The Stovebolt Site Forums The Shop Area The HiPo Shop First Inspection of My Differential Gears

Hey Bolters,

I am updating my AD to an open driveshaft and I'm hoping to use a 1964 Chevy 12-bolt rear end I have on hand in my build.

I opened the pumpkin today, drained the oil, cleaned it out with brake parts cleaner, took a visual inspection of the gears for wear, cracks and chips, used a dial indicator to check backlash and finally put white lithium grease on a few of the ring gear teeth to check the wear pattern. Below are my findings and some photos of the ordeal. Any thoughts and advice is most certainly appreciated!

The gears all moved smoothly, but I noticed a few nicks in the housing that holds the smaller gears (not sure what that's called).

I also noticed some wear on the ring gear, all the way at the heel of the teeth, like a taper. I wasn't sure if it was machined that way, or caused from excessive wear.

I noticed a small nick in one of the pinion gear teeth.

When I coated about 6 teeth with white lithium grease, I held a little resistance on the pinion shaft, then rotated the ring gear several times in each direction, when I did that, almost the entire drive side and coast side of the ring gear was missing grease. The face and flank had grease on them, but the sides of the teeth were nearly bare. This made sense too be because I was only able to read a backlash of 0.002" tops with a friend holding the pinion shaft in place.

And last but not least there was a fairly large amount of rust inside on the ring gear and other locations.

I am trying my best to save money, but I'm also dropping in a SBC 383 that when built I expect to bring 400+ HP and torque. So my priority is safety and doing things right. After viewing the photos, I would appreciate it if you all chimed in with advice on rebuilding a diff myself vs. trusting this one vs. having a pro take every penny I have. I've read several articles and forum posts concerning rebuilds and it sounds like if I'm patient and careful, I can get it done. But I've had people give me the impression that rebuilding a diff is a mystical process and only the pros can get it right.

Local gear specialty shop said depending on the condition of the rear end, I'm looking at $800-$1800 for him to rebuild it.

I tried to embed the photos and for whatever reason I can't ever get it to work, so if anyone knows what I'm doing wrong, please help me out on that topic too.

Thanks as always Bolters!

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Based on your post, this rear sounds like it is in god shape. The only question I have is the last few photos show some pitting on the ring gear. Do you have a better photo of this?

The rust is from water standing in the housing, displacing the the lube at the bottom. I don't think there's enough damage to warrant a rebuild, but there might be a low-pitched hum created by the rust pits as the gears mesh. Nothing drastic, but possibly annoying.

I'd suggest going at the rust with a steel scrub brush and some Diesel fuel, WD-40, or other lightweight oil, followed by a good flush with a pressure washer or a trip to the coin car wash. Rear ends are incredibly rugged, so don't worry about doing any damage with a cleanup. The blemishes on the carrier housing are just casting flaws that were not completely machinde away when the carrier was manufactured. No sweat there. Does the gear ratio suit your purposes?
Jerry

I have other photos, but of the same quality as what is posted here. I have to admit, all I see in the photos are the spots of rust that wouldn't wash away without scrubbing. Could you be specific about where you see the pits and I can look for a better photo. I think the rust debris and my poor photography might be what appears to be pitting. I did not scrub off the rust, so there may be pitting underneath, but I did not notice much, if anything wrong with the surface of the ring gear. But that doesn't mean it's not there.

The gear ratio is 3.73 and I think I'd like to stick with that since my trans will have a final output of about 0.70.

It looks like a good rear end to me. Check the carrier brgs. There should be no side to side play in the carrier assem & the same with the pinion brgs. That rust will lap itself out after you run a ways. You might change the grease again after a thousand miles or so.

The photo I referring to was the last two in the initial post.At the top of the ring gear there are spots. It coulf be camera angle, lighting or my screen. It could be nothing.

Ahh, ok. Those spots are all either rust that the brake cleaner didn't knock off or part of a rag I mistakenly used to rub off oil and it left lint behind. I cleaned the gear up more afterward and the small spots were all gone and just some patches of rust remained.

Run it!
You can rebuild it later, if it needs it...it'll let you know.
Inspect & change the oil after a few hundred miles, anyway.

cm