix' was to think the indicator pin was missing an o-ring, so i added one. But the leak was from the main seal. Note that the diameter of the piston of the main seal is much larger in diameter than the piston of the indicator (the pin itself). If the pin's 'seal' does not leak, pressure builds behind it, against the backside of the main piston, and the main piston can't move outward then because of the pressure built up!

It is easy to replace the o-ring. I have no part number but for 20 bucks you can buy a whole box of o-rings and find an appropriate one. Then you have 99 (or more) o-rings left over to fix other stuff.

Here is a thread on the problem http://www.steelsoldiers.com/showthread.php?143089-hydraulic-latch-release&highlight=cylinder

Took me 15 minutes of searching and I knew what I was looking for! Our thread titling sucks LOL

Bob
 
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Awesomeness

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I have a 2007 FMTV and the hydraulic system calls for MIL-PRF-5606A fluid. I do not know how critical this is but since it was not that expensive, I ordered a gallon from Sky Geek:

http://www.skygeek.com/phillips-104...aign=froogle&gclid=CJTJ3_Slmc4CFZGFaQoduIsPLQ
For anyone that reads this thread in the future, the reason to use the red military fluid is that it contains anti-corrosion additives. Regular hydraulic fluid doesn't, and so over time your system/pump/cylinder/latch/etc. will rust out.
 

aleigh

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For anyone that reads this thread in the future, the reason to use the red military fluid is that it contains anti-corrosion additives. Regular hydraulic fluid doesn't, and so over time your system/pump/cylinder/latch/etc. will rust out.
It'll also rust out because nothing is really stopping rain or humid air from getting into the vent on the power pump.
 

Awesomeness

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It'll also rust out because nothing is really stopping rain or humid air from getting into the vent on the power pump.
Most of the trucks (as originally constructed) have a cover over the pump, so rain doesn't really have a straight path into it (any more than any of the other axle or transmission vents, etc.). Even with water in the fluid, the military anti-corrosion fluid will help it survive [longer].
 

aleigh

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Yeah the bracket for the chem detector right, but even so it'll draw air in and water will condense on the walls. I was erroneously told that the muffler had a desiccant in it, which it does not, but now I plan on adding one. The fluid swap is a good idea though, I did it. My valves were terrible.
 

Awesomeness

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Yeah the bracket for the chem detector right, but even so it'll draw air in and water will condense on the walls. I was erroneously told that the muffler had a desiccant in it, which it does not, but now I plan on adding one. The fluid swap is a good idea though, I did it. My valves were terrible.
Well, that's why I was mentioning/wondering that everything on the truck has similar breathers/vents, with no real ill effects, and most of the other components aren't using special anti-corrosion oil or anything. If you put the cover (chem detector mount bracket) on, or some other shield, and use the anti-corrosive fluid, you'll probably be good for pretty much forever. Also make sure the o-ring on the dipstick is good, since that part remains uncovered even with the shield in place.
 

spankybear

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Someone mentioned aircraft fluid that has some kind of desiccant properties in another thread. Has anyone looked into this?
DO NOT use skydrol (aircraft fluid)! This will ruin the entire system! If the system isn't designed to use Skydrol it will eat and destroy every part in the system that isn't metal! (I work at a major aircraft company and see what skydrol does to stuff... and that is turn stuff to goo rubber, plastic, paint)
 

Aernan

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I figured out you can by hydraulic oil by the gallon and 5 gallon pail. I just added some to bring the level back up. I'm not going to buy any special fluids unless it's required. It's actually novel to be able to buy fluids anywhere.
 

aleigh

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Someone mentioned aircraft fluid that has some kind of desiccant properties in another thread. Has anyone looked into this?
I was the one who brought the fluid up originally. [FONT=arial, sans-serif]Mil H 23282 (better) or 5606 (worse). The real problem seems to be that moisture gets into the system via the vent on the pump. A solution to that would be to rig up some kind of desiccant pack on the breather to prevent the humidity from getting in there, but the trick would be to do it in such a manner that it doesn't become contaminated with the fluid. [/FONT]
 

Aernan

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So my Cab latch does not engage. There is no leak? Do you think the seal is the problem?
I have personally torn down and refreshed the seals in the cab tilt latch. Here is my advice. YMMV.
  1. Tilt the cab full open so it sits stable.
  2. disconnect the hydraulic line from the cab tilt latch (some dribble there)
  3. unbolt the latch entirely (4 bolts)
  4. Take it into your garage and take it apart. After removing the giant nut the piston should pull out with some force (pliers).
  5. Inspect all the seals. If any are bad contact Joe Goodenough found on this board or Facebook. He sells complete seal kits. You can buy the o-rings locally from most parts shops (so I'm told) and the part numbers are buried in a thread somewhere.

This is my guess. The cab tilt is the highest point in the system and air and garbage accumulate there. The piston is pushed closed with a spring which should always work unless there is buildup of junk in there.
 

Aernan

Member
508
14
18
Location
San Jose/California
I was the one who brought the fluid up originally. Mil H 23282 (better) or 5606 (worse). The real problem seems to be that moisture gets into the system via the vent on the pump. A solution to that would be to rig up some kind of desiccant pack on the breather to prevent the humidity from getting in there, but the trick would be to do it in such a manner that it doesn't become contaminated with the fluid.
I suspect that the tank being on top of the transmission near the engine does heat up a bit (I hope) and I'm hoping that moisture boils off as it comes to temp. (wishful thinking). I suspect that you should change all the fluid once in a while to ensure the moisture leaves the system.

A desiccant pack would work but ideally heating the fluid to 100F (engine coolant temp) would cause moisture to evaporate. Who knows it might be possible to add a circuit from the radiator overflow tank to heat the hydraulic fluid tank.
 

spankybear

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WA
I figured out you can by hydraulic oil by the gallon and 5 gallon pail. I just added some to bring the level back up. I'm not going to buy any special fluids unless it's required. It's actually novel to be able to buy fluids anywhere.
Why not just use ATF? It's basically hydraulic oil with a some additives for the clutches. It should not adversely harm anything.
 
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