[DeTomaso] Techno Question: Stock half shafts torque tolerance

[cengles at cox.net]

Dear Mike,


                 Thanks for the excellent review on stock half shafts. 
It was very helpful.  Now, where did I put those old stock half shafts?

                                Warmest regards,  Chuck Engles



On Fri, Jun 15, 2012 at 9:23 AM, MikeLDrew at aol.com wrote:


In a message dated 6/15/12 7 03 51, cengles at cox.net writes:

                How much power or torque can one put through 40 year old
stock half shafts?   Stock power only?  400 ft/lbs?  550 ft/lbs?

                Would there be any reason not to upgrade to Spicer half
shafts?

>>> Spicer driveshafts are not an 'upgrade'.   In fact, it's possible 
>>> the driveshafts themselves might even have less torque tolorence 
>>> than the stock ones.

The only reason the vendors were pushing that idea was because of 
failures of stock driveshaft U-joints.   They were the weak link in the 
system, but the driveshafts themselves were fine.   Replacement U-joints 
used to cost a fortune, which helped make Spicer replacements more 
attractive as well.

For awhile, Hall Pantera modified (and I use that word kindly) stock 
driveshafts to accept generic USA U-joints.   Apparently they used some 
sort of adapter pressed into the driveshaft, and used a 
smaller-than-stock U-joint.   History has since frowned on that 
modification and it's not done anymore, as the machining ruins the 
driveshaft for stock U-joint use.

For the past quite-a-few years though, stock replacement U-joints with 
much greater strength have been available cheaply from the vendors. 
Some have reported that they were actually slightly modified Toyota 4x4 
U-joints, although I don't think anybody has ever offered any proof of 
that, nor is there any suggestion that this is what they are still using 
today.   In any event, good U-joints for stock driveshafts (which are 
good) are available relatively cheaply.   I think the production of 
Spicer driveshafts for Panteras has all but ground to a halt in recent 
years.

FWIW, I have personally witnessed one Spicer driveshaft failure and 
recall at least one other, due to improper welding, where the end of the 
driveshaft (that holds the U-joint) broke away from the tubular portion 
of the shaft itself--thankfully at walking speed so there was no damage. 
Meanwhile, I have never heard of a stock driveshaft failure (not 
including stock U-joint failure).

Dennis Quella told me years ago that the Pikes Peak buggy racers that he 
builds ZF gearboxes for, use stock driveshafts.   They put out so much 
power and hammer them so hard that they actually twist like licorice 
sticks, and he showed me one with about a measurable twist in it from 
such abuse.

It did *not* break.

He said that what they would do is swap the driveshafts side-to-side 
between runs, so that it would twist once, then un-twist on the second 
run!   They would thus work these driveshafts again and again, but 
eventually would surrender them to the scrap heap.

Will you (or anyone) ever be able to impart a measurable twist into your 
driveshaft with your Pantera, even driving it as hard as you can on a 
track, with track tires?

No. :>)

Mike