I have a knocking noise at the front left (passenger side on a RHD car) of my 1997 SL500 which is quietly driving me nuts. The noise only appears at slow speeds (<10 kph) when braking or more often, when accelerating. Doesn't seem to be related to road bumps or turning the steering wheel. I can actually feel the knock through the floor pan – feels substantial rather than cosmetic. The noise goes away (or isn't discernable) at speed.
I've opened the bonnet and rocked the car up and down - no noises whatsoever. My bonnet latches are well oiled - nothing feels / appears loose.
My car shows 55,000 km (but 'clocking' notorious in Hong Kong hence could easily be twice that) - say 70,000 miles (110,000km)
I have searched the forum and have come up with the following ideas as to what it could be:
1. steering damper / shock (though think this may have been replaced recently)
2. motor mounts
3. front strut mount bushing
4. sway bar bushings (though think this may have been replaced recently)
5. ball joints
Anyone care to put them in order of likelihood or have any further thoughts to add to my investigative list?
Cheers
Alan
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1997 Benz SL500
2000 Benz CLK230 Cab
HONG KONG
Location: Living with two V8s and a dodgy Government
Posts: 268
Is the knock spasmodic, ie it will knock once on moving off and not again until you brake - is it quite severe, almost like someone giving the suspension a very sharp blow with a hammer?
Vehicle: ML320, 1998. SL500, 2001, 125.000 +mls no problems
Location: Beirut, Lebanon
Posts: 97
Hi ahmorris.
After what you describe,
"I can actually feel the knock through the floor pan – feels substantial rather than cosmetic", I would take the car to a workshop immidiatly. You might soon loose more than your sanity.
Is the knock spasmodic, ie it will knock once on moving off and not again until you brake - is it quite severe, almost like someone giving the suspension a very sharp blow with a hammer?
Hi Hal
Knock does appear to happen when going very slow. Doesn't happen just with stopping Seems to be realted to goign slow (turning / waggling the steering wheel doesn't seem to make it worse or better) - it's hard to replicate it at will.
Noise sounds like a metal to metal contact, like something when a rubber bush has part perished hence metal to metal contact in certain circumstances.
I had the steering looked at a few months ago because it was rather woolly and making lots of noise /movement over bumps / potholes. Think my indy changed the steering damper plus steering-related bushes to tighten whole lot up. Steering now perfect hence my thoughts that it's not steering-related - unless my man missed something.
It's not that I'm obsessed with noises...but years ago I had a Volvo 850 Turbo Estate which had an intermittant noise when braking / accelerating. It would disappear for weeks then return. Turned out to be a plastic golf ball stuck in the floor pan tubing - which every now and then got wedged at the end of the tube until I braked / acclerated hard and set it off again. That one almost drove me mad finding it but I got there... :-)
Hi ahmorris,
I had a similar problem on my 1991 500SL which turned out to be a fractured torsional support tie, You will need to get under there & check out the integrty of the ties under chassis. They help give the frame it's rigidity
Vehicle: 2000 Obsidian Black Metallic Mercedes SL 320 V6
Location: Northern Italy near Milan
Posts: 1,810
Hi ahmorris since the sound is not related to bumps or road imperfections I would eclude the steering dumper because (from experience) it gets usually noisy on bumps or ramps.
Hope this helps.
Cheers.
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I drive like I stole . . . YOURS
I recently had the front anti roll bar mounting bracket fatique and snap on my car, get that checked. On mine it then sawed through the ADS hydraulic line! Didn't notice any noises even after it snapped though, just a puddle of very expensive hydraulic fluid on the floor!
Thanks for the suggestions to date. I have just dug out my old service docs are the following (as written on the service sheet) were changed / repaired in the last 4 months:
Replacement of suspension anti-roll bar & bushing (two - inner & outer)
Replacement of steering tie rods (two)
Replacement of central link
Replacement of idler arm bushing
Replacement of steering absorber
Four wheel alignment
Location: Living with two V8s and a dodgy Government
Posts: 268
Alan
it really could be a number of things which will be impossible to pinpoint exactly without being with the car.
I had one like yours - a really sharp metal to metal sound which i could not find. Eventually a Mercedes dealer found it to be the road spring shifting position due to the zinc bedding plate worn away. But yours does not sound like this. So, I guess I will not be any help.
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