I am retubing the half shafts for a BB car. The fabricator wants to know the metalurgy of the yokes or flanges at the ends of the half shaft. Does anyone have the fabrication or supplier specs on the ends of the half shafts that the tube portion is welded to? GM specs would be great. Or if you can point me in the right direction to chase it down I'd appreciate it. Jerry
-
-
Re: Big Block Half Shafts GM Specifications
Jerry------
I don't know that metallurgy specs were ever published for the drive shaft or half shaft end yokes. They are forged steel, though. My guess would be that the alloy is 1053 or similar.In Appreciation of John Hinckley -
Re: Big Block Half Shafts GM Specifications
Joe we use these in Vintage racing and a friend of mine just crashed by having a half shaft weld tear at the yoke. My fabricator is concerned about the welding procedure that is used to replace the tubing. ie how much penetration, what material to use If there is any heat treating required etc. I would think GM put out engineering specs to the supplier. I'd like to talk with the suppler or an engineer that can advise us of the correct procedures. There are lots of folks who can do a nice cosmetic retoration on the half shafts but I'm concerned about our folks doing restorations that there will be a failure and they will loose control of their car. JerryComment
-
Re: Big Block Half Shafts GM Specifications
Jerry - the wall thickness of the tubes themselves was 0.120 thick, make sure your shop has this. I had a set retubed for my 67 a couple years ago and they could only find 0.095" wall thickness tubes. I got them back, and them seemed lighter to me, compared to another set I had...I inquired and found out. I was NOT HAPPY they didn't inform me, and he said he had checked all their suppliers and the thicker tubing was no longer made, but given the length, there would be no twist issues. Maybe not, but I can't live with that, so I ended up finding a super clean set of shafts at Bloomington instead. Anyway, beware...I think Gary Beaupre did find a supplier of the correct seamed 0.020 wall thickness tube in the bay area. By the way, the welds came out great on the retubed set, they machine welded the shafts and they looked superb, but the tubes were just thinner. He went to great pains to insure they were centered correctly, since the support core of the yokes is designed for the thicker tubes. Also check the length carefully, that they match them to a current set of shafts, and they come out uniform, with no rotation of the yokes etc....CraigComment
-
Re: Big Block Half Shafts GM Specifications
Jerry-----
I think that the 63-74 half-shafts were of internal, GM manufacture. The 75-82 units were manufactured by Spicer. These are functionally interchangeable, but the 75+ are larger diameter tube (it's thinner, though).
As I mentioned, I've never seen a blueprint or material specs for these half shafts. If you are concerned about strength and integrity, then I would suggest that you NOT have the shafts re-tubed. Leave them as-is. The only reason for re-tubing is cosmetic. You'll have to decide if the cosmetic attributes of the shafts are more important than strength/durability issues. Quite frankly, I wouldn't consider having driveshafts re-tubed for cosmetic purposes-----I'd simply clean them up and re-finish as best I could. If yours suffer from pitting corrosion, look for another set. They aren't too hard to find. Big block half-shafts were shot peened. So, if you have a non-pitted set, simply have them shot-peened (with extra small size shot) and they'll be pretty well restored. The "extruded tube" appearance so hard to restore without re-tubing is applicable to small blocks, NOT big blocks.
Otherwise, you can have half-shafts made up by a driveline shop. Then, the tube and yoke material will be a known quantity. I'll bet that Spicer yokes are available which are superior to what GM originally used.In Appreciation of John HinckleyComment
-
Re: Big Block Half Shafts GM Specifications
This is a vintage Corvette racing applicaion so we replace or retube on an annual basis. That's why we want to know yoke metallurgy. For us it's not a cosmetics issue. I understand for some of our members it is so I think this information is a good heads up for NCRS folks. I'm asuming the later larger diameter halfshafts are not as strong as earlier BB halfshafts. I'll try and contact Spicer about yoke metallurgy. JerryComment
-
Re: Big Block Half Shafts GM Specifications
Jerry-----
I don't know if the 75+ style are any less strong than the pre-74. However, I don't know that they're any stronger, either. I think they're about the same strength, but different configuration. The 75+ shafts, GM #360912, are also the SERVICE replacement shafts for all 63-74 Corvette applications, including big block. If the 360912 shafts were any less strong than the 63-74, I don't think that GM would have catalogued them as replacements for the 63-74 shafts. They would simply have noted the 63-74 shafts as "discontinued".
Like I mentioned, if cosmetics is no issue for you, then you can have new half-shafts made up from known metallurgy, brand new components. The end yokes are available from most driveline shops. You can likely even obtain real high strength pieces for racing applications. Their configuration might be a little different, but that's not an issue for you. This way, you can have a half-shaft that is stronger than OEM and it will be ALL NEW. Spicer would be a good company to check with.
By the way, usually the weak point in the Corvette rear drive system is not the half-shaft, anyway. The weak points are the u-joints and the u-joint flange. I've seen half shafts twist from high torque (the 63-74 style half shafts; I've never seen a 75+ style twist, but they may have), but usually if actual breakage is going to occur, it occurs at the u-joint or flange.In Appreciation of John HinckleyComment
-
Thanks Joe Ours break at the weld to yoke *NM*
Comment
-
"Shafts made of SAE 4240 steel ....
and, with the universal joints, shot peened to resis fatigue failure"
This is from Karl Ludvigsen's America's Star-Spangled Sports Car, pg 196, describing the changes for the L78. I'M sure this was taken from some tech document that I've also seen somewhere. Unfortunately, this doesn't clarify if the tubes and yokes were both of this same material.Comment
-
Re: Thanks Joe Ours break at the weld to yoke
if you have the car lowered a great deal how is your half shaft alignment? do you have them on a bind on acceration squat? do you have the diff mounted solid in the frane,no rubber bushing anyplace to let the things get out of alignment. the big problem we had with road racing BB corvette was keeping the rear gear in the car from burning up. road racing should not be hard on half shafts like drag racing because you do not use standing full throttle starts. any good outfit that builds driveshafts for drag racers should know what to use to prevent breakage. your other choice would be to replace them every so many races. when we drag raced these cars we change the shafts at a certain number of passes. cheaper then repairing the broken parts.Comment
-
Re: Good Advice Clem
Everything is mounted solid and aligned. Not a whole lot of travel in the suspension. We have been using about 25 hours as a replacement point. A buddy of mine had one come loose this weekend so It's on my mind. In our discussions at the track we were trying to figure out how they should be fabricated. The stuff you get from GM looks like it was done in a muffler shop. JerryComment
-
Re: Good Advice Clem
you can get up to .150 wall in driveshaft tubing,that is as thick as i have ever used and there may be heavier but for drag racing we did not want to make the drive shaft to heavy.Comment
Comment