Untraceable clunk from car - driveshaft ?

[CompoSimmonite]

I've got an untraceable clunk on my car a 05 Smart Fortwo.
It doesn't seem to have a trigger and can happen on a glass smooth road yet hit a pot hole or speed hump where normally you'd expect such a clunk to occur and nothing Braking or accelerating doesn't cause the clunk either.
The clunk has only recently started (within last 20 miles and rapidly got worse during that period) You can now physically slightly feel the clunk though the floor as well as hearing.

Braking, steering, ABS & handling all as normal. Rocking car when stationary doesn't generate the clunk.

I recently changed both the front wishbones and drop links. The bottom ball joints were still good and antiroll bar mounts sound. I'd previously changed front springs due to a (pot hole) break so know front shocks and upper mounts OK. I've been back under the car yesterday to double check and no loose bolts, broken bits, deteriorated parts, steering rack has no play, track rod ends alright so have eliminated front end as being the source of the clunk.

Checked rear (De-Dion) and springs / shocks good (both springs changed last year after another break), tie rod bushes unworn, no play in subframe mounts.

All 4 wheel bearings smooth and no play. Brakes not sticking.
It passed a MOT just a few hundred miles ago with no advisories other than part worn brake pads and surface rust on one brake pipe.

The only thing I can now think of is it could be a worn CV joint but no noticeable play when checked by hand. FWIW this is a rear engine and RWD car.

Could a CV joint create such a clunk that is impossible to generate "on cue" ?

Cheers.

Paul H

 

[slim_boy_fat]

.......I've been back under the car yesterday......

Was that with the car on a ramp and the weight off the suspension?

 

[dobbslc]

Loose wheel, big screw stuck in a tyre?
Did you have the whole subframe off? Could it be a loose fixing on that?

 

[rikrobson]

I have a clunky rattle in the audi. Something is loose but I can't find it. It's not the running gear and it passed an mot with it. When I picked up the lathe with 250kgs in the back it didn't make a sound. Check loose panels, exhaust seats etc.

 

[CompoSimmonite]

Was that with the car on a ramp and the weight off the suspension?

Tried both.

It's so frustrating as with being a small car it's not possible to even get an idea which area it's coming from as would happen with an ordinary vehicle. When it first started I THINK it was coming from the rear but recent dismantling the front suspension to change the wishbones made me wonder if related to that. Also local lanes have been flooded so another thought was something had got washed into the full underbody tray but couldn't find anything - it'd have to be half house brick anyway to make the clunk I'm now getting.
I forgot to say the clunk doesn't seem to happen until I've driven 1/2 mile / few minutes and not straight away. Might be co-incidence though.
Engine runs smoothly as do gear changes / autoclutch so don't think it's related to those components.
Brand new, complete, driveshafts are only £34.99 each so at worse it's not going to be an horrendous amount to replace them if I can't find any other cause even if they then prove to be faultless on examination. I suppose I could peel back the CV gaitors to see if there is any visible fault with the joints. No leaks so can't see it being dry joint but wonder if a ball might be breaking up

 

[Paul.]

My wifes KA had a loud knock, mainly when going over speed humps which from the drivers seat you would have sworn was at the rear, it was still under a used car warranty so I took it back and they fitted a ns front suspension arm, it was just a bush creaking and being amplified and transmitted through the car, I couldn't make it do it with the car stationery though, just shows how noise travels through a car.

 

[CompoSimmonite]

Might have discovered D'oh situation

There is no workshop manual available for the Smart so you have to trawl the web of information on how to do various jobs.

I changed rear springs using this method (instead of the "approved" method which involves dismantling all the rear suspension) -

Just been looking for drive shaft problems of the Smart and find that it's possible to damage the inner joint when changing the rear springs. The inner joints are tripod rather than CV. So if one of the rollers of this tripod joint is in the wrong position when jacking the De-Dion beam away from the subframe then I suppose it could do some damage.

 

[Cobbler]

I don't know whether this is applicable to the Smart, but the nylon bushed rose joints used on some of the cars can make a terrible nose when they go dry. I had a Vectra & the rear trailing arm bushes went. It made an unbelievable noise. Sometimes it creaked, sometimes it knocked & banged. If you hit a big bump, it made no noise because it moved suddenly, but over the smaller undulations it was awful. It was also very difficult to replicate & showed no wear, but resonated right through the car.

 

[garethp]

Does sound like a similar noise that my dad had on his bmw, totally random bang every now and again, tell tale was one cv joint would move slightly more side to side more than the others but wasn't sloppy if that makes sense?

 

[CompoSimmonite]

Does sound like a similar noise that my dad had on his bmw, totally random bang every now and again, tell tale was one cv joint would move slightly more side to side more than the others but wasn't sloppy if that makes sense?

Both drive shafts move easily in the splines on the inner and outer joints but I assume that is normal. No rotational play anywhere though.

 

[Shedendman]

My god,you've not bought THE MEGANE have you

 

[CompoSimmonite]

My god,you've not bought THE MEGANE have you

Had the car nearly 6 years and during that time only had to replace discs / pads, all 4 springs due to breakages and bulbs, battery plus service items (oil, filters and all 6 spark plugs !) and set of tyres (aged - not worn). One of the wishbone bushes was perished so I changed both wishbones / drop links rather than changing just the one bush as they were cheap. Everything else is original plus it's been 100% reliable. Now at 65,000 miles and doesn't use a drop of oil between changes. I manage low 70 mpg on a run as long as I stay just below 60 mph - over and economy suffers quite a bit.

 

[slim_boy_fat]

This isn't you, is it?

 

[Wedg1e]

I had a random clunk on the TVR a few years back, it showed up after reversing and then going forward but then wouldn't do it predictably... until the next time you reversed.
I eventually found a chunk of a rear wheel bearing outer race had fractured off and got stuck in the grease. As long as it got stuck in one place it'd go round with the balls and make no noise but when you reversed, it moved the chip which would get snagged by the next ball.

 

[CompoSimmonite]

Had a mate with me in the car earlier today. He says definitely coming from offside rear. That is the driveshaft I suspected I might have damaged when changing the springs as it's only a short item. Decided to change both drive shafts anyway as won't break the bank and the car is a "keeper".

 

[CompoSimmonite]

I had a random clunk on the TVR a few years back, it showed up after reversing and then going forward but then wouldn't do it predictably... until the next time you reversed.
I eventually found a chunk of a rear wheel bearing outer race had fractured off and got stuck in the grease. As long as it got stuck in one place it'd go round with the balls and make no noise but when you reversed, it moved the chip which would get snagged by the next ball.

This is sort of what I think might have happened to the tripod joint.