This was before I started to take it apart - hopefully it will look like that again eventually.

Now that I have my posi unit disassembled I thought I would start a new thread on this.


My posi unit was slipping at times (with drag radials, on the track surface) and there seems to be some wear on the cluch discs - to my untrained eye.


Everything else appears OK - including springs and plates, not pictured. My spiders are the 17 / 10 units which I think are the better ones. I talked to Gary GTR1999 and due to his backlog, I think I'm going to do a much more simplified, do-it-myself fix here, with Gary's generous advice on parts selection and some assembly help from my brother in law. He did this stuff years ago. I'm planning to replace / upgrade the clutches and upgrade the stub axles.

 

I would replace the clutch pack, with Kevlar if you can afford it, and step up to the yellow springs. That should restore/improve factory performance. That and a rebuilt kit from Yukon should do it. You'll have to source the idler (spider) gear cup bearings from another source as they don't include them in the kit for some reason. I got mine off of Amazon. Be sure to shim the clutch pack as tight as you can: 100 - 120 ftp's to turn one axle while holding the other in a vice.

Posi carrier - I meant to say shim the carrier as tight as you can.

 

Gary is great with the advice even when he is not building it.
Have you thought about polishing the posi case and tuning it? You eliminate the spring pack.
See Gary for details.
Good luck doing this yourself.

 

I wrote a long explanation but my pc had issues and lost it so I am not going to do that again.

However to recap what I wrote:
1- check the posi case for cracks, use if none found
2 - Polish the case inside and out, radius the windows smooth so there are no edges. Those that say you shouldn't polish a case because it makes it weaker either don't know how to do it or don't know what they're talking about. All you are doing is blending, removing the peaks and not going beyond the valleys.
3- Use your 10-17's radius the edges
4- Tune the posi. Use new solid steels only. If you don't want to try and tune it make sure the lash is 002" and use new springs. To Tune it watch Tom's video. When correctly done you will have about 800 revs CW & CCW on the clutches, the cross shaft will slide out freely in any position, there will be no lash, and the posi will have a smooth action without any binding.
5- Fit a LH Steel cap. You can make or buy one of Tom's. They have to be machine fit for 001" rock in the cap on the race. A RH steel cap is not needed and will not offer much of a benefit other then to pad a rebuilders invoice or give someone a false sense of improvement.
6- Use a solid sleeve, again these have to be fit. If you need a steel cap you need a solid sleeve.
7-ARP ring gear bolts, use them over the those in the kits or reusing old ones. Use Loctite 271 or 272. Clean with Acetone first.
8-If you are reusing your gears, you should have witness marked where they were on the posi case. Set the pattern to where is was, set the lash to 006-007. There shouldn't be more then 002" change through 360* on the gear lash. If you see 003 or more check for burrs, dirt, etc between the gear and flange.
9- Use USA Timken bearings, use full compliment axle bearings not the caged ones that come in some kits.
10- Axles- recheck yours. If yours are in the 185-200" distance from the face to snap ring they are good. Check the hardness of the faces, they should be 48-55 Rc, if they are soft you can have them hardened to reuse. Original axles, hardened and in spec, are better then rebuilt or new axles sold today. If you want stronger then 17 spline you can go to Tom's 30's but the good spiders are long gone now. I still have stock but you won't find them anywhere. Presently there are imported 30's or new Eaton's. I would use the new Eatons over the imported ones but they are not as good as what Tom had made.

If you want to check locally you will probably find a shop to do a cryo batch if you want some added strength. REM polishing is very good too but really not required for most applications. If you plan on long high rpm road racing it will cut down on heat but for a street car with some trips to the track it's not needed.

If you build it like I mentioned above it will hold up for application and more. It takes time and patience, you have the machine tool access which most do not.

Good luck.

 

Great info Gary^^^^^ and why you get paid for this work........Thanks for the great explanation.

BTW-I especially chuckled about your statement, "Those that say you shouldn't polish a case because it makes it weaker either don't know how to do it or don't know what they're talking about"

 

Great post Gary! Thanks for the info...and the headache. 😬

 

Thanks guys.
Bruce take your time but check all your parts first. I will stop back from time to time to see how you are making out.

 

If you'd like a detailed description with about 200 pics, here is my thread from 2017 of Gary building my Super 10.
Great details about what makes a tuned posi.

The man is a craftsman and a gentleman.

https://www.corvetteforum.com/forums...ial-build.html

 

bman - Thanks for the link. I went though the whole thing. Gary's work and documentation are amazing.

Gary- Thanks for you response. I printed it for reference. BTW - I did witness mark the ring gear. Also, I checked my axles - both are .200 from spring clip groove to face. I will check into getting them hardened.

Re parts: The only vendor I see with steel clutches is Van Steel. Didn't see them, for C3, on Tom's website.
Springs and plates are also hard to find. I see them on Zip website. These are the 400lb units. Is that what I need?

 

solid steel clutches are still available. I never use springs or plates, with a correctly tuned posi they are not needed. Any eaton distributor will have the parts. Some of the new parts I see I don't care for, some places are still selling the old snowflake clutches so buyer beware - do your due diligence. Build prep is as important as the procedures of the build.

What direction are you planning on going with the build?

 

Springs and plates by Eaton are available at Summit for around $45 for the set if that is the route you choose. Summit also has the spider gear thrust washers.

 

Van Steel has solid steel clutches. I plan on getting those. (BTW the clutches I took out are steel). I don't really want to tackle the tuned posi option, so I'm planning on going with new springs and plates. Is 400 lb the right spring rating?

Is the Corvette rear known as an 8.2 or 8.5?

Thanks for that info. I checked Summit and they do have the 400 lb set - for $48. Amazing. Just confirming the 400 number at this point.

 

Yes, the 400# yellow spring is the next up from stock. I'm no expert, but I understand this a good rate for a street driven car. The 600# springs might cause some tire chirping in tight turns. The other posters would know better then I.

 

Well I've got the 400 lb springs and plates on order from Summit and the steel clutch set from Van Steel.