Hi Guys,
First off this is NOT a solicitation, it is more of a public service advisement.

Spring is here and many guys are still home working on their C2-3's, which is great. Many of you have emailed or called me with questions on how to polish and tune a posi. So maybe this thread will help those of you out there and save me from answering the same questions in the middle of the night.

When you or your shop or whomever is building your posi gets to the point of wanting a polished and tuned posi, you have to have some good understanding of just want that means. If you don't and you just rely on watching Tom's YouTube video, I will bet most will not do this correctly. The posi will work but it won't be right, maybe even be acting like an open diff.

First the posi has to be blended, radiused, and polished to help protect it from future crack formation. I'm not going to get into all that detail other than to say it takes me 3 hours to do that and I have done 100's of them. If you think it's a 1/2 hr job or your guy thinks cleaning up the windows is all that's needed, STOP now and just build it stock and it is what it is- which won't be anything close to the real deal.

Tuning involves more than leaving out the spring pack, again if that is what is going to happen, STOP and go back to the stock posi. A tuned posi will not, repeat, will not have a spring pack in it if it's correctly built. I don't care what your friend's friend had done or said, a spring pack is not used in a tuned posi.

Posi shims come in 005 increments. Most times, they are not going to be the right size for your posi. Every posi is machined differently because they were/are a production-built part and the QC on them shows. This holds true for the new in box loaded posi's, those are a whole other story.

Tom's video shows he had some shims ground in the middle of the standard size ranges and those help a lot but many times I have to use a surface grinder to remove maybe 001" not 0025" to get them right. You cannot file or use a die grinder to do this as some have asked me. For example, I just finished one today and it ended up with 030 on one side and 040 on the other, I tired various ground shims to see if I could get them closer but this posi case required those shims for it to be balanced between the sides, provide a smooth transition, and there is no backlash in the spiders.

The reason most won't offer a polished and tuned posi is because of a couple of things.
1- they don't know how to do it- big reason Ever stop at a diff shop and ask them to do one? Most times you will be told it won't work.
2- if they do and maybe have done a couple it will take 5-6 hours alone to do them correctly. Rebuilders will have 1/2 the diff done in that time for stock level builds, so that would be a 6 hour add on and shop rates are about $100 an hour for those that know what they're doing, well maybe that's not 100% since some of what I see come from shops that charge that but don't know what they're doing- in respect to some corvette specific things.

So, I hope this answers some of the common questions I see and get. I will still offer help but I am not going to be on the phone for an hour at night explaining this over and over, some of you have called me many days in a row with the same questions. If you don't get it that's ok - build it stock or have it done someone that knows how to do it.

Thank you and good luck.

 

What's this all about now? I'm not following.

 

Heh Gary..
with your advice and 600 miles later, no springs, polished (ok not perfect but i needed 4 hours).. no noise, no leaks and 2 black marks!
https://www.corvetteforum.com/forums...ay-advice.html

 

I wonder how many guys Gary has talked through this over the years...

 

A lot.
Those posi's look pretty good, nice work.

Something else I just recently found out in respect to the posi cross shafts. I mill the case for better support, nothing new there but I purchased a new cross shaft from a well-known supplier. I usually use Tom's shafts but this time I figured I would try the new vendor one. After 300 rev's I noticed there was wear forming on the shaft where it rides in the case and were the axles hit it. I never had that happen with any of the 100's of Tom's shafts I used over the years. I checked it with my hardness file set and it was softer than it should be. I was very surprised to see this and a new lesson learned-another part to check . I bought 2 of these so the next batch of axles I send out for hardening I will include these and that will take care of them. The originals were hardened and almost always show wear but we're comparing original shafts with 100k miles to a new one with 300 corners turned- Not good.

 

Well, other than replacing some seals and my yokes. My diff is still original. One of the few parts I haven't rebuilt.
So that said one day no doubt it will need it.
Shipping my diff to Gary from Australia and back may be prohibitively expensive. But probably worth looking into.
None the less. When the time comes, most likely soon now that I've mentioned it and jinxed myself. I promise not to ring our resident expert and bug him.
I can only hope that I can come on here for expert advice if and when it's needed.
And me, most likely a stock type rebuild will be fine.
Hey, after 45 years the original is still working. A standard rebuild with a few upgraded parts should outlast me.

 

Per request of the OP, I have removed posts that are apparently in competition with his thread.

As well, please do not attempt to promote Non Supporting Vendors that have been removed from the site.

This thread will be closed by OP request at this time unless he chooses to re-open.