Upgraded half shaft?
Tech Contributor
Joined: Aug 1999
Posts: 15,173
Likes: 3,982
From: Connecticut, USA
The 1/2 shaft broke or the u-joint in the shaft broke OR the axle in the diff broke?
1/2 shafts don't usually break unless from very extreme abuse. U-joints, especially zerked ones, will snap in 1/2 usually at the trailing arm. If you have an original 79 diff then the axles were bad from day one.
1/2 shafts don't usually break unless from very extreme abuse. U-joints, especially zerked ones, will snap in 1/2 usually at the trailing arm. If you have an original 79 diff then the axles were bad from day one.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Stock half-shafts will break if the engine is putting out more than 500hp, the rear tires are very wide and sticky, and the rear suspension isn't properly upgraded to handle that level of torque and grip. Mostly on dead-start take-offs which generate a lot of wheel hop. That creates high stress shock-loading pulses that just destroy the shafts.
You should do more than just buy beefier shafts, if you are creating wheel hop condition....
You should do more than just buy beefier shafts, if you are creating wheel hop condition....
Pro
Joined: Jul 2012
Posts: 707
Likes: 147
From: St. Petersburg Florida
I've been using these for a couple years now on my cars.
https://fortwayneclutch.com/product/...350_1-2sh3x95/
https://fortwayneclutch.com/product/...350_1-2sh3x95/
Tech Contributor
Joined: Aug 1999
Posts: 15,173
Likes: 3,982
From: Connecticut, USA
Tom's has the strongest shaft. Those shown are stock 3 x 095. Tom's are 3.5 x 134" HOWEVER- the weak link is not the tube it is the yoke and joint. We broke a Tom's shaft when the solid spicer sheared and destroyed the yoke, the shaft is fine. Sounds like there are more issues at play here as 7T1 mentioned.
Thread Starter
Racer
Joined: Jan 2020
Posts: 388
Likes: 117
From: Tacoma, Wa
Well here is the whole story, yesterday I went out for a drive. When I was pulling into my neighborhood, I thought I'd kick her sideways. Instead of tire squeal, I heard a BANG then thud thud thud thud thud thud thud thud thud thud thud thud. I pulled over, and the half shaft was laying on the ground. It looks like it snapped from the U joint and the wheel. I'll replace both half shafts, and everything that goes with them I'll probably move to a composite spring leaf as well. Who knows what the diff looks like. I'll have a look in there when I get to it. I'm at work right now, when I get home I'll take some pictures of the half shaft. The car is at my buddies house who has an industrial lift.
1979 4 spd L48 ~300hp crank.
1979 4 spd L48 ~300hp crank.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
The stock shafts should be able to handle that amount of load...shock or not. But, we don't know what condition the shafts were in, being 40+ years old, etc.
If you can put up some good close-up pics of the damaged half shaft, maybe we can diagnose 'how' it failed and where the point of failure initiation might be.
If you can put up some good close-up pics of the damaged half shaft, maybe we can diagnose 'how' it failed and where the point of failure initiation might be.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Team Owner
Joined: Jul 2004
Posts: 40,404
Likes: 791
From: Redondo Beach, California
Upgraded strength 1/2 axles are available. For instance, 3 1/2 inch diameter, 0.095 inch wall thickness. The do require larger U-joints, 4 1/2 inch width, 1 3/8 inch cup sizes. I'd guess these upgraded azles are available from CF suspension vendors.
................................
When Chevy sold the fabled C2/C3's with the L88 engine, it was rated at 550 hp and as far as I know, the L88 cars had the same IRS rear ends that the other cars had. However the L88's used for track racing, had low gear ratio differentials, 3:08, 2:76, and for track racing, the rear end didn't see the shock loads of drag racing. With all upgraded IRS components, I've read advertisements claiming a C2/C3 IRS rear end can tolerate 1000 hp in drag race applicartions. This requires a 12 bolt differential.
................................
When Chevy sold the fabled C2/C3's with the L88 engine, it was rated at 550 hp and as far as I know, the L88 cars had the same IRS rear ends that the other cars had. However the L88's used for track racing, had low gear ratio differentials, 3:08, 2:76, and for track racing, the rear end didn't see the shock loads of drag racing. With all upgraded IRS components, I've read advertisements claiming a C2/C3 IRS rear end can tolerate 1000 hp in drag race applicartions. This requires a 12 bolt differential.
Last edited by 68/70Vette; Sep 9, 2020 at 03:46 PM.
Tech Contributor
Joined: Aug 1999
Posts: 15,173
Likes: 3,982
From: Connecticut, USA
That is from abuse, maybe not by you but the car was beat up. The inner u-joint sheared, the outer axle snapped you still have the axle nut on the end of the axle?
The 1/2 shaft is not the cause. You are going to need to rebuild the trailing arms and look at the diff for internal damage. You are going to learn a lot about vette IRS now.
What power, trans, traction and use do you have? If the power is around 500hp that will do it with some launches, if it's the stock 200hp or so motor with automatic the car was flogged badly.
You should be able to look through the flange
The 1/2 shaft is not the cause. You are going to need to rebuild the trailing arms and look at the diff for internal damage. You are going to learn a lot about vette IRS now.
What power, trans, traction and use do you have? If the power is around 500hp that will do it with some launches, if it's the stock 200hp or so motor with automatic the car was flogged badly.
You should be able to look through the flange
Last edited by GTR1999; Sep 9, 2020 at 05:05 PM.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Yep. U-joint failed in fatigue. Finally snapped and the shaft was left spinning on the backside of the wheel...until that battering broke out most of the spines in the hub.
That joint has passages to allow grease fitting and pressure lube. The passages actually weaken the part; but when used normally, there would be no problem. If you put power thru the U-joints regularly, it would be better to use joints without zerk fittings and lube passages, as they are stronger.
That joint has passages to allow grease fitting and pressure lube. The passages actually weaken the part; but when used normally, there would be no problem. If you put power thru the U-joints regularly, it would be better to use joints without zerk fittings and lube passages, as they are stronger.
Thread Starter
Racer
Joined: Jan 2020
Posts: 388
Likes: 117
From: Tacoma, Wa
Yep. U-joint failed in fatigue. Finally snapped and the shaft was left spinning on the backside of the wheel...until that battering broke out most of the spines in the hub.
That joint has passages to allow grease fitting and pressure lube. The passages actually weaken the part; but when used normally, there would be no problem. If you put power thru the U-joints regularly, it would be better to use joints without zerk fittings and lube passages, as they are stronger.
That joint has passages to allow grease fitting and pressure lube. The passages actually weaken the part; but when used normally, there would be no problem. If you put power thru the U-joints regularly, it would be better to use joints without zerk fittings and lube passages, as they are stronger.
