Nasty Tailshaft Vibration - Please Help!

CNS45 · 12-22-2005, 05:56 AM

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.

12-22-2005, 05:56 AM	#1
CNS45 Stock Join Date: Dec 2005 Posts: 2	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.