89BlwnRs

I recently decided to swap 3.73s and a Zexel-Torsen Posi into my 89 RS that originally had 3.08s and an open differential. This was quite a task and if you're considering this I hope you'll read this and try to think of things in advance that I didn't.

First, I gave the guy who was installing it the Posi, the Richmond gear set for a 3 series carrier, and a Richmond Mega Installation Kit (includes axle bearings, etc). Everything I gave him would have worked if my car had come with 28 spline axles like you see in most catalogs. Unfortunately it didn't. So to make the Zexel-Torsen posi work, I had to order some 28 spline axles to fit it (an Auburn unit would cost $300 and uses clutch packs, the Zexel-Torsen is a "gear type" and doesn't have clutch packs to wear out, plus new Axles were only $240).

I originally tried Strange Engineering but they told me that they didn't make axles for Chevrolet 10-bolt 7.5/7.625 rear end that I was using. So after Strange, I went to Moser who made me a set of 28 spline axles with metric studs for about $240 and they had them to me in 3-4 days.

Then, after brining the Moser axles to the place where I was installing them, we found that the diameter of the axles ends past the C-clips was slightly larger than the stock axles (a matter of a few thousanths of an inch). In a normal posi this wouldn't matter because the extra diameter would not effect the cross pin. BUT, Zexel's posi has a billet block with a cut out in it in which the axle end actually fits into, I guess for added stability? So I had to take the axles to a machine shop and have them take the axle end past the C-clips down by a few thousandths.

After having the axles machined to a perfect fit (actually closer than I would've liked), I brought them back to have them installed and then we found that the axles were too long by almost exactly .040". We originally though that this was due to the difference in the thickness of Zexel-s billet "C-clip retained" and the stock cross pin. After measuring with a micrometer, we found they were almost exact, in fact they were off by less than .002". SO, Moser just simply made the axles too long!!!!!! Now it was back to the machine shop to have .040" taken off the length of the axle.

After that trip to the machine shop, the axles actually fit into the carrier. And everything was fine. I'd also like to say that the Richmond Gear Set and the Zexel-Torsen posi gave an excellent contact patch between the ring and pinion. Richmond's installation kit was complete and ready to use.

So far, the speedo has NOT been recalibrated, and the rear end is just a tad noisy, not nearly as loud as I expected. The posi is slightly noticeable during hard turning in which the wheels don't break lose from the pavement. Lock-ups seem to be solid with this posi and very consistent. So far the rear end has about 400 miles on it and it's still going good.

I did Richmond's recommended break in procedure 3 times, and took it easy of them for a while. The rear was filled with Mobil 1 synthetic gear oil and 1 bottle of GM limited slip modifier. We couldn't find anything about this Posi in any GM manuals (even though SLP claims it's off a newer Z28) so we guessed as to what fluid to use as well as the friction modifier.

Just wanted to let you all know what a pain this can be, if you've got a 7.5/7.625" rear end, don't trust the book. Pop it open first to count the axle splines and save some trouble. Although overall I guess I cam out on top b/c the Moser axles are 28 spline (stronger than 26) and they don't neck down near the c-clips like the stock ones did.

Hope this helps somebody and saves you all some trouble.

If you know what kind of gear oil to use with the Zexel-Torsen positraction, please let me know. Also, should I have used the friction modifier???

Jason

82camaro

I'm not saying anything bad about the Zexel-Torsen limited slip. A powertrax would have much easier, and cost about the same or cheaper.


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82 camaro--original steering wheel, brake/gas pedals, seats--everything else modified
82camaro

RGZWS6

That sucks about the axles! Now I'm worried if mine will be 26ers. I have an 89 Formula with 2.73s. Do you have to pull the pan or can you check at the drum. For some reason I thought they were slotted at both ends. How much did the installer charge for the rear set up?

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89 Formula 305 TBI
160* stat, 200* fan switch, K&N, Headers, 3in Flowmaster (hollow cat) back, pullies, 1.6 full roller rockers, B&M trans cooler, home-made ram-air
3.73 Richmond gears and SLP Zexel Torsen Posi (waiting for install)

Omega

iTrader: (1)

RGZWS6, you may or may not have 28 spline axles. For 89 they just started the transition between the 2 spline types. You have to take the axle out of the rear to check (or check the #'s on it) Chances are you do, but you will never know for sure unless you check.



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• 89 Formula 305 WS6
  SFC's,
  LCA's,
  Air foil
  Flowmaster cat back
  Tranny Cooler
• 90 Eagle Talon 2.0
  (winter beater)

MRZ28HO

Cheaper than $99 plus shipping? Where? That's a very good deal. 89BlwnRs is probably refering to the SLP Torsen take off posi unit from new Z28s (TAs) converted to SSs (RAs).

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George P. Lara
1984 "L69" A4
1994 LT1 M6
Member:
SCCA, SCFB, SC3GFB

JeffT

Blwn, sounds like a pita dude. Just a couple of notes--the Auburn is not a clutch type unit. It uses an assortment of springs with a cup/cone assembly to provide traction to both wheels. It's also deemed a throw away unit--when it wears out throw it away because it's none servicable. The ZT being a gear driven unit shouldn't require any GM friction modifier because there are no clutches that heat up and grab which causes the popping noises on slow speed corners. Also, most bearing manufactures like a non-synthetic break in and then switch to synthetic. I doubt the synthetic will hurt anything and it sounds like you took your time breaking it in so you should be good to go. Later.

89BlwnRs

Yeah, I'm referring to that SLP unit for $99. You can't beat it in my opinion. And the lock-ups are rock solid.

RGZWS6:
I'd be willing to bet that it will have the 26 spline axles. I was told that many 89s have them, especially in the lower ratios like 3.08 and your 2.73s. The 28s were reserved for the higher gear ratios for some reason. The only way to check is to remove the rear-end cover and take out the c-clips, then pull that axle out (after removing the brake drums) and count the splines. The installer charged me 5.5 hours labor for the install, plus another 1.0 labor for all the hassle I put them through. They were VERY decent about it. Keep in mind I provided all parts, down to the bearings, gaskets, marking paint, etc.

JeffT:
Didn't know the Auburns didn't have clutches, I assumed the cup/cone was essentially a clutch and that's what would wear out. As far as the friciton modifier goes, will that hurt the ZT gear posi??? What exactly does this do. The ZT posi does "pop" a little under hard cornering, is this normal?

Thanks for any help you can offer, Jeff if you can fill me in on the friction modifier I'd appreciate it,

Jason

JeffT

Blwn, the friction modifier shouldn't hurt anything its just not necessary. As far as the popping you have now--I don't know because I have never used one in a car. My most educated guess would be that this unit just makes noise due to the fact that it is gear driven and all the gears inside the unit have a tolerance value and it stacks up in the drive train.

The friction modifier allows the clutches to mesh together more easily. In essance, it stops the clutch chatter internal of the traction unit which in turn stops the "popping" noises that you hear during low speed cornering.

89BlwnRs

Thanks for the info JeffT, it's appreciated.

Jason