M1078 Hydraulic functions idea

[markgjsquires]

Hello everyone. I have been up and down as many threads as I can find pertaining to the cab lift/spare tire hydraulic system. I have recently been able to start working on my ‘96 M1078 and have come to a problem. None of my hydraulic functions are working. I have tried working the valves seven ways to Sunday. The air unit has not worked since I’ve gotten the truck running and after reading all the different threads I’m basically down to going through and rebuilding/repairing the complete system. Here in is my question. I have no need for the spare tire lift. Nor the suspension setup either. Has anyone used a small 12v electric/hydraulic double action pump as their source to raise lower the cab. Then I can delete all the maze of hoses and assembly for systems I won’t need. I have a “plan” for this truck and am just throwing an idea out there. I’m hoping someone at some point has had this idea and tried it with luck. Or no luck

Thanks
-Mark

 

[Ronmar]

Yes some have done it, I plan on doing it. The installed valve has restricted orifices to limit the flow to a level that keeps the safeties in the cylinders from tripping. The safeties are there to keep the cab from free falling if you break a hose or fitting. Having timed and checked pressure on mine it takes 60 seconds to raise the cab with the cylinder volume of 0.2GAL. The highest pressure was at the start of the lift at 1400 PSI. so to get what the air op pump provides, you need a 0.2GPM@ 1500 PSI unit. that is a small pump and most of these electric units are limited in duty cycle, typically to 30 seconds or so.

At some point using a larger pump you will trip the safeties and will need flow restriction to keep that from happening. You will need this anyway on the lowering side so the weight of the cab dosnt drastically increase flow while lowering. A 0.6GPM unit for a 20 second lift is a little easier to find, but I dont know if the safeties would accept that much flow.

all the ones I have seen doing it so far are using larger multi-GPM units which is overkill IMO And pulls a buttload out of the battery(hundreds of amps) and requires large cables and contactors, with only a little of that energy actually performing the work. I have asked several times for people who have done it for how much actual time it takes to raise their cab to get a better idea how much flow they can actually force thru the control valve with the larger pump, without tripping the cylinder safeties, but no one has supplied that info...

I have not yet setup a way to test how much actual flow the safeties can accept before locking, and I am a little busy building a house so it wont happen any time soon. For best efficiency and use of materials you want the pump sized so its peak output is just below the flow that trips the safeties. This way all the pumped fluid performs work and pump pressure never gets high enough to open the pump relief valve. If it can accept 0.4-0.5 GPM(little better than 30 second lift), I should be able to do that for under 90A @12V. A 24V unit would be even better, small wire and contactor, and easy to put just about anywhere...

Good Luck!

 

[markgjsquires]

Yes some have done it, I plan on doing it. The installed valve has restricted orifices to limit the flow to a level that keeps the safeties in the cylinders from tripping. The safeties are there to keep the cab from free falling if you break a hose or fitting. Having timed and checked pressure on mine it takes 60 seconds to raise the cab with the cylinder volume of 0.2GAL. The highest pressure was at the start of the lift at 1400 PSI. so to get what the air op pump provides, you need a 0.2GPM@ 1500 PSI unit. that is a small pump and most of these electric units are limited in duty cycle, typically to 30 seconds or so.

At some point using a larger pump you will trip the safeties and will need flow restriction to keep that from happening. You will need this anyway on the lowering side so the weight of the cab dosnt drastically increase flow while lowering. A 0.6GPM unit for a 20 second lift is a little easier to find, but I dont know if the safeties would accept that much flow.

all the ones I have seen doing it so far are using larger 2-3 GPM units which is overkill IMO And pulls a buttload out of the battery and requires large cables and contactors, with only a little of that energy actually performing the work. I have asked several times for people who have done it for how much actual time it takes to raise their cab to get a better idea how much flow they can actually force thru the control valve without tripping the cylinder safeties, but no one has supplied that info...

I have not yet setup a way to test how much actual flow the safeties can accept before locking, and I am a little busy building a house so it wont happen any time soon. For best efficiency and use of materials you want the pump sized so its peak output is just below the flow that trips the safeties. This way all the pumped fluid performs work and pump pressure never gets high enough to open the pump relief valve.

Good Luck!

Thank you for the response. I understand from many how well the factory system has worked after repair/maintenance/upkeep. And I’m sure it does. Being my truck is older and from what I’ve encountered so far has been a period of rest. I know I’ll have issues to fix. Im a farmer and I think on a parts shelf I have a small hydraulic unit used to open a tailgate for trucks during loading and unloading. Once I find the unit and get appropriate fittings for it I will try it out. I have a larger one that I ordered the correct fittings for but I don’t want it to be overkill. With that if I start small and work up I “should” be ok. Either way I will report my findings accordingly and let everyone know how I make out. There is something about this military stuff I fell in love with when I was 15 and we got our first deuce and a half on the farm. From there it’s tugged at me. And with this site being the great source of information I hope I can help others out in some way...