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I just learned that the half shafts on 63-74 C3's are made with 2-1/2 inch diameter tubing and the ones on 75-79 C3's are made with 3 inch diameter tubing. Can the 3 inch diameter shafts be installed on cars that had the 2-1/2 inch diameter shafts and if so is it worth doing? Is there a strength increase with the 3 inch diameter shafts? If so is it a big increase or just a negligable one? Why did Chevy make the half shafts bigger in diameter on the cars with the weakest motors anyway, was there a strength problem with the 2-1/2 inch shafts that they decided to fix after it was too late to worry about having factory engines with enough power to break them?
They interchange. I don't remember if there was a reduction in wall thickness when they went to 3" but I don't think so. If not...they would be a good bit stronger.....
I ran some in my car with the 427 years ago. Never hurt one. Killed a few outer stubs but never a halfshaft.
Good driveshaft shops can "tube" yours with thicker tubing for not too much money usually. I have 3.5"x.134" wall shafts in mine that were made for me by a local shop.
They will swap in no problem. The 2.5" were stronger then the 3". The 2.5" wall was .130" & the 3" 095". Tom's made a 134" wall 3.5" shaft but they are out of stock.
I also switched to 3" when I refurbished my suspension, it what was on hand and on sale.... Please excuse the crooked picture and the nasty exhaust pipes......
Larger diameter is NOT stronger, in this case. The 3" shafts were made with thinner material, but needed to be larger to achieve adequate strength (for the low-power late '70s C3's). The smaller diameter shafts of the early C3's were the BETTER shafts.
I agree with what has been stated here but there is a little more to it than diameter and wall thickness.
I found that some half shafts are manufactured using welded seam tubing rather than solid tubing.
I found several half shaft manufacturers do use the welded seam 3 inch tubing which will not take the torque applied to them with a performance build.
Another aspect is to make sure the half shafts are balanced, as there are several manufactures out there that will not balance their half shafts and tell you is not necessary do to the shortness of the shaft.
Van Steel sells chrome moly half shafts that they state are stronger yet lighter because they can utilize thinner tubing, but they could not give me a torque rating on the chrome moly half shafts.
If anyone uses Van Steels chrome moly half shafts please chime in.
My research also revealed that Denneys Nitro Ready, 3 inch half shafts use solid thick wall tubing, are balanced and rated for high torque applications.
They will swap in no problem. The 2.5" were stronger then the 3". The 2.5" wall was .130" & the 3" 095". Tom's made a 134" wall 3.5" shaft but they are out of stock.
Thanks...that's the part I wasn't sure of!!
I didn't realize the 2.5" were that thick either.....
Both will fit a 72....Mine had a 3" on the drivers side and the correct 2 1/2" on the passenger side....I have since put a 2 1/2" on the drivers side as well.
On the 2 1/2 shafts less the u-joints are the ends the same as on the 3 inch? The reason for the question is that I purchased 2 used 3 inch shafts before I found out they were made if thinner wall tubing. I just cannot imagine that the tubing is butt welded to the ends, I suspect the ends have a slight stub for the tubing to slip onto, hence putting thick wall 3 inch tubing on the 2 1/2 ends would be weaker than replacing to heavier wall tube on the 3 inch ends? T
Last edited by terrys6t8roadster; 01-16-2018 at 02:11 PM.
Reason: clarify previous question
Terry - I believe there is a "stub" on the yoke so it fits within the tube and would say it is like that on all sizes. I would have to get the samples I have and look inside to see but that is my recollection.
Jim- Like many others I guess I didn't pay a lot of attention to the shafts until I had a bad set in off a 67 years ago. At that time i cut the end off and mic'd it. Later I found a bad 3" and did the same. I use them along with many other display parts at the seminars I hold at Carlisle and other locations. Most guys just think the 3" are stronger due to sizing. A couple of years ago a GM engineer stopped by my both after a seminar the previous day. He was very detailed orientated guy, as you would expect a GM engineer to be, and spent some time that evening calculating the strength differences between the 2 shafts given the wall thickness's and diameters. I may be wrong but I think his calculations show the 2.5" were about 22% stronger. I just simplified it by saying the 2.5" are stronger. Now maybe in your racing, ( abusive subjection of parts on yours or friends vettes have seen a twisted 1/2 shaft? I have not. I have broken u-joints and with our drag vette have broken u-joints, shaft yokes, diff's, 4 spees, outer axles, inner axles, tongue bracket mounts,etc but never twisted a shaft. We did twist a driveshaft with a dead hook. Now that I built a 1480 12B setup and added some of my mods that solved the problems....for now. An interesting note. When I speaking with the tech at the noted supplier they were also unaware of the GM tubing sizes or how Tom had a 1350 3.5" 134" wall shaft. That was several years ago so things possibly changed.
I guess my point is with a stock system and abuse you will probably see other areas fail before twisting a GM shaft. The only reason the Tom's 1350 shaft broke was the solid spicer literally sheared in half on that dead hook and blew apart the yoke. The shaft was fine and all it needs is a new yoke welded in. Since these may no longer be offered I held on to them, the other side was fine.
Dub,
wow, that is something. It answers the question of the "stub" on the yoke. Was there corrosion at the yoke/tube seam? What wall thickness was it, if you checked it. Given some of the abuse we pushed GM shafts over the years never saw one peel open like that. Was the rest of the IRS in good shape?
I went back into my files and found some pictures. This 2.5" measured .125" I don't know if I have pictures of the 130" wall or if there was a possible measuring error at the time or not.
I see a seam on the 3" tube but don't on the 2.5", I have to get out to my shop and dig those yoke end out to see if the 2.5" was also seamed tubing. I expect it was but...?
I see a seam on the 3" tube but don't on the 2.5", I have to get out to my shop and dig those yoke end out to see if the 2.5" was also seamed tubing. I expect it was but...?
Dub,
wow, that is something. It answers the question of the "stub" on the yoke. Was there corrosion at the yoke/tube seam? What wall thickness was it, if you checked it. Given some of the abuse we pushed GM shafts over the years never saw one peel open like that. Was the rest of the IRS in good shape?
I believe I still have the parts so I can show people.
There was absolutely no rust or anything that showed a point where the 'peeling' would start from.
The rest of the suspension was fine...because like I believe I wrote...it happened when he was backing out of his driveway.
****JOKING****
The seam in the 3" tube is a torque indicator. IF a 3" half shaft is being used on a Corvette with a lot of torque...it is designed to peel apart and fail. ***END OF JOKING****
Granted.... I have never seen a half shaft that looked like that before and I am sure I more than likely never will.
01-14-2018, 11:00 PM
Half shaft question
