M51A2 trouble shooting

[5ton-Ulysses]

Hi guys. Long time lurker and first time poster.
Over the winter I purchased a 68 m51a2 that’s been converted to a cargo bed. It ran and drove great when I did take it for a drive but overall I didn’t have much opportunity to take it out over the winter.
Well now that spring is here I decided to take her out and see how she did. On my way back from my buddies farm (just a few miles down the rd) I lost all pressure in the clutch and she went right to the floor. I know Typically this would this be a master cylinder issue. I’m not to familiar with working on these trucks (or anything air over hydraulic) I’ve looked through the TMs and the service manuals but so far no luck. Any help would be appreciated.

thank
ken

 

[NDT]

Clutch???? Pin musta fallen out of the linkage.

 

[5ton-Ulysses]

I’ve checked the linkage and everything seems to be in check. There is a tiny bit of pressure on the clutch pedal but I have to put the pedal to the floor to feel it.

The clutch is currently engaged (thankfully we were close and could float gears to limp her home)

 

[Mullaney]

I’ve checked the linkage and everything seems to be in check. There is a tiny bit of pressure on the clutch pedal but I have to put the pedal to the floor to feel it.

The clutch is currently engaged (thankfully we were close and could float gears to limp her home)

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By default the clutch would be engaged. Pressure plate holds the disc and the transmission turns. Sucks, but you could crank the truck in first and drive it slowly home or "sync and shift" like it sounded like you may have?

You mentioned hydraulic. Best I can tell that is a mechanical clutch - but I do see reference in this particular book about a "rotochamber". JUST GUESSING, but maybe there is fluid that needs to be in that chamber? (Maybe making it a hydraulic clutch?)

Troubleshooting guide (Technical Manual) TM9-2320-211-20 is here and talks about clutch pedal and linkage on Page 128. Anyhow there are some pictures and troubleshooting steps in the book. I don't have one so I can't give you any first hand knowledge...


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[5ton-Ulysses]

.
By default the clutch would be engaged. Pressure plate holds the disc and the transmission turns. Sucks, but you could crank the truck in first and drive it slowly home or "sync and shift" like it sounded like you may have?

You mentioned hydraulic. Best I can tell that is a mechanical clutch - but I do see reference in this particular book about a "rotochamber". JUST GUESSING, but maybe there is fluid that needs to be in that chamber? (Maybe making it a hydraulic clutch?)

Troubleshooting guide (Technical Manual) TM9-2320-211-20 is here and talks about clutch pedal and linkage on Page 128. Anyhow there are some pictures and troubleshooting steps in the book. I don't have one so I can't give you any first hand knowledge...

View attachment 893771
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Thanks for the info, I’ll have a look at the manual and see if I can find anything out.
That’s exactly how we got it home with the sync n shift. First time I ever had to do it on with a truck this big (luckily there was almost no traffic and only one light)

 

[NDT]

The rotochamber is only on wreckers. The clutch has no hydraulic aspect at all. If all the linkages outside the bellhousing are connected and moving, the issue is inside the bellhousing. Prepare for an unpleasant repair.

 

[GopherHill]

I think the clutch lining has broken loose and wadded up between the pressure plate and clutch disk. Have seen this issue a couple of times. Gather clutch replacement parts.

 

[87cr250r]

As an avid motorcycle rider clutch masters and rear brake masters often suddenly don't work one day. Very annoying. European bikes or worse because they use mineral oil in the clutch circuit for whatever reason.

Use a volunteer or your phone camera and observe proper movement of the components.

 

[5ton-Ulysses]

Quick update for those following, it was the throw out bearing! Replacement parts have been ordered, hopefully everything goes smooth from here on out. I plan on bringing the flywheel to a machine shop to have it resurfaced while everything is apart. Would anybody happen to know the tolerances by chance?

 

[87cr250r]

Make sure you use a shear stable grease for the pilot bearing. Lithium grease separates too easily from centrifugal forces leaving behind only the thickener.