Drive Shaft Concern

[Rick B.]

Recently after rebuilding the 454 in my '72 I had an immediate rear thrust bearing failure which resulted in having to tear down the engine once again.
During the brief period in which I was able to drive it and break it in I was less than impressed with the increase in power that I had somehow anticipated from the rebuild. Consequently, this time around I made some "internal changes" within the engine while keeping it completely original looking from the outside.
I dyno'd the engine last week and was able to get 590 ft./lbs. of torque from it and 468 h.p. with the original carb and air cleaner ! While I am very pleased, I decided to freshen up my transmission and torque converter to ensure everything could handle the extra muscle. Not stopping there I naturally replaced the u-joints with some h.d. Spicer units and while doing so I noticed a strange mark on my main driveshaft tube.
It would appear that possibly sometime in the cars' earlier lifetime the emergency brake cable may have hung down loosely enough to make contact with the driveshaft tube. This is the only possible explanation I can come up with for this perfectly concentric line I found neatly "cut" into the surface of the driveshaft.
I carefully did a non-destructive test of the driveshaft tube and found the wall thickness to be very consistent at .187 inch (3/16") except at the point of the groove which is at .177 inch. The groove is almost 1/16 wide.

My question is this :
Is there any way of accurately predicting what such a wear mark may cause in terms of overall weakness to the tube under hard/heavy acceleration? In other words is the reduction of 10 one-thousandths of an inch going to cause a potential fail to occur under extreme loading or are these driveshafts built so beefy that it should be little or no concern?

Access to quality driveline shops in my area are limited and I have not had much luck finding someone sympathetic to my quest in repairing this one or manufacturing another to orig. specifications.

Any comments or advice would be greatly appreciated.

Thanks, Rick

[Edward J.]

Re: Drive Shaft Concern

Rick, you maybe able to find a used shaft on flea/bay. otherwise you can do a internet search I know there are many driveline companys out there that do re-tubing of a drive shafts using the same yokes.(and some will built a custom shaft for the high horse cars) there are some here in the Boston,Ma. area.

[Rick B.]

Re: Drive Shaft Concern

Given some horror stories I have heard from others regarding excessive vibration after they've had driveshaft work done, I probably wouldn't feel comfortable sending my work to anyone without at least hearing good recommendations from others on this site or elsewhere.

[Terry M.]

Re: Drive Shaft Concern

Rick,
Are there really no driveshaft shops near you? That would be your best solution. Even a shop that does four x four work can do the Corvette shaft.

[Rick B.]

Re: Drive Shaft Concern

The local shops all specialize in large commercial truck applications. When I brought the driveshaft in to show them what I was dealing with they offered to re-tube it but stated they likely would not be using the same diameter tube and could not garantee the wall thickness to be the same if they were fortunate enough to find the same outer diameter stock.
I have issues with that simply because I really don't think there is alot of room to play around with even a slightly larger diameter tube, let alone the fact that it would not even remotely appear original.
I don't want to label them with unflattering words but I routinely find it difficult to find people willing to go the extra mile to please serious enthusiasts. I respect they typically deal with customers just wanting to get the job done and for least amount of money, but I am willing to pay more for the same/better OEM quality and not just something that most people would be satisfied with.
So to answer your question, I would rather send it somewhere else ( or buy a replacement outright) then take a chance with them cutting up mine only to have new and different set of problems (potentially). I did my best to spend some time talking with them to get a feel for what my options were, but in the end I did not come away in the least bit confident.

[Joe R.]

Re: Drive Shaft Concern

Recently after rebuilding the 454 in my '72 I had an immediate rear thrust bearing failure which resulted in having to tear down the engine once again.
During the brief period in which I was able to drive it and break it in I was less than impressed with the increase in power that I had somehow anticipated from the rebuild. Consequently, this time around I made some "internal changes" within the engine while keeping it completely original looking from the outside.
I dyno'd the engine last week and was able to get 590 ft./lbs. of torque from it and 468 h.p. with the original carb and air cleaner ! While I am very pleased, I decided to freshen up my transmission and torque converter to ensure everything could handle the extra muscle. Not stopping there I naturally replaced the u-joints with some h.d. Spicer units and while doing so I noticed a strange mark on my main driveshaft tube.
It would appear that possibly sometime in the cars' earlier lifetime the emergency brake cable may have hung down loosely enough to make contact with the driveshaft tube. This is the only possible explanation I can come up with for this perfectly concentric line I found neatly "cut" into the surface of the driveshaft.
I carefully did a non-destructive test of the driveshaft tube and found the wall thickness to be very consistent at .187 inch (3/16") except at the point of the groove which is at .177 inch. The groove is almost 1/16 wide.

My question is this :
Is there any way of accurately predicting what such a wear mark may cause in terms of overall weakness to the tube under hard/heavy acceleration? In other words is the reduction of 10 one-thousandths of an inch going to cause a potential fail to occur under extreme loading or are these driveshafts built so beefy that it should be little or no concern?

Access to quality driveline shops in my area are limited and I have not had much luck finding someone sympathetic to my quest in repairing this one or manufacturing another to orig. specifications.

Any comments or advice would be greatly appreciated.

Thanks, Rick

Rick,

Please share with us what the mods to your engine were. It is a torque monster!

Joe

[Terry M.]

Re: Drive Shaft Concern

I sympathize with your dilemma in finding craftsmen who will respect originality in the terms we understand it. Those of us in large metropolitan areas fare no better. While we may have more choices, my experience is all that results in is more rejects of people who will only do the work one way because "that's the way we have always done it."

I have seen other posts here that indicate that the tubing is no longer made in the original diameter or wall thickness -- so it may be that your source is simply being honest with you. That is certainly a much better situation that the attitude "We can do it" only to find out they can do it on their terms and not your terms.

Perhaps there is someone who has a source for the proper tube. Many would beat a path to their door if that were the case. I believe we have plowed this ground already though, and nothing has flowered. Of course the supply situation is always changing, but it is seldom for the better.

All that may be just a little unnecessary though, in most judging situations (unless you ware working on a potential Bowtie car -- in which case STOP) access to the driveshaft is limited so a small change in the OD will not be detectable and there is no way a judge can determine the wall thickness of the tube. Configuration of the driveshaft ends and the universal joints are visible and will be noted, so that is one area worth focusing on.

I hope you can find a source you are confident in, but you will have to balance the risk of sending your original parts some distance; perhaps even out of the country, against the chances of better communication with someone you can look in the eye to evaluate their sincerity. Allowing someone else to work on your parts is always a matter of establishing trust, and that is difficult to do over many miles or kilometers.

[Dennis B.]

Re: Drive Shaft Concern

Any comments or advice would be greatly appreciated.

Thanks, Rick

Personally I would not fool with it. I would replace it ASAP. If it is repaired, will you trust the repair? Is there any possibility you have a small micro torque stress in there too? I would always wonder whether the guy did a good job, or whether the new vibration I feel is from the repair. (there will be one, so will this add paranoia?)

It may be a lost sleep/safety issue more then a lets try to keep the original part issue. It would be for me anyway. I would replace it.

[Timothy B.]

Re: Drive Shaft Concern

Rick,

I would paint and install it for the time being then fnd a nice used driveshaft to restor and install later. I see them for sale all the time and I don't think you will have any trouble finding one.

[Dick W.]

Re: Drive Shaft Concern

Many of the older tubing sizes have, in fact, been discontinued. I am be confused, but I believe the older tube was DOM tubing and the newer tubing is not, or just the opposite. Wall thickness has also changed. With the advent of newer materials, the thicker wall is not necessary.

[Paul J.]

Re: Drive Shaft Concern

Rick, it's unlikely that it will break, despite that torque. If it were me I'd get out the MIG and stitch weld along the groove. Then I'd grind the weld down. The balance should be the same and it will be as good as new (more or less).

Paul

[Dick W.]

Re: Drive Shaft Concern

Rick, it's unlikely that it will break, despite that torque. If it were me I'd get out the MIG and stitch weld along the groove. Then I'd grind the weld down. The balance should be the same and it will be as good as new (more or less).

Paul

Most likely the spindle will give up the ghost before the driveshaft.

[Michael W.]

Re: Drive Shaft Concern

My question is this :
Is there any way of accurately predicting what such a wear mark may cause in terms of overall weakness to the tube under hard/heavy acceleration? In other words is the reduction of 10 one-thousandths of an inch going to cause a potential fail to occur under extreme loading or are these driveshafts built so beefy that it should be little or no concern?

The answer to your question is yes, it can be accurately calculated and predicted. The problem is that most likely no one here has access to the information and tools required to do such a task with any degree of credibility or assurance- either on their part or yours. My gut feeling is that the shaft would be just fine.

1) it's been damaged for many years and shows no secondary signs of distress
2) failure of driveshafts on C3s are virtually unheard of despite some owner's best efforts to destroy them
3) shock loading from an auto transmission is minor as compared to the potential of a manual box and an abusive left foot

on the assumptions (ewwww) that

1) GM would have engineered in all sorts of damage tolerance on this shaft knowing the results of a fractured shaft digging into the pavement while the vehicle is in motion
2) normal deterioration of shafts through corrosion and/or impact while in average service would have reduced the overall integrity to the level of your shaft
3) the damage incurred is limited precisely to what you've described above, ie- is free from sharp edges or other faults which could act as stress risers

In other words- there's no real precedent to say yes, "I did the same thing 20 years ago and everything is fine" or "here's GM analysis showing damage limits". Even so, you'll know the shaft has this defect and will worry about it in the future no less than you are today.

Given that undamaged original shafts are available from recyclers, to me the choice is obvious.

Just curious- did any of the shops you talk to given an opinion on serviceability?

[Rick B.]

Re: Drive Shaft Concern

I very much appreciate all your thoughtful input, gentlemen !
Since my initial post I contacted a couple of reputable driveline specialists in the U.S. that deal with high-horsepower race cars.
Both places were very honest and up front with me, advising that indeed they were not aware of currently available tubing matching the same specifications as original, and commented that metallurgy has progressed to the point where higher strength could be attained using different size and/or material. While I expressed a wish to maintain as close to the original size/appearance as possible, I will now be in the 2.5-3" dia. range to handle the torque specified.
They feel a 3" dia. tube will give an extra measure of protection but will require dropping the differential to slide the shaft in from the rear.
The bottom line was that both did not feel it would be wise to utilize the driveshaft in its' current state. Oddly enough neither person seemed to expect a sale from me (and in fact one company flat out stated he would be unable to manufacture and balance a shaft that short in his equipment) so I am confident the info provided was not connected to trying to procure business from me. Neither stated it was sure to fail but both understood the apprehension I was having.
As for repairing my driveshaft in its' present state, no one wanted to weld material over top of the groove in order to build up the material sufficiently to allow it to be machined down to the original profile. All suggested that in doing so I would be weakening that area even moreso and potentially forcing a failure to occur at the site of the weld. I cannot comment as to the validity of that opinion as I have no in-depth knowledge of welding procedures to draw from.
Local shops wanted to re-tube it but many people I have spoken to, who had similar work done by these shops for their race cars, had a variety of complaints - none gave positive recommendations whatsoever.
I believe I will simply purchase a replacement driveshaft from the other company I had spoken to. I've been able to find some positive feedback online from other customers not affiliated with the company, so that is good news!
So when I consider that a failure occurring forward of the differential may be unlikely ( as the torque is multiplied after by the diff. ), I know it would be nagging me and spending another $450 will be worth the piece of mind to me in the end.

Thank you again to all who helped out by replying to my post !

Rick

[Jim L.]

Re: Drive Shaft Concern

I believe I will simply purchase a replacement driveshaft from the other company I had spoken to.

Rick,

If you haven't already contacted Inland Empire Driveline for a custom driveshaft, let me suggest you do so. They've made two custom driveshafts for my vintage racer. The shafts look like pieces of jewelry and I've never had a problem with their work. Here's a link to their web page:

http://www.iedls.com/

Jim