12 bolt Refresh Questions [Archive] - Chevelle Tech

: 12 bolt Refresh Questions

Chicken Coupe
Jun 10th, 08, 4:45 PM
Had a few questions. Looking for someone experienced to respond.

Stock posi 12 bolt in 1970 Chevelle unless welding the tubes to the pumpkin is not stock. 3:31 gears to the best of my knowledge and passed the eyeball test of axle turns, vs. driveshaft turns etc. to verify.

I don't think it's ever been rebuilt. When I pulled the brakes and axles to remove the backing plates, there was some dried up remnants of gear lube in there, brakes were shot, completely shot. Can't figure out why they put on new drums, but they were in nearly new condition.

The ring and pinion wear look great, the pinion seal did not seep even a drop after driving and then sitting for months, and there is not noticable play at the axles, pinion, or slop in the gears.

Doesn't seem to need much, so before throwing money into something that doesn't seem to need it so my plans are to replace the axle bearings and seals, and button back up. I'd like to install a nicer rear cover too. I like the Moser unit, but as I will basically be installing for looks alone, anyone have experience with the Summit version and/or the Moser?

But I am not sure of the axles. I would like to get an axle diameter measurement to compare to what's there now. If they have worn too much, I'd rather spend a few hundred to do that on top of bearings and seals so I don't begin dripping axle seals after a few hundred miles.

Any rear end specialists that can throw some feedback, specific or in general and provide the axle diameter? Any guidelines to fluid and additives?
Thanks in Advance!

Jun 11th, 08, 10:16 AM
Just look at the axles where the bearing rides on them and you will be able to tell if they are shot or not. If there is no groove where the bearings ride and it is not chewed up there either I'd say your good to go. Add the posi additive from GM first when you go to refill it and it should be fine. The tubes are not fully welded to the pumpkin from the factory so somebody has been it there ahead of you.

442 Harv
Jun 11th, 08, 10:27 AM
Also if there is a groove in the axle, you can buy axle saving bearings for it, the seal lip rides in a different spot. Used them on two cars.

Chicken Coupe
Jun 11th, 08, 11:29 AM
Hmmm. Bearing areas look odd. No signs of wear to speak of, but there are a few spots in the bearing area that appear to be lower than the machined area. Not chewed up, lower, like a bad casting.

I have to go do some real work but I'll try to post a photo as time permits.

Jun 12th, 08, 9:56 AM
Sounds like a couple of new axles may be in order. I had similar damage on one of my axles so my welder machinist buddy offered to fix it. He welded it up and turned it back down on a lathe. Looked great but wore like butter. I had to replace the axle shortly after since we had screwed up the heat treat and the bearing wore a groove in it.

Chicken Coupe
Jun 30th, 08, 5:50 PM
Needed axles. Bearings and seals had been replaced before but the axles were too worn down and the seals were leaking.

Did not whine when I drove it. Ring and pinion looked darn near new as did the 4 pinion gears, pinion shaft, and thrust washers. Someone had the carrier apart before, hopefully to put in new carrier bearings and clutch discs. There were no center section leaks when I got it (not even a drop) so I decided to leave well enough alone. Put on a new alum rear cover and filled it up.