leigh1322

It all depends on the useage, the HP, and the abuse. Shock loading at the track during a launch is the worst.

My Buddy George twisted / pretzled his 2-1/2" GM H/S with a ZZ427, a Tremec and 4.11s, with 11" Nitto street tires, and a drags strip style launch, on the street. But he does have a 11.8 first gear and 500TQ. The clutch drop did it. 500X11.8 is a big 5900 TQ at the H/S.
I know of a vintage 650HP road race car that runs 3" GM H/S and 1350s and treats the U-joints on a maintenance program. 2200# TQ on the H/S at speed, but for hours.
GTR's son snapped his 1350 solid spicer U-joints clean in half, with a modded L82, stick, slicks, and a high rpm launch at the track. 3.73? Gears, but it dead hooked. 3" H/S. Guess the spicers were the weak link that time. Maybe 3800# TQ. So the sudden shock loading killed that one. An auto would hit softer.
There is a Canadian 496 C3 that got 10.5s out of his at least a couple of times, with an auto, and stock sized parts, a wheels up launch at the track with slicks. Then he prudently upgraded everything.
BKBroiler has lots of runs at the track. 12.15 w/ a 383 and a Q-Jet. Auto, 3000 stall, drag radials, 1.69 @ 60 ft. 3.0" H/S, 300 runs, 1350 u-joints. Changes u-joints @ 4 years. 4200# TQ @ H/S.
AJRotham has a 698HP 496, 1972, auto, 3.36 gears, and runs 10.5 at the track or on the street. 3.5 Tom's H/S with 1350s have held up for many many runs. Drag radials IIRC. 1.51 @ 60 ft. 5800# TQ @ H/S.
427 Hotrod has 1100+ HP and his Tom's 3.5 x .135" wall H/S, with huge 1480 u-joints, and they hold up fine, at the track. IIRC he runs 9s or lower. Likely the fastest C2/C3 on here. Rare Dana 60 diff tho.

That help?

The Spicers are supposed to Yield at 2200# TQ. (4400# for two). That means they bend some and do not spring back. Several of these cars push them that hard or harder on launch. (With the shock load of a clutch, you may not even get that lucky). After they bend a little a couple times, the needle bearings will start to bind up. They won't last long after that. You can feel the binding if you remove the H/S and rotate the spicers by hand. If you catch it in time.

gearheadz

Yes and I was just thinking the same as I was reading the responses to the post? As a 40+ year drag racer and street C3 owner for 30 years, unless you have an extremely high HP street car (~1000hp) or have a modified car running slicks/drag radials on a prepped track on a recurring basis, these high buck drive/half-shafts are extreme overkill. The weakest point of failure are clearly the u-joints. If you have HD Spicers or equivalent and serviceable shafts, the average C3 of any factory engine/trans combo (even modified for higher HP) does not need large diameter, thick walled, chrome moly or carbon fiber shafts. They are more eye candy than anything. There's nothing wrong with eye candy but if you are cost conscious or under a budget, your cash can be used for far higher return on investment and cost effective purchases.