Nasty Tailshaft Vibration - Please Help!
 

Hi ppl. I have a 1994 Supra TT & recently took my car in for a general service. My Mechanics report said "Extreme Vibration, appears to be Tailshaft", he said that I "Needed to get it looked at", but didn't say anything else. I was doing a little research on the web & found this at one website which seems to match my problem:

Tailshafts
Fortunately, not a lot to be said about tailshafts. There's only a couple of tricks to them, and by far the most important one that people often don't know is -
- The universal joints at either end MUST be lined up exactly parallel to each other. By this I mean that the cups at the end of the tailshaft must be in line as you look down the tailshaft. If this isn't the case, then the tailshaft will destroy itself and the universal joints rather quickly! The reason for this is because as they spin around uni-joints don't follow a constant rpm. This increases with the deflection angle, so if you have them out of line on your tailshaft then one end is trying to do one rpm, and the far end is trying to do a slightly faster or slower one, every revolution! This can sometimes be felt as an incurable vibration in the car which gets worse as the speed builds up.
- Try to keep the diameter as small as possible to reduce rotational inertia. As a general rule though, the smaller the diameter then thicker the tailshaft tube metal has to be, partly negating the advantage of a smaller tube.
- The correct length is when the car is at ride height, the front yoke's back face of the tailshaft is flush with the back of the gearbox housing. Make sure that there is at least 15mm to 20mm of further travel in both directions (In & out) of the tailshaft at full bump & droop on the rear suspension.
- Most modern cars have a two piece tailshaft. This is only to reduce vibration. (Have a look at one if you get a chance - One part is always longer than the other to reduce harmonic vibration. Clever!) For a performance car, this is a waste of time, and it should be replaced with a one piece unit.
- A lot of modern tailshafts also have the uni-joints peened in so they can't be changed an so you have to buy a new tailshaft, at great expense! Not so - Just take it to a decent engineering shop and get them to re-fit the tailshaft with normal, replaceable type uni's. The cups that sit in the yokes will have to be bigger than they were, but that's no big deal compared with the alternative ...
- A universal joint is ok when it shows no signs of 'feeling tight' when you work it around with your hands. If it feels the slightest bit tight or overly 'loose' at any point, then change it.
- There are types of tailshafts that have the uni-joints held in with small U-bolt type devices. These are junk, and should be replaced with fully enclosed (The metal goes all the way around type) yokes.

Can anyone shed some light on this? Will it be solved by checking the balance on my tailshaft? I don't want to throw good good money after bad trying to guess at what the problem is. Thanks ppl.

Did you feel a vibration? There are many things can cause a vibrations
if he wants to start tossing parts at it, get a garentee in writing first that what he does will fix it.. otherwise take it to some one who can actually determin a problem. i admit vibrations are tuff to figure out. or crawl under and look at cv boots for tears and feel u-joints for slop..

i had 5 vibrations in my car..

1. lack of hubcentic rings on aftermarket wheels
2. bad tires
3. bad lower ball joints
4. warped rotors
5. missing a pilot bearing in the crank to center the clutch.. (that was a tuff one)

Thanks for your help. Here is some further info: I knew I had a wheel bearing that needed replacing on the front left, but that has been done & all others are ok. Its not a wheel balance or alignment issue, as that was done also. Yes, I have felt the vibration & the web site I quoted seems to explain it the best when it says: "...This can sometimes be felt as an incurable vibration in the car which gets worse as the speed builds up."
The Vibration is defintely coming from the behind me & feels like its located at the center of the vehicle where the drive shaft runs.

Here are some of the other replies I've gotten on another Supra Forum. Might they be right?:

are you missing any of the counter weights welded onto the shaft that balances it...the part about the universal joints lining up is called in phase and if it is out of phase that can cause the shaft to turn at different speeds depending on the angle in the shaft....but yours is a balancing problem,a transmission specialist should be able to balance the shaft for you.


&

It's very rare for a tailshaft to go out of balance for no reason at all. Tailshaft vibrations are far more likely to occur because of a dodgy centre bearing and/or worn uni's. Either way, take it to a driveline specialist and they'll be able to tell you exactly what the deal is.

Any input is greatly appreciated. I've already thrown thousands of dollars at this car fixing issues & dont want to waste my money trying to find & fix a problem using too much "guess work". If I can narrow it down to a couple of things that will need to be checked, i'm sure that will be cheaper in the long run. Thanks again.