Mercedes Benz SL W107 (1971 - 1989) - 1989 3 litre rear axle area knock. | Technical matters | Back Room Forum

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Mon 12 Nov 2007 22:06

1989 3 litre rear axle area knock. - motorprop

My W107 1989 MB ( last year of that shape ) 3 litre straight - six , owned and garaged by me for the last 7 years , has developed a strange ' knocking ' noise emanating from the back axle . This car is a weekender - have just returned from a 500 mile round trip . I think the noise comes from the off side ( it is RHD ) , but then again it could be because that's the side I am sat on .

There is a knocking sound coming from the back - axle area when driving . Initially, when cold there is no noise which has made it difficult to let mechanics listen / diagnose , as they get into the car when parked and report nothing. The noise has become louder , although I Ist began to hear it about 2 years ago ( 6000 miles travelled in that time ). It does increase with speed travelled , but when I press the brakes , it disappears , for as long as the brakes are applied . It either disappears over 55 mph , or the increased noise drowns it out .

I had new tyres put on about a year ago and at the time examined the rear brakes and all looked fine , no bits hanging off etc ..

This car is an auto and has covered 100 k miles from new .

Anyone got ideas ? somebody mentioned the drive shafts but it wasn't based on listening to the noise , just to my description of it ...

slt

Edited by Pugugly {P} on 12/11/2007 at 22:11

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Tue 13 Nov 2007 08:50

1989 3 litre rear axle area knock. - Roger Jones

Try:

sl107.com/

home.hiwaay.net/~gbf/107sl.html

www.mbclub.co.uk/

forums.mbworld.org/forums/

www.mercedesshop.com/shopforum/index.php

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Wed 14 Nov 2007 10:17

1989 3 litre rear axle area knock. - Roger Jones

Have those links helped you at all?

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Wed 14 Nov 2007 14:14

1989 3 litre rear axle area knock. - motorprop

thanks for those , good links to clubs etc , but was hoping to find specific advice on this problem .

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Wed 14 Nov 2007 15:11

1989 3 litre rear axle area knock. - Peter D

Is this a once per revolution of a tyre knock serveral per revolution like a busted diff crown wheel or a failed rear wheel bearing. You are not giving us much to go on. Regards Peter

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Wed 14 Nov 2007 15:24

1989 3 litre rear axle area knock. - Roger Jones

If you post to the forums on some of the links, you will hit plenty of 107 owners who may be able to pinpoint your problem much more quickly and effectively than the non-specialist community here, among whom there may be no-one with 107 experience. Indeed, owners on those forums may well have experienced identical problems and solved them. There are 107-specific sections in some forums. Do report back when you have made some progress -- results are always of interest.

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Wed 14 Nov 2007 15:52

1989 3 litre rear axle area knock. - motorprop

I will , thanks , though they do seem to be mostly shermanic ...

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Wed 14 Nov 2007 15:49

1989 3 litre rear axle area knock. - motorprop

hard to say, but it's not tyres as the noise stops when the brakes are applied . It could be one per wheel revolution , or a bit faster than that . No noise when cold , it builds up after about 5 minutes . strange .

thanks for all contributions so far .

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Wed 14 Nov 2007 16:59

1989 3 litre rear axle area knock. - Number_Cruncher

If the noise doesn't come and go when you go on and off the throttle - i.e., drive and overrun, but only goes when you actually brake, I would not be looking for things in the final drive or driveshafts. I would be concentrating my efforts around the wheels, the brakes and the wheel bearings (and possibly exhaust too).

If there's no noise from cold, then I would also make sure that the brkes aren't rubbing and getting too hot - it's easy to check after a run.

Are these cars fitted with rear disc brakes with a small handbrake drum within?

With the car making the noise and travelling very slowly, does the noise go away if you apply the handbrake?

Are the brake pad anti-rattle / squeal shims in place?

Number_Cruncher

p.s. while model specific help might be very helpful, I'm not a great beleiver in poke and hope fixes, and I think it's much better to be sure that you have found the fault, because while there are common faults for each model of car, there are also uncommon, or one off faults, which can often leave "experts" completely baffled!

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Wed 14 Nov 2007 17:04

1989 3 litre rear axle area knock. - Peter D

This may even be a cracked spoke on an alloy rim or cracked weld on a steel rim. Regards Peter

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