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What is the best method to clean out hydraulic lines on an FMTV?

Reworked LMTV

Reworked LMTV

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Hi Guys!
I need to clean out the cab lift hydraulic lines and check valves on my m1088. I assume the check valves are in the manifold?
What is the best method to do this? Do you flush with anything in particular? Push air through the lines? Add a little alcohol? Are the little filters in the manifold cleanable?

All new to me : )
 
Suprman

Suprman

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You can take the manifold filters out. As far as cleaning lines I think you can take them off and blow out with air. If your hyd system got water in it and you have milky stuff everywhere then you are going to have issues and I dont think a quick flush is going to help.
 
simp5782

simp5782

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You just do a general purge flush on it. Refill, run and let it cycle. then drain. Repeat if necessary. Do the systems have a filter on them? If so you will want to replace that for sure a few times. Just use hydraulic fluid. luckily it is cheap at tractor supply. They generally have a 15 percent off coupon on their website for hydraulic fluid.

You can use diesel or kerosene but it will attack seals if it isn't all removed.
 
Doug Roberts

Doug Roberts

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I'm at total failure with my hydraulics. I rebuilt my air/hydraulic power unit, and now in review of this, I see an error I made, so I'll take it apart and start over. I have a '95 M1078 , and I don't think I have the hydraulic filter on my truck ( illustrated in TM 9-2320-365-20-2) . I now don'thave hydraulic pressure in the manual pump , and can't raise the cab. fun fun fun
 
R

Ronmar

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There are filters in the valve body, I believe at different locations depending on which valve model you have.

There are flow limit check valves in the cab tilt and tire crane cylinders that are there to prevent a cab or tire falling in the event of a hose failure. There are restricted orifices in the control valve return plumbing that control the overall flow to a limit that keeps the flow limit safeties in the cylinders from activating during normal use..

Because of the installed safeties I would not flush the system with the crane and cab cylinders in the circuit. Since they are narrower passages you could flush crap into them and trap it there.

I would disconnect the lines at the lift and tire crane cylinders and connect the lines to each other with a bushing. I would drain and refill the AOP with clean fluid or kerosene. I would disconnect the return at the AOP and run it into a bucket, then operate all circuits(crane and tire cylinders bypassed) to force the old fluid back to the return. Once I start seeing new fluid or kerosene at the return I know the loop is purged. Don't let the pump run out during this process. Once all the circuits are purged(cycle suspension cylinders all the way in and out), If you used kero, Refill the AOP with clean fluid and do it again until you only get new fluid out. you will have to either suck the old fluid out of the manual pump or cycle it during this process to get the old fluid out of it and into the system. Once you are only getting new fluid out, reconnect the return to the AOP and confirm proper level.

The cab and tire cylinders I would disconnect from the structure and do individually by hand with clean oil or kerosene either using a hand pump or compressed air and a pressure bottle to cycle clean fluid thru them.


After everything is purged, I would then pull and clean/replace the main valve filters...
 
R

Ronmar

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Doug Roberts said:
I'm at total failure with my hydraulics. I rebuilt my air/hydraulic power unit, and now in review of this, I see an error I made, so I'll take it apart and start over. I have a '95 M1078 , and I don't think I have the hydraulic filter on my truck ( illustrated in TM 9-2320-365-20-2) . I now don'thave hydraulic pressure in the manual pump , and can't raise the cab. fun fun fun
Click to expand...
Is there fluid in the hand pump reservoir? There is a filler plug on the top left/front corner...
 
coachgeo

coachgeo

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So not looking forward to this. Just only recently learned that an uncovered pump will get water in it thru the brass breather.... so this task is now on the list of todo's

thanx RonMar for info. Makes since to do this is similar fashion as doing brake bleeding. was wondering how I could purge air after cleaning out..... and if kero/diesel might be a good cleaner.

question.... how do you purge and refill cab lift and tire cylinders separately as you propose? Example... My tire ram (was not installed prior) I want to install but discovered U can NOT push in the ram due to check valves without hooking it up to the manifold. Suspect cab ram is same as a safety feature?

So in general for others would it be best for both tire and cab ram

>keep them installed at first and FULLY extend them with pump..
>brace everything proper
> then remove them.
>Affix the lines together and clean out everything as you suggest above.....
>find someway to drain what is in these rams and refill with new fluid before reattaching.... (this is the question of the day)

>then do whole system again like doing brakes bleeding? (bucket with some oil in it and return line in it along with keep reservoir topped off)
 
Last edited:
Reworked LMTV

Reworked LMTV

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When my cab was stuck in the open position I believe I ran two hydraulic lines to the ram from the hand pump. I flipped the leaver back and forth on the pump with the pump pressure to get it to break free.

coachgeo said:
So not looking forward to this. Just only recently learned that an uncovered pump will get water in it thru the brass breather.... so this task is now on the list of todo's

thanx RonMar for info. Makes since to do this is similar fashion as doing brake bleeding. was wondering how I could purge air after cleaning out..... and if kero/diesel might be a good cleaner.

question.... how do you purge and refill cab lift and tire cylinders separately as you propose? Example... My tire ram (was not installed prior) I want to install but discovered U can NOT push in the ram due to check valves without hooking it up to the manifold. Suspect cab ram is same as a safety feature?

So in general for others would it be best for both tire and cab ram

>keep them installed at first and FULLY extend them with pump..
>brace everything proper
> then remove them.
>Affix the lines together and clean out everything as you suggest above.....
>find someway to drain what is in these rams and refill with new fluid before reattaching.... (this is the question of the day)

>then do whole system again like doing brakes bleeding? (bucket with some oil in it and return line in it along with keep reservoir topped off)
Click to expand...
 
Reworked LMTV

Reworked LMTV

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I am eliminating the air over hydraulic pump. It is just too prone to failure.

One wonders why there is no check valve on the brass filter to prevent ingress of h2o.
 
R

Ronmar

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coachgeo said:
question.... how do you purge and refill cab lift and tire cylinders separately as you propose? Example... My tire ram (was not installed prior) I want to install but discovered U can NOT push in the ram due to check valves without hooking it up to the manifold. Suspect cab ram is same as a safety feature?

So in general for others would it be best for both tire and cab ram

>keep them installed at first and FULLY extend them with pump..
>brace everything proper
> then remove them.
>Affix the lines together and clean out everything as you suggest above.....
>find someway to drain what is in these rams and refill with new fluid before reattaching.... (this is the question of the day)

>then do whole system again like doing brakes bleeding? (bucket with some oil in it and return line in it along with keep reservoir topped off)
Click to expand...
I described a way. you need a pressure container with a valve though. I have used old gas cylinders and fire extinguishers for this to pre-lube engines and cycle cylinders. you can also use plain compressed air. 120 PSI X3.14 SQ/IN piston surface area = 360 pounds of force on the piston...

fill clean pressure container 1/2-2/3 with oil, pressurize container with compressed air and close valve. Remove air fitting and connect/adapt fittings to attach to cylinder port. invert container so oil covers valve and open valve slowly. make sure return port from cylinder is ported to a suitable catch basin. with air or fluid you must go slowly as too much flow will lock the safeties.

You should also be able to move them mechanically, you just cannot move them too fast otherwise they will lockup. I recall you describing this, but I am thinking yours were just stuck(moved too fast and locked or sticky from setting).

As far as I know there is no pilot mechanism in them and mine do not act as if they do. On mine you can lift the cab half way then shift the valve to lower and the cab will start down on its own under gravity. if it were pilot operated you would need to apply some down pressure to cycle the pilot valve.

You could also do as Reworked suggested, once the hand pump is purged and filled with clean fluid, you could connect it directly to a port and cycle the cylinders slowly with the hand pump. Couple of ways to fry this fish...
 
Doug Roberts

Doug Roberts

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I'm sure there's no fluid in the hand pump reservoir. This certainly helps , and I have to pull the air/hydraulic power unit and redo it with the right stuff. The rubber bumper washer feels like something left out. I'll follow this fix list I have. Tomorrow I'll pull it.
 
Doug Roberts

Doug Roberts

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so I took the pump off and assessed what I needed that I did'nt have in my kit. Sent that request to MRO, ate lunch and injured my right hand. So I'll heal while I'm waiting for that to arrive. I appreciate the help so much. I feel more certain about it coming togeather now. I'll be back on it soon.
 
S

SausageGuy

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To put new fluid in my air over hyd system I removed return line from pump and put in a jug behind air filter and ran system when ever i needed to and just kept adding new fluid. Eventually it was all new that way.
 
coachgeo

coachgeo

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SausageGuy said:
To put new fluid in my air over hyd system I removed return line from pump and put in a jug behind air filter and ran system when ever i needed to and just kept adding new fluid. Eventually it was all new that way.
Click to expand...
have not looked close so it may be obvious... but just in case will play stupid and ask....... which is the return line?
 
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