Rotors

[ejm3]

Does anyone know if the rotors on a 135i can be machined or do they just have to be replaced whenever you change the pads?

[Matticus91]

Usually people do not turn rotors on these cars, but there's a lot to be said on this... If they are thick enough they should be fine, otherwise replace.

[STR8-6IX]

what makes a 135i rotor different from any other rotor?

if you have enough surface left, refinish them. no use in replacing a perfectly good rotor.

[ianc]

I didn't even bother to get them turned when I did pads. I measured them to be within spec so just installed pads. It took a few weeks for the pads to bed in to the rotors, but they've been fine...

ianc

[ejm3]

On other cars it seems like sometimes they can be cut and other times not.
Honestly I think its a ploy for more money because honestly I never actually check the thickness for myself.

I will not do pads without either machining the rotors or putting new ones on though.

[Stewy_604]

The minimum thickness is stamped onto the rotor hats. Just measure them and see if they can take some additional mileage. From what I've read, the rotors usually do have more life in them, but not enough to see end of a 2nd set of pads. Make sense?

[WDE82]

I've read that German cars tend to have a pad and rotor material combo that sacrifices more rotor and less pad than a US domestic design typically does. Apparently this is part of the reason for the large amount of dust seen on these makes. So our rotors may not last two full sets of pads with turning. If you're changing to the same type of pads and you know the starting thickness of your rotors and what will remain after turning, you can estimate if by the end of the second set if the turned rotor will end up below minimum thickness. If it doesn't, then go for it.

[zx10guy]

I've thought about this situation. People may disagree with me but I don't know if turning/machining rotors are actually a good thing. You're taking material off of the rotor which decreases the thickness of the rotor. Depending on how hard you beat on your brakes, this can manifest itself in decreased strength and heat dissipation capacity.

If the surface isn't too buggered up, I tend to just throw new pads on and leave the rotors alone. I would also consider checking the run out of the rotor which I think is as equally important as rotor thickness.

[sandlion]

so on my Land Rover, replacing rotors was part of a normal pad replacement. I asked about it, and they said that was the tech book requirement, because they made the rotors lighter weight and disposable to increase weight savings. kind of makes sense.

[ianc]

You're taking material off of the rotor which decreases the thickness of the rotor. Depending on how hard you beat on your brakes, this can manifest itself in decreased strength and heat dissipation capacity.

I'm a subscriber to this theory. The small ridges in the rotor should not affect the car's stopping ability once the pads have bedded in to them, and turning them only decreases the rotor's thermal mass. Everyone has their own idea on this tho...

ianc

[ejm3]

I'm sure I'll probably just bend over and let the dealer bone me for new rotors.

I agree that if the thickness is close then in my experience the dealerships (non-BMW anyway) won't machine them. I've had them tell me that maybe an independent shop will but they won't.

But honestly how much rotor actually wears during normal use? I expect the pads to wear but significant rotor wear surprises me?

[WDE82]

Originally Posted by ejm3

I'm sure I'll probably just bend over and let the dealer bone me for new rotors.

I agree that if the thickness is close then in my experience the dealerships (non-BMW anyway) won't machine them. I've had them tell me that maybe an independent shop will but they won't.

But honestly how much rotor actually wears during normal use? I expect the pads to wear but significant rotor wear surprises me?

As I said, BMW pads are more abrasive than domestic makes usually are so the rotor wears more. Much of the black dust is iron from the rotor. They wear a decent bit.

Why are you letting the dealer do brakes? They'll rape you. You should be buying aftermarket brand (think Ate, Zimmerman, Bosch, Brembo) rotors/pads and installing them yourself or at worst an Independent shop. Brakes are simple.

[ejm3]

Yeah I have a decent shop not too far away from me who I may use instead.

I'll get a quote from the dealer and from that independent guy. I was going to ask him about aftermarket pads and rotors to see if there's something better.

Honestly I have neither the time nor motivation to do them myself.

[Tommm]

Originally Posted by ianc

I didn't even bother to get them turned when I did pads. I measured them to be within spec so just installed pads. It took a few weeks for the pads to bed in to the rotors, but they've been fine...

ianc

Same here. I bought stop tech street/track pads for about $60 an axle and pressed hard a few times in case the pads are running on the lip of the rotor. They worked fine on the track.

If you are not tracking the car extensively, there is no need to worry about heat dissipation. Cutting the rotor takes off thousandths of an inch. When my daughters $1,500 ice skates are sharpened, he takes off 3/1000 of an inch.

Because I used the rotor on a second set of pads, and because I want to error on the side of caution, I have new Bosch rotors and another set of pads on a shelf. I will replace them when the pads are about 2/3 worn instead of 4/5 worn.

[zx10guy]

Originally Posted by Tommm

Same here. I bought stop tech street/track pads for about $60 an axle and pressed hard a few times in case the pads are running on the lip of the rotor. They worked fine on the track.

If you are not tracking the car extensively, there is no need to worry about heat dissipation. Cutting the rotor takes off thousandths of an inch. When my daughters $1,500 ice skates are sharpened, he takes off 3/1000 of an inch.

Because I used the rotor on a second set of pads, and because I want to error on the side of caution, I have new Bosch rotors and another set of pads on a shelf. I will replace them when the pads are about 2/3 worn instead of 4/5 worn.

I disagree with the comment about not worrying about machining the rotors if you're not tracking. It depends on your driving environment. If you're in the lovely areas where your highways are parking lots for hours in the morning and afternoon, then you do have to worry about it. I've had rotor warpage issues with a few cars because of the constant stop and go that goes on for 30+ miles.

[Tommm]

Originally Posted by zx10guy

I disagree with the comment about not worrying about machining the rotors if you're not tracking. It depends on your driving environment. If you're in the lovely areas where your highways are parking lots for hours in the morning and afternoon, then you do have to worry about it. I've had rotor warpage issues with a few cars because of the constant stop and go that goes on for 30+ miles.

I lived in NYC for many years. How does machining a set of rotors that are not warped stop them from warping when new pads are installed?

Are you saying the rotors should be machined before installing new pads in order to get rid of the deposits on the rotor. Deposits that people call warpage, or actual warping of the metal disc?

[jlc45]

Buying new rotors is not necessary if you maintain your pads and calipers regularly.
It seems most people just drive forever until their brakes start making weird noises. By that time the calipers are sticking or seized, the pads are worn or cocked and stuck and the rotors are gouged by metal on metal. If you remove and clean the pads and lube the calipers, your rotors can easily run 100,000 miles. I've done that on several vehicles. I just bought my 135i last fall. Supposedly all looked after by the dealer.
The first thing I did was remove all wheels and calipers and rotors and clean and lube everything.
Dealers and brake shops rarely do this carefully and thoroughly. They don't really care. It's not their car. They want you to come back and buy new parts as often as possible.

[KNS]

^^ Spot on.

I usually go far past 100,000 miles on my rotors.

[WDE82]

My 330's rotors are at about 90K. They're still smooth as silk and I've pad slapped them twice (didn't like the pads I tried). My 128i rotors are in shit shape. Trying to get the replaced under warranty soon haha.

[jlc45]

Yeah, sometimes it's not the owners fault. Acura ILX came straight from the factory with noisy faulty rotors. It took them a while to figure it out. Rotors were cracked. Perhaps another "made in China" savings plan?

[Mr Rooty Von Tooty]

Even on new BMWs, you'll find the rotor surface is rather rough to the point of being grooved. Also the stock pads throw off a lot of dust. The idea is the stock pad has more stopping bite when braking from very high speeds like I guess they do in Germany?

I always remove the stock pads for something that doesn't throw off a lot of dust and mess up the look of my wheels. Are you thinking I'm not concerned with safety? Well I am seldom slowing down from triple digits.

I use these for replacement pads:

https://www.tirerack.com/brakes/brak...2&autoModClar=

These stop my car better than the stock, they throw off very little dust, bed quickly, and don't make any noise.

A tip before changing rotors. I never machine rotors regardless of their appearance. You can usually judge wear by examining the lip of each. I slap on the new pads, and if they don't make any noise and stop OK, I'm good to go!

BTW, I have a set of stock pads with 50 miles of wear. I'll trade for some wheels.