Cab and spare hydraulics problems M1078 LMTV

[Ronmar]

Or you have gotten air in the cylinder. Because of the angle that cylinder sets at it is succeptible to the inconsistent flow caused by air pockets in the oil. This can cause the cylinder to lock in the up position as the load/safety check gets pushed against its seat and held there by the force created by a trapped air pocket. Tge safety is tgere to catch the load if you blow a line or break a fitting. It is supposed to leak away eventually and unlock but the passages that allow that may clog over time.

You can sometimes unlock the check by alternately shifting between raise and lower while pumping. Look on youtube under username rronmar (that is one of my videos up a few comments). I did a video on manually releasing that safety check. You disconnect the rear facing fitting on the tire cylinder, fish out the little debris screen then you can slide a thin probe in there to push the check ball off the seat and release the trapped pressure in the cylinder. Replace the screen and fitting and you should be able to lower the tire...

 

[MatthewWBailey]

Sounds like a clogged restrictor

Where's that? On the cylinder?

 

[FarmingSmallKubota]

Manifold should have 2

 

[Awesomeness]

Manifold should have 2

I think there's [at least] one in the cylinder too. Otherwise, if you blew a line, it couldn't save you. So there has to be something in the cylinder itself.

 

[Ronmar]

There is a safety check ball in the cylinder base. It is held off of its valve seat by a spring. The fluid flows around the ball and past the spring. If the flow gets to fast it compresses the spring and the ball seals and locks the cylinder. This check works with the restricted orifice in the control valve which is supposed to keep the flow low enough that the safety doesnt lock.

Air in the system can mess with this relationship though...

 

[MatthewWBailey]

Or you have gotten air in the cylinder. Because of the angle that cylinder sets at it is succeptible to the inconsistent flow caused by air pockets in the oil. This can cause the cylinder to lock in the up position as the load/safety check gets pushed against its seat and held there by the force created by a trapped air pocket. Tge safety is tgere to catch the load if you blow a line or break a fitting. It is supposed to leak away eventually and unlock but the passages that allow that may clog over time.

You can sometimes unlock the check by alternately shifting between raise and lower while pumping. Look on youtube under username rronmar (that is one of my videos up a few comments). I did a video on manually releasing that safety check. You disconnect the rear facing fitting on the tire cylinder, fish out the little debris screen then you can slide a thin probe in there to push the check ball off the seat and release the trapped pressure in the cylinder. Replace the screen and fitting and you should be able to lower the tire...

I tried alternating the valve to no avail. It tries to push about 1/2" then stops. I'll look at the video you made first.

 

[MatthewWBailey]

Manifold should have 2

Great video. I'll inspect those

 

[Ronmar]

I tried alternating the valve to no avail. It tries to push about 1/2" then stops. I'll look at the video you made first.

Yea they usually wont move at all when the safety is hung up. It isnt still chained down is it

If it moves, that sounds more like a clog at the control valve orifice. If you loosen the fitting facing to the rear of the truck on the cylinder, and you can move it further than 1/2" and fluid comes out that fitting, that would support a clogged orifice in the control valve.

 

[MatthewWBailey]

Yea they usually wont move at all when the safety is hung up. It isnt still chained down is it

If it moves, that sounds more like a clog at the control valve orifice. If you loosen the fitting facing to the rear of the truck on the cylinder, and you can move it further than 1/2" and fluid comes out that fitting, that would support a clogged orifice in the control valve.

I asked myself the same question while holding the securing strap in my hand lol. I thought there was another strap for a bit! Denial is a powerful force. I can actually push the cradle as there's play in the cylinder pin. The cradle is up off its home position about 1-1.5" and won't go up or down now. When I switch functions the pressure releases and tire moves 1/2" back towards home. Then the pump will push it back up 1/2" then stall. It's a new problem since I had lowered the tire 2 months ago when it was warm. I'll check the manifold restrictors first. I was initially confused by the terminology. I worked in press hydraulics and they always use the term orifice. Now it makes sense.

'04 M1078 A1. I learn something new every time I read threads on here. Thank god for you guys.

we just did the local Christmas parade good thing I didn't have a flat.

 

[Awesomeness]

I asked myself the same question while holding the securing strap in my hand lol.

Unrelated to your problem, but there is supposed to be a safety chain too. The spare tire has the black ratchet strap thing, and a safety chain that goes through the wheel. I just mention it, in case yours doesn't have one, and you didn't know you were missing it.

 

[MatthewWBailey]

Unrelated to your problem, but there is supposed to be a safety chain too. The spare tire has the black ratchet strap thing, and a safety chain that goes through the wheel. I just mention it, in case yours doesn't have one, and you didn't know you were missing it.

Yes I have that one. I learned about that one the first time I had the spare tire down. It was all rusted up so I couldn't get the tire off. I replaced the small Clevis and cleaned up the chain and painted it black.

 

[GeneralDisorder]

Yes I have that one. I learned about that one the first time I had the spare tire down. It was all rusted up so I couldn't get the tire off. I replaced the small Clevis and cleaned up the chain and painted it black.

No - there's TWO chains. The lifting chain with the threaded clevis and then a SAFETY chain that goes around the wheel and attaches to the spare tire frame with spring hooks.

You can see the safety chain hanging from my van frame to the right of the carrier:

 

[MatthewWBailey]

No - there's TWO chains. The lifting chain with the threaded clevis and then a SAFETY chain that goes around the wheel and attaches to the spare tire frame with spring hooks.

You can see the safety chain hanging from my van frame to the right of the carrier:

View attachment 886696

I only have one chain and one nylon strap...

 

[coachgeo]

I only have one chain and one nylon strap...

me too on both my fugly trucks

 

[MatthewWBailey]

Or you have gotten air in the cylinder. Because of the angle that cylinder sets at it is succeptible to the inconsistent flow caused by air pockets in the oil. This can cause the cylinder to lock in the up position as the load/safety check gets pushed against its seat and held there by the force created by a trapped air pocket. Tge safety is tgere to catch the load if you blow a line or break a fitting. It is supposed to leak away eventually and unlock but the passages that allow that may clog over time.

You can sometimes unlock the check by alternately shifting between raise and lower while pumping. Look on youtube under username rronmar (that is one of my videos up a few comments). I did a video on manually releasing that safety check. You disconnect the rear facing fitting on the tire cylinder, fish out the little debris screen then you can slide a thin probe in there to push the check ball off the seat and release the trapped pressure in the cylinder. Replace the screen and fitting and you should be able to lower the tire...

The cylinder is/was locked in up position. I
Could not get those ball checks to release. Took the whole cylinder off. I pushed the check ball in with a small center punch and got a bath. There was a lotta pressure in that cylinder. The manifold restrictors were clean no blockages. I'm rethinking the whole design as that was a pain in the butt. The two hydraulic lines are badly frayed up near the top. So they might have to go. Oil is clean/reddish.

I'm going to experiment with a 2k Jack screw that I have in hand 24v. Curious if that'll lift that tire. Seems like the fulcrum is not advantageous on the lift so the tire weight looks to be 3-4x heavier as seen by the cylinder.

 

[Ronmar]

In the video up at comment #38 in this discusdion, my system took i think 2100PSI to lift the tire. A 2" piston with a 1" rod has about 2.35sq/in of piston area in pull. Multiplied by 2100PSI, thats just shy of 5000# of pulling force to lift the tire with that horrible geometry...

Getting a shot of fluid out when you unseated the safety check means you had air in the cylinder which compressed by the hydraulic fluid, stored that pressure, keeping the check ball seated. The orientation of the cylinder makes it virtually impossible to clear the air.

They should have placed the restricted orifice at the cylinder. This would not stop the tire from lowering if you blew a line, but it would still come down at its normal slow rate. Still safe, and far less prone to issues like this...

 

[Awesomeness]

Oil is clean/reddish.

The correct oil is from aircraft, and is colored red. So this is expected.

Seems like the fulcrum is not advantageous on the lift so the tire weight looks to be 3-4x heavier as seen by the cylinder.

This is true, because for the hydraulics it's a piece of cake to lift that much weight, even at a disadvantage.

 

[MatthewWBailey]

In the video up at comment #38 in this discusdion, my system took i think 2100PSI to lift the tire. A 2" piston with a 1" rod has about 2.35sq/in of piston area in pull. Multiplied by 2100PSI, thats just shy of 5000# of pulling force to lift the tire with that horrible geometry...

Getting a shot of fluid out when you unseated the safety check means you had air in the cylinder which compressed by the hydraulic fluid, stored that pressure, keeping the check ball seated. The orientation of the cylinder makes it virtually impossie to ckear the air.

They should have placed the restricted orifice at the cylinder. This would not stop the tire from lowering if you blew a line, but it would still come down at its normal slow rate. Still safe, and far less prone to issues like this...

In the video up at comment #38 in this discusdion, my system took i think 2100PSI to lift the tire. A 2" piston with a 1" rod has about 2.35sq/in of piston area in pull. Multiplied by 2100PSI, thats just shy of 5000# of pulling force to lift the tire with that horrible geometry...

Getting a shot of fluid out when you unseated the safety check means you had air in the cylinder which compressed by the hydraulic fluid, stored that pressure, keeping the check ball seated. The orientation of the cylinder makes it virtually impossible to clear the air.

They should have placed the restricted orifice at the cylinder. This would not stop the tire from lowering if you blew a line, but it would still come down at its normal slow rate. Still safe, and far less prone to issues like this...

do you know what the port size is? SAE#? I may just switch to an aftermarket cylinder that has orifices instead of checks. I looked at a few from Magister that are SAE 6 ports.

 

[Ronmar]

All the ports on the hydraulic system are SAE-4. They use SAE-JIC adapters to match up to the JIC-4 hose ends…

Once you remove the screen, hollow Allen spring retainer and outer spring, You could probably unscrew the check ball seat using an easy-out, or drill it out, to remove the seat, ball and inner spring(whole check-valve assembly) then make a restricted orifice using an SAE pitch allen head set screw with a tiny hole drilled in it(probably the same size as the orifice in the control valve), screwed into the port. Or you could re-install that hollow Allen screw, and sandwich a disc with a orifice drilled into it, between the allen and the SAE-JIC hose adapter.

They use an Allen screw orifice on the cab cylinder in the port opposite the safety check assembly. I think its intent is to control the cab movement, when you lift the cab over the balance point, to slow the lurch when the pressure shifts onto the return line.

You could also use a flow control valve like a prince WFC-400, attached to the cylinder port. That is what I use on my hand pump only cab system to control the lowering speed. It gives full flow when raising and adjustable restricted flow when lowering(its in one of my videos).

Then you could use the same cylinder…

 

[MatthewWBailey]

All the ports on the hydraulic system are SAE-4. They use SAE-JIC adapters to match up to the JIC-4 hose ends…

Once you remove the screen, hollow Allen spring retainer and outer spring, You could probably unscrew the check ball seat using an easy-out, or drill it out, to remove the seat, ball and inner spring(whole check-valve assembly) then make a restricted orifice using an SAE pitch allen head set screw with a tiny hole drilled in it(probably the same size as the orifice in the control valve), screwed into the port. Or you could re-install that hollow Allen screw, and sandwich a disc with a orifice drilled into it, between the allen and the SAE-JIC hose adapter.

They use an Allen screw orifice on the cab cylinder in the port opposite the safety check assembly. I think its intent is to control the cab movement, when you lift the cab over the balance point, to slow the lurch when the pressure shifts onto the return line.

You could also use a flow control valve like a prince WFC-400, attached to the cylinder port. That is what I use on my hand pump only cab system to control the lowering speed. It gives full flow when raising and adjustable restricted flow when lowering(its in one of my videos).

Then you could use the same cylinder…

That sounds feasible. I'll try to extract those ball seats this weekend. I wonder how many times that cylinder has seized with the trucks in actual service.