M1090 Dump bed not Descending!?

[spalinko]

A previous mechanic started working on a m1090 dump truck he took apart a lot of wiring and disassembled most of the hydraulic systems. I was able to get everything put back together, including the electrical system, Runs Great! bed goes up but will not come down...

I've looked through the technical manual one through five, all the troubleshooting, I've checked that the hydraulic lines are hooked up right, then the electrical systems, there's a brand new four-way valve on it.

The only thing I've found damaged was the valve subplate, the 6x6x6 aluminum block that all the hydraulic lines feed into. There was a plug that was stripped, but with lock tight it is holding and oil pressure. I've been trying to find that Parker subplate, but it's obsolete nobody has one on eBay or anything so I'm trying to get an equivalent part.

I don't think it's the subplane and I don't think it's the four way valve and everything else seems to be working right nothing else has been taken apart any suggestions? is this a common problem?

 

[spalinko]

So I just checked that electric for away control valve thing and it's working and I swapped the wiring and it still works so my wiring is good and that four-way is good.... You can see in the picture The cylinder goes directly into that subplate.... maybe that's the thing I need to a look at

 

[NDT]

Does the Parker valve spool have plungers that you can manually push in on the ends? If so try pushing those to see if you get movement in the ram. I think I see the safety brace up? Don't want ya getting squashed.

 

[spalinko]

That's an excellent suggestion I did not think of that I did take the Parker Valve off, I set my phone in front of it, and recorded while I toggled the up down function and it did move both directions.

Tomorrow I'll take a look and see if I can manually move those valves

Does the Parker valve spool have plungers that you can manually push in on the ends? If so try pushing those to see if you get movement in the ram. I think I see the safety brace up? Don't want ya getting squashed.

 

[coachgeo]

Look up threads on Cab and Spare Tire cyclinders that will not retract (check ball issue). Am willing to bet your bed cylinder has a check ball too.. and may actually be your issue.

 

[chucky]

Is there a visable vent for the cylinder you can see like on the hyd fluid tank ? Have you pushed on the bed with like a backhoe bucket to see if its tweaked somehow ? Most dumps dont have down pressure other than the weight of the bed ! What lever/ whatever lets your bed down normally ive never seen the controls for a 1090

 

[spalinko]

That is a good point but since the bed does go up either direction I put the valve, does seem that the valve is working also, I checked the wires continuity, all good.

The ectric valve seems to be working but the subplate is my guess, he took it apart... and stripped a plug which I was able to fix with some loctite....But the subplate is obsolete and I'm trying to find a new one or compatible part from Parker. Before I tear into it

 

[spalinko]

So after messing around with this morning manually actuating the four-way directional valve operates the dump bed into the up position but still will not put it in the down position looking me to believe that something's wrong with that Parker sub plate it's too simple of a system to have any other issues anywhere else

 

[coachgeo]

So after messing around with this morning manually actuating the four-way directional valve operates the dump bed into the up position but still will not put it in the down position looking me to believe that something's wrong with that Parker sub plate it's too simple of a system to have any other issues anywhere else

still sounds to me like check ball in the cylinder that prevents it from coming down as a safety feature. It is suppose to release when you operate the valve to make it to come down.... but they stick and nothing happens...... how much similar in conceptual design does the dump bed cylinder look from the spare tire cylinder and the cab lift cylinder? do they look to be same company for the cylinder? The valves to operate are apparntly different companies... but cylinders may not be..... thus it could have same check ball as the others

 

[spalinko]

That check ball is probably going to be in that Parker subplate hu?

Honestly I haven't looked at the cabs hydraulic system, it has been operating fine and there are more lines coming in and out of it compared to the bed lift's valve system.

If it's inside that subplate I'd like to find the diagrams, The Parker company is trying to get them for me but I don't expect them to be in any rush. I suppose it could be in the hydraulic tank?

The bed lift is such a simple hydraulic system there's only two important things in there, the valve and subplate, three if you count the cylinder. That four-way valve and the subplate are the only two things that do anything in that system that I can find in the diagrams...

huh

still sounds to me like check ball in the cylinder that prevents it from coming down as a safety feature. It is suppose to release when you operate the valve to make it to come down.... but they stick and nothing happens...... how much similar in conceptual design does the dump bed cylinder look from the spare tire cylinder and the cab lift cylinder? do they look to be same company for the cylinder? The valves to operate are apparntly different companies... but cylinders may not be..... thus it could have same check ball as the others

 

[chucky]

The fluid has to have somewhere to go when its time to come down so since the tank is low with the fluid being in the mast try taking off the fill hole of the tank like your adding oil to see if its hydolocked like nowhere for the air in the tank to escape to let fluid back into the tank for cylinder to collapse down ! Or start breaking lines loose one at a time till one starts squirting out and the bed starts down

 

[spalinko]

Yes, So as the hydraulic ram moves, the "wadding" moves forward or backward, hydraulic oil comes out and through four way then fills into the other side of the rams wadding. if I watch the hydraulic tank as I'm actuating the cylinder it only rises or lowers a tiny amount in the hydraulic tank it stays within the safe range (about a half an inch drop and rise) as it's designed.

So if the hydraulic cylinder is fully extended there is oil in the entire cylinder but as the cylinder comes down oil goes into the back side of the wad, there is no air entering the back side off the wadding as the cylinder depends, so the oil level in the tank doesn't rise or fall very much at all it's almost constant as it should be.

Also the hydraulic tank breather is working perfectly fine.

to

The fluid has to have somewhere to go when its time to come down so since the tank is low with the fluid being in the mast try taking off the fill hole of the tank like your adding oil to see if its hydolocked like nowhere for the air in the tank to escape to let fluid back into the tank for cylinder to collapse down ! Or start breaking lines loose one at a time till one starts squirting out and the bed starts down

 

[coachgeo]

That check ball is probably going to be in that Parker subplate hu?

Honestly I haven't looked at the cabs hydraulic system, it has been operating fine and there are more lines coming in and out of it compared to the bed lift's valve system.

If it's inside that subplate I'd like to find the diagrams, The Parker company is trying to get them for me but I don't expect them to be in any rush. I suppose it could be in the hydraulic tank?

The bed lift is such a simple hydraulic system there's only two important things in there, the valve and subplate, three if you count the cylinder. That four-way valve and the subplate are the only two things that do anything in that system that I can find in the diagrams...

huh

they are in BOTH cylinder and manifold (sub plate) of cab and spare. system.... Power Packer manifold used by cab tilt and spare lift systems appears to be similar to your Parker Sub Plate in part of it's function. Not sure exactly. Just speculating. Hence why the question to you about how similar that big ram for the dump is, to those other cylinders..... if it is the same...... then likely the ram has check ball also. Maybe search generic dump truck articles about ones that are stuck in up position. This might shed some additional light on this. FMTV is mostly commercial truck parts.

 

[chucky]

If the cylinder comes down the fluid has to go back in the tank . They are just swapping spots ! get a big bucket /sweet feed bucket put it under the truck where the supply hose goes into the cylinder get big ass open end wrench and brake that line loose a few threads so it leaks good but no where near enough to come all the way off to see if the bed slowly starts to come down like 1 mast section if it does the mast isnt stuck so some hoses got swapped and plumbed the wrong way or get some big braces /blocks /what ever and throw that plumbing block contraption away its causing way to much drama a reg tri axle dump truck hoist is stupid simple so copy that tank /hose / cab controls / i feel sure its pto driven off the side of the transmission ! Just an over engineered safety block blah blah blah thats causing all your problems if it is plumbed correctly ! KEEP US POSTED !

 

[spalinko]

So out of the two lines going into the hydraulic cylinder I would assume you're talking about the one on the bottom. I understand I could allow oil out of the bottom side of the cylinder, by doing doing that oil would still have to move through the four way the four way valve filling the top of the cylinder as the wadding moved correct?

It is a standard hydraulic cylinder, if I bleed oil from one side oil still has to enter the other side and if the Parker subplate is not working properly then oil may not enter the top section and I could end up with air entering the system correct?

 

[chucky]

So out of the two lines going into the hydraulic cylinder I would assume you're talking about the one on the bottom. I understand I could allow oil out of the bottom side of the cylinder, by doing doing that oil would still have to move through the four way the four way valve filling the top of the cylinder as the wadding moved correct?

It is a standard hydraulic cylinder, if I bleed oil from one side oil still has to enter the other side and if the Parker subplate is not working properly then oil may not enter the top section and I could end up with air entering the system correct?
View attachment 901905

To make sure the mast/bed isnt just stuck /twisted / hung by letting some oil out of the cylinder thru loosened leaking hose into bucket to see if bed will come down then you know its all in the 4 way contraption !

 

[chucky]

And please do not get under the bed or up in the framework without heavy bracing cause this stuff will gladly kill you rite now and laugh about it ! Easy peasy and your all done .........

 

[spalinko]

The bed will bleed all the way down if left for 5-6 months without the braces up (that's how I found it) and rise perfectly with the electrical switch that controls the four way on top of the sub plate.

The four way operates perfectly though. I took it off the subplate and used my phone to film it actuating. Also manually activated it while running same symptoms.

I also turned the four way around and all that did was make the down button raise the bed and the up button do nothing.

 

[chucky]

Something is not letting the fluid out of the mast or something not letting the fluid back into the tank the fluid is bleeding by the problem if it will come down in 6 months ! I say get a bucket of fittings and bypass the block just temp with the return to tank line just stuck in a bucket to see if that lets it down !