Resonance under braking

[SteveP55]

I've recently acquired a 2003 SL55 and have a question about the brakes which I hope the collective knowledge can advise on before I take it down to the dealer.

When I brake from any speed above 40mph, as the speed decreases and passes 40mph, I get quite a loud noise which sounds like it is caused by resonance of some sort - it happens at the same speed each time and at no other speed and appears to be worse if the car has been left to stand for a few days.

It seemed to decrease after several braking cycles, but it is still there.

Does anyone have any ideas?

 

[television]

I've recently acquired a 2003 SL55 and have a question about the brakes which I hope the collective knowledge can advise on before I take it down to the dealer.

When I brake from any speed above 40mph, as the speed decreases and passes 40mph, I get quite a loud noise which sounds like it is caused by resonance of some sort - it happens at the same speed each time and at no other speed and appears to be worse if the car has been left to stand for a few days.

It seemed to decrease after several braking cycles, but it is still there.

Does anyone have any ideas?

You should check with MB that the SBC recall has been done, and check to see if the SBC damper mod applies to your car.

Malcolm

 

[stumpy]

Could it be pad deposits collecting in the holes? I know M3s can have rumbly brakes.

 

[SteveP55]

As far as I know, all recall repairs have been made to the car, as it went in recently for other repairs and they picked up on one that hadn't been done. I will check about the SBC damper mod though.

The discs are drilled, so I'll check for deposits

If anyone out there has had similar experiences, I'd like to hear from them

Thanks

 

[Flying Scot]

I've recently acquired a 2003 SL55 and have a question about the brakes which I hope the collective knowledge can advise on before I take it down to the dealer.

When I brake from any speed above 40mph, as the speed decreases and passes 40mph, I get quite a loud noise which sounds like it is caused by resonance of some sort - it happens at the same speed each time and at no other speed and appears to be worse if the car has been left to stand for a few days.

It seemed to decrease after several braking cycles, but it is still there.

Does anyone have any ideas?

IF this is after the car has been sitting for a while and decreases after several braking cycles - it 'could' be just a light surface rust on the discs getting cleaned off by the pads - i dont know why it would cause a sound and vibration that would give you cause for concern - and speed related does seem 'strange' - what does this sound - sound like?

record it on your phone and post it here

for sure i have a similar problem with my SL500 no 'specific' speed sound though - but it is a sunday car and well can we say it gets cleaned a lot and the discs end up looking quite brown after a few days sitting - that and my driving style which is press on but does not involve much use of the foot brake means that before i end up back at home i need to do a bit of F1 style brake work - before the car gets put away - so that the discs are at least clean and shiney to start with - for sure the brakes moan a little initially but nothing excessive and nothing unexpected

 

[SteveP55]

Thanks for the reply.

It's not disc surface contamination, pretty sure of that, as I know what that sounds like and if I do have any that (like after washing the car), it clears quickly with a few low speed stops.

Because it happens at precisely the same speed, it makes me think that something to do with the brakes is resonating something else in the car which is then amplified throughout the car. It isn't a grinding sound or anything like that, more like a loud hum.

The brake pedal doesn't pulse or vibrate nor does the steering wheel, but you can sort of "feel" it through the car. It is quite wierd. Braking performance is also seemingly unaffected.

When I get chance, I'll run it down to the dealer for them to have a listen, see what they think.

 

[stumpy]

Cross drilled discs do this. IMO all normal

 

[Birdman]

Without claiming this is what you are experiencing, I have had patching on the discs of my E55 and this causes a distinctly noticeable rumble when braking at the low-ish speeds you mention, without transmitting to the steering but creating a low frequency vibe felt through the seat and floor pan.

My patching is probably due to uneven pad compound deposits on the discs - rust it ain't. As for 'warping' that's a bit of an urban myth. On lightweight uber-sports bikes with thin discs, yes. But not on a Mercedes.
Doing a number of hard stops clears the problem for a while. Then it comes back. Problem is, the new pads either weren't correctly specified, or properly bedded in.
My experience, maybe not yours.

 

[television]

r 'warping' that's a bit of an urban myth. On lightweight uber-sports bikes with thin discs, yes. But not on a Mercedes.

My experience, maybe not yours.

I can assure you that Disc do warp on a MB and any other car for that matter, I have even had them split. being made of cast iron, that is a very unstable metal. warping can occur after a high speed stop for instance, and is caused by heat, exactly the same as when a cylinder head warps after boiling.

Malcolm

 

[television]

Just adding one more thing to do with cast iron. In its cast state it is fairly stable, once machined other things can happen as stesses are imposed and relieved. The most important thing is that once heated it should be allowed to cool as uniformly as possible. After servere braking the pedal should be released as soon as possible to avoid the area in the grip of the pads cooling before the rest of the disc. the pads and calliper acting as a heat sink.

malcolm

 

[Birdman]

If the brakes are very hot following a single long stop from high speed and the brakes are kept applied after the vehicle comes to a complete stop it is possible to leave a telltale deposit behind. This kind of deposit is called pad imprinting

Cast iron is an alloy of iron and silicon in solution interspersed with particles of carbon. Every time that the leading edge of one of the imprinted deposits rotates into contact with the pad, the local temperature increases. When this local temperature reaches around 1200 or 1300 degrees F. the cast iron under the deposit begins to transform into cementite. Cementite is very hard, very abrasive and is a poor heat sink. The amount and depth of the cementite increases with increasing temperature and so does the brake roughness.

Presuming that the hub and wheel flange are flat and in good condition and that the wheel bolts or hat mounting hardware is in good condition, installed correctly and tightened uniformly and in the correct order to the recommended torque specification you will not encounter a warped brake disc during normal road use.

The phrase “warped brake discs” is used almost universally by uninformed vehicle owners to describe the cause of brake judder. The actual underlying causes of brake judder are, without a doubt, the most misunderstood aspect of automotive braking. The overwhelming cause of brake judder is a condition called Disc Thickness Variation (DTV). In other words the disc develops a lack of parallelism between its inboard and outboard friction surfaces. This is sometimes called "patching".
So if you are looking for the true cause of brake judder, warping should be at the bottom of the list.

 

[television]

As you say birdman = Warped

Warp =

To twist or cause to twist out of shape.
To turn or cause to turn from a true.
the state or condition of being twisted out of shape.
To twist,distort or bias.

Sorry. not being funny, but everything you say equals warped disc, and they have to be re ground or replaced as they have changed from the original shape, = warped

Malcolm

 

[Birdman]

Televison, you are confusing 'warped discs' with Disc Thickness Variation (DTV).

 

[television]

Televison, you are confusing 'warped discs' with Disc Thickness Variation (DTV).

I will assure you that im am confusing nothing WARPED = to Deviate from original and in any case ai have only used the same language as used through out the motor trade

Malcolm

 

[Birdman]

If the motor trade calls Disc Thickness Variation 'Warping' it is perpetuating a myth. Not least, because much of DTV is preventable through correct bedding-in of the pads. Maybe if the trade better understood the adhesion technology underlying disc brakes, and talked to us owners about the importance of bedding-in new pads to get a uniform material transfer to the disc, owners would get fewer problems with brake judder. The answer is out there.

 

[television]

If the motor trade calls Disc Thickness Variation 'Warping' it is perpetuating a myth. Not least, because much of DTV is preventable through correct bedding-in of the pads. Maybe if the trade better understood the adhesion technology underlying disc brakes, and talked to us owners about the importance of bedding-in new pads to get a uniform material transfer to the disc, owners would get fewer problems with brake judder. The answer is out there.

Yes, but the disc still have to be re ground or replaced what ever the reason, dependent on the thickness of the disc because the disc has deviated grom its original form or warped, for want of a better word.

Malcolm

 

[Ultymate]

All my time in the motor trade I've only ever heard the terms warped discs or disc run out whatever if if it's causing vibration machine them or bin them. In all my time I've never heard of DTV sounds like pie in the sky, no thats deep vein thrombosis

 

[Birdman]

It's true that binning or re-grinding resolves the problem of DTV. Better to avoid it altogether by understanding the causes.

http://www.powerbrake.co.za/pages/tech_01_judder.htm
http://www.powerbrake.co.za/pages/tech_02_bedin.htm
http://www.powerbrake.co.za/pages/tech_03_warping.htm

 

[Ultymate]

Brake pads, shoes, clutch drive plates and the likes and to a lesser degree discs drums and flywheels are sacrificial items that continually wear out being constantly treated to cycles of heating and cooling whilst being dowsed with all the weather can throw at them so sooner or later they will wear out distort or whatever this is an inevitable fact of motoring life. Yes driving style or prevalent conditions will have a bearing on longevity but the articles you linked to were thinly diguised advertising to sell one range of brake components. whilst on this subject some competition brake lining materials have to be deliberately abused during the bedding in process otherwise they will never yield their full performance

 

[Birdman]

... the articles you linked to were thinly diguised advertising to sell one range of brake components....

The company is clearly a successful commercial venture proud both of its laboratory facilities and technical know-how. The articles were written to demonstrate to the more technically minded driver the results of their engineering development programme.

Here are some more technical papers, from another company that has accumulated massive experience and technical competencies in the same field. I suggest any comments should address their substance.

On the "Warped" Brake Disc and Other Myths of the Braking System
http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml

Technical White Papers on Brake Technology
http://www.stoptech.com/tech_info/tech_white_papers.shtml