1/2 shaft length

[Gary R.]

Hi Guys
I have checked the archives but didn't find the answer I am looking for. Possibly some of you will know.

I am looking for the spec of the center-to-center length on the 2.5" & 3" 1/2 shafts, I expect them to be the same. I know the tube wall thickness of both, .120" & .090" respectively.

Here is the concern. I have some new shafts in stock, non-GM, but HD. I never had any issues with them in past but got a call from a guy I am building a stronger diff for who also bought the same shafts. He measured the center to center and got 13.687" or 13 11/16.

Off the top of my head, I said they were a nominal 13 7/8" center to center but I would check the new ones I had to compare.

I don't have a shadowgraph or access to one anymore which would have been nice. So, I got some joint caps, measured them both, and tapped them in one of the new shafts. Next, I supported a 1.5" ground parallel against one cap and used a 12" caliper to measure from the parallel to the other cap, added up my measurements with a small margin of variance.

The new shafts I have I don't like, one is 13.715" and the other is 13.680- close to what I was told my customer had measured, again with a small margin of variance.

Next, I pulled out a 10+ year old HD shaft we used at the track. I measured it the same way and got 13.750". I know this shaft worked as we got the car aligned without any issues, until my son broke both Solid Spicers on the LH shaft at the drags.

Still satisfied with the ranges I was finding, I pulled 2 used GM 2.5" shafts and measured them the same way as well. They were different years, one a 69 and the other 71 or 72, which shouldn't matter. They were dead on, again with my measurements. I doubled checked them as I was surprised. They are 13.827" which may be considered "nominal."

In addition to seeing what the actual spec is if anyone has it, I am concerned about the short shafts and alignment of the IRS. I recall about 15 years ago when Ft Wayne came on the scene and made shaft 14-14.250" and guys could not get past positive camber with them that long, what is the range on the other end of the spectrum, there must be a range somewhere showing it.

Anyone run into this?

Thanks
Gary

[Jack J.]

[Gary R.]

[Gary R.]

Re: 1/2 shaft length

I am surprised no one knows what the GM print for Center-to-Center length is and more importantly what would be minimum length acceptable for shafts?

[Richard M.]

Re: 1/2 shaft length

Gary wouldn't the manufacturer of the reproduction have a GM drawing?

Do you have a part#? I could check with our Archives director to see if it's in his list.

Rich

[Richard M.]

Re: 1/2 shaft length

Gary I poked around using the part# 3847899(which appears to be a assembly part #) as shown in the AIM, then searched here on the TDB.....

Joe Lucia did extensive research on the half-shafts, my gosh, back in 2002! Here (Thank You Joe!)

Now he doesn't show length specs, but maybe if he has time and sees this he may be able to get a measurement for you from his NOS stock.

Rich

[Gary R.]

Re: 1/2 shaft length

Hi Rich,
Thank you for checking the number, I just came in from my shop and did the same thing, pulled the assembly number from one of my AIM's.

I read some of the old threads and found discussion on the tube wall thickness and 2.5 & 3" diameter, which I knew, but I didn't see any mention on length, which I find interesting. I knew about BB shafts and posi cases being shot peened and in reality, it didn't help the posi cases as I have found a lot of broken BB C2 & C3 posi cases.

The two GM shafts I checked were dead on, my method I would rate close, but even with say a 005" +/- spec they are the same- now the aftermarket ones, all over the place.

That's what got me thinking about actual tolerances for length. Some may recall FT Wayne had shafts too long when they started, and they were over 14" if I recall correctly. In addition to that their tubing is thinner than what GM used in both the 2.5 & 3". These are not Ft Wayne shafts i have been checking.

Without an actual print showing the length and tolerance I can only go by the GM shafts I measured. Jack's measurements are shorter than mine but the method may be different and that can mean a lot or they were just shorter. The shorter the shaft the more neg camber which I don't know if stock rods will adjust out, I am sure that adjustable rods will.

[Chris D.]

Re: 1/2 shaft length

Happen to have 63 and 79 shafts on hand. Both measure 13 7/8". Haven't calibrated my tape measure in while so these are not high accuracy observations.

[Gary R.]

Re: 1/2 shaft length

Thank you, Chris, for checking your shafts and interesting to hear they are both the same one being 2.5" and the other 3" diameter.

I have checked several shafts to see where they fall and compared to some new and some new advertised shaft lengths.

The original Gm shafts I checked as well as the info from you and others runs between 13.750"- 13.875" that's an 1/8" window.

Jack J shafts worked at 13.750 as did a set of HD aftermarket shafts I have that are also 13.750" I feel good with that at the min length. The GM shafts I checked are 13.827" and spot on from different years.

Ft Wayne advertise theirs between 13.875-13.937" that is not too consistent, so I won't use their high number.

I'm thinking that 13.825" +/- 020" should work and that is what I will spec out for my new shafts.

[Jack M.]

Re: 1/2 shaft length

Sorry if this info is too late.
I went thru all the 1963-82 Info Kits from the GM Heritage Center...
There were only two years (63-64) where the shaft lengths were documented:
Axle Drive Shafts - 1963 Chevrolet Corvette.jpg

I've heard that half shafts were similar from 1963-79... and a little smaller from 1980-82.
(unfortunately, I can't verify or confirm any other specs)

[Gary R.]

Re: 1/2 shaft length

Jack- thank you for effort and research, very much appreciated. The information you provided is great and in line with what my conclusion was earlier today.

13.833" is very close to the 13.827" I measured with my 69 and another unknown year shaft. Wall thickness I had at .120 and I never measured the OD.

If they are made to the 13.825 +/- 020" they should bolt into any 63-79 vette.

[Richard M.]

Re: 1/2 shaft length

Great find Jack!!!