3.0 Vibration when heavy accelerating issue

[Cooper01]

Hello fellow Zedders! I hope someone her can assist with this issue.

I have a 2001 3.0i VIN LL33415.

When I accelerate quite hard to heavy I get this repeated bad vibration / banging sound which seems to be where the auto transmission is. I can't seem to pinpoint which gear it is in or be consistent rev readings. Anyway, it goes thud thud thud very rapidly for less than one second then goes away quite early in the acceleration. At first I thought I ran over a piece of wood and it was tumbling under the car.

I just replaced the tail shaft carrier bearing with no change. [today]
The rear subframe is in excellent condition.
The shocks seem to perfectly fine.
The wheels seem good.
The driver's side auto trans mount is a little bit squished [looks like it is leaning over a bit] but the mechanic said it is fine. There is almost no movement in the trans when pushed heavily on.
Engine mounts are good.
Diff mount and surrounding area is good.
the exhaust and mounting rubbers are like new.
there is no visual damage from any parts hitting anything that can be seen.

You can see, both me and the mechanic are at a loss. I am wondering if that slight deformation of the trans mount is the cause. Any suggestions people?
Can something be wrong within the trans?

Cheers, Graeme

[BladeRunner919]

Have you checked the giubo (the flexible joint at the front of the propshaft)? I gather that they can look ok even if they are damaged, and you need to unbolt the propshaft to really assess their condition. I assume the tailshaft carrier bearing you mention is the bearing that supports the prop?

Other than that I'd be thinking along the lines of the torque converter or one of the transmission drums. Does your mechanic have a lift that you could run the car on in the air and see if you can get a look at what's happening?

[Cooper01]

Thanks. I forgot to mention that the flex disc was changed in January this year. I spent 2 hours under the car on a lift today doing the mid shaft carrier bearing.

I might have to resort to finding a dyno with a mechanic watching and assessing. Automatic transmission internals...... Well that is something I am finding hard to get information on.

Cheers.

[lightning]

I had exactly the same fault with my Porsche 928 S4.
Nobody could find anything wrong. After a while the noise stopped, and then the auto box failed (no drive)

[Cooper01]

Damn.

[Del]

My experience of bushes and mounts under my own Z3 is that ones which look slightly mis-shaped or slightly cracked, have turned out ton be completely knackered. I think age plays a role and accentuates the problem. Vibration under load is difficult for us to "pick up" on a forum - common mechanical causes are mounts and/or drive shaft joints or sometimes engine misfiring issues like plugs, coils and fuel supply issues.

[Cooper01]

Thanks. I should probably change both of the transmission mounts and see what happens. I hope someone else had the same symptoms and solved it without a complete trans failure! Lol

[Del]

I should probably change both of the transmission mounts and see what happens

I agree, on a newer car one might consider that sort of thing a waste of money but when I'm chasing problems on my own Z3 I don't consider it a waste of money to renew a few 18-year old rubber components on the way to solving the problem.

[therealdb1]

I had a similar problem on a supercharged Jaguar.
Took me several years to work out what the cause was but that gearbox had a friction damper on the top which was basically a steel post sliding in a large rubber o-ring. The rubber part had perished so there was no damping and at certain conditions there was horrendous vibration.
A £10 rubber ring cured the problem completely and it was an entirely different car to drive after that!
Just remember when you are investigating rubber mounts is that you cannot check their condition just be looking and trying the 'push' test on the gearbox you are only using the force you can generate with your bodyweight through your arms. The vibration is being generated with the combined weight of the engine and gearbox and a couple of hundred horse power as well.

[Cooper01]

Thanks. I am ordering the mounts first thing tomorrow!

[lightning]

I hope that fixes it.

Thinking about it, the noise on my 928 S4 was not so much a vibration, more of a "dub dub dub dub dub" noise under load and at tickover.

So yours might be just the bushes as suggested.

[Vanne]

I had the same issue on my 3.0 when i bought it, turned out to be a rooted drive shaft. (after i bloody replaced the guybo, diff carrier and tranny and engine mounts.. Got one shipped from the US for 300 bucks, chucked it in, been good as gold since.

[4wheels]

the rubber bits are really cheap... but a pain in the arse to change!!

[Cooper01]

I had the same issue on my 3.0 when i bought it, turned out to be a rooted drive shaft. (after i bloody replaced the guybo, diff carrier and tranny and engine mounts.. Got one shipped from the US for 300 bucks, chucked it in, been good as gold since.

Vanne, was there any visible deformation to the shaft? I inspected mine carefully yesterday. I suppose you changed it as a last resort in desperation right!

[Vanne]

yep, shaft looked good, it was pretty much the last thing.. looked no diff than the one that replaced it, except there was no vibration when driving.. go figure.

[Cooper01]

Hey Vanne I just want to confirm......

You only had the intense vibration when accelerating hard right? I can go 150KPh with no issues, just hard acceleration with it happening at change of auto gears. Moderate acceleration with no issues.

Cheers,