[ScottJoGTO]

I just had a local shop which does a lot of muscle car work replace the clutch and U-Joints in my 65 GTO tri-power, M-20 wide ratio four speed. The car is very original, including the rear springs which are sagging quite a bit.
When reinstalling the driveshaft, he commented that it was very, very difficult to get the driveshaft back in and suggested that it may be too long. He said that it is made worse by the sagging rear end, but that just installing springs would probably not raise it enough to make a big difference.

I am considering ordering new springs for the convertible model from Performance Years, as I understand they will raise the rear slightly taller than it was with good stock springs.
I researched this forum on driveshaft entries and found several bits of conflicting info regarding driveshaft length.

1) Is there any stamping on the original driveshaft to indicate originality or application?

2) Anyone with a bone stock driveline the same as I have stated above who would be willing to measure the driveshaft on your car, as well as the size of the rear yoke?

3) Anyone done enough work on these to have encountered this symptom before and found that rear end ride height varies enough that it could cause this problem?

4) Anyone installed either convertible or stock springs from PY? WHat is the height of the rear bumper from the ground? (please specify wheel/tire sizes for clarity).

Thank you.

[TRKN]

Welcome! From your post I would say you do not have a rear suspension problem. If your car has the original driveshaft you should not experience any problems even with the sagging springs. The slip yoke is designed to do exactly that, slide in and out of the trans with the travel of the supension. That being said if someone used a incorrect lenght shaft that was to long it would cause major problems that you would have already experienced. I have a 64 original 4spd shaft that I can measure for you tomorrow and will post the measurments. If your shaft is original it will have a tube with stepped diameters( front will be smaller diameter and than flare up to larger diameter). As for the slip yoke not sliding into the tail shaft easily that should have nothing to do with the suspension. The shaft is not connected until after the yoke is into the trans. Possible causes are: worn slip yoke, worn tail shaft bushings(allows the tail shaft to sag until the yoke is inserted causing resistence) or I have even experienced a out put shaft seal that worked so well it wouldnt bleed off any trapped air in the trans to pass by,causing resistance. I will measure that shaft and post the measurements tomorrow and even take some picts. Not sure how to post picts but I will try. Hope maybe this helps. J.

[superdutydave]

Install whatever springs/suspension decided upon and after done install driveshaft on level ground and front yoke should slide into tranny no more than 3/4 of its length. You can work with slightly more than 1/2 length used, certainly not less. Idea is that when car hits bump rear suspension moves and driveshaft moves in/out of trans so play is needed, otherwise yoke would bang back of trans output shaft.

[ScottJoGTO]

Thanks, J, I really appreciate your willingness to provide measurements if it's not too much trouble. Fascinating that a seal could fit that tight, but hey, it could be that simple.
Scott

[ScottJoGTO]

Thanks Dave, I'll verify that yoke length with wheels on the ground when I get the new suspension parts installed. I appreciate your response.
Scott

[TRKN]

Hi Scott, when I replied last night I was tired and didnt think of this until today. If the person installing the drive shaft had the car on the lift he could have had a hard time installing the shaft on the rear end yoke. This would happen because the rear was hanging down at full extension and because of the 4 link design, the housing moves foward and down as it drops, and backward and up as it compresses. Again nothing that is a cause of worn springs or would be corrected by raising the back of the car. I think this probably what really happened and the guy didn't realize it. As for the measurements here they are: 1.overall 62 9/16 " 2. center to center on the tube 55 3/16'' 3. yoke- center top of the u-joint cap holder to end of the slip yoke part 5 7/8'' This drive shaft is the original out of my 64 4 spd car and to the best of my knowledge has never beeen apart. 64 -65 were the same so your car should measure up in that neighborhood. Remeber that you will get slightly different measurements if you measure it in the car or if you dont support the yoke in the same spot as I did. just make sure there isn't a major difference. Good luck and let me know what you find. J

[ScottJoGTO]

Thanks for providing these specifications, as well as the thoughts around the angle when the car is off the ground with no rear axle support and the effects on the yoke. I'll get underneath in the next day and compare. Really appreciate this!
Scott