Intermittent metal knock when depressing and releasing accelerator

[DJW]

Hi Gents,

I'm hoping one of the gurus amongst you might be able to lend some advice.

My Zed has been knocking - fairly regularly when depressing or releasing the accelerator (speed not a factor) - The knock varies in volume - it can get uncomfortably loud. I can also go on a journey without hearing it at all.

My local garage couldn't hear the knock - unfortunately it wasn't making a sound on the two times they drove it - and couldn't see or feel anything wrong when they inspected it. They called the local BMW specialist - Autobase in Chipping Sodbury - who said they were really confident it was the prop. So I got another prop (second hand) and they fitted it. On the first test drive, it seemed fixed but the knocking soon returned.

Roads seem to be leading to the diff - which feels like an awfully expensive outcome - before we head down that route - is there anything else we could be missing?

Huge thanks in advance.

 

[Smartbear]

I’d stop buying replacement parts until they can show me some evidence of wear, if the knock wasn’t speed dependant wouldn’t that rule out the prop?
Rob

 

[DJW]

Hi - thanks for your thoughts - I haven't been clear - When I say not speed dependant - I do have to be moving - I just mean it will happen at 5 miles an hour as well as faster speeds...

 

[Smartbear]

Hi - thanks for your thoughts - I haven't been clear - When I say not speed dependant - I do have to be moving - I just mean it will happen at 5 miles an hour as well as faster speeds...

Does the knock stay at the same tempo even when the speed varies?
Rob

 

[DJW]

Hi Rob, The volume of the knock varies all the time - so hard to map against speed - plus the extra sound coming from the car at higher speeds. The largest knocks certainly feel like they're happening when moving off and travelling slowly around the village.

David

 

[Smartbear]

Hi Rob, The volume of the knock varies all the time - so hard to map against speed - plus the extra sound coming from the car at higher speeds. The largest knocks certainly feel like they're happening when moving off and travelling slowly around the village.

David

Check the tightness of the under bonnet strut braces as they’ve been known to clonk at low speeds.
Rob

 

[jamie_z4]

might just need a propshaft donut or centre bearing

mine 'clicks' when setting off in 1st and reverse, a fairly common issue on the 85/86 due to the grease in the coupling drying out against the diff from the prop, learnt to live with it now.

 

[Chris1981]

might just need a propshaft donut or centre bearing

mine 'clicks' when setting off in 1st and reverse, a fairly common issue on the 85/86 due to the grease in the coupling drying out against the diff from the prop, learnt to live with it now.

That would be my feeling too... mine does it and bothered me at first, given the work require to rectify i'll just live with it!

 

[RustyZ4]

You haven't got an Arial with a bloody rubber thingamjig stuck on it have you, my mate who owns a garage, and shall we say a non male customer came in with a golf, complaining of a knocking noise at speed, turn out the Arial had a rubber whatever it is, stuck on the end, and it was banging on the roof

 

[DJW]

You haven't got an Arial with a bloody rubber thingamjig stuck on it have you, my mate who owns a garage, and shall we say a non male customer came in with a golf, complaining of a knocking noise at speed, turn out the Arial had a rubber whatever it is, stuck on the end, and it was banging on the roof

Ha - no ariel thingamajig!

 

[DJW]

might just need a propshaft donut or centre bearing

mine 'clicks' when setting off in 1st and reverse, a fairly common issue on the 85/86 due to the grease in the coupling drying out against the diff from the prop, learnt to live with it now.

That would be my feeling too... mine does it and bothered me at first, given the work require to rectify i'll just live with it!

Yeah - sadly it's not a click - def a clunk

 

[wonkydonkey]

Do you get the clunk if you engage first gear with the handbrake applied and then bring the clutch up to biting point with the handbrake still applied? If so, you could get someone to move around the car and locate the source. Could it be related to tired engine mounts allowing excessive engine movement?

 

[Markos_Z4]

i have also a clunk noise wen i pull up and reverse

start with the flex disc and check al the way to the differential ( Driveshaft Center Support Bearing / gearbox bushings / all the driveshaft joints / greasing propschaft replace oil seal ) if this not fix the problem then i replace the differential bushings )

next week i go to my garage if they find the problem i replay in this topic !

info with pictures : https://www.pelicanparts.com/techarticles/BMW_Z4M/125-TRANS-Driveshaft_Replacement/125-TRANS-Driveshaft_Replacement.htm

 

[JamieZ4C]

i have also a clunk noise wen i pull up and reverse

start with the flex disc and check al the way to the differential ( Driveshaft Center Support Bearing / gearbox bushings / all the driveshaft joints / greasing propschaft replace oil seal ) if this not fix the problem then i replace the differential bushings )

next week i go to my garage if they find the problem i replay in this topic !

info with pictures : https://www.pelicanparts.com/techarticles/BMW_Z4M/125-TRANS-Driveshaft_Replacement/125-TRANS-Driveshaft_Replacement.htm

I have a similar clunk noise. When in gear, not when selecting gear (so not the donut). Most noticeable at very slow speeds and when I press and depress the accelerator pedal. Almost as if trying to bunny hop it on purpose. It definitely sounds prop related to me. I wonder if it needs greasing.

Will be interested to hear how you get on.

 

[Clobber]

This is a bit of a sad noob confession but the first knock I started to get worried about turned out to be the BMW keyring metal bit banging on the steering column....