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Learn from Chucky..., FMTV cab support tool

serpico760

serpico760

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I accidentally came across this while searching for something else in the TMs the other day. Cab support tool, haven't found the section yet that shows you how to use it but here it is.
TM_9-2320-366-20-1, unit maintenance 1 of 5, E-4, page E-7, actual page #s are 1537-1540. I have modeled it in SolidWorks 2022.
Cab support tool Step file
Cab Support Tool SolidWorks 2022
 
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Ronmar

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Unless of course it is the cylinder and rod end where you must be working. Raise the cab just short of the balance point, take a measurement from the top rear engine lift bracket to the top rear of the engine tunnel on the cab. Since the rear of the cab comes down past the top of the tunnel there is a pocket formed there. Cut a 2X4 to length and raise the cab just far enough insert the 2X4 where it will be captive between the two measured points. Take a tie-down strap and attach from the rear engine lift bracket and the cab latch and tighten it down to put the 2X4 under a little more compression. There iwll be very little force exerted on the 2X4 with the cab so close to the balance point(2X4 is about 100X what is required for support:)), the strap will insure the cab and crutch stay put… now you can work on any part of the hydraulic cab lift system safely…
 
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Ronmar

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Lostchain said:
Why don’t you use the factory one?

View attachment 919111
Click to expand...
Thats not an up lock, the only “lock“on this cabs motion is hydraulic, that and the raised position is typically past the balance point… That is a folding “keep the cab from toppling off the front of the truck if the cylinder or mount fail, strap” they do not normally fully extend as seen in your pic…

If you mis-align the cam in the rod end, so it is in the long slot when the cab is raised, you can get the cab to move far enough forward and fully extend that folding restraint, but even then you can still lower the cab normally as it does not lock when fully extended And simply folds back up. Did this a few times learning how that dual function rod end was supposed to work. Scared the hell out of me the first time I brought the cab back over the balance point at the top, with the cam in the long opening. Without the cam in the short opening to control movement when the cab is raised, the cab lurches perhaps 18” as the rod shifts from tension to compression and the cam slides in the long slot. The cam rotating intot he short slot as you raise the cab keeps the transition over the balance point smooth. The long slot is only used at the bottom to allow free cab movement while riding on the air suspension…

 
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Lostchain

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Ronmar said:
Thats not an up lock, the only “lock“on this cabs motion is hydraulic, that and the raised position is typically past the balance point… That is a folding “keep the cab from toppling off the front of the truck if the cylinder or mount fail, strap” they do not normally fully extend as seen in your pic…

If you mis-align the cam in the rod end, so it is in the long slot when the cab is raised, you can get the cab to move far enough forward and fully extend that folding restraint, but even then you can still lower the cab normally as it does not lock when fully extended And simply folds back up. Did this a few times learning how that dual function rod end was supposed to work. Scared the hell out of me the first time I brought the cab back over the balance point at the top, with the cam in the long opening. Without the cam in the short opening to control movement when the cab is raised, the cab lurches perhaps 18” as the rod shifts from tension to compression and the cam slides in the long slot. The cam rotating intot he short slot as you raise the cab keeps the transition over the balance point smooth. The long slot is only used at the bottom to allow free cab movement while riding on the air suspension…

Click to expand...
I usually give a little tap to my pivot pin after the cab is at the balance point and it rests on that strap. I feel this is pretty safe as gravity isn’t going to give out any time soon.
IMG_0810.jpeg
 
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Ronmar

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The few times I have had that strap fully extended, there was no action required to lower the cab, it simply folded as i started pumping the cab back over the balance point(no restraint whatsoever)… there is nothing in the op manual about any form of locking mechanism on these trucks, just the caution to support the cab via other means when working on the lift mechanicals or hydraulics…
 
Third From Texas

Third From Texas

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GeneralDisorder said:
I will only add that the military technically requires troops to use a support - piece of 4x4, etc - to block the cab up while working under it.
Click to expand...

I wonder how they crack open the hydraulic system for work w/o raising the cab, though.

The M1078 isn't bad if you're reaching over from the bed. But my M1079 has no room to really work on the pump or latch for a rebuild. Even with the spare down it's a job for a much smaller and younger monkey than me. The cab will need to be up when I break the lines open.
 
chucky

chucky

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Third From Texas said:
I wonder how they crack open the hydraulic system for work w/o raising the cab, though.

The M1078 isn't bad if you're reaching over from the bed. But my M1079 has no room to really work on the pump or latch for a rebuild. Even with the spare down it's a job for a much smaller and younger monkey than me. The cab will need to be up when I break the lines open.
Click to expand...
Here Kitty Kitty !!!!!!!!
 
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GeneralDisorder

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Third From Texas said:
I wonder how they crack open the hydraulic system for work w/o raising the cab, though.

The M1078 isn't bad if you're reaching over from the bed. But my M1079 has no room to really work on the pump or latch for a rebuild. Even with the spare down it's a job for a much smaller and younger monkey than me. The cab will need to be up when I break the lines open.
Click to expand...
Easy. Army maintenance bays have overhead cranes. They just pull the box off. Four nuts, a wiring connector, and the quick connect diesel hoses for the heater.

They have cranes on the HEMTT wrecker that could do it in the field.

Mostly though - they get rid of the trucks or have them depot level overhauled before they are old enough to have that problem. Turn that junk in and it either goes to auction or comes back out of Oshkosh as an A1P2 with electric over hydraulic cab lift.
 
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