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Old 06-21-2018, 06:27 PM   #1
Randy Schonscheck
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Default 8.5 S Spring Posi

Ok here we go. I've changed the posi clutches numerous time on my 80 Camaro since it was new. Always used GM clutches and basically had no problems installing them. So now since my dealer said they are no longer available from GM I had to go to the after market. The kit comes with 2 .060 shims which have to be used and then they have 2 of each, .010,.015, .020. The new clutches are a little thicker than the factory ones too. From the factory it came with a .094 on one side and .098 on the other. In a previous rebuild I also put a .012 shim on each side. The thing I'm running into is when the clutches are in at about the tightness I've done in the past the spider gear shaft can't slide between the axles (C clips) . If I take out some shim thickness out so the axles can get by the splders are sloppy. I've heard of guys installing thinner c clips or grinding or buffing the axle ends. If anyone has any ideas or what I'm missing or screwing up please let me know. Thanks, Randy
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Old 06-21-2018, 06:59 PM   #2
Alan Nyhus
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Default Re: 8.5 S Spring Posi

Not sure what thickness yours are but Dorman #81050 has one each of .150 and .155 thick. I believe the end play should be about .022-.025 max. Sometimes you need to juggle clip thickness to get it right. GM used to sell a package of 10 with five different thicknesses. -Al

P.S. You can also take out a clutch pack shim and shim the pinion gears a bit more.
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Last edited by Alan Nyhus; 06-21-2018 at 07:01 PM.
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Old 06-21-2018, 11:31 PM   #3
Randy Schonscheck
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Default Re: 8.5 S Spring Posi

Thanks Alan, My clips are in the .147 to .150 range. I'm going to see if I can hunt up some thinner ones or have some machined to thinner specs. I've run into silly problems in the past but this one takes the cake.
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Old 06-22-2018, 06:33 AM   #4
Alan Nyhus
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Default Re: 8.5 S Spring Posi

You can also machine a flat on the cross shaft. -Al
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Old 06-22-2018, 12:37 PM   #5
Tom Broome
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Default Re: 8.5 S Spring Posi

Street car I hope. I'm with the others, clearance the cross shaft (do they still make the notched ones) or thinner clips.
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Old 06-23-2018, 08:47 AM   #6
Greg Reimer 7376
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Cool Re: 8.5 S Spring Posi

On the late 70's-early 80's 10 bolt, there was a tendency for the axle retaining C locks to get wallowed out and a bit thin in use with the result of them falling out, then the tire,wheel,brake drum and axle would come out while the car was going down the road. Not a happy scenario.If you need that last little bit to get the spider gear post in,thin down the end of the axle a bit-not over .010" at a time, then try again. Be sure the C lock groove on the axle and the C locks fir snug-sometimes axles show that they are getting wallowed out from a bunch of loose motion between them. Make sure the C locks aren't worn thin or bent or they might be able to slip out as well. If the axles and the C locks are nice and snug, try thinning down the end of the axle a little at a time so as to maintain a minimal clearance there. You want axles that exhibit as little endplay as you can get to eliminate stuff getting looser with age and use and coming apart. This works on a 12 bolt as well,both rear ends are quite similar. Keep the spider gears snug in the differential carrier as well, too much looseness results in issues as well, but you don't want them so tight that lube has a difficult time getting in between parts that need it.
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Old 06-29-2018, 10:27 AM   #7
dwydendorf
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Default Re: 8.5 S Spring Posi

The original posi units were made by Eaton. I think you can still get the original type clutches through a dealer that handles the Eaton parts.
The factory clutches were broken in on a break in machine after being soaked in a pan of gear lube. You could do something similar by assembling the differential with preload plates and springs and turning the axle a half dozen times in each direction. It won't apply as much pressure to the clutches as the breakin machine did but it would be better than what you have now.
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Old 06-30-2018, 10:25 PM   #8
Randy Schonscheck
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Default Re: 8.5 S Spring Posi

Sorry been gone for a while. Got things working by doing the install with lots of gear lube and then rotating it about 30 to 40 tomes in each direction, It seems like it gives it alittle breakin mode to take the "fuzz" off. Everything fit perfect. Most experts on differentials do not like synthetic lubes either on limited slip posi 's. So I'm going to give that a try too. Been using synthetics for 30 years. Anyways, thanks guys for your help and advice. Randy
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