Dink / Clonk When Driving

F

Flakmunky

Member
Hi,

I'm new to the forum and we bought a used Z4 for my wife on Friday and have noticed a sound which we don't believe was there when we took it for a test drive...

Basically, in first or second only, releasing the clutch or with the clutch released stepping on the accelerator or easing off the accelerator one can hear a metallic 'dink' sound coming from the centre of the car.

Have tried bouncing the rear suspension but cannot recreate the sound...

Going back to the garage on Tuesday but would like to know if anyone has any ideas what this is... Don't want to get fobbed off!

Thanks,

fM
 
Hi,

Its worth pointing out that this is a 3.0se and that this sound only occurs at low speed. Under moderate acceleration it can't be heard. The sound is not constant, and only ocurrs when the drive is taken up...

TIA,

fM
 
Hi,

I think I can recreate the sound with the car in gear, clutch out and engine off, rocking it back and forth...

Thanks,

fM
 
Yep, just sounds drive train related.

The first few days driving mine with the radio off (wasn't working :lol: ) I had plenty of time to listen to the clunks/clacks at lower speeds while at speeds where you are neither accelerating much, or decelerating, just ambling around gently against the drive train.

If it's something quite loud and distinctive, maybe worry more, but if it's just generally a bit noisy vs cars you are used to I'd not worry so much. You sit right near the rear diff, and just behind the gearbox/clutch, with not much sound proofing, so plenty to listen to if the radio isn't on and the roof is up :D

I didn't notice the sounds at all on the test drive, only when you start to drive it as you do day to day would you notice it. I noticed mine doing it in stop start traffic on my way home after picking it up, but not at all on faster drive about an hour before I hit the traffic.

Dave
 
Hi,

I wouldn't say it is very loud, about as loud as the bashes and crashes you get when going over speed bumps. Incidentally, I *think* I can hear it when going over speedbumps too fast, but as I say there are so many other noises its hard to say!

I have tried rocking it in gear and I can't recreate the noise (but then I can't apply the same amount of torque the engine can!) and I have jacked it up, applied the handbrake and tried to turn the output driveshafts to see if there is any play in them - nada... So maybe the U-joint or a worn bush in the suspension? Hoping (praying) it ain't the diff!

I have had a 350z and an *ahem* MGF (Trophy 160, so give me a break!) so am used to roadsters being a little more noisy than my Audi barge...

The other thing I wondered about was whether it was a worn engine mount given the very close proximity of a plate underneath the back end of the gearbox...

Anyway, I'm going to BMW to get the keys programmed tomorrow and will ask them then if the mech will take a ride with me... Then I'm back to the non-franchised garage I bought it from!

Will let you know.

Thanks,

A Worried Munky
 
Took it a BMW dealership who looked underneath it and declared the suspension ok, and diagnosed it somewhwere in the drivetrain, possibly the drive-shaft or the diff.

Took it to the garage who I bought it from who in turn sent me to their 'RWD Specialist' who is a dedicated gearbox mechanic who seemed a really genuine guy. He drove it round and thought it might be one of the half-shafts but is taking it in on Monday to see more. This guy rebuilds Landy gearboxes, 3-series diffs and a whole lot more. Said he does a lot of work for main dealers too... We'll see...

Anyway, not driving the car any more until then in case we need to reject it, however I would rather get the thing repaired - we got a good deal, including 4 new tyres and a service... But if it turns out to be the diff, the garage might just refuse to fix it...

Anyway, thanks for your suggestions. I'll post back and let you know. Hopefully I'll be able to post some nice pics soon....

Regards,

fM

PS Was anyone here bidding on that rigid slipstream deflector on Ebay last Sunday?
 
Did you solve the noise issue?

Put mine on a ramp on Friday to have a look at my clonking. Turns out that it's coming from the output shafts of the diff when they are initially put under load. It can visibly be seen (prob about 2mm movement on each side) by looking at the gap between the diff casing and a flange type cover next to the diff.

Has anyone eles got experience of this. Do I just live with it or is there a fix? I don't want to go to the trouble of removing the half shafts if nothing can be done about it.
 
Hi,

No I didn't get this fixed... Can you explain what you could see a little more clearly, please, as I'm not sure I understand how they were moving... Are the output shafts moving outwards towards the hubs when they are put under load? Or are they twisting?

I have heard on another forum that it could be cured by changing the output drive shaft seals, but I can't get any information on this....

I've got what seems to be the same sound at the moment.
I mentioned SIB 33.04.08 last time I was at the dealers which is something to do with replacing the pinion seal and lubing the flange of the diff
Click to expand...

Thanks,

fM
 
Yes, the output shafts are moving about 2mm on each side when you take up drive. Spoke to a recommended BMW specialist on the weekend about it (OCS in Rugby), who said nothing can be done about it without stripping the diff and replacing the output shaft seals and circlips.
His suggestion was to live with the noise and monitor if it gets any worse, or spend £500 having the diff stripped and rebuilt. Needless to say I'll live with it for the moment!
 
I started to notice a definite clunk from the rear of the car in the multi-storey at work going up ramps in first gear. Also does it a bit when engaging reverse. Dealer had a look when the car was serviced and reckon its the diff thats the problem. Car is going back tomorrow to have the fix done (can't remember exactly what they said this was but I'll post up here tomorrow after its been done).
 
When driving slowly over minor bumps, I have a clonk (or clunk) which seems to be coming from the front - either from the behind the dashboard or from the engine compartment. I can't duplicate it by bouncing the the body up and down when stopped nor does happen as much when driving at normal speeds. It doesn't seem to coming from the suspension and it doesn't transmit any vibration through the steering column. I didn't think about the drive train until reading these posts, but since it's coming from the front, perhaps that's not likely. I'd would appreciate any thoughts that might help me diagnose this problem. Thank you in advance!

Brian
 
Brimoon, another forum suggested that my sound was due to the bolts attaching the cross bracing under the bonnet needed tightening. Try that.

As for my problem, the sounds remains. No worse. No better...

Will see if it develops!
 
I get the dink sound when engaging reverse, I figured it was simply a little drive shaft play on the diff/box. This is my first RWD car so figured it was normal. If its not, then I have a weeks warranty left and someone needs to tell me ! lol
 
Slightly related, brimoon especially....i had the EXACT same symptoms your describing.

After two visits to BMW they said they couldn't see anything wrong with the suspension. It felt a lot like top mounts had given up to me.
So after getting fed up i visited my local indy and posed the problem to them. I had my rear eye wishbone bushes changed as they were shot. Caused by hitting to many potholes etc. £120 all in and now feels solid.
 
I think this 'diff clunk' is a common issue. Ive seen plenty of threads on it before, also on the //M's. Mine does it also and doesnt really bother me - the dealer said it was a little play with the ring/pinion gears that is regularly reported; they said it's not an issue but noted it while my car was under warranty. That was 6 months ago and it isn't worse. :)
 
For Brimoon,

Definitely sounds like the bolts on the cross members where they attach to the firewall. Check the torque, mine were WAY loose and having the same noise issues.

Will
 
All - Thanks for the comments and suggestion; I appreciate them.

Will, is there a torque specification for those bolts or did you mean that they just felt loose when you checked them? If there is torque spec, I would appreciate learning what it is. Thanks in advance!

Brian
 
Brian,

The factory spec (I was told) for these is N-m 41, or 30 foot pounds. This felt about right when I tightened them so I would go with that, but do what feels right on yours. Also, I put a little dab of aviation torque seal on them for visual inspection to see if they are loosening again. You can see in the pic how the left one was moving causing the clunk! Easy fix with amazing difference!




Will
 
Will, You're a genius! I tightened both nuts to 41 Nm / 30 ft lbs, problem solved. The nut on left side took about a half turn and the one on the right almost a full turn to get to that torque setting. I took the car on test run and no more thunk or clonk. I can't thank you enough for your help on this; the noise was really bothering me, mainly because I couldn't locate the source and had visions of a big repair bill.

Kind regards and happy motoring, Brian
 
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