'71 LeSabre drive shaft

Will a drive shaft from a '71 Centurion 2 door hardtop with a 350 2bbl. fit a '71 LeSabre Custom sedan, 350 4 bbl? My guess is that it will but I want to be sure. I have a driveline vibration and have been told my driveshaft has a slight bend to it. Not sure why or how that happened....

I don't have an exact answer to your question, but any '71 Centurion should be equipped with the 455 4-bbl.

The driveshaft differences are specific to the transmission in the car: TH400; TH350. Only the nose is different and that can be swapped.

Isn't that a two-piece driveshaft with that "fancy" joint in the middle?

You probably need to get that vibration fully diagnosed BEFORE you do anything else. If it's a two-piece driveshaft, it could be the "carrier bearing" rubber that has the problem rather than the shaft itself. Might also be a worn u-joint in the front. SEE IT FOR YOURSELF, which a good mechanic will gladly do, BEFORE you do anything else!

Enjoy!

NTX5467

It's not a 2 piece.

As Brian said, the 71 Centurion should have a 455/400 from the factory, and would not interchange with the LeSabre 350. If someone along the line has replaced the drivetrain, then I would guess it's possible. I would be concerned about the rear end, though, since the Centurion has the big 9 3/8, and the LeSabre has an 8.5. That might effect driveshaft length.

Thanks for that clarification, Adam. I recalled some GM driveshafts from back in that general time which few dealership techs wanted to touch. This led to these shafts typically being purchased as "reman" units from specialized rebuilders--got to be a pretty profitable industry for some.

Still, make sure what the problem is and where before any work or "mods" are undertaken.

Enjoy!

NTX5467

I was sure the car was a Centurion but it definitely had a 350, so guess it must be a LeSabre. I have been told that the '71-'76 Buick had one of the longest single piece driveshafts ever used on an American car. Not sure how mine got "bent" because it was fine when my uncle gave me the car in 2000. I did have the U-joints replaced a few years ago and that's when the vibration came to light. I was told by the garage that replaced them that they were difficult to do.

I was sure the car was a Centurion but it definitely had a 350, so guess it must be a LeSabre. I have been told that the '71-'76 Buick had one of the longest single piece driveshafts ever used on an American car. Not sure how mine got "bent" because it was fine when my uncle gave me the car in 2000. I did have the U-joints replaced a few years ago and that's when the vibration came to light. I was told by the garage that replaced them that they were difficult to do.

Sounds like when the shop did the u-joints, they didn't mark the driveline before taking it out of the vehicle, or they didn't line it back up.

John

That is a long driveshaft but the shaft itself is probably not bent. That driveshaft has a normal universal joint at the front and a constant velocity double Cardan joint ( 2 universal joints joined by a ball and socket joint ) at the rear. From the factory these joints cannot be greased, so they fail. The trouble is all of the universal joints are glued to the yokes. There is no consensus among driveline shops as to the proper way to replace. I have had them pressed out--->bent the yokes; impacted with BFG --->bent the yokes; heated --->bent the yokes. You cannot see the bends, but you can feel the vibration. The only vibration free shafts I have had on my 76 Delta were the original shaft and 2 unmolested original shafts (used). This type of joint is used in many vehicles past and present, including trucks. The next time I have to service the driveshaft I will have one constructed from new parts.

If you have a replacement that fits, hopefully it has been serviced and is vibration free.

Willie

Willie - the mechanic I had work on the car (not a the dealership that replaced the U-joints) took the drive shaft out and had it balanced. The place that he took it to called him and said it had a slight bend to it and that they would do the best they could. Consensus was I really needed a new driveshaft. I do recall them telling me about the double U-joint in the rear. My concern about driving the car any distance is that the vibration will eventually cause damage to some other component, such as the transmission. Any thoughts on that?

John

The "double Cardan" joint is the "fancy u-joint" that I was thinking of, but had forgotten that it was at the rear of the shaft.

It was common for many GM u-joints to have the "plastic bead" holding them in place from the factory. Usually, the replacement joints used clips on the u-joint cups for retention. The lack of retention clips on the u-joint bearing cups, I suspect, would be indicative of the "glued-in" bearing caps.

In building a driveshaft, there are many different shops that can accomplish that job but by different means. Many factory-production driveshafts have sections with different outside diameters in them, obviously for harmonics control, plus to better adapt from a possibly smaller front u-joint to the larger diameter flange needed for a larger rear u-joint. Usually, these varying diameter shafts are replaced by one of a constant outside diameter when they are rebuilt.

At one point in time, in the later 1970s to early 1980s, we were having some issues with driveline harmonics on production Chevy truck driveshafts. When we sent them to a driveshaft shop, they all needed to be rebuilt. Initially, the shop did not have a balancer, but we were told that as the tube stock was of the same gauge throughout, it was "in balance". The new u-joint flanges were all machined on their inner areas, rather than being rough cast as many of the production flanges were at that time, but which had been machined in prior times. Therefore, the totally machined flanges were "in balance". The u-joints would be "in balance" too. End result was that as long as the completed assembly was spun up with basically zero runout, everything was "in balance" and required no additional balance weights. Generally, they were correct.

Only thing was that the driveshaft harmonics from the constant diameter tube could be accentuated. For that? Filling it with two-part liquid polyurethane foam. This worked until the harmonics destructed it over a period of years.

Having seen these things over the years, I'd recommend making sure that any run-out of the main tube was "in spec" (there is a factory spec for this!). The visual "bend" might end up being "acceptable", according to these specs. IF something was done to affect the concentricity of the u-joint in the respective flange, THAT might need some attention, but that, too, could lead to a new shaft needing to be built.

Seems like somebody builds a kit to rebuild those double Cardan joints! Otherwise, the driveshaft reman people couldn't rebuild them. But I seem to recall that it takes some special tools or holding fixtures to do the job. Many mechanics just didn't want to touch them back then. Seems like there's a centering spring in there? Hence it was easier and quicker for the shop to procure a reman shaft from a rebuilder and do it that way.

Just some thoughts . . .

NTX5467

Willie - the mechanic I had work on the car (not a the dealership that replaced the U-joints) took the drive shaft out and had it balanced. The place that he took it to called him and said it had a slight bend to it and that they would do the best they could. Consensus was I really needed a new driveshaft. I do recall them telling me about the double U-joint in the rear. My concern about driving the car any distance is that the vibration will eventually cause damage to some other component, such as the transmission. Any thoughts on that?

John

You're correct in assuming that the vibration will damage other components (in addition to being aggravating). On mine with the TH400 transmission the tailshaft bushing wore, leading to failure of the gear on the governor, resulting in limping home in L low gear.

If the tube itself is bent, they should be able to straighten and balance. I would suspect the U-joint yokes at the rear...you cannot see or measure easily the bends, but it puts things out of kilter enough to cause vibration, especially when power is applied.

Willie

The vibration I feel does not occur until about 50-52 mph. As long as I stay below 50, it's smooth as silk.

Swap the shafts and see what happens. Another thing to try: unbolt from the rear and rotate 180*...this changed the vibration on mine, but did not eliminate.