My brake rotor thickness...

[apoc]

Hey people,

Recently got some of those slotted brake rotors from ebay. They look fine, and seem to be the right item, I am yet to fit them... prolly a job for the weekend.

Now the new rotors arent the problem its my old ones. I mainly did the rotor upgrade as a bit of a **** type thing but after going out and measuring the thickness of my old rotors (front) I found that they appear to be 26mm thick Now, that reading is taken including the rusty ring around the edge so the part that the pad runs on may be about 0.5 thinner still. From what i saw in the technical info section the minimum thickness for the rotors is supposed to be 26mm and that a new one is supposed to be 28mm as my new ones are.

So does this mean that in the life of my car (190,000k) it has had 2mm of material machined from the disc? How much do you have to remove when machining the rotors? What are the consequences of having a brake rotor less than 26mm in thickness?

Cheers,
Simon.

[GK]

From what I understand Simon, they generally go 0.5mm each go and may need to do that a number of times if the first grind doesn't fix the warp.

Last time I had my fronts in the wagon done, the right only needed one go, the left a couple.

There is probably someone here though who does this for their bread and butter, so they may have more detailed and accurate info.

Cheers,

GK

[AU dude]

Dont forget, before you install the new rotors, wash the oil off them. This is there to stop them from rusting while in storage. If you dont wash them your brakes will be smoking after each time you brake and smell really bad. I'd use kerosene or turps to wash them with.

[apoc]

Cheers for the replies,

GK - "From what I understand Simon, they generally go 0.5mm each go", is this per side or a total, as obviously 0.5mm each side = 1mm in total so theoretically maybe the brakes have been machined twice, or at 0.5 a go up to 4 times.

AU dude - "Dont forget, before you install the new rotors, wash the oil off them. This is there to stop them from rusting while in storage. If you dont wash them your brakes will be smoking after each time you brake and smell really bad. I'd use kerosene or turps to wash them with." Well my rotors are supposed to be treated against rust and i dont feel any oil on them but i might give em a wipe with turps just in case.

Now another thing when i put them on, the slots are supposed to go from the inside of the disc to outside of disc, sloping towards the rear (like so / ) when the slot is at the top of the disc correct?

Also i recently changed my pads, so they are still quite new, is it really necessary to replace my pads to put these rotors on?

Cheers again,
Simo.

[AU dude]

I think they are meant to go \ on the drivers side and / on the passenger side.


This is the drivers side, so the slots go \, same with rear.

This is the passenger side, so the slots go /, again same with rear.

Edit: Sorry I couldnt find an AU or the same car for that matter. i just did a quick google image search and was the first this I could find.

[JC]

Originally Posted by apoc

Cheers for the replies,

GK - "From what I understand Simon, they generally go 0.5mm each go", is this per side or a total, as obviously 0.5mm each side = 1mm in total so theoretically maybe the brakes have been machined twice, or at 0.5 a go up to 4 times.

AU dude - "Dont forget, before you install the new rotors, wash the oil off them. This is there to stop them from rusting while in storage. If you dont wash them your brakes will be smoking after each time you brake and smell really bad. I'd use kerosene or turps to wash them with." Well my rotors are supposed to be treated against rust and i dont feel any oil on them but i might give em a wipe with turps just in case.

Now another thing when i put them on, the slots are supposed to go from the inside of the disc to outside of disc, sloping towards the rear (like so / ) when the slot is at the top of the disc correct?

Also i recently changed my pads, so they are still quite new, is it really necessary to replace my pads to put these rotors on?

Cheers again,
Simo.

It is recommended, but not necessary, to change pads. If yours are new, just use them, but I would still bed them in to the new discs.

Slots always sweep towards the rear when viewed at the top of the disc - same as the images in the post above.

[apoc]

Yeah thanks AU dude, i was only visualising it from one side, didnt think about that... I should be all good with it now though.

Cheers,
Simon.

[apoc]

JC - "It is recommended, but not necessary, to change pads. If yours are new, just use them, but I would still bed them in to the new discs."

Yeah my pads are pretty damn new so ill use them, as for the bedding in process what is involved? Braking gently or severely, time to bed things in properly etc. I will be doing a search aswell...

Thanks,
Simo.

[JC]

To bed the brakes in, you need 8 to 10 moderate stops from 60 kmh down to about 5kmh (not a full stop). Between each stop, accelerate back to 60 and do 200 to 300 meters at that speed, then brake not gently, but not full on (somewhere in the middle). If your brakes start to smell while doing this, leave more space between stops, and brake a little gentler.

[apoc]

With regards to changing pads i found another thread and it has a link to another forum in which it is said that it is best to use previously bedded in pads.

http://www.mrtrally.com.au/forums/to...p?TOPIC_ID=103

What do people think about this?

Simon.

[EvilChief]

i machine rotors at work on a daily basis. they measurement are taken from the deepest groove (some rotors taper in due to uneven wear, sticky pistons, abuse etc). normally there is minimum thickness stamped on the rotor itself, from memory au2 rotors are 23.6mm min, but double check with the dba catalogue (www.dba.com.au, download the australian catalogue and check coloumn D for min thickness). we normally machine .3mm on the first rough cut, sometime we have to take a second rough cut at another .2mm if rotors are badly warped and then go for a fine cut at .1mm

[Mechan1k]

Also when it comes to which way the slots are slanted ... it depends on the manufacturer ... but when it come to putting them on the car ... the rotors will only go on one way

I did run with rotors under minimum thickness for a little while ... although I had new pads put in at the time ... so it compensated slightly ... for a short time. It was very noticable when it came to breaking as the calipers really didn't have the clamping pressure to slow down the "thin disc".

I am surprised your rotors have lasted 190,000km ... sure they have been replaced at least once during this time ... unelss it has been all highway kays and very little braking.

[apoc]

Hey there bit of an update...

Firstly though....

Mechan1k - "but when it come to putting them on the car ... the rotors will only go on one way"

I think id have to disagree with that as if you look at both the rotors side by side the slots are running in different directions... as they should be. So with both the rotors there you can either put them both on backwards or both on normally.

Mechan1k - "am surprised your rotors have lasted 190,000km ... sure they have been replaced at least once during this time", dunno i brought the car at 190 now its actually got 193, no service history... :(

I have the rotors on... was a piece of **** only problem I had was mainly with the calipers and getting them to compress enough to take the new thickness of the rotors. My pop made a tool for the commo to compress the piston was just a piece of steel with a threaded rod with a twisting end like that on a G-clamp going through it. put it in the caliper and turn the thread nice... only that it doesnt fit the two piston caliper at all... so a big pair of multigrips is what i used in the end after finding that they opened wide enough to be of use it was easy... give both pistons a bit of a squeeze alternating between the two as they pumped each other out a bit when compressed.

Went for a bit of a cruise to bed in the pads, started off cruising round a few quiet blocks up to 60 hop on the chocks a bit swing round corner repeat for a couple of laps then headed out onto a bit more open road slowing from 80-100km down to 40 odd then off again. First corner i went to take was a bit hows it goin as i had next to f all brakes, after cruisin around the brakes felt solid and I have nice clean sections showing full contact so i think im in business.

EvilChief - "normally there is minimum thickness stamped on the rotor itself, from memory au2 rotors are 23.6mm min", yes you are right they do have the min thickness stamped on them and on my rotors it was 26mm not 23.6mm
DONT TRUST YOUR MEMORY IT LIES lol its all good

Think thats about it, pretty satisfying to do taking about 30mins for first rotor and about 10 for the next, looks good.

Cheers all,
Simo.

[GK]

Good job! You have the satisfaction of knowing that you have done it all yourself.

GK

[EvilChief]

Originally Posted by apoc

EvilChief - "normally there is minimum thickness stamped on the rotor itself, from memory au2 rotors are 23.6mm min", yes you are right they do have the min thickness stamped on them and on my rotors it was 26mm not 23.6mm
DONT TRUST YOUR MEMORY IT LIES lol its all good

i machine so man diff rotors in a week, i cant memorize all of them, hence i use the ref book, but we also have a lot of cars which arent listed in our ref book, which make my life so much more interesting