Strange ARB issue (W209 CLK500)

esprit200

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Hello MBclub,

Looking for some input; I recently purchased a 2002 CLK500 with 150k on the clock. I have been working my way through the maintenance tasks usually neglected on such cars and have hit a bump in the road.

I get a fairly heavy knocking noise when travelling on road undulations or speed bumps, especially ones which "wobble" the car from side to side.

I thought I had isolated it to the anti-roll bar, as when disconnecting it, the noise disappears.

However, drop-links now replaced with Febi Bilstein, anti roll bar bushes replaced with Mercedes genuine, and the noise persists although maybe a little reduced and the car is handling better.

Is there a possibility that the roll bar is putting extra force on the tired old shocks or top mounts, thus causing the noise which disappears when the roll bar is disconnected?

Look forward to hearing your thoughts,

Regards,

Jon.
 

Bellow

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I thought I had isolated it to the anti-roll bar, as when disconnecting it, the noise disappears.

However, drop-links now replaced with Febi Bilstein, anti roll bar bushes replaced with Mercedes genuine, and the noise persists although maybe a little reduced and the car is handling better.
.

Which ARB, and how is the one at the other end of the car?
 

DSM10000

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Jon

Have you been underneath with a pry bar and tried levering on all ball joints etc?
 

grober

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ENGINE MOUNTS ??--- the roll bar stops the body from "shimmying" but maybe that big V8+gearbox still retains its inertia!
 
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esprit200

esprit200

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Which ARB, and how is the one at the other end of the car?

Front ARB, noted that when replacing the bushes, the bar was corroded, cleaned up with 80 grit emery cloth. Is it possible for the roll bar itself to be worn?

Jon

Have you been underneath with a pry bar and tried levering on all ball joints etc?

Have been jiggling and levering most arms, seem fine.

ENGINE MOUNTS ??--- the roll bar stops the body from "shimmying" but maybe that big V8+gearbox still retains its inertia!

Don't see how the engine mounts would be effected by the anti roll bar, but willing to listen to a theory?

My main point is that if I fully disconnect the roll bar, the noise disappears, but having changed the bushes and drop links, it seems unlikely the roll bar is at fault?
 

Bellow

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My main point is that if I fully disconnect the roll bar, the noise disappears, but having changed the bushes and drop links, it seems unlikely the roll bar is at fault?

I have to confess I missed the part in bold.
Leftfield, but the front ARB will limit the roll that when it is removed, is directed rearwards. My point being that maybe the more forceful roll now present at the rear (front ARB removed) may be masking rattles that are there when the rear ARB is less stressed (front ARB fitted).

Front ARB, noted that when replacing the bushes, the bar was corroded, cleaned up with 80 grit emery cloth. Is it possible for the roll bar itself to be worn?

Theoretically, yes. Test the theory by wrapping tape around the part that bears on the bush to build up its diameter and eliminate any potential play. Temporary as the tape will soon disintegrate but useful as a diagnostic.

To answer an earlier question. The ARB when twisted transfers load to the other spring on the same axle. Depending on where the drop link connects to the suspension (eg wishbone) it can induce motion not normally experienced. Eg, if the drop link connects at a mid point on the wishbone between the outer ball joint and inner bushes, the wishbone will be pushed and pulled vertically and the ball joints and bushes have to restrain that. The forces though are in a different direction to say, cornering loads.
 
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esprit200

esprit200

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Thank you for that input, I will test the tape method.

Front ARB attaches at the midpoint of the shock absorber casing using a metal tab. Could well be rattling the old tired shock around and causing the noise?
 

Bellow

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Front ARB attaches at the midpoint of the shock absorber casing using a metal tab. Could well be rattling the old tired shock around and causing the noise?

Separate damper - ie double wishbone not MacStrut? If so, its mountings are worth a look.

edit PS.
Suspect it has MacStrut if ARB drop link directly attached to damper.
 
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esprit200

esprit200

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Macpherson not double wishbone. Will take a look at mountings and bearings when changing damper (already have new front dampers so may as well put them in).
 

grober

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Don't see how the engine mounts would be effected by the anti roll bar, but willing to listen to a theory? My main point is that if I fully disconnect the roll bar, the noise disappears, but having changed the bushes and drop links, it seems unlikely the roll bar is at fault?
Imagine if the car goes over a road imperfection that shakes the entire car from side to side. If you think of a line /axis running thro the cars centre of gravity front to back starting at the engine crank pulley and running roughly along the line of the propshaft to the back. When subjected to a rotational moment from one side of the suspension the cars body plus engine is going to try to roll /rotate round this axis in reponse With the anti roll bar off that entire mass [ body+engine] is going to rotate together. With the rollbar on --- the ARB is going resist this body rotating moment but now this comes into conflict with the engines tendency to continue rotating due to inertia putting more strain on the engine mounts. that's the theory anyway. Does the engine show a lot of rotation or tendency to knock if the throttle is blipped open when stationary?
There is no direct connection between the roll bar and engine mounts its action is indirect by effecting body movement revealing a weakness elsewhere - this is similar to Bellows suggestion that good front roll bar action possibly transfers body rotational forces to the rear antiroll bar assembly ????
 
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Bellow

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Imagine if the car goes over a road imperfection that shakes the entire car from side to side. If you think of a line /axis running thro the cars centre of gravity front to back starting at the engine crank pulley and running roughly along the line of the propshaft to the back. When subjected to a rotational moment from one side of the suspension the cars body plus engine is going to try to roll /rotate round this axis in reponse With the anti roll bar off that entire mass [ body+engine] is going to rotate together. With the rollbar on --- the ARB is going resist this body rotating moment but now this comes into conflict with the engines tendency to continue rotating due to inertia putting more strain on the engine mounts. that's the theory anyway. Does the engine show a lot of rotation or tendency to knock if the throttle is blipped open when stationary?
There is no direct connection between the roll bar and engine mounts its action is indirect by effecting body movement revealing a weakness elsewhere - this is similar to Bellows suggestion that good front roll bar action possibly transfers body rotational forces to the rear antiroll bar assembly ????

Other way around. When front ARB is removed, rear ARB has to work harder to contain roll. That, would take up any play in the rear ARB and its mountings. With the front ARB in place. rear ARB has less to do and more possibility of it rattling/knocking.

Worth remembering how deceptive noise source and perception of source can be. The knock from the 'front' of my W123 was from the rear pads - enough said.
 
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esprit200

esprit200

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Interesting points and a reminder that I should not presume that because it *sounds* as though it's from the front, that it actually is.

I will check the rear of the car as I have not looked there at all yet. I did find my front wheel bearings to be too loose, front discs heavily glazed with pad deposits, brake lines partially perished etc so I'm sure there are many more pleasant surprises lurking at the back.

Engine mounts seem fine, nothing untoward at idle, when revved, or when accelerating hard.
 

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