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Transmission- or differential issue?!

F

FMFHMMWV

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Just driving on city streets and I lose power in H. I have an m1123. I pull over and shut the truck off and shift in HL. the truck is then able to move but I get a clunking sound coming from underneath (possibly the rear), I thought maybe it was the transfer case, but I just took it apart and I don't see anything wrong with it, no shavings at all and the magnet is clean. (haven't looked at the internal transfer case differentials). took off the rear diff plate and didn't see anything wrong with the diff upon first glance. No busted parts at the bottom.

HOWEVER... while the truck is parked and all wheels are on the ground, I am able to spin the drive shaft input to the rear diff. parking brake on, all 4 wheels on the ground and chocked, but I am able to spin the yoke from the drive shaft into the rear diff. I didnt think this is right but some dude from a transmission shop said on some cars I can.

million dollar question. is my problem the transfer case or the rear diff?
 
C

Coug

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transfer case is possible though not likely.

Most commonly when we see someone post about only being able to move in HL it's a failed half shaft/CV joint. Not uncommon for the bolts holding the shaft to the differential flange/brake rotor to back out and shear off.

I've only heard of a couple times where it's something internal to the differential.
 
F

FMFHMMWV

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Coug said:
transfer case is possible though not likely.

Most commonly when we see someone post about only being able to move in HL it's a failed half shaft/CV joint. Not uncommon for the bolts holding the shaft to the differential flange/brake rotor to back out and shear off.

I've only heard of a couple times where it's something internal to the differential.
Click to expand...
both front and rear shafts were taken off and are in good condition. am i supposed to be able to spin the pinion yoke while all of the trucks wheels are on the ground and parking brake is up?
 
NDT

NDT

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FMFHMMWV said:
just tried to spin the front yoke and it wont move. wont budge a bit. but the rear one I can freely spin. so Im thinking that the only reason why I was able to get home in HL is because I was front wheel drive due to the front and rear interlocked.
Click to expand...
That is correct. Nearly every time this happens, it’s a blown cv joint, but not if you have the ebrake holding the rotors tight.
 
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osteo16

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Sounds like a sheared pinion... Not very common I'd say, but if you didn't see anything unusual about the gears then that would be my next guess. See if you can remove driveshaft and pull yoke forward out of case... 😯

This is assuming you can turn yoke freely without feeling any gear resistance.
 
Mogman

Mogman

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It would be possible to turn the pinion shaft with the P brake on if all the bolts were missing from one of the inboard CV joints.
But that should be pretty obvious.
If you did shear a pinion the input yoke would certainly have some slack in it (in/out)
 
F

FMFHMMWV

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osteo16 said:
Sounds like a sheared pinion... Not very common I'd say, but if you didn't see anything unusual about the gears then that would be my next guess. See if you can remove driveshaft and pull yoke forward out of case... 😯

This is assuming you can turn yoke freely without feeling any gear resistance.
Click to expand...
Ill have to try that after I get home. I had the rear drive shaft off and was able to spin the yoke but I have not pulled on it to see if it would pull out.
 
F

FMFHMMWV

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Mogman said:
It would be possible to turn the pinion shaft with the P brake on if all the bolts were missing from one of the inboard CV joints.
But that should be pretty obvious.
If you did shear a pinion the input yoke would certainly have some slack in it (in/out)
Click to expand...
Ill have to check on the status of the cv joints when I get a chance. This is all very good information and I cant thank you guys enough!
 
Maxjeep1

Maxjeep1

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You sheared your pinion off… if you can spin the driveshaft freely that’s the only outcome. I think it’s a very robust pinion and I’m surprised that it failed.
 
REF

REF

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I have seen sheared pinions but only in things with much more horsepower than a HMMWV could dream of.
If it is the input i would bet its more likely the yoke got lose and stripped out it's splines. with that in mind if the diff turns when you turn the pinion I would look at the output flanges and their splines.
 
Maxjeep1

Maxjeep1

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REF said:
I have seen sheared pinions but only in things with much more horsepower than a HMMWV could dream of.
If it is the input i would bet its more likely the yoke got lose and stripped out it's splines. with that in mind if the diff turns when you turn the pinion I would look at the output flanges and their splines.
Click to expand...
Yoke that got loose would be leaking before it stripped the splines? Seems pretty easy to diagnose if we were hands on
 
F

FMFHMMWV

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had to work the last two days but will be able to provide more info on tuesday. there is some resistance from the yoke but i can spin it with one hand. is there an internal clutch in this diff?
 
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