Bad Driveline Vibrations

[BoostedG6E]

Hi all,

I’m chasing down a vibration issue with my G6E Turbo MKII that’s gotten so bad the car is basically undriveable under power. At the moment, I need significant spacers on the center bearing just to get it up the road.

A bit of background:

• About 2 years ago, I pulled the engine for a freshen-up and had the ZF clutches replaced. I also fitted a new hot side setup, but otherwise everything went back as it was.

• On the first drive, I noticed a light/medium vibration starting at 80 km/h, which built up to medium around 100 km/h, then became less noticeable when cruising above 100. Under heavy acceleration, it wasn’t noticeable at all. I even raced the car at heathcote with no issues at all under heavy throttle.

• Had my wheels balanced and found the fronts had a buckle (though I never had vibration before that). Got them repaired, but the vibration remained.

• The car has an upgraded tailshaft with a uni at the diff instead of the factory CV.

I took the car back to the shop that installed the tailshaft/Truetrac 4+ years ago. After a week of diagnosing, they couldn’t figure it out. They added 30mm spacers to the center bearing bracket to bring it down, thinking the gearbox-to-bearing angle was off (which shouldn’t really be possible with everything bolted to factory locations).

On a wet test drive, it felt about 90% better with only a very slight vibration — nothing major. But the next day, when I gave it medium-heavy throttle, a new vibration appeared. Felt like it was vibrating more towards the diff this time as you could feel it in the seat and noticebly hear it in the rear of the car but not really in the wheel, It went away when lifting off but got worse if I stayed on the throttle. I also had a significant vibration on a 4→3 downshift.

I showed this to the shop, but they couldn’t fault it and weren’t keen on going further, saying it was “as good as it gets.” For me though, it was now worse than before. So I asked them to return it to how it was when I dropped it off — including the flogged center bearing and no spacers.

When I picked it up, I drove up the street with light throttle and it felt okay, but on decel it was terrible — the whole car shook and was undriveable, even slowing from as little as 10–20 km/h. I didn’t dare test it at higher speeds. The shop eventually refitted the 30mm spacers, which at least makes it driveable again, but I can’t accelerate without vibration and it still shakes badly on 4→3 downshifts.

What I’ve tried since:

• Replaced the center bearing with a new one (still needs 30mm spacers to drive).

• Tested different spacers: 10mm and 20mm reduce the vibration progressively, 30mm is “best.” Haven’t tried 40mm yet.

• Replaced the gearbox mount in case it was sagging — no change.

• Shop said the tailshaft was balanced and looked fine.

 

When cruising on the freeway now since I put the spacers back in with the new centre bearing I dont have much of a vibraiton at 80-100 but if I let go of the throttle I feel the vibration come back like how it was initially.

 

At this point I’m stumped. I went in with a slight vibration at 80–100 km/h cruise and came out with a car that can’t accelerate without vibration and relies on 30mm center bearing spacers just to drive.

 

I’m thinking of taking the tailshaft elsewhere to have it re-checked/re-balanced, as it’s the only thing that makes sense since the vibration changes with spacer height.

 

Any insights or advice would be greatly appreciated.

[k31th]

Definitely sounds like you need somebody to accurately measure the driveline angle and to run it up on a system that they can poke around with weights/spacers etc to ensure the driveshaft isn't vibrating...

 

But if the shop that fitted it all have no idea then the chances of us diagnosing it properly on here is pretty much a stab in the dark

Does sound frustrating enough to be taking the driveshaft back to the actual driveshaft shop.

[xr6tForMe]

From reading all of that, I think you might have 2 different, but similar issues.

- the center bearing on the original shaft is no good

- something is not right with the new shaft you got (maybe balance)

 

Putting in spacers seems strange?  I would have thought it should all work with the normal positions?

 

Is there any chance you can attach something like a gopro camera to record the centre bearing and/or diff end of the shaft and see what is going on?

 

Are you able to arrange to swap in a tailshaft from another car which I know drives fine to test?

If that fixes it, you know its a problem with the tailshafts you have, if it does not fix it, then you know you need to look somewhere else.

 

[xr6tForMe]

My experience with center bearings causing thumping has only been with Commodores.  They would make a thumping under load some of the time, at fairly low speed.

 

I suspect the description of vibration building up from 80-100kph and then going away is a tailshaft balance issue

[BoostedG6E]

On 09/09/2025 at 11:37 AM, k31th said:

Definitely sounds like you need somebody to accurately measure the driveline angle and to run it up on a system that they can poke around with weights/spacers etc to ensure the driveshaft isn't vibrating...

 

But if the shop that fitted it all have no idea then the chances of us diagnosing it properly on here is pretty much a stab in the dark

Does sound frustrating enough to be taking the driveshaft back to the actual driveshaft shop.

Yeah im struggling to find a shop that does this exactly, are you aware of any shops in melbourne that can check this correctly?

 

The shop that fitted the shaft also make them and they assured me it was balanced correctly and the shaft is not the issue, im going to take it out and try get it balanced at another shop and see how it goes.

 

On 09/09/2025 at 3:46 PM, xr6tForMe said:

From reading all of that, I think you might have 2 different, but similar issues.

- the center bearing on the original shaft is no good

- something is not right with the new shaft you got (maybe balance)

 

Putting in spacers seems strange?  I would have thought it should all work with the normal positions?

 

Is there any chance you can attach something like a gopro camera to record the centre bearing and/or diff end of the shaft and see what is going on?

 

Are you able to arrange to swap in a tailshaft from another car which I know drives fine to test?

If that fixes it, you know its a problem with the tailshafts you have, if it does not fix it, then you know you need to look somewhere else.

 

Sorry my post was super wordy, the shaft I have now isn't new and has been in the car for years now without any issues at all. It only started when I freshened up the engine/box. After this it was only a slight vibration at 80-100, it got worse and unreverseble after I picked it up few weeks ago from the shop that originally fitted the shaft years ago.

 

I agree its very strange, just cant understand why if I remove the spacers the car doesn't behave how it did when I dropped it off a few weeks ago, now with no spacers its undriveable.

 

I will try get a gopro on it, I had it on the 4 poster a few days ago with a lift on the diff so I could get under and see exactly what it was doing. The entire shaft was shaking to the extend the diff was moving up/down also.

 

Issue is I have swapped the CV to a uni joint so the standard shaft wont work, I might have to just source a standard shaft and get uni's welded on and try that out.

[xr6tForMe]

If you are able to, the method in this video may help.

What do you think?

 

[xr6tForMe]

Just thinking about this issue.

 

Since it happened along with the gearbox freshen up, could something have happened during that work?

 

Maybe a balance weight was knocked off the tailshaft when the gearbox work was being done?

Was anything done to the shaft during the gearbox work? (eg painting)

 

Are there any balance weights on the shaft?

Are there any marks where it looks like there was weight that has come off?

[BoostedG6E]

Finally got this sorted, took it to another shop to look into it and turned out it was a busted universal joint and the shaft was way out of balance. When I took it to the first shop recently (initially installed it years ago) they must have got something wrong. Got a balance from Knox drive shafts (unbelievable service here highly recommend) and it’s now smoother than the family RAV4 car. 

[k31th]

excellent result