I have a 1983 Z28. It has that 7.5" rearend with 26 splines. I am wondering if anyone knows how much more can 2 measly little splines increase the strength? I want to buy a Torsen Posi to replace my weak posi now. I will be putting in 3.73 gears. About 400 HP and 400 lbs.-ft. torque. I am just worried that the axle will snap like a toothpick the very frist solid launch I have?
Any comments or better yet what do you have for a rearend, and engine power?

 

Two little splines make a huge difference. I know that going from 28 to 31 splines increases torque capacity about 31% assuming the same axle material.

If you're really making power, aftermarket axles are alot stronger and not just surface tempered like OE axles. IMO an aftermarket 26 spline would prolly be stronger than a stock 28 spline. You could get better 28 spline axles and the torsen and convert your housing over and add a pretty good unit for cheap.

I wish I could find some cheap 28 spline axles (stock would be OK). The lowest price i'd seen so far is $125 a piece and junkyards around here seem hard up....

 

With the stock rears, the axles arn't the primary concern, its the housing. The housing flexes causing the gears to improperly mesh.. thefore BAM! Beef up the housing. Get an aluminum cover with the bolts that preload the bearing caps, weld the tubes and you should be able to hold on to the rear a lot longer. Of course if you are running slicks with that engine, the 10 bolt just will not tolerate it for that long. Hope that helps

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• 89 Formula 305 WS6
  SFC's, LCA's,
  Spohn Panhard Bar
  Air Foil
  Flowmaster Cat Back
  Tranny Cooler
  A/F Ratio Meter (not a mod but it sure spurs interest)
  Trans Temp Gauge
  Most "Free" Mods
  3:73, Zexel Torsion Posi
• 90 Eagle Talon 2.0
  (Winter Beater)
  Mods? Um, no

 

I might have some 28 spline axles. I took swaped the rear in my 89 Formula.. have to check which spline count they are.. arg. Email me if you want me to look.

 

I've converted to 28 splines and have beefed up the 10 bolt as mentioned in the above post. So far only 6 hard passes down the track (see times below) and the diff hasn't exploded yet. This season will be the real test to see how long a 10 bolt will last. Once it goes, a 9" goes in.


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Follow my racing progress on Stephen's racing page
and check out the race car

87 IROC-Z SuperPro ET Bracket Race Car
461 naturally aspirated Big Block

Best ET on a time slip: 11.242 altitude corrected to 10.69
Best MPH on a time slip: 121.52 altitude corrected to 127.76
Altitude corrected rear wheel HP based on power to weight ratio: 504.5
Best 60 foot: 1.546

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

 

Omega, what type of rearend do you have now that you swapped? How is it, and can I ask how much they cost?

Thanks everyone for your help

 

Stephen 87 IROC

What exactly do you have for a rearend?

 

A 1986 10 bolt. I originally had a 3.27 geared 9 bolt but there was nothing available performance wise for it.

The 10 bolt has aftermarket 7 5/8" 4.10 gears, 28 spline carrier with aftermarket axles. The axle tubes have been welded and I have a LPW Ultimate rear cover.

 

I got a pair from Camaro Heaven (1-800-CAMARO1) for $75 each. At the time he didn't have two disk brake ones, so I had to turn down the flange on one drum brake axle.

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1985 Yellow IROC-Z 5.0 HO, T-5 3.73 Torsen, 4 wheel disks
PFCM pads, GTA wheels, Koni yellows, B&M Ripper, Dynomax

 

Thanks, if Omega's don't check out at 28, that's what I was looking for. I'm not in any hurry though.