Tailshaft phasing/vibration

[azzfox]

Hey all, got a driveline vibration issue. Its always been there since I bought the car but its getting a little worse.

Happens the most at 50k's. Load doesnt make a difference, rolling with clutch in doesnt make a difference, disappears at higher speeds. Center bearing mount is perfect which leads me to believe its been changed before. Phase seems out of wack!

I've always thought the uni's had to be phased 90degrees. Unlike cv's they dont rotate at the same speed, therefore the yoke and pinion can rotate at the same speed while the rest of the shaft is constantly slowing down and speeding up. No? While a shaft thats "in phase" is constantly changing speed end-to-end. My tailshaft at the moment is somewhere in between.

Its more of a wobble than vibration, a slow but sturdy wobble. Causes the gear stick to move around quite a bit. No steering vibration.

Anyone experienced this before or can shine a light on the situation?

Cheers!

 

[LAP004]

i had the same thing in my vp sedan daily. ended up been excess play in the rear uni joint at the diff.
i had a spare tailshaft so i through it in and fixed the problem.
mine could be wobbled back and forward about 4mm where as the front one had no play at all.

good luck mmate

 

[ephect]

CV's only provide an angle to the 2 shafts and rotate the same speed as the rest of the shaft. Unis will either be out of phase or simply the tailshaft is unbalanced.

 

[azzfox]

Just checked the uni's and the rears tight like the front. CV has the most play but bugger all, boots torn though. The shafts actually not far off being "in phase", read that 45 degrees is common but its not even close. Hopefully this means a new boot and a spline or two of adjustment.

CV's only provide an angle to the 2 shafts and rotate the same speed as the rest of the shaft. Unis will either be out of phase or simply the tailshaft is unbalanced.

I agree with the CV part but uni's will only rotate at the same speed when in a straight line. Some shafts actually have a 3rd uni instead of a CV, and some dont have a 3rd joint at all.

 

[Circlotron]

Don't forget the front and rear uni must be at identical angles for one to exactly undo the fast-slow motion the other one produces.

According to this -> https://forums.justcommodores.com.au/threads/replacing-tailshaft-center-beaing.186136 vn/vp the uni joints need to be 45 degrees out with the input side leading. Didn't know that.

 

[Cheap6]

Yep ^. The amount of correction (radial offset) depends on the model involved.

Other factors include the length of the rear suspension lower links (there are a few different part numbers for them), the condition of the rear suspension bushes, the position of the spacers on the centre bearing bracket and the condition of the engine and transmission mounts.

 

[monkeys437]

What model of commodore? For the VN/VQ/VP models it can be phased 37.5°, 60°, or 90° depending on the Gearbox, engine, and wheelbase combo. I've done a bit of industrial balancing so I've seen this before, and the input side only leads for about half of these combos so be careful you don't turn it the wrong way.

 

[azzfox]

Thanks for the replies guys, sorry for the late reply. Turned out to be a flat spot on the front L/H tyre! Probably from when the previous owner collided with a deer.

Forgot to update that I borrowed a mates spare (original) tailshaft which diddnt make a difference. It also turns out that both shafts are phased 45 degrees with the TAIL section leading (spins clockwise looking down shaft towards diff end). VP and VS V6/T5 wagons.

 

[LAP004]

good to hear that the problem is fixed. easy fix too