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2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Hi Gary,
You are a true craftsman and I am grateful that you take the time to explain all the details that you encounter while keeping our differentials and steering boxes in serviceable condition.
No one ever thought that our Corvettes would be around for 50 years and many other craftsman have aged out.
So many suppliers are gone and so are the talented people that serviced the different components.
Gary, you have my thanks after helping me fix what what I was sure were bad wheel bearings, turned out to be just a dirty position unit in need of a fluid change.
Your pic shows a lit of grinding and polishing on that case. Is that part of your tuneup work, to remove stress risers?
I’m still grateful for Garys help he gave me. Running fantastic and polished and tuned. Not to the level he does but I’m proud..and it really helps handling with tight hardened axles.
took me hours to polish.
That must be a very common point for a stress crack to start. I found 3 cracked posi units in a row, all cracked in that same corner. That corner is almost directly in line and underneath the ring gear teeth, and pretty hidden by the gear when assembled. Plus in this pic you can see how rough the original casting is. So with Gary's help, I feel confident my fourth one is crack free and much stronger!
BTW I found all of those cracks while cleaning the old oil off with carb cleaner. Nothing fancy. The heavy oil just stuck in the crack a little longer and was easily visible, if you were looking for it.
So if you go in there, please look for cracks.
Friends don't let friends drive around with posi s ready to explode! LOL
Now forgive my ignorance......but if the crack was not that long......couldn't one relive the metal in the area....grind it back until crack is gone.....I mean, it would look goofy but seems to me it could be a viable save.
Thank you Pete.
Yes, the old timers are gone now. I was the "kid" doing these now I'm the old guy.
Welcome to the club. When I was a kid working on small blocks, I was surrounded by old-timers working on flatheads. I thought they were dinosaurs. Now I'm still working on small blocks, and it's all kids working on LS motors. Now I'm the dinosaur.
I saw an article on a process similar to shot peemng that ARP uses on there bolts that makes them stronger. Have you considered using that or a similar one on tge cases after polishing?
From another thread currently up but also applicable to this one.
Think about all the work to remove the diff, then go through it and build it better than the common junk sold today. I get to a cracked posi and want to risk it to save some upfront money? If I was a liar and conman as some are, I wouldn't even tell the customer there is a crack, wouldn't polish or tune it, and use it. When it broke, I would tell them to send it back for another reRIpbuild. Sound crazy- it's been happening for many years. Perfect example of a current "race vendor", selling a rebuilt diff to a guy who never installed it. He brought it to me years ago to check and look what was under the cover. That same place is still in business and some here just bought diff's from them.
“No man has a right to expect to succeed in life unless he understands his business, and nobody can understand his business thoroughly unless he learns it by personal application and experience.” – P.T. Barnum
I’ve often wondered whether a cracked posi case could be repaired with the Metal locking process where the crack is stitched together? We used to have it done to cracks that formed in diesel engine crank case under where the cylinder liners were fitted.
I’ve often wondered whether a cracked posi case could be repaired with the Metal locking process where the crack is stitched together? We used to have it done to cracks that formed in diesel engine crank case under where the cylinder liners were fitted.
Interesting suggestion but I’d worry about the locks migrating. Loose metal and gears/bearings aren’t a good combination.
Well a posi housing is very highly stressed, and heat treated to harden it even more. Welding would destroy the strength from the heat treating. Now I suppose you could anneal it, weld it, and then re heat treat it, but ........ cheaper to buy new at that point, unless the part is crazy rare.
I even cryo treated my posi housing to harden it even more. And the amazing thing was you could HEAR the difference. It RANG like a BELL afterwards.
I could see that stich repair or welding working on a cast iron engine block tho, as they are not heat treated and not as highly stressed. Welding cast iron can be a little touchy, best left to experts, so the stich repair could be more reliable for many. Some have the skill to do cast iron welding. Cracks will continue to grow if not physically stopped. Then cover it with JBweld to seal it, and keep the oil in.
Hey Gary,
Thanks for the ever going information.
I’m still waiting for my body and paint shop to get me in.
Should be mid June.
Soon after I’ll be sending you my rear end.
I haven’t forgotten!
