Hi, I just got purshased a restored 71 gs(x) 455 turbo 400 and have a few small trans oil leaks. One leak is a the yoke seal which leads me to my question. My car does have a one piece driveshaft with the rubber insert. As a mechanic, I have previous driveshaft (good and bad) experiences on other vehicles heres my question: Being a one piece driveshaft, the trans end should be a slip yoke, correct? It appears with the diff hanging down (car on 2 post hoist) the yoke is pushed all the way into the transmission, I would think the yoke should be out somewhat so when the rear axle travels through the suspension travel the yoke can slide in and out of the tail of the transmission. So what should be the length of my propshaft? I see in anouther post it makes a difference what size diff, how will I know, I believe I have a 10 bolt rear end. As an added question, whats the overall length of my tranny suppose to be? thanks Gord o No:
I just picked up a Buick Service Information Manual for '71. The '71 shaft, mated to a TH400 should be 54.241" long, c to c the universal joints. 1 green & 1 yellow stripe as marker, if it's still even there. The '70 was a tad longer @ 55.10 ", 1 brown & 1 blue stripe. Manual states using a '71 shaft in a '70 car will cause premature slip yoke failure due to inadequate spline engagement. Should a '70 shaft get be installed in a '71 car,the slip yoke may damage the rear bearing support & seal.
thanks alot for the info, I am waiting for service manuals to arrive but thought I'd ask a quick question. The colour codes are gone but I believe the driveshaft is too long (possibly alot) and I will have some sort of failure soon if I don't get this sorted out. Thanks again... Gordon
RACENU, The shaft length as Steve stated for the 71 is correct. It also would be for 72 as well. The 70 had an 8.2 as 71/72 have 8.5 10 bolts which is the reason for the length differance. Also make sure your shaft (considered a one piece because two piece have carrier bearings) is not twisting near the rear portion of the shaft. They do have this tendency as the internal rubber rings deteriorate with age. You will notice that your front and rear driveshaft yokes are not in-line with one another (out of phase) if the rubber is bad. Most of the time the shaft "shortens" itself (collapses) and you will see that your trans yoke is pulling backward out of the trans. You normally have 3/4" to 1" of your trans yoke seal surface showing when its installed. As the rear hangs it does push into the trans but not enough that you can't take it out of the differential end yoke.
driveshaft removal thanks for the additional info Speed70. My driveshaft has a red stripe? it appears to be about 55" long.. need extra hands to measure acurately. So, if I read you correctly when the suspension is unloaded, the slip yoke goes into the transmission not out as I would have thought. I noticed the driveshaft is alittle "out of phase" and understand the importance of it being in phase, I don't get a vibration but will have this addressed before I put any more miles on. Some old school guys have mentioned to me that some driveshafts come new "out of phase" with some lead built in intentionally so when the torque comes on the yokes are perfectly lined up. I figure baloney with steel drivelines but possibly true with rubber dampening. What matters to me is whether the gs came perfectly phased , any thoughts? ps. With the car on the hoist and the suspension unsprung the slip yoke is pushed into the tranny so far that there is no way I'll get the driveshaft off the diff. I'll have to jack the diff to get enough room for the driveshaft to slide forward so I can get the rear ujoint out past the diff yoke.
Well it sounds like you'll need an inch to inch and a quarter shortened off the front of yours providing the shaft is in phase and the rubber rings haven't deteriorated. This shaft IF not original to the car could've been from behind a SB 350/TH-350 trans and they just changed the trans yoke to a 400. If it has the original front nylon seated u-joint (no inside clips) then that is not a possibility. New shafts being built "out of phase" is news to me. Being that I custom built and repaired driveshafts for 13 yrs. 6 days a week for just about anything you can think of. ONE exception to that rule are most 67-69 Camaro's and Firebirds which were built with the yokes about 45 degrees out of phase. Now there is a 3 degree yoke phasing tolerance and one could build a "lead" in the proper direction into a shaft if desired but I never came across an OEM rubber element shaft that had it. When a steel shaft twists under load the "twisting" if you will is EXTREMELY minimal, as you said "BALONEY" because after all if you twist steel its not going to just twist back. Aluminum is another story. So although I'm somewhat old school myself it seems the old schoolers you've talked to in this case aren't exactly driveline specialists.
That red striped shaft came off something else! I had the original driveshaft in my 71 GS 455 and there was about 3/4"-1" clean shaft showing at the transmission as others have stated there should be.
One red stripe agrees with a '71 GS 4 speed car, 54.429" long. Could be other GM cars it will also fit but only reference I have is the Buick Manual. Two red stripes show as a '71 sedan L-6 engine only. Much longer at 59.144".
My driveshaft is 55" long center of u-joints it appears it should be 54.241" long which explains why it appears to tight. I'll get that taken care of over the winter and once i get my manuals for more research. Steve you hit the nail on the head, this car was going to have a 4 speed so it thats why the red stripe..the car had gotton a 400 auto instead and with a wrong year driveshaft which is too long by ~.8". Problem solved!!! Thanks everyone for your help, Gord. p.s. "speed 70" i had a good look at the rear diff and see that i does swing and get farther away as the suspension collapses, rumor has it...driveshafts that may have had built in lead where off, big mine haul trucks, long shafts lots of torque, not automotive applications. I take it you suggest I should shorten my shaft on the transmission end which is what i will have done by a driveline shop, thanks for your input as well. Gord
Cool Gord! My suggestion for shortening off the front is to keep the weld heat away from the rear section. The tube yoke can be replaced after 3/4" is taken off the tube providing it is still 2 3/4 tubing at least 1" from the prior shaft weld. In most cases there is plenty. Sounds like a couple of u-joints and a balance after that and your "good to go!" PS, The only time I left red stripes on a shaft is when I cut my finger on the edge of the tube after lathing the tube yoke out....OUCH!! ou:
Excellent advice speed70, I was looking at the shaft and was wondering why shorten on the trans end, it makes sense not to heat the rubber from welding, thanks I'll have to relay that info to the driveshaft shop when I take it in, if they don't know already. G
