2006 e85 3.0si - knocking noise from the rear

[simonm]

Hi folks,

My z4 has recently developed a knocking noise from the rear end, which manifests itself on badly surfaced roads (ie nearly all the time). It appears to be coming from underneath the passenger seat - and sounds like someone banging the floor pan with a hammer!

The car has recently had new OEM rear springs, shocks and trailing arm bushes; is running on nearly new Michelin PS4s and has had a four wheel alignment.

Nothing looks amiss with the rear suspension and the exhaust isn’t touching the body.

Any ideas on what might be causing it?

 

[ph001]

If it’s had oem springs then it wouldn’t surprise me if one has snapped again.... they really are that bad. Suplex is a much better choice for oem ride.

 

[z4pilot]

I would guess at a back box hanger bracket - they're notorious for snapping at the weld on the box itself

 

[bazza190]

Top mounts? Meyle ones and Bilstein shocks give a knocking noise, even when brand new.

 

[ph001]

I would guess at a back box hanger bracket - they're notorious for snapping at the weld on the box itself

oh yeh - that has come up before. First thing to check I think.

 

[Smartbear]

I would guess at a back box hanger bracket - they're notorious for snapping at the weld on the box itself

oh yeh - that has come up before. First thing to check I think.

Had the same on my 3.0si, easy enough to get a welded repair carried out
Rob

 

[Doddsy]

Did you get this sorted? I know you said you checked the rear suspension but are you sure the rear anti roll bar drop links are still in one piece? I’ve had them snap in half before

 

[Scooba_Steve]

The lower control arm bushings will also give a noticeable knock, usually when turning in the opposite side e.g. OSR knocks when turning left.

If it's intermittent, only in one direction and difficult to replicate (but does it consistently at the same point on a journey for instance) then that's what I'd look at. MOT will pick it up with a pry bar.

https://www.realoem.com/bmw/enUS/showparts?id=BU52-EUR-03-2006-E85-BMW-Z4_30si&diagId=33_1139

Item 3 but upgrade both sides with item 2. You will need a bushing kit.

 

[AlphaEchoAlpha]

I would guess at a back box hanger bracket - they're notorious for snapping at the weld on the box itself

That was the source of the knocking on mine when I got it... not the rear top mounts, which I did before having the backbox changed :roll:

 

[simonm]

Thanks for all your suggestions! The car went in to my local Indy today for them to have a proper look - and the culprits were the top mounts - which were only fitted in June along with new shocks

They were Corteco mounts (as suggested by Euro Car Parts when I said I wanted OEM quality). I’m having new mounts fitted tomorrow, supplied by BMW at great expense (£65 each) so let’s hope they last longer than the 2000 miles I’ve driven in the last 7 months

On the plus side, it sailed through its MOT today, so looking forward to getting the top mounts fixed and taking it for a blast at the weekend - on my way to buy “essentials” of course