Not quite Lloyd...... Your interpretation (and others) was that the rubber was causing the vibration due to misalignment. The tailshaft is out of balance, hence the vibration. The position of the bearing within the rubber plays no part in the equation as far as balance goes.
No Ian, my comments were entirely directed at why this mysterious vibration "goes away after 15 minutes, but returns the next time I use the car". I made no assumptions about the root cause of the vibration(although I have considerable experience in regard to vibration in hi-speed rotating mass)as I spent several years balancing industrial machinery in my younger days(Centrifugal Fuel Separators and the like). A small point, but valid in my opinion.:rofl::br:
ok... so the theory is..... out of balance tailshaft cold rubber around the centre bearing transmits the vibration readily through the car Once the rubber around the centre bearing 'warms up' the rubber absorbs much of the vibration.... thus giving the impression of it "dissappearing" sweet .... that I can easily see and accept but wait ..... there's more ..... I've driven many other cars with suspect tailshafts, even a few with 'home-made' shafts fitted..... None of them vibrate like this one does, its a harsh vibration to the extent that the empty passengers seat back rest physically moves, nothing placed on the console will remain there..... but its actually a nice massage in the drivers seat :rofl: When I replaced the auto I checked the tailshaft for damage, it was straight and I couldnt find any marks that indicated that a balancing weight had fallen off or been dislodged.... for all intensive purposes it 'appeared' to be in good condition. The other thing I cant get my head around is the fact that this vibration is just as intensive on really hot days as it is in mid winter, surely the ambient temp should have an effect on the time the vibration lasts for even if its only a few seconds..... & shouldnt it also effect the intensity of the vibration aswell ??? My daily drive to work see's this vibration dissappear at the exact same whitepost whether its stinking hot or the usual 7degrees and frosty.... Kingy
The vibration from a sagged centre bearing is caused by incorrect driveline angles on the uni joints, a sagged c/b will cause vibration guaranteed. Kingy, this is why when they lift solid axle hilux's etc, the front and rear diffs are shimmed to point the pinions up. This keeps the correct drive angles on the uni's to stop vibrations. The uni joints are designed to operate with very precise angles when coupled to a rear pinion c/v. All uni joints must have the same drive angle, a sagged c/b does not allow this. Usually a shaft will have a uni at each end, one may run at +4 degrees, the other will run at -4 degrees. When the uni's are phased correctly, the force exerted at each end is equal but exactly opposite and cancel each other out. As a uni joint rototes it is speeding up and slowing down, it is not a smooth rotation when there is any other than 0 degrees angle. Now throw one of those uni's away and put a cv joint at one end like the 300ZX, how can you smooth out the operation of the uni's now. Max uni working angle is 7 degrees when coupled to another uni the same. Max angle for a uni/cv combo is <2 degrees. Sagged engine mounts, trans mounts, cb mounts, missing cb spacers, worn pinion bushes all give more than the accepted driveline angle. An out of balnace tailshaft will vibrate all the time, softening of the c/b mount will not stop the vibration, it will just allow the tailshaft to whip more, the tailshaft will not stop vibrating once things come up to temp.
I had a shot CB rubber..... You could physically move the tailshaft centre "all over the shop" but NO vibration whatsoever. I had the tailshaft removed (appropriately marked) and a new CB fitted. It now vibrated the fillings out of your teeth It was like driving with all 4 wheels out of balance. Pulled the tailshaft and had it balanced. Was informed the balance was WAY OFF, and cv/uni's & cb were all perfect. Refitted the tailshaft and not a wobble in sight. During the whole process of vibrate/balance/no vibrate, the shaft was not disassembled, so no blame can be placed on the cv/uni joints, cb or cb rubber. The ONLY alteration was to the tailshaft balance. You figure it out.
I have the same problem on my Zd..some vibes the first 10 minutes or so..then right as rain. However, I took off on a hill and rather gunned the engingine..the car shook and bucked something terrible..then after warm up all was ok. stands to reason something changes when somethinh in the drive train warms up or, relocates itself..got to be the Cbearing..as nothing else can change characteristics. I lifted the car up and put it into drive..lots of shacking. More then when all wheels are on the ground.. I had a quick look at the match marks..and they are not aligned. I will take the shaft out, replace the bearing, check the shimms and Uni joint alignement for and aft. Also get it re-balanced. I had shafts balanced before and sometimes they are still not good..I guess it depends who does it..if an apprentice with a 'hang over' does it, things might be not so good..lol
you have no idea,,being a mechanic myself i must say youve told everyone you know what it is ,well your wrong, the reason it has a centre bearing it to keep ,the vibration under control 90 percent of cars today that are rear wheel drive has this ,system ,its called insulation,,,when said insulation goes to heaven you get a vibration,,SIMPLE your reply not needed cheers
