Knock from Rear End ?

[sparkyman]

Hi All,

Thanks to all who responded to my first issue - hoping for some insight on this next issue...

I've noticed a knock from the rear end on accelerating/decelerating

My first suspicion would be engine mounts ?

I intend to have a closer look as soon as I can get the rear of the car jacked up

Is this a common issue, as I see all 3x mounts readily available on eBay ?

Any way to test, prior to a visual inspection, as I can't quite get in to visually inspect the rubbers at the moment (for perishing/detachment etc) - Car has done 92K


...or could it be a suspension issue ... ?

Thanks

[10:45PM]

I'd suggest the visual before buying bits

[sparkyman]

.. trouble is, I don't know what a good one looks like - can't see any detailed photos on eBay, just oblique angle shots. I'm not sure if I'd be able to get a good visual inspection at all, as they mounts appear to be quite well masked by various chassis members etc .... ?

[Big Performance]

Where are you in UK ?
If you let us know we can recommend an independant

[sparkyman]

Thanks for the offer Big Performance, I tend to do all maintenance & repair work on my cars & motorcycles myself. I was just curious for an experienced insight into determining if the engine mounts require replacement - the Roadster is new to me (2 weeks), so yet to get familiar with it. I live in Cornwall ....

[Thrumbleux]

Can't say for certain that it applies to Roadsters but with fortwos the exhaust and the K-bar (onto which the the inner ends of the transverse links are affixed) are in very close proximity and any exhaust misalignment brings them into contact. Presumably excess engine movement would also. Tell tale contact marks show on the alloy heat shielding fitted to the K-bar.

[sparkyman]

Hi thrumblemeux - thanks for the info.

Not come across mention of "K" bar on Roadster so far, and not familiar with fourtwo design, but would you be talking about the rear suspension cross brace which links the DeDion tubes together (X-Brace, Track Control etc) ??

I'll have a quick look up underneath this evening to see how close the silencer is....too anything at the back !

[Thrumbleux]

[QUOTE=sparkyman;n874949, but would you be talking about the rear suspension cross brace which links the DeDion tubes together (X-Brace, Track Control etc) ??

[/QUOTE]

Yep, that's the badger.

[sparkyman]

Morning All,

Had a quick look underneath last night - noted the heatshield riveted to the X-brace, but no evidence of any contact between exhaust. Had a good look all around the exhaust and no signs of contact with anything. Also grabbed the edge of the sump, in various places and attempted to rock the engine looking for play. Seems tight when pulling sump towards rear of car, and a little compliance when pushing towards front of car, but nothing I would consider as excessive ?

Engine is clean - no oil leaks (with exception of turbo connection hose on intercooler), so I would assume no damage to engine mounts through oil contamination, but at 92K, maybe there just suffering from old age ?

Will keep investigating ....

[tolsen]

You really need a good high lift trolley jack and axle stands. Front engine mount tends to wear out first. Its rubber splits or debonds. Easy to check with an inspection mirror and torch. Right hand side mount tends to loose it heat shield due to rust, especially when exposed to salt treated wintry roads.

Jack up rear end by placing trolley jack under bell housing. A suitable piece of conveyor belt will suffice as cushion.

Perhaps exhaust is not sitting properly centred and is therefore touching something. Try rocking engine when rear end is lifted up. The nuts that hold exhaust to exhaust manifold are usually in a bad state and may require replacement before you can realign exhaust. Best to replace with brass or stainless steel nuts.

[sparkyman]

Hi Tolsen,

Thanks for the info - so it is OK to jack underneath "bell housing" - is this the diff casing ?

I intend to get the rear up on axel stands this wekend and have a good look in daylight

Thanks for your help

[tolsen]

Yes same as diff casing. I've used that as a jacking point when lifting my 450 Cdi since day one. Mine still has the original engine mounts from 2002 in spite of now having clocked 200,000 km.

[sparkyman]

.mmmmmm..... 200K ? Makes me think maybe it's not engine mounts then, only 92K and no oil leaks, so probably no perished rubber.

Still on the list for checking though ....

[Mr T]

Can you get someone to try pulling away whilst the handbrake is on & you looking in the engine bay?

[10:45PM]

Preferably not in reverse and not close to a wall lol

[sparkyman]

Ahh.... hadn't thought of that .... damn good idea, will try it this weekend Mr.T