1/2 Shafts

[Gary R.]

Hi guys.................Last week at Carlisle I was asked about the stock 1/2 shafts used on the cars from 63-79. There was a concern the 2.5" shafts are weak compared to the 3" shafts. I had a 2.5 shaft cut in 1/2 but didn't get to cut a 3" in half until today when I found a junk one.The 2.5" have a .125 wall & the 3" have a 095 wall. Be aware some aftermarket shafts being sold today use thinner walls. I have not seen any GM shafts fail but that doesn't mean they haven't. I have seen broken u-joints and recently sheared solid u-joints. For comparison the shafts I use on cars with power are .134 wall 3.5" shafts sold by Tom's.

[Joe L.]

Re: 1/2 Shafts

Hi guys.................Last week at Carlisle I was asked about the stock 1/2 shafts used on the cars from 63-79. There was a concern the 2.5" shafts are weak compared to the 3" shafts. I had a 2.5 shaft cut in 1/2 but didn't get to cut a 3" in half until today when I found a junk one.The 2.5" have a .125 wall & the 3" have a 095 wall. Be aware some aftermarket shafts being sold today use thinner walls. I have not seen any GM shafts fail but that doesn't mean they haven't. I have seen broken u-joints and recently sheared solid u-joints. For comparison the shafts I use on cars with power are .134 wall 3.5" shafts sold by Tom's.

Gary-------


Yes, sometimes you will see the 3" half shafts advertised as "heavy duty". I've been telling folks for a long time that they're not "heavy duty" because the tube wall thickness is thinner, just as you've proved here.

I don't know why GM went to these 3" shafts in 1975. However, I do think the manufacturer changed and that may have been the reason. I think the 2-1/2" shafts were of GM internal manufacture. I think the 3" were manufactured by Dana-Spicer. Maybe GM wanted to get out of the business of manufacturing these half shafts for a low volume application like Corvette. About the same time they replaced the axle u-joint flanges, which I believe were originally of GM manufacture, with the Dana-Spicer manufactured flanges.

GM did replace the 2-1/2" shafts with the 3" for 1963-74 SERVICE in October, 1976. So, apparently, they considered them equally strong.

[Gene M.]

Re: 1/2 Shafts

Resistance to rotational twist is a function of diameter as well as cross section. Increasing the diameter increases the cross section. I guess GM felt the diameter increase to 3" justified the wall section decrease to 3/16". One needs to do the math to confirm or dispute GM's decision.

[Louis T.]

Re: 1/2 Shafts

Hi Gene,

Did you mean 3/32 (0.09375)? (That's more in line to what Gary measured.)

Save the wave!

Louis

[Louis T.]

Re: 1/2 Shafts

Hi Gary,

Thanks for the great seminar at Carlisle - as always, lots of excellent information!

Save the wave!

Louis

[Gene M.]

Re: 1/2 Shafts

Hi Gene,

Did you mean 3/32 (0.09375)? (That's more in line to what Gary measured.)

Save the wave!

Louis

Louis,
Correcto, I must of had a brain fart. thanks for the correction.

[Gary R.]

Re: 1/2 Shafts

Hi Louis...... I'm glad you enjoyed the seminar at Carlisle. I really enjoy them as well too bad I can't get into the detail I do when someone stops in here. I can break down their work with them so they can see what it's all about.