MK48 LVS Need Hydraulics Help - Motion Control Valve

[bigmellon]

Alright Gents... I am hoping someone can help steer me in the right direction on how to get this valve body fixed. (Pun intended)

I took delivery of my MK48 FPU just 2 days ago. We got it running the first evening with a fluid top off and new batteries. Purrs like a kitten... BUT the Motion Control Valve is missing 2 fittings on the top of the unit. And hydraulic fluid gushed out on the fire up (helping to point out the issue). The hydraulic steer knuckle can be pushed side to side by hand with the vehicle off. Also, the hydraulic reservoir is empty... Looks like this is why this unit was DRMOd.

So, my research indicates that the hydraulics may have been "week" creating difficulty in turning. My guess is that someone opened this thing up to measure the pressures, and just never put it back together. I have the basic TM manuals for this truck, but the best it provides is identification of the name of the faulty unit... I need to find a detailed rebuild manual for this part. Can someone help me?

I also tried to find a fitting to cap the valve body, but am having trouble matching the thread. Maybe it is 15/16" ? Can't tell if it is metric or standard, does not look like an NPT or an AN fitting... But I sure can't run her for long all open like this. Lastly... It almost looks like there may be a needle valve that needs to go inside and is also MIA.

I did some searched on here and came up dry... Hoping someone can provide some insight so that I can accumulate some miles

Thanks!

 

[Beerslayer]

As a last resort, have you considered contacting Oshkosh? I bet they have parts for it available.

 

[gringeltaube]

.......................................I also tried to find a fitting to cap the valve body, but am having trouble matching the thread. Maybe it is 15/16" ? Can't tell if it is metric or standard, does not look like an NPT or an AN fitting... .....................

Definitely not metric - probably 7/8"-14 (UNF) if its a tube fitting boss or retaining plug that's missing?

G.

 

[bigmellon]

Here is an exploded diagram with part number for reference...

View attachment 1430670.pdf

 

[Stalwart]

If you end up purchasing from Oshkosh, IF they will sell directly to you, prepare to bring a REALLY fat wallet!

 

[Coldfusion21]

It's mostly likely not metric as noted, and it should be a standard hydraulic tube fitting. The needle valve and interior components could be made specifically for this app, you might be stuck replacing it.

What exactly does this valve do? Almost looks like some sorta check valve setup?

 

[bigmellon]

The motion control valve is what controls the hydraulic knuckle motion. It gets an input from the front steer axle and translates that movement into the hydraulic bend in the middle of the truck.

 

[BradBMI]

Another questions you guys may be able to help me with.

I have an MK48 which had a leaking hydraulic cooler. We repaired and reinstalled it. Someone in my yard started and tried to drive the unit before we refilled the fluid causing the automatic hydralic yaw steering to disengage to come on. The front wheels turn but second set will not. Anyone encountered this? If there a way to bleed the system if that's what's wrong? Looking at TM but scratching my head.....Any help is much appreciated.

 

[Guyfang]

Big Mellon.
If there is a procedure for the repair for the valve, its in the -34 TM's. It may not be a repairable item. If you look at and understand the -24P, the only items in the valve you can order are seals, and "O" rings. Nothing else. That leads me to guess, that its not a Army repairable item. No, I have not looked at the -34 TM's. But thats where you need to start.

Another reason I "Assume", (and thats always a bad thing to do) its not repairable is the fact that the DS Repair Companies that I have been in, did not have any hydraulic repair facilities. Gages, to test with, yes, but not much more then that. Crack the -34 TM's open.

 

[gringeltaube]

Guy, I doubt the OP will ever read your post; he has vanished almost a decade ago!
It may help Brad, though.

 

[Guyfang]

Yeah. Oh well.

 

[98G]

@BigRig379

 

[simp5782]

I didn't think the 2nd set of axles turned. Only the front and then the hydraulics on the RBU connection did the turning

 

[BigRig379]

Another questions you guys may be able to help me with.

I have an MK48 which had a leaking hydraulic cooler. We repaired and reinstalled it. Someone in my yard started and tried to drive the unit before we refilled the fluid causing the automatic hydralic yaw steering to disengage to come on. The front wheels turn but second set will not. Anyone encountered this? If there a way to bleed the system if that's what's wrong? Looking at TM but scratching my head.....Any help is much appreciated.

Few things to check. Make sure the aux hydraulics selector valve is pushed in. Either the brakes have to be release or put in drive to actuate yaw steering. Or start the truck and turn off the power/ ignition switch. It takes power to turn the steering off. You can try driving it and turning hard left or right to purge the air out