Author Topic: Posi rear end question?  (Read 3650 times)

Offline MEXICANKAMIKAZE

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Posi rear end question?
« on: January 10, 2016, 12:24:21 AM »
So I have a 79 c20 and I was wondering what do I need to do to make my rear end posi? Any info on this subject would be appreciated.

Offline SkinnyG

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Re: Posi rear end question?
« Reply #1 on: January 10, 2016, 01:25:00 AM »
The "easiest" is a "lunchbox locker."  These can replace the internal guts of your open differential, and can be done by anyone with reasonable mechanical skills.  I have not heard a lot of positive about them, but I have not run one.

Any other type of posi requires removing the differential carrier, swapping the ring gear, and then re-setting the back lash.  This is a bit more advanced, but with a cheap dial indicator and (potentially) some extra shims, it can be done.

If you are changing the ring and pinion as well, you either need to be very disciplined and patient and have some special tools (including a hydraulic press) to setup the gears with the proper pinion depth, pre-load, and backlash.  I seriously would not recommend this to most people.

If your axle needs a full rebuild (it ~is~ over 30 years old, eh?!), you may want to consider farming the whole thing out anyway.
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Offline Greybeard

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Re: Posi rear end question?
« Reply #2 on: January 18, 2016, 12:30:47 AM »
If you are really wild and don't care about your tires you can add a Lincoln locker. To do this you remove the cover, wash the gear oil out really good, fire up your Lincoln tombstone style arc welder and start welding the spider gears together, clean the rear end out really good again and fill with gear oil. Now you have a locked read end.

But you asked about a posi different animal altogether. There's no actual 'posi' anyway, it is a brand name used by GM long ago, limited slips just got that name over time. A limited slip can come in many different configurations from what is called a mechanical locker to a clutch activated one. Most of these need the entire rearend disassembled to install. However, there are some that just replace the guts as as SkinnyG said. these would include the Powertrax, EZ locker, and a few others. You'll have to check them all out to see which one is easiest to install.
« Last Edit: January 18, 2016, 12:42:23 AM by Greybeard »
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Offline Greybeard

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Re: Posi rear end question?
« Reply #4 on: January 18, 2016, 11:05:21 PM »
Yup ^^^

And after looking down the line this popped out >>

http://www.ebay.com/itm/GM-Chevy-12-Bolt-Yukon-Spartan-Locker-30-Spline-SL-GM12-30-Posi-Locker-NEW-/371512400029?hash=item567fdd589d:g:pKsAAOSwBLlVQu3m&vxp=mtr

It would be the easiest to install since the carrier does not have to be removed. Just pull the axles, remove the retention bolt for the cross shaft push the cross shaft out enough to remove the guts of the carrier, transfer what is necessary onto the new locker push it into the carrier, push the cross shaft in, replace the retainer bolt, push the axles back in, put the cover on and fill with oil. Sounds simple right?

http://www.ringpinion.com/b2c/PartCats.aspx?SearchMode=SubCat&ParentID=11
« Last Edit: January 18, 2016, 11:12:58 PM by Greybeard »
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Offline csdineley

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Re: Posi rear end question?
« Reply #5 on: January 19, 2016, 10:11:35 PM »
Since the OP stated he has a C20 wouldn't he be more likely to have either a 14 bolt Semi floating or Full Floating axle rather then a 12 bolt?
1987 V20 Custom Deluxe, Vortec Headed 350, SM465,Np205 14Bff 4.10

Offline Greybeard

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Re: Posi rear end question?
« Reply #6 on: January 20, 2016, 09:00:15 PM »
Good point!  :-[
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Offline wz7u

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Re: Posi rear end question?
« Reply #7 on: November 10, 2021, 05:09:46 PM »
At dire risk of resurrecting a zombie thread with my second post here, I also have a '79 C20 (BB, TH400) with the 14 bolt differential in a 4.10:1 ratio. I would like to see a posi in Pearl, but I'm thinking I should just give it to the differential specialist. Before I go bugging him for numbers and such, any ballpark estimates on something like this? No, not interested in a Lincoln posi (lol), but would like to get my mental ducks in a row prior to taking the plunge. I'm finding go-fast stuff for C20 is orders of magnitude less available than for a C10. I want to tow the house off its foundation, but also want to smoke BIL and his SB '81 C10 in the 1/8 or even the 1/4.  ;)

Still reading through the pages to see if my question has been asked/answered prior. As a retired wrench I appreciate the brain trust here. Thanks for looking.
'79 C20 454/th400 "Pearl"

Offline VileZambonie

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Re: Posi rear end question?
« Reply #8 on: November 12, 2021, 08:35:57 PM »
If you are looking to pay to have it done, you best just get a price from whoever you want to do it. Obviously, you'll save $ if you do it yourself but if you don't have the means then expect to spend in the $2k range
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