GTR1999

In an attempt to help some of you newer guys out there doing your 1/2 shafts, take note of the flanges and tubes before you start.

I addressed this many times over the years but still get calls from guys who go out and buy new Spicer solids and wreck them trying to install them.

Look at the tubes for flat spots, that is where someone in the past crushed the tube in a vise removing old joints. If the tube is badly crushed or pitted very thin, get another shaft. I am not going to debate which shaft is stronger- 2.5 were used from 1963-1974, 1975-79 were 3", I never work on 80-82 shafts. Shafts were never balanced and never a problem. Some aftermarket shafts are balanced, it's a nice selling point. Some aftermarket shafts use thinner tubes than GM did. Again another case of doing your homework today and not buying into ads by some.

The flanges bent easy. Many times they are not picked up as bent and joints are forced into them. Either the clip will pop out -if its hammered in or the cap will bind, either way the joint will fail.

Many attempt to hammer in the joint caps, fight with the clips and then attempt to remove the joint if they haven't already wrecked it. Some remove them without damage others wreck a $30+ new joint.

I use a plate I machined from 3/4 steel. The plates sold will work but they're thinner, I don't like them. You can make something as well. Point is you need a good flat plate the flange will sit on. It is used to install and remove joints but also as a test plate since if the bare flange rocks on the plate- the flange is bent. Attempting to install the Spicer solid joint in a bent flange is not going to work. Trust me on this.

Some will attempt to rebend flanges and reuse them. Some do this because they are trying to keep an original part, others do it because they're cheap and don't want to spend the $ on a new Spicer flange or even a new knock off flange. I use the new Spicer flanges and the joints install all the time without a problem.

I do a few things in the process to seat joints and fit clips, but bottom line is this. When installed, seated, clipped, the joints should be smooth and may be slightly free or snug. They should not bind in any direction.

My recommendation is to weigh the cost of new flanges vs old bent ones. Practicality should prevail in a non NCRS car that will be driven.

Good Luck.

cottoneg

Can I ask a question that I always wondered about? Why not use solid material instead of a tube?

I assumed unsprung weight.

69L88

The physics and mathematics surrounding this question are substantial and I would have to dust off some very old textbooks to go into a detailed explanation but essentially, with a mass-produced product, it almost always boils down to the production cost. I am sure the engineers went through a number of design considerations and negotiated with the bean counters to arrive at the optimum choice. For the 1/2 shafts, they were originally 2.5” in diameter but went to 3” later, albeit with a change in wall thickness.

leigh1322

With a hollow tube;
I think you get 90% of the strength, for like 10% of the weight.
Kind of a win-win.

4-vettes

I remember in one of those classes I took years ago. This very topic of strength of a tube as apposed to a solid shaft. And my memory brings up similar numbers. Can you imagine the weight of a solid 3 inch shaft spinning unbalanced under your car??
Pretty sure they made the right choice going with a tube.

vetteman061

@GTR1999 Do you have pictures of your process in a thread? All the u joints on my '75 need replacement and visual aids are very helpful for a guy like me.

leigh1322

I played with a torsional hollow shaft calculator online, and there was very little difference in stiffness. Hollow vs solid.

Both increasing the diameter and the wall thickness made the shaft stiffer.
But the diameter does make a larger difference in stiffness than increasing the wall thickness of the tubing.
That was how I came up with my estimate that the GM C3 3" half-shafts are about 20% stiffer than the 2.5" half-shafts, even with different wall thicknesses.

Now if you got 3.0" thick-wall shafts, or Tom's 3.5" shafts, I imagine it would be hard or impossible to break them!

Works for sway bars too.
But they have a small enough diameter you only save about half the weight.

GTR1999

I recently removed a lot of my old pictorials and probably the one on shafts was in that group. Some took advantage and some have for a long time, so off they came.

GTR1999

I was figuring you would take the time to calculate the shafts, it has come up in the past. You may recall the story from Carlisle one year. I had finished up a 2-3 hour seminar which included shafts. I had cut aways of both 2.5 & 3", same pictures I have posted before. One of the GM engineers with the chevy display attended and came over to my spot later to say he was going to calculate the shafts that night. He came back the next day, which would have been Saturday, and told me the 2.5's were stronger. I never bothered to check and had no reason to doubt the man. Since then and several threads later I have seen both sizes being touted as the strongest.

The weak link is the joint. While solid Spicers are what I use and are very good, they can be broken. When the joint breaks, it takes out the yoke so in reality, 2.5-3- or even 3.5" can be broken at the yoke. We did it with 3.5 x 134" wall shafts. The tubes didn't twist but the joint blew apart the yoke completely, taking out the hokey shaft loops many think are good. We did too but after seeing how well they didn't hold up went to Tom's loops, mounted on the center of the shaft. A lot better than mounting them at the out end of the shaft.