cab raise bleeding help

[Crazyls2]

I promise I tried to figure this out using the TM's and I looked through the forum. I feel like the TM's might as well be written in Greek because I have a hell of a time finding things in them. I was able to use them for the fan clutch and a few other things but it takes me 3 days to get to the section I need most times.

A few weeks ago my truck started seeping oil from the cab lock cylinder. Recently while trying to raise the cab so I could try attacking my oil leak it shot out all the hydraulic fluid. I ordered a rebuild kit and rebuilt the cylinder but now I can't seem to get the air out of the lines so the cab lift isn't working. How do I bleed that system? I refilled it with AW-32 ( as I recall) because I had found a few people on here saying it was a suitable substitute for the MIL spec fluid in the truck. Any help would be greatly appreciated.

 

[Ronmar]

Disconnect the lift hose on the cab lift cylinder and run it into a container.

Run the AOP till fluid comes out of the hose end. Reconnect hose end, top off AOP reservoir and lift cab…

 

[Mullaney]

I promise I tried to figure this out using the TM's and I looked through the forum. I feel like the TM's might as well be written in Greek because I have a hell of a time finding things in them. I was able to use them for the fan clutch and a few other things but it takes me 3 days to get to the section I need most times.

A few weeks ago my truck started seeping oil from the cab lock cylinder. Recently while trying to raise the cab so I could try attacking my oil leak it shot out all the hydraulic fluid. I ordered a rebuild kit and rebuilt the cylinder but now I can't seem to get the air out of the lines so the cab lift isn't working. How do I bleed that system? I refilled it with AW-32 ( as I recall) because I had found a few people on here saying it was a suitable substitute for the MIL spec fluid in the truck. Any help would be greatly appreciated.

.
AND, just so you know... Those TM's are good and wonderful things EXCEPT THAT they sometimes talk in a completely different language than you (or me or a lot of us - til we learn it).

A really good example of that is when I was trying to find what the TM's call a "Cab Support" that other folks might call a "Biscuit" or maybe a "Rubber Bushing". If you don't know what THEY call it you just won't find anything useful when you search. It gets better with time. The more you crack open the books the more they start to work for you.

-------

Somewhat related, here is a screen capture of one of the troubleshooting sections for the cab jack.

Top Right is the book that I was in.

The Series 20 (also called -20) book means "Unit Maintenance". Stuff actually gets fixed using the troubleshooting flow charts in this book.

The Series 10 (also called -10) is like the "Owner's Manual". This one says what the tire pressure should be, how to use the troop seats, and basic considerations for cold starting and so on.



We almost need to have a book on how to use the books - and chances are good that somewhere along the way - somebody wrote one

 

[Ronmar]

That info, how to use the manual, is usually passed at the school where the techs who work on the vehicles get training

I have been to schools where more than half the course was on JUST how to use the manual…

 

[Crazyls2]

.
AND, just so you know... Those TM's are good and wonderful things EXCEPT THAT they sometimes talk in a completely different language than you (or me or a lot of us - til we learn it).

A really good example of that is when I was trying to find what the TM's call a "Cab Support" that other folks might call a "Biscuit" or maybe a "Rubber Bushing". If you don't know what THEY call it you just won't find anything useful when you search. It gets better with time. The more you crack open the books the more they start to work for you.

-------

Somewhat related, here is a screen capture of one of the troubleshooting sections for the cab jack.

Top Right is the book that I was in.

The Series 20 (also called -20) book means "Unit Maintenance". Stuff actually gets fixed using the troubleshooting flow charts in this book.

The Series 10 (also called -10) is like the "Owner's Manual". This one says what the tire pressure should be, how to use the troop seats, and basic considerations for cold starting and so on.

View attachment 853504

We almost need to have a book on how to use the books - and chances are good that somewhere along the way - somebody wrote one

Thank you. This is very helpful.

 

[Crazyls2]

That info, how to use the manual, is usually passed at the school where the techs who work on the vehicles get training

I have been to schools where more than half the course was on JUST how to use the manual…

I can read manuals on communications and computer systems as if it were my first language, seems the Air Force knew what they were doing when they didn't make me a mechanic.

 

[Crazyls2]

Thank each of you for your input or humor.

Earlier today I got tired of looking for videos or info and started thinking about how I had to get air out of my tilt trim motor on my boat after it ran low. So I went and topped off the hydraulic fluid and pumped the hand pump until the cab went up about an inch. I then the cab selector back to lower and once it went back down I went back to raise and pumped until it went up even further than the time before and again released pressure. After doing this several times I was eventually able to get the cab completely opened. I cycled it twice from closed to open then closed again. Now the button will raise it and the hand pump. Ronmars way would have been far more efficient

 

[Ronmar]

In most hydraulic systems, all you have to do is fully cycle the system to purge air, like you did. The issue you can run into on the LMTV revolves around the load safeties used in the cylinders to keep a load from falling if a hose fails. Air pockets trapped in a cylinder can be compressed and store energy. When you shift a valve direction, this stored pressure can be released quick enough to lock up the safety, and if there is still stored pressure, hold that safety in the locked position and keep the cylinder from moving. It doesn’t seem to happen on the cab cylinder but it is a fairly common occurrence on the tire cylinder, probably because of the angle the cylinder is mounted at.

I have a fair bit of experience with electronics types working in engineering sections. In my experience ET’s typically make fine engineers as they already typically understand flow and flow control. Valve = switch or variable resistor, check-valve = diode, restricted orifice = resistor, accumulator = battery or capacitor, ect… and system analysis for understanding and troubleshooting comes easier to them…

 

[Crazyls2]

In most hydraulic systems, all you have to do is fully cycle the system to purge air, like you did. The issue you can run into on the LMTV revolves around the load safeties used in the cylinders to keep a load from falling if a hose fails. Air pockets trapped in a cylinder can be compressed and store energy. When you shift a valve direction, this stored pressure can be released quick enough to lock up the safety, and if there is still stored pressure, hold that safety in the locked position and keep the cylinder from moving. It doesn’t seem to happen on the cab cylinder but it is a fairly common occurrence on the tire cylinder, probably because of the angle the cylinder is mounted at.

I have a fair bit of experience with electronics types working in engineering sections. In my experience ET’s typically make fine engineers as they already typically understand flow and flow control. Valve = switch or variable resistor, check-valve = diode, restricted orifice = resistor, accumulator = battery or capacitor, ect… and system analysis for understanding and troubleshooting comes easier to them…

I spent about 15 years traveling from one 3rd world dump to the next as an engineer before getting sidelined. Most of the time my trouble shooting abilities are good but this hydraulic problem was getting annoying.

 

[INFChief]

I can’t believe that these aren’t self-bleeding. I wonder if you could also pull the A/H reservoir dipstick and purge air by pumping the manual Jack and alternately selecting raise / lower to cycle the OHA back to the reservoir?

 

[Ronmar]

well thats pretty much what he did the AOP reservoir is vented, so you don’t even have to pull the dipstick…