Brake treatment (how hot to let them get)

[edde]

Ok so I went for a bit fo drive round and although I drove slowly for about the last few minutes (about 3). Looking at the brakes from the porch light I can see the brakes are very dark coloured, from a distance they look almost black but the lights not to good.

Nothing I can much do now about it. But how much cooling down should brakes get after a run? Anything I should do ie not put the handbrake on ect (I live on a very slopy drive so leaving it with the handbrake off is a big no no.

I was hard on the brakes but they didnt go weak on me.

Think I might be of to look for some new disks. Any recomendations anyone?

I take it it will be obvious if they are warped?

 

[JAY172]

you would feel vibrations through the car/brake pedal if the discs were warped.

[Edited by JAY172 on 09 May 2004 at 12:27am]

 

[Jonesy]

I got bendix replacements for 15 quid each from http://www.eurocarparts.comwww.eurocarparts.com

 

[BenR]

If there is no decrease in performance then dont worry about it.

Contradictory to popular belief, and like ive said a billion times....brake discs dont warp...especially those of the vented varierty....its virtually impossible to create teh heat needed to warp both sides of the disc without cracking the disc.

What actually occurs is one of 2 things. Runout from improper mounting of the disc....a grain of sand can cause over 10 thou o runout, which is a massive vibration.

the second and mods common cause of vibration is pad depositing. This is where you get the disc hot and then stop and hold the braked at a standstill. This soaks heat from the disc through the pad and bakes a small layer of pad material onto the disc surface, about 3 thou. This creates an area of higher mu than the disc and pad combo...leading to juddering.

You can usually see the pad finger print if you look close enough or if its bad enough.

 

[JAY172]

Quote: Originally posted by BenR on 09 May 2004


If there is no decrease in performance then dont worry about it.

Contradictory to popular belief, and like ive said a billion times....brake discs dont warp...especially those of the vented varierty....its virtually impossible to create teh heat needed to warp both sides of the disc without cracking the disc.

What actually occurs is one of 2 things. Runout from improper mounting of the disc....a grain of sand can cause over 10 thou o runout, which is a massive vibration.

the second and mods common cause of vibration is pad depositing. This is where you get the disc hot and then stop and hold the braked at a standstill. This soaks heat from the disc through the pad and bakes a small layer of pad material onto the disc surface, about 3 thou. This creates an area of higher mu than the disc and pad combo...leading to juddering.

You can usually see the pad finger print if you look close enough or if its bad enough.

weve had brake discs at work with clean non scoured surfaces on virtually new cars but you still get the pedal vibration. you change the discs and all is well. so the disc is very low mileage with no excessive wear or markings on its surface so other than it being warped there cant be anything else wrong with it.

 

[edde]

Quote: Originally posted by BenR on 09 May 2004


If there is no decrease in performance then dont worry about it.

the second and mods common cause of vibration is pad depositing. This is where you get the disc hot and then stop and hold the braked at a standstill. This soaks heat from the disc through the pad and bakes a small layer of pad material onto the disc surface, about 3 thou. This creates an area of higher mu than the disc and pad combo...leading to juddering.

Ok thanks Ben for repeating the same thing again I realy should have searched but IE keeps crashing. Im not worried unless there problem I drive the car quite hard and do the minimum needed realy ie no extra servicing.

I take it the reason people put blocks to stop the cars moving after track days is because of the pads soaking the disks then with residue?

 

[BenR]

Sorry, at this point i will have to strongly disagree.

Youll all dispute me no end, but the problem is that traditional runout tests do not tell the full story, and unfortunately....the age old myth has been cast in stone for so long that people no longer bother to contest it.

In all cases where a vibration is felt and runout is measured its almost always from pad deposits or thickness variation. he disc itself can cone where there is a rigid hub or very tight mouning bell. Due to the design of the disc having only 1 side of the swept area actually mounted to the mounting bell. With temp variatons that change rapidly (going through puddles etc) can lift the edge of the mounted side up, coning the disc and leading to runout from the inner edge to the outer.......yet this is still nto warp as the face is still concentric to eachother.

The other case where its not pad depositing is where the friction material between the vanes collapse and create a ripple, leading to thickness variation, yet to total striaght edge is not affected and the brakes have not warped.

A traditional warp as many concieve where one face of the disc is convex and the otehr concave can only truely occur when a crack propagates from teh edge of the disk and the expansion of the matierial collapses around it.

I say most of the time its friction material depositing primarily because of incorrect bedding of the pad and disc together. Most go for the 200 mile light braking, in which case, even with light braking say off a motorway the same heat is generated, just over a longer preriod.....ad they sit at a standstill at the junction/roundabout below......this is where their new brakes deposit material onto the discs and then they thikn theyve warped the disc.

If they bedded them properly, like i have explained many a time before, then there wouldnt be a problem.

 

[BenR]

Quote: Originally posted by edde on 09 May 2004

Quote: Originally posted by BenR on 09 May 2004


If there is no decrease in performance then dont worry about it.

the second and mods common cause of vibration is pad depositing. This is where you get the disc hot and then stop and hold the braked at a standstill. This soaks heat from the disc through the pad and bakes a small layer of pad material onto the disc surface, about 3 thou. This creates an area of higher mu than the disc and pad combo...leading to juddering.

Ok thanks Ben for repeating the same thing again I realy should have searched but IE keeps crashing. Im not worried unless there problem I drive the car quite hard and do the minimum needed realy ie no extra servicing.

I take it the reason people put blocks to stop the cars moving after track days is because of the pads soaking the disks then with residue?

people dont use parking braked when they park up after a track day......the pad sticks to the disc and when you unleash it you can get a massive chunk of pad ripped right off. So i dont see why most refuse to admit that it cna happen during normal braking and on the fronts.

The warped disc syndrome and diagnosis has been so set in stone that nobody bothers to think why.

 

[edde]

Quote: Originally posted by BenR on 09 May 2004

people dont use parking braked when they park up after a track day......the pad sticks to the disc and when you unleash it you can get a massive chunk of pad ripped right off. So i dont see why most refuse to admit that it cna happen during normal braking and on the fronts.
The warped disc syndrome and diagnosis has been so set in stone that nobody bothers to think why.

Least your trying to tell people than continue the lie.

The corret procedure is to bed them in hard but not to a stand still isnt it ie brake from 60 to almost standing still a few times but dont stop it dead?

This would only be for new disks then? For new pads and old disks then you wouldnt be worth it then (assuming the pads are clean).

 

[BenR]

No, for any replacement, since it is the pad resins that you are trying to burn off.