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  #16 (permalink)  
Old 11-24-2010, 07:59 AM
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Originally Posted by big gear head
The GM Traction Lock that was used in the car 8.5 rear ends through '81 was a good unit. This is thee one with the S shaped spring in it. Parts are no longer available for it, so if you have one with good clutches in it then use it. If it's worn out then it's no good. I like the Eaton Posi best, but on a tight budget the Duragrip is hard to beat. It's just like the Eaton Posi except it used a different clutch material. The Duragrip uses a Rabestos material similar to the Ford Traction Lock and it's about $60 less than the Eaton Posi.

If you get the money later to build a good rear end then I recommend getting a 30 spline Eaton Posi, a set of Moser 30 spline axles and upgrading the whole rear end. This makes a very good, strong rear end. I've built many of these and as far as I know none of them have broke.

If you decide to up grade in the future you can beef up the rear to equal a 12 bolt by installing a posi unit for a 12 bolt along with the axles for the 12 bolt. Both need to be changed as the 12 bolt axles have a larger diameter. I did this with my 70 Nove rear 2 years ago. All components fit with no mods. The rear needs to be a 8.5" in order to do this.

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  #17 (permalink)  
Old 11-24-2010, 09:44 AM
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You can't install a 12 bolt differential in a 10 bolt. You can install a 30 spline 8.5 10 bolt differential in a 8.5 10 bolt that had a 28 spline differential. You can install 30 spline axles in a 8.5 10 bolt that had 28 spline axles, but the axles must be made for the 10 bolt. The 12 bolt axles have a .312 thick c clip button and the 8.5 axles have a .250 thick button, so 12 bolt axles will not fit without having the button cut down to .250. If you try to use a stock 12 bolt axle in the 8.5 then you will not be able to install the cross shaft in the differential.

I've built many 8.5 10 bolt rear ends with 30 spline axles. I've been through all of this many times. It would take MAJOR machine work and modifications to get a 12 bolt differential in the 8.5 10 bolt housing. First of all a 10 bolt ring gear will not bolt on a differetnial with 12 bolt holes. It just won't work.
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Old 11-26-2010, 12:30 AM
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Well I have to call you on this one as I can even post the reciept showing the number. You are dead wrong axles and center section fit the 8.5 rearend, as for the ring your correct I replaced the ring and pinion in the rebuild.
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Old 11-26-2010, 10:52 AM
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You also can't put 12 bolt gears in the 8.5 housing. The 12 bolt pinion shaft is 1 inch shorter than the 8.5 pinion shaft. You wouldn't be able to get the pinion nut on the shaft.

I'm going to have to see this before I can acccept it. I've been building rear ends for 29 years and I've owned my own rear end shop for over 13 years and I have never seen this done, or figured out a way of doing it. There is really no reason to do it because there are plenty of 30 spline 8.5 differentials available and 30 spline axles that are made to fit the 8.5.
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Old 11-27-2010, 09:37 AM
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[QUOTE=big gear head]The GM Traction Lock that was used in the car 8.5 rear ends through '81 was a good unit. This is thee one with the S shaped spring in it. Parts are no longer available for it, so if you have one with good clutches in it then use it. If it's worn out then it's no good.


I picked up the housing yesterday, he had the Traction Lock unit, he says it worked great when they took it out the car, it looks good. Is there anyway to tell how good it is or not? Measuring clutches or something? I still need to get some axles, gears and c-clip eliminators for it..
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Old 11-27-2010, 10:26 AM
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The only way to know if the clutches are good is to remove them and look at them. There is a swirl pattern cut into the plates. If this pattern is worn then the clutches are worn out. These clutches almost always need to be shimmed tighter, but there are no shims made for this unit. I have found some shims that work in it, but they are not cheap. Setting up these old Traction Lock differentials is getting to be more difficult now that the clutches are no longer available.
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Old 11-27-2010, 11:50 AM
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As far as shimming the clutches in an old s-spring GM unit, I have bought shim stock sheet from an industrial supply house like MSC in .005" and .007" thicknesses and cut my own using tin snips. Crude, but it works fine.
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