I have a 8.5-28 spline limited slip differential out of a 1978 Trans Am. I don't really have the money to buy the clutch kit from Yukon but I have all of the original clutches and the friction pattern on them seems pretty much in tact with a few minor worn areas as to be expected. I was wondering if I could put the differential back together with all the original clutches and it still function properly.
GM 8.5 Rear End Questions
- Thread starter BlackOldsmobile
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If its already out and taken apart, why not just wait and save up the money? Its much easier than doing the work twice...
I guess it depends on how bad you want your car back on the road. I'd try to save up like 86-blk 442 said.
my question is... how were you able to find a clutch kit from Yukon?
Do you know if you have a S-spring style posi? Or Coil pack style?
The S-spring type is a factory Eaton in Gbodies. I don't know if TransAms came with the Coil packs
the clutch packs for S-spring types, have been discontinued a few years ago and no longer available thru anyone.
With some help, I was able to dig up a source on an Abody forum, a guy who started manufacturing his own. I can give you his contact, he charges $209.00 for a set, comes with clutches and shims.
Do you know if you have a S-spring style posi? Or Coil pack style?
The S-spring type is a factory Eaton in Gbodies. I don't know if TransAms came with the Coil packs
the clutch packs for S-spring types, have been discontinued a few years ago and no longer available thru anyone.
With some help, I was able to dig up a source on an Abody forum, a guy who started manufacturing his own. I can give you his contact, he charges $209.00 for a set, comes with clutches and shims.
khan0165 said:
It's the S-Spring with the Square'd Ear Clutches, Which I can't seem to find anywhere. Now yukon makes some that have round eared clutches. I'm skeptical to wether they would fit or not. But you seem to be a rear end guy, The clutches I have are original and look to be in pretty good shape. The "Sea shell" grooves (best description I can give) in them look like they have quite a bit of life left in them. I'm not sure but I think the diff was taken out at about 40k-50k miles. It was taken out by the previous owner of my house quite a few years ago. (Trans Am enthusiast) He left the diff with all the parts. (What luck!) Everything is cleaned up and in good shape. I'd send you a pic of the clutches but I don't have a camera at the moment. Let me know what you think.
I'm not an expert, but I recently had to learn all this for mine.
The round ear'd clutches are for the Coil pack posi, everyone makes them, and they will not work for the S-spring posi. I believe they have different dimensions.
As for clutch life and wear, I can't be much help. Mine has been on hold until I can round up the funds. It slips and needs new clutches, but I haven't had it apart and don't know what the worn ones look like.
If you decide to buy new clutches, here's the contact:
[email protected] , the name is Bruce, he charges $199, plus $5.35 shipping, total $204.35
I believe this same cost as GM charged when they produced them, but you also get clutch pack shims included.
The S-spring itself is still available thru some dealers. http://gbodyparts.com/ carries some. I believe you can buy ones with different stiffness's.
the reason I have not yet bought the clutch pack... I am wanting to install larger gears, which requires setting up the carrier again, which requires a setup kit. Once you factor in all the costs, rebuilding my carrier with new clutches is nearly the cost of a new carrier. The new Coil pack style carriers are widely available, and all components are available for them as well.
If I was just refurbishing my carrier, without new gearing or re-setup, buying this clutch pack is by far the cheaper option
The round ear'd clutches are for the Coil pack posi, everyone makes them, and they will not work for the S-spring posi. I believe they have different dimensions.
As for clutch life and wear, I can't be much help. Mine has been on hold until I can round up the funds. It slips and needs new clutches, but I haven't had it apart and don't know what the worn ones look like.
If you decide to buy new clutches, here's the contact:
[email protected] , the name is Bruce, he charges $199, plus $5.35 shipping, total $204.35
I believe this same cost as GM charged when they produced them, but you also get clutch pack shims included.
The S-spring itself is still available thru some dealers. http://gbodyparts.com/ carries some. I believe you can buy ones with different stiffness's.
the reason I have not yet bought the clutch pack... I am wanting to install larger gears, which requires setting up the carrier again, which requires a setup kit. Once you factor in all the costs, rebuilding my carrier with new clutches is nearly the cost of a new carrier. The new Coil pack style carriers are widely available, and all components are available for them as well.
If I was just refurbishing my carrier, without new gearing or re-setup, buying this clutch pack is by far the cheaper option
youd know if the clutches werent going to grab. They can get really worn down before they become real loose. Remember, when the engine is pushing the car via the gears, there is a LOT of pressure on those packs. when theyre gone, they look it.
I would recommend shimming the side gears to about .010 from the spider gears UNDER PRESSURE. put the spiders in and the cross shaft with one clutch pack and its side gear. Use a screwdriver to pry between the side gear and cross pin, thus loading the pack. use a dial indicator and check the lash available to the spiders. Shim the side gear until you get about .010
RAtech used to make the shims - and Summit used to carry them - not sure if they still do.
All this does is tighten up the preload a bit, giving the packs a quicker path to "locking up" and less of a chance of wanting to break free. Factory spec for new is like 40 lb*ft breakaway I think but I have used old clutches with 25 breakaway and had no trouble at all.
Do both sides and add a new S spring to the posi unit and youll be fine for street use, and likely some strip unless youre making 500 horses or something.
I would recommend shimming the side gears to about .010 from the spider gears UNDER PRESSURE. put the spiders in and the cross shaft with one clutch pack and its side gear. Use a screwdriver to pry between the side gear and cross pin, thus loading the pack. use a dial indicator and check the lash available to the spiders. Shim the side gear until you get about .010
RAtech used to make the shims - and Summit used to carry them - not sure if they still do.
All this does is tighten up the preload a bit, giving the packs a quicker path to "locking up" and less of a chance of wanting to break free. Factory spec for new is like 40 lb*ft breakaway I think but I have used old clutches with 25 breakaway and had no trouble at all.
Do both sides and add a new S spring to the posi unit and youll be fine for street use, and likely some strip unless youre making 500 horses or something.
techg8 said:
If I put all of the original parts back in the factory configuration would it be okay? I don't have a dial indicator. It came with 1/16 inch shims. If I do this it's going to be a super tight fit with NO play in the gears whatsoever. Is that what you want when putting a rear end together? No Play?
Well if the clutches dont look totally wasted then it probably would be ok in stock config. But I havent seen the clutches either.
If it goes together that tight then I say youve got nothing to worry about, the unit probably wasnt beat up too hard. Be sure to check the play when the clutch packs are compressed.
For the spiders and side gears you want them nice and tight, but not zero clearance
For simplicity's sake A fresh clutch pack isnt a bad idea if you have the money - its good for sure and then youll never have to take the posi apart again.
you have choices.
If it goes together that tight then I say youve got nothing to worry about, the unit probably wasnt beat up too hard. Be sure to check the play when the clutch packs are compressed.
For the spiders and side gears you want them nice and tight, but not zero clearance
For simplicity's sake A fresh clutch pack isnt a bad idea if you have the money - its good for sure and then youll never have to take the posi apart again.
you have choices.
techg8 said:
I put it all back together last night. It is very tight and I can't get anything to move by hand. I'm sure it's going to be fine. The spider gears don't have any play in them, it's a tight fit. With the s spring in there. (I'm sure it'll have some movement in 85W gear oil) This is all temporary though. I'n a few years down the line I'm just going to get an Eaton posi anyways. Parts are more readily available. But for now this will do. I don't make crazy HP somewhere around 385. The one wheel peel out is embarrasing though. So this should be the remedy for now. When you put a differential in I hear if you don't put it in right it will whine. Can you tell me the proper lash for the ring and pinion? And can it be done with a feeler guage?
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