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  #1  
Old 06-15-2006, 02:37 PM
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Default posi unit?

I just purchased an open 8.5 rear end and I want to go to posi. How difficult is this and who makes an affordable kit? I am not going to be racing, just want the posi unit for ****es and giggles.
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Old 06-15-2006, 03:21 PM
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Lightbulb Re: posi unit?

First, congrats! That will be a lot tougher piece than that 7.5" that you've been running.

Second...a new diff would be available from Eaton or Auburn. Clutch type from Eaton, or cone type from Auburn.

Avoid the locker type from Eaton: only engages at low speeds and is designed for trucks. The Auburn is a 'cone' type and not rebuildable. I would suggest the "Pro" series if you go with the Auburn.

A 28 spline unit will work with your stock axles just fine.

Either way, a new piece will retail for ~$400-450. Might find a deal for closer to $300 on Ebay or the net. A used one could be an option, but it might have worn clutches/cones and you'd have to rebuild it. Then its no bargain. The new style Eatons should last a LONG time. The shop who just installed my new Eaton (30 spline) thinks they may never need to have the clutches replaced with proper lube/additive changes. We'll see...
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Old 06-15-2006, 07:07 PM
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Default Re: posi unit?

The job is not too difficult, it is time consuming. There is a tech article on the website for it. You'll need a dial indicator with a magnetic base for the backlash measurement. And, I think you need new bolts for the ring gear. I didn't change the pinion on mine. The big savings here was that my tooth pattern was good so all I had to do was shim the new posi to hit the backlash number.
I found the shimming to be the most tedious part.

Patrick
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Old 06-15-2006, 07:25 PM
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Default Re: posi unit?

In most cases, if your not changing the pinion, and just replacing the posi unit.
You can just swap the units and reuse the exact same shims. Just make sure to install the bearings on the new posi unit correctly.
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Old 06-17-2006, 09:30 PM
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Default Re: posi unit?

I'm in the process of upgraded my diff and I still have the stock posi unit if your interested. My vehicle has 42k on it. Everything worked as it should before removal. Im dropping a 700hp motor in so stock wont do.
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Old 06-23-2006, 05:25 PM
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Default Re: posi unit?

Ron PM'd you.....thanks
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Old 06-23-2006, 05:27 PM
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Default Re: posi unit?

will any 8.5 3.42 10 bolt GM posi unit work? I have seen ones on eBay for camaros, trucks, etc for fairly cheap. Will they interchange with the G Body rearend? I plan on completely rebuilding the rear brakes, replacing all bearings and seals before installing the rearend into my car.
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Old 06-27-2006, 11:24 PM
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Default Re: posi unit?

yes, i had one put in my diff from a 79 or 80 camaro, works great
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Old 06-28-2006, 12:09 AM
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Exclamation Re: posi unit?

Note: Avoid the 'locker' type Eaton units. These are usually take-offs from trucks, and do not actually engage over some fairly low wheel speed. (30 MPH?) The Eaton clutch type units are much preferred.
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Old 06-28-2006, 12:16 AM
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Default Re: posi unit?

Quote:
Originally Posted by Keller
Note: Avoid the 'locker' type Eaton units. These are usually take-offs from trucks, and do not actually engage over some fairly low wheel speed. (30 MPH?) The Eaton clutch type units are much preferred.
i agree totally
i seen many of the cone style auburn break, The insides of em look like a monkey clock.
On the higher HP cars ive built i usally just go with a spool or mini spool m but if im gonna cruise it alot, i always stick with the clutch style units from GM.
There are a few tricks and upgrades you can do those also , like adding extra clutches, stiffer spring, etc..
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