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I own a 1969 corvette coupe with a mildly built 350, 4 speed, and a 336 rear end. I need to change one of my half shaft U joints, so I am going to change all 4 of them. I have some questions that I would like answered before I start. I have 2.5" half shafts on my car now, Is there any benefit or advantage by going to a 3.0" shaft? First, will a 3.0" shaft fit in place of a 2.5"? Would I have to change the wheel flange and the differential yoke to make the change? Are all 4 of the U joints the same part number? I plan to use Spicer non greaseable U joints no matter which way I go. I guess what I am asking is, will I be better off as far as durability with the 3.0" shafts, or just replace the U joints in my 2.5" shafts? Any info you can give me will be greatly appreciated. bvette1000
All 4 joints are the same and you will be fine re-using the 2 1/2" shafts. 3" shafts came along later, but the tube wall I believe was thinner, so little or no strength improvement.
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Originally Posted by gbvette62
As "75 said, all 4 u-joints are the same, and the larger half shafts were made from thinner steel, so they are no stronger than the smaller ones.
The same half shaft u-joints were used from 63-79, while a couple different u-joints were used on 80-82 half shafts.
Are you sure? Unless you know the actual wall thicknesses, and do the math, you're just guessing.
IIRC there was a similar thread a couple years back. With the (rumored) wall thicknesses of the 2.5 and 3.0 inch halfshafts, the 3" parts calculated out to be both lighter and stronger.
If you know the true, actual wall thickness of these halfshafts, post'em up. The math is pretty simple after that.
When you are pressing in the u-joint on the wheel side of the half shaft be sure to pull the spindle flange off of the trailing arm and bolt it on the u-joint flange or you will most likely bend your u-joint flange. If you bend your u-joint flange you cannot bend it back, it’s junk.
check out the bottom of the page on this link for pics of somebody that bent one
When you are pressing in the u-joint on the wheel side of the half shaft be sure to pull the spindle flange off of the trailing arm and bolt it on the u-joint flange or you will most likely bend your u-joint flange. If you bend your u-joint flange you cannot bend it back, it’s junk.
check out the bottom of the page on this link for pics of somebody that bent one
Another way is to bolt the two half shafts together and do one u-joint at a rime T
I bent the outer flange at the shop pressing out the U-joint and had to buy a new one for the customer. My co-worker told me to always bolt the two together.
Thanks, Richard. I'd already done these calculations earlier using the "back of an old envelope" method, and it's nice to see my calculations confirmed.
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Originally Posted by '75
I'm interested to know what the strength of each is now that Gary posted the thickness. Who knows how to do the math?
The math is pretty easy. The strength of a tube (whether in a driveshaft or a sway bar) goes up as the diameter to the fourth power. A little extra diameter gives you a helluva lot more strength, which means you can then use less of the material to get an actual weight reduction in the process.
If you all remember, back in the late 60ts some GM u-joints from the factory did not use clips of any kind, they were plastic injected and the only way to get the u-joints out was to use a gas axe to cut them out which also melted out the plastic. T
If you keep the same half-shafts, my recommendation would be to remove them and take them to a good driveshaft shop to have the U-joints replaced PROPERLY. Simple and inexpensive job, and it will eliminate any possible [unintentional] damage done by you. For strength, install U-joints without lube capability (no cross-drilled passages nor Zerk fittings).
Last edited by 7T1vette; Jan 15, 2019 at 04:01 PM.
c3 half shafts
I bent the outer flange at the shop pressing out the U-joint and had to buy a new one for the customer. My co-worker told me to always bolt the two together.
