Using Sandpaper to Roughen up Brake Rotors

[Jesterarts]

By the way, I found the thread where everyone was telling me NOT to use sand paper on rotors.

http://forums.justcommodores.com.au/vt-vx-holden-commodore-1997-2002/185124-brakes-question.html

Just to confirm, one if the sponsors on here who has a wealth of experience and have proven time and time again also agreed its a bad idea to sand rotor. I would like to know what expertise the people who are sayong it is fine to sand have?

Also, the advice the OP of this thread gave in the other thread was to sand rotors AND pads to eliminate squeaking. As described in the other thread this is dangerous as any pad material that has bedded to the rotor surface will be removed and next time the driver goes for the brakes they will not perform as as they dis previous to sanding them.

Since we all know that its the friction of the brake pad on the bedded pad material on the rotor that stops the car rather than pad on rotor metal. Thus, why we bed brakes when rotors or pads are changed. I'm assuming all the experts in this thread are keeping up this time.

And just to confirm what I mean by dangerous; doing something to the vehicle that will have a negative effect on its performance compares to what the driver is used to and expects.

Finally, I am assuming that the benefit some of you are putting forward of sanding brakea is to remove the old bedded material and aid bedding.

Two issues with this;

One, if you put new pads in they can be bedded in without sanding. So why bother?
Two, using sand paper causes groves and ridges in the surface on the surface of the rotor. It becomes course. This means that in order to bed properly, the pad material has to fill in the groves and wear down the ridges until the braking material is evenly layered on the rotor surface. Until that time, braking performance will not be at 100%.

To be clear... the objective of any disc machining or sanding if you sill is to SMOOTH the surface as much as possible rather than to make is course. Thus, sanding them to "roughen up brake rotors" is doing the opposite of what the goal should be.

At the end of the day, all the above probably won't have affect on the average driver as we rarely ask our brakes to put out 100% of their potential. Pulling up at the lights you won't notice the car takes an extra metre or two pulling up as you just apply 20% braking force instead of 15%.

But you will notice when you need to do an emergency brake and instead of scaring the crap out of the idiot pedestrian who ran out on the road, stopping only inches from them and pulling up 2m past the point you hit them.

Small difference in the equasion variables, big difference in result.

 

[ari666]

That was mainly the bedding in procedure for asbestos brakes, there is no need to do that with brake pads these days.

ill try and find one of the warning notes that come in packs of brembo brakes that advise you to use the break-in proceedure. not sure where you get your info from, but i think ill contiune to listen to brembo.

 

[Jesterarts]

it was funny to read that they all said it was a bad idea and also dangerous, but not 1 person had any evidence to back up their conclusion......its like when u glue 2 flat surfaces together u have to rough it up a little to increase the surface area and friction between the 2 surfaces...... id say this would apply to the brakes also upon bedding them in

Oh dear.

1. Care to provide evidence of your conclusion? Otherwise, pot meet kettle.
2. Glues don't work on friction, they work on adhesion.

 

[Jesterarts]

That was mainly the bedding in procedure for asbestos brakes, there is no need to do that with brake pads these days.

RRRRRRRrrrrreeeeeeeeeeeeeeeeeally?

Why You Should Bed in your Brake Pads & Rotors - YouTube

brembo-faq

Bedding In Update TB 08 (This one even talks about the have that asbestos has been removed as an ingredient and betting is needed regardless.)

DBA Bulletin - Basic Initial Brake Bedding In

 

[ari666]

man, this is getting painful.

roughing up the discs is a proceedure you use on old worn rotors. what it does is

1. remove any glaze that forms on old rotors that have gotten hot and had burned. there sometimes is a ultra smooth coating formed on the surface of the rotor and it needs to be removed when you chage to new pads.
2. creates a rough surface in which you will wear the pads quicker which helps them form to the exact shape of the rotor. im not aying you gough the **** out of it, you do exactly the same thing as running the honig stones over your bores. you create little cross hatch scratches on the rotor purely and simply to wear the pads rapidly for the first 50 odd kms. the scratches wear down really quickly so they dont affect the longevity of your pads.

break in on new rotors is pretty much the same thing. you will notice that when you get your rotors machined, or you buy brand spankers the surface is course. they do that to bed the pads. if they were a mirror finish, the pad wouldnt have anything to grab in its initial break in and your ability to stop is greatly affected. the roughness dissappears after a couple of kms of regular driving and you lose 1/100000th more of a pad than you would have if it hadnt been scuffed up. the sacrifice of that pad loss is your pads marry up to the rotors in a few kms, rather than 300 odd.

thats my opinion from what i have read/been taught/done for years.

 

[PSI_KING]

The purpose of "sanding" the rotor is to deglaze it which not only assists in the 'bedding in' procedure of the pad but also ensures the braking capacity is maintained at its optimum. It can also assist in eliminating/reducing brake 'squeal'

If your vehicle sees regular track work where the brakes are constantly applied heavily then it is also common practice to deglaze the brake pads. Both are a very simple procedure which can be done easily at home with the necessary tools.

For brake rotors use a 120 grit sandpaper and ensure both sides of the rotor are treated. The aim is to eliminate the 'shine' from the rotor surface. Ensure the rotor surface is adequetely cleaned with a brake cleaning solvent to remove any sanding media.

For brake pads (if being re-used) use an 80 grit sandpaper and a flat sanding surface. It will only require a few passes to remove the glazing from the pad material.

The procedure of proper brake pad bedding should be adhered to upon completion of brake rotor and/or pad deglazing.

Regards,

PSI KING

 

[Jesterarts]

The purpose of "sanding" the rotor is to deglaze it which not only assists in the 'bedding in' procedure of the pad but also ensures the braking capacity is maintained at its optimum. It can also assist in eliminating/reducing brake 'squeal'

Completely agree. If the rotor needs deglazing then the issue needs to be addressed and one of the ways is to sand it. And during the deglazing process more then likely most of if not all the bedded material will be removed and so they need to be bedded.

The end objective of de-glazing it to acheive a smooth braking surface, ensuring the rotors bed well and are running at 100% capacity as quickly as possible.

Rotors work best when they are bedded. Therefore is you sand them to "roughen then up" as per this thread or to "reduce brake squeal" there is no bedded material they will not work effectively until they are bedded again.

If you already have a bedder rotor.. why would you remove the material that si already bedded when changing pads?

The OP even acknowledged this in his opening post.

Unless there is actual glazing on the brake surfaces OR you are changing pads to a pad that has a significantly different compound to your old pads, sanding the surface is a unnecessary process which will REDUCE the effectiveness of your brakes for a period after you fit them until the pad material is bedded to the rotor surface.

Therefore, in my opinion sanding rotors is dangerous as it has as it will cause the vehicle to not me able to brake at it's optimum until the surfaces have been smoothed and the pad material is bedded.

I think the main thing being missed thus far is CONTEXT. In the other thread it was suggested to sand rotors to reduce brake squeal. Sanding = bad since brakes will pointlessly work worse for a while before they bed again.

If the context was "Sand the rotors to deglaze them" then get them machined orsand away because it's required. But the objective is not to "roughen them up" but remove the glazing. The brakes are already not working at 100% due to the glazing and therefore it's unavoidable that something will need to be done.

Personally, my mechanic looked like we was going to

 

[ari666]

what is this "bedding material" you speak of? a bedded pad and rotor are when they are both contacting with as much surface area as possible...

there shouldnt be any material between the two surfaces?

 

[Jesterarts]

what is this "bedding material" you speak of? a bedded pad and rotor are when they are both contacting with as much surface area as possible...

there shouldnt be any material between the two surfaces?

Pad material on the disc. Brakes work best when the pad is making contact with a layer of PAD material on the surface of the disc and not the rotor metal.

This pad material on the surface of the rotor is what I am refering to.

 

[ari666]

hmmm, notsureifagreewithyouonthatone