GM 12 Bolt Rear End

[1978Blazerk5]

Hey I have a 78 Blazer with a 12 bolt rearend G80 Gov-loc and 4.56 gears.the rear end hums wheel i punch it(it only happens during hard acceration).i dont know if that is the locker or if there is a problem with the rear end.need some help.


Thanks

 

[Hogback Fabrication]

Sounds like gears to me.

 

[1978Blazerk5]

you think its starting to break or do you think it because of the size of the gears?

 

[Hogback Fabrication]

The gears are not contacting each other correctly and are probably toast.

Since you have 4.56 gears I assume they are aftermarket? If they are, the setup on them was probably done incorrectly.

If its stock, I bet you're pinion bearings are toast (truck 12 bolts have tiny pinion bearings)

 

[1978Blazerk5]

i am 90 percent sure that this was setup right.i knew the previous owner really well the truck never was doing this in the 6 years he owned it.

could i pull the cover and see if the gears are not contacting each other.(i know nothing about differentials i know how they work thats it)

 

[pauly383]

Sometimes the pinion nut can loosen causing problems , especially if bearings or a yoke are replaced without using a new nut .

You could also chock the wheels , stick the case in neautral , and see if the yoke can be moved back and forth . Thats just another thing to look at , and it doesn't cost you but five minutes .

 

[Hogback Fabrication]

i am 90 percent sure that this was setup right.i knew the previous owner really well the truck never was doing this in the 6 years he owned it.

could i pull the cover and see if the gears are not contacting each other.(i know nothing about differentials i know how they work thats it)

You can pull the cover and take a pattern to see how they are contacting each other. The ring and pinion have to contact each other just right (to the thousandth of an inch) or else they will make noise and wear quickly.

If you want to take a pattern, pull the cover, clean both the ring and pinion teeth with brake cleaner and put some kind of marking compound (which I'm sure you don't have, yellow mustard works fine) evenly across the entire face of a few ring gear teeth (in a row, use a small paint brush). Spin the pinion (via the yoke/driveshaft) while creating drag on the ring gear (create as much drag as you can and still spin the pinion) and make the painted teeth go through the pinion in both forward and reverse. Rotate the ring gear so you can see the teeth you painted, take pictures and post them up here.

Even if the gears were setup correctly some of the ring gear bolts could be coming loose (from reusing old bolts, not torquing them correctly or not using red loctite).