FMTV Air Hydraulic Unit Repair

Reworked LMTV said:

Like this...

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Is your a photo of a unit on a MTV or a concept of one?
I’m interested……

abfisher1798 said:

Is your a photo of a unit on a MTV or a concept of one?
I’m interested……

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on MTV

Yea you can replace the air op unit with a 12 or 24v DC hydraulic power unit. It also doesn’t take one very large to simply run the cab lift or tire crane. In fact you want one sub 1 Gallon Per Minute(closer to 1/2GPM). Any more than that and it will simply build to full pressure and push the excess thru the relief valve. and it will draw electric current in relation to the flow it can produce, so small is a good thing…

it is real easy if you keep the manifold valve. If you get rid of the manifold valve you need to provide for flow control like the manifold does with restricted orifices. The cylinders have a safety feature that they can only flow fluid so fast or they will lock up. You need to control the flow speed like the orifices in the manifold do to keep this from happening…

Ronmar said:

Yea you can replace the air op unit with a 12 or 24v DC hydraulic power unit. It also doesn’t take one very large to simply run the cab lift or tire crane. In fact you want one sub 1 Gallon Per Minute(closer to 1/2GPM). Any more than that and it will simply build to full pressure and push the excess thru the relief valve. and it will draw electric current in relation to the flow it can produce, so small is a good thing…

it is real easy if you keep the manifold valve. If you get rid of the manifold valve you need to provide for flow control like the manifold does with restricted orifices. The cylinders have a safety feature that they can only flow fluid so fast or they will lock up. You need to control the flow speed like the orifices in the manifold do to keep this from happening…

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I've read the earlier discussions on the DC power unit, though it was not clear to me on how to pick an adequate replacement.
For those that have made the DC conversion, what power unit did you end up using? A PN or link would be very helpful. Maybe even a few photos of the install.

Thanks!

abfisher1798 said:

I've read the earlier discussions on the DC power unit, though it was not clear to me on how to pick an adequate replacement.
For those that have made the DC conversion, what power unit did you end up using? A PN or link would be very helpful. Maybe even a few photos of the install.

Thanks!

Click to expand...

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Hi abfisher1798 ,

I was watching a YouTube video this morning that had a M1078 that was converted to a 20k (payload) dump truck. I did a search and it seems that Northern Tool website has a NorTrac 12v, with a 2.5 Gallon tank and a 2 horse motor. The picture looks a lot like the video I was watching... There are several that were a lot cheaper and smaller might be better if the goal is to replace the hand pump. (Roughly $450) One of the returned searches was half that money for a smaller pump can reservoir.

Except for the plastic hydraulic tank, it looks a LOT like the MaxCo lift gate on one of our trucks.

Not sure where it is made.

abfisher1798 said:

I've read the earlier discussions on the DC power unit, though it was not clear to me on how to pick an adequate replacement.
For those that have made the DC conversion, what power unit did you end up using? A PN or link would be very helpful. Maybe even a few photos of the install.

Thanks!

Click to expand...

If you are just replacing the AOP, something like the below unit should work. The cab lift cylinder for instance requires just under 0.2 gallons of fluid to lift fully. My AOP lifts mine just under 60 seconds, so it is about a 0.2 GPM pump. That is a bit long of a duty cycle for a small electric pump, so to stay within a reasonable duty cycle of say 30 seconds, you would want a pump around 0.4GPM capacity At the required pressure.

It takes about 1500PSI to lift my cab and a little over 2000PSI to lift the spare tire so you are looking for something in that target flow range and pressure.

as for a rule of thumb for picking a replacement, the existing AOP uses -4 ports. You probably want the replacement to use -4 ports to get similar flow rates…

This is the one I was going to use until I decided to go straight manual. It is not horrifically expensive, It is a pretty good flow range, but not too excessive and will probably lift the cab in around 20 seconds without pulling a crapload of current(~100A?). it has SAE-4 ports which will accept the same SAE-4 TO JIC-4 adapters used throughout the hydraulic system, so would connect right up to the existing hydraulic lines. This one was designed to drive a dual acting cylinder directly so to replace the AOP, I would remove the solenoid valve controls and fix the valve rod in one position and permanently designate a supply and return port like the AOP uses. This would be a requirement to also keep the hand pump functional. Then you would only need to power the motor solenoid to turn it on or off Like the AOP. I would probably also set the relief down around 2200PSI…

Hydraulics are a bit like electricity. Power = current X voltage. For hydraulic power units, power required = flow X pressure. If the load cannot absorb all the flow, the power unit doesn’t care and will continue to build pressure to make the load move faster, if it can. If it cannot move faster, pressure will rise until it reaches it’s relief pressure(very high load). Since there are restricted orifices in the system, it will always be flow limited, so using a pump any larger than about 0.5GPM will keep the pump continually at max pressure sending excess fluid thru the relief valve and will just suck current out of the batteries, require larger wires and contractor and heat the oil unnecessarily…

Ronmar said:

If you are just replacing the AOP, something like the below unit should work. .....

New Arrivals | www.surpluscenter.com

New Arrivals, 2.954"(75mm) x 30.125"(765mm) x 2.954"(75mm) SA DISPLACEMENT HYD CYL Unused old inventory. Welded, single acting

www.surpluscenter.com

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here is specs incase they sell out or link goes bad for some reason


SPECIFICATIONS

• Voltage 12 Volt DC
• Amperage 119 Amps max.
• Duty Intermittent
• Flow 0.48 GPM at 2000 PSI
• Pressure 3000 PSI max.
• Relief Valve Setting 3000 PSI
• Pendant Control Not included
• Valve Type Double Acting with work ports open to tank in neutral
• Valve Operation Dual 12 Volt DC solenoid spring centering
• Valve Model Number Deltrol DSV-080-34M
• Ports SAE 4
• Mounting Horizontal
• Reservoir Size Useable 31 cubic inches (0.13 Gallon)
• Reservoir Material Plastic
• Size 14-3/4" x 4" x 7"
• Shpg. 15 lbs.

Ronmar said:

.....
This is the one I was going to use until I decided to go straight manual. .....

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what is the one you are thinking of for straight manual?

coachgeo said:

what is the one you are thinking of for straight manual?

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A 1.5cu/in Prince Wolverine. It is a dual action pump, so pumps handle up and down(installed pump is only single acting). And it has a valve for controlling a dual action cylinder(extend&retract).

The installed pump is about .25-.30cu/in per pump stroke, but the lever force is quite light, it also takes around 180 pump strokes to lift the cab(~45 cu/in). This one will be nearly triple that, so more lever force, but since I want to mount it in closer to the frame anyway, a longer lever will mitigate that. With it pumping .75cu/in each time the lever moves, it should take about 30 full pump strokes to raise the cab…

I am not using it for anything else but cab lift/lower, so will be doing away with all the other plumbing, except perhaps a unidirectional flow restrictor(free flow one way, restricted the other) to control the lowering speed…

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Reworked LMTV said:

First run. No control valves or tweaking yet. Yep, draws serious current, but don't care.

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That spare was moving like it had a purpose

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Reworked LMTV said:

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Can’t see the videos

coachgeo said:

what is the one you are thinking of for straight manual?

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I received the Wolverine hand pump and mocked it up to test it. The math(and guestimates) were pretty close, but it only takes 26 full strokes for the cab to reach the balance point from down and locked. I calculated the peak force to be around #45 on the end of the 20” lever, but it is actually less than #42 at the high pressure point just above the cab latch, as I can hang a 5gal bucket full of water on the end of the handle and it will just move the lever down. Considering how often the cab is typically raised, not an unmanageable load to pump. I brought it up and down 5 times in quick succession and my arms were starting to get a little tired after that It is also fast, I can pump the cab up faster than the AOP with full air tanks

It does need some flow control or a control lever limit/stop for lowering. With the valve lever in the full lower position, It lowers fast enough to start to trip the safety lockout on the cylinder(cab starts bouncing as the safety locks & unlocks). It is also faster than I am comfortable with, but I think it will work out well for my plans…

Ronmar said:

... With the valve lever in the full lower position, It lowers fast enough to start to trip the safety lockout on the cylinder(cab starts bouncing as the safety locks & unlocks). It is also faster than I am comfortable with, but I think it will work out well for my plans…

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could one put a variable flow restrictor (fancy needle valve) in one of the lines (return?) to slow it down more for lowering cab?

coachgeo said:

could one put a variable flow restrictor (fancy needle valve) in one of the lines (return?) to slow it down more for lowering cab?

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Yep, I have already specced the part and it is in a shopping cart awaiting my next order the one I planning on using will go on the line to the bottom of the cylinder. it incorporates a check valve so will be full flow during raise and restricted/metered during lowering... I will get a video of it and should probably start a new thread as this is a little off topic(but we were discussing alternatives)...

Ronmar, updates?.. all bugaboos found and corrected?... needless to say a manual pump, bypassing the fussiness if the a/o system would be a must have..

BERZERKER888 said:

Ronmar, updates?.. all bugaboos found and corrected?... needless to say a manual pump, bypassing the fussiness if the a/o system would be a must have..

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Works good, except for me leaving its vent uncovered and saturating the oil with water. Just relocated it back behind the fuel tank so I can start cutting huck bolts to remove the mid structure, and changed the emulsified oil…

I did not use the flow control device I discussed earlier and opted for a limit stop on the control lever. Now this works simply and limits return flow to control the lowering speed, but thinking about it a little further it also limits the potential flow to the backside of the cylinder. I have noticed the backside doesn’t draw fluid very well as the cab comes down under gravity. Since it doesnt draw fluid it must be drawing air someplace(control valve or cylinder rod seal), which is probably not good...

I am going to go ahead and install the uni-directional flow control I specced in the video which will only restrict fluid returning so the supply path to the back side of the cylinder will be as unrestricted as it can get…