Protruding Circumference of Worn Brake Disc.

[W L Ow]

The protruding circumference (the unworn part) of a worn brake disc always causes the brake pad warning wire contact to touch the disc activating the warning light before the brake pad is really worn out. I am tempted to use an angle grinder to grind off the protrution when replacing the brake pads. Has anybody done that before. Any advice whether this may cause wheel balancing problem or brake pad failure?

Thank you in advance

 

[grober]

The protruding circumference (the unworn part) of a worn brake disc always causes the brake pad warning wire contact to touch the disc activating the warning light before the brake pad is really worn out. I am tempted to use an angle grinder to grind off the protrution when replacing the brake pads. Has anybody done that before. Any advice whether this may cause wheel balancing problem or brake pad failure?

Thank you in advance

You can easily scrape off loose rusted metal in this area with any sharp metal blade,which may help, but if the discs are badly lipped they probably need replaced.

solid disc width
new 12mm
min limit 10mm

vented
new 22mm
min limit 19.4mm

 

[W L Ow]

The brake disc and the brake pads were replaced about 60,000km ago at the same time. The pads are now worn out. If the disc also needs replacement at the same time, it means the disc can only last as long as the brake pad. Is this normal? I have not measured the thickness of the worn disc yet.

 

[Parrot of Doom]

The disc will outlast the pad easily.

Are you using the correct size pads?

 

[W L Ow]

The replacement pads I used were definately not Mercedes original. I do not think anybody does here anyway. The pads do not covers the entire disc surface leaving about half mm from the edge of the pad to the outer edge of the disc. The wearing down of the disc thus leave a half mm protruding ring at the circumference of the disc.

 

[miro]

The disc will outlast the pad easily.

Are you using the correct size pads?

That is not the specified requirement with W163 ML and W220 S, W215 CL. A change of pads also requires the changing of the rotor.

There is no such generic rule as rotor > pads.

 

[miro]

The replacement pads I used were definately not Mercedes original. I do not think anybody does here anyway. The pads do not covers the entire disc surface leaving about half mm from the edge of the pad to the outer edge of the disc. The wearing down of the disc thus leave a half mm protruding ring at the circumference of the disc.

The non-original pads may create less dust and remove more metal from the rotor material. It is pure physics after all .... the difference between surface properties determines the rate of wear.

Softer pads remove less rotor material and create more dust.

There are several factors in the outcome apart from distance.

 

[richard]

That is not the specified requirement with W163 ML and W220 S, W215 CL. A change of pads also requires the changing of the rotor.

There is no such generic rule as rotor > pads.

Just a thought here, is this 'MB advice' because these car's eat brake pads / disks (rotors) so quickly, and thus if the car is being serviced once every 14000 miles, if you change the pads, its often possible the disks won't last to the next service ?

- i.e Same reason why MB dealers want to change the pads at a service even though the light isnt yet on - as it saves you a trip to the dealer on very short notice if the light does come on.

On my ML, I change the pads when the light comes on (or if they start squealing and look very low), and check the disks at services and at pad changes, and in between if I know they are a bit low. If I had to change disks every time I changed pads on it, i'd be broke ;-) (and have back ache, since the disks are so heavy)

Richard

[edit, ps - I always uses MB disks and pads]

 

[W L Ow]

You can easily scrape off loose rusted metal in this area with any sharp metal blade,which may help, but if the discs are badly lipped they probably need replaced.

solid disc width
new 12mm
min limit 10mm

vented
new 22mm
min limit 19.4mm

I have measured the remaining thickness of the disc and am surprised that they are reduced to just 20mm in one replacement of the brake pads. 2 mm of the metal surface is gone (from both sides). The disc will not last for another pads replacement to stay within the 19.4 mm limit assuming another 2 mm will be gone by the next disc replacement.

Thank you for all the advices.

 

[Ian B Walker]

Please don't use an angle grinder on the disk. It will end up out of balance. If anything take the disk to a machine shop and have them either turn or cylindrically grind the edge off.

 

[miro]

Just a thought here, is this 'MB advice' because these car's eat brake pads / disks (rotors) so quickly, and thus if the car is being serviced once every 14000 miles, if you change the pads, its often possible the disks won't last to the next service ?

- i.e Same reason why MB dealers want to change the pads at a service even though the light isnt yet on - as it saves you a trip to the dealer on very short notice if the light does come on.

On my ML, I change the pads when the light comes on (or if they start squealing and look very low), and check the disks at services and at pad changes, and in between if I know they are a bit low. If I had to change disks every time I changed pads on it, i'd be broke ;-) (and have back ache, since the disks are so heavy)

Richard

[edit, ps - I always uses MB disks and pads]

I think the equation is about as long as my arm and even more hairy. You saw that arm last time I was in town.

 

[Dave K]

Modern discs are designed to wear more quickly. That's how they get far better braking performance than cars seen many years ago. The materials they are made from combined with the materials of the pads give far better braking performance than you got with harder discs that lasted forever. As a rule of thumb, you need to change the discs after 2 sets of pads.

 

[wongl]

Modern discs are designed to wear more quickly. That's how they get far better braking performance than cars seen many years ago. The materials they are made from combined with the materials of the pads give far better braking performance than you got with harder discs that lasted forever. As a rule of thumb, you need to change the discs after 2 sets of pads.

My personal experience on this (with 2 different W202's and W168) would concur with this (using either original MB parts or OEM from Eurocarpars) almost regardless of motorway or intown driving (we keep one W202 for long distance Motorway driving and the other for intown London and school runs).

Could it be that Ow's dealer is using sub-standard discs or alternatively extremely hard wearing pads? I would expect the front pads on my W202 to last around 20,000 miles before they needed replacing, and therefore my front discs around 40,000 miles. I think Ow said that his pads lasted 60,000km which is about 40,000 miles. Bingo!

 

[Dieselman]

I thought the increased disk wear was a result of not using asbestos in friction material anymore. The alternative materials are harder wearing on the disk for the same amount of braking effect.
Add to this the trend towards heavier cars with better stopping power and there is only one place for all the energy to go to, the disk and pad.

I don't think disks have changed at all, they are still made from soft iron as they always were.

 

[Vclass]

Going back to the original post, I may have the same issue. So two questions:
1. There looks to be around 3mm on the pads, at what point should they be replaced?
2. Would the brake disk widths quoted in the reply from grober apply also to my V-Class? I am only as far as checking the front, they are vented.

solid disc width
new 12mm
min limit 10mm

vented
new 22mm
min limit 19.4mm

The car has done 63K, I would need to check carefully how many new pads have been fitted but I think this is coming up to 3rd or even 4th on the front.

 

[TVRTASMIN]

I've just removed the front disc pads on my E300D and noticed that behind the MB stick on anti-chatter pad it says Textar.
I know Textar to be a budget aftermarket brake pad.

The discs have a slight lip to both sides so i positioned an angle grinder next to the disc edge and rotated the disc to remove the aforementioned lip.

I have ordered a set of EBC Greenstuff pads which i have used on many cars without problems.
In fact they out perform OE quality pads and give less brake dust.

 

[grober]

TEXTAR certainly used to be OEM for Mercedes?? I clearly recall Mercedes brake pads also marked Textar together with the MB symbol.

 

[TVRTASMIN]

You could be right there.
I did a bit of research and found Porsche use them and some Saab owners have found them to perform better than OE.

I might try some on the estate, as that needs some new discs and pads shortly. Don't really want to go to the expense of EBC next time.

 

[Satch]

Braking systems are really complex in terms of the interaction between the "friction pair", the pad and the disc. Material used have changed and the wear rate of the discs tends to be higher. Some makers are using iron alloys that have better wear characteristics but they are not quite so good in terms of braking performance: there is no ideal solution.

http://www.tupy.com.br/downloads/guesser/wear_resistance_cast_irons_brake.pdf

But the type of driving you do and individual driving style is the key. Hard braking causes much greater brake wear and the roads cars tend to dive forward so that the front brakes take most of the load.