Replacing brake rotors: Fact or Fiction?

[boardburton]

My brakes are getting low, I have been told that if I replace my pads and sensors that I should replace my rotors. I have never had to do this on any other car I have owned, but is this something particular to BMW's?

Do they just want more money out of me or is it a good idea.

[Rigmaster]

Not necessary, unless the rotors are warped or scored badly or below minimum thickness.

In fact some people say that it's best to replace EITHER rotors OR pads, but not both at the same time- not sure if I believe them though.

Bret.

[Fetch]

In fact some people say that it's best to replace EITHER rotors OR pads, but not both at the same time- not sure if I believe them though.
Bret.

hmmmm..I'm interested to what other people say about this, because I hope this isn't the case, as soon enough my pads will be pretty low, and my rotors have huge lips on them, so I'm assuming they are very worn down, so I am planning on replacing both at the same time.

I would think that as long as you followed that one bedding in process, that you would be good to go on the pad and rotor side of things?

[Rigmaster]

hmmmm..I'm interested to what other people say about this, because I hope this isn't the case, as soon enough my pads will be pretty low, and my rotors have huge lips on them, so I'm assuming they are very worn down, so I am planning on replacing both at the same time.

I would think that as long as you followed that one bedding in process, that you would be good to go on the pad and rotor side of things?


I agree with your line of thinking on this. I've done it this way many times over the years on many different cars and trucks and have not had any problems.


Bret.

[Blitzkrieg Bob]

both rotors and pads at the same time for many cars, and to add danger even the calipers too.

Most of the time I had too, wife runs em down till they are on rivets and the rotors are scored and blued.

[MTV]

I do have a rather irritating shimmy under braking which suggests a warped rotor. I was thinking of getting them cut since there is hardly any lip on them. But read in one of my searches that cutting them was not suggested. Is that true?

[silver-e34]

the proper way to do it is replace all 4 pads as sets and either replace the rotors if they are below spec thickness or have them turned at a machine shop but never install new pads without new rotors or at least turning you old ones , this is to prevent your brakes from squeeling and many other funny noises,when you remove your old pads you will see the rotors are very shiny were the pad makes contact with it and probably has a lip, that needs to be removed and the surface should be a little rough not shiny to avoid noises,however the dealer and some shops dont want to turn rotors they just wanna replace them since its faster and easier for them but more expensive for the customer

[Zeuk in Oz]

I do have a rather irritating shimmy under braking which suggests a warped rotor. I was thinking of getting them cut since there is hardly any lip on them. But read in one of my searches that cutting them was not suggested. Is that true?
This shimmy under braking could also be your thrust arms - at what speeds does it occur ?

[genphreak]

There are good reasons on these cars not to turn the rotors... but some get away with it. However they are not that much oversize in the first place so replacement is not a bad idea oftentimes.

The reason that makes me invariably replace the rotors is that they are exceedingly cheap when you consider the cost of doing wasting half a set of pads on some scored ones and/or paying (and waiting) to have your current rotors turned. Brakes are a dirty job, so they are best done properly each time AFAIAC. Also, due to the sensitivity of the e34 front end to shimmy, its really worth avoding anything that might make one have to troubleshoot shakes or esoteric wobbles once a brake job is complete.

But some don't mind messing around with them; I guess if I tracked my car I'd probably not be replacing everything each time...

I just like her to work the way she's designed to once she's all buttoned up.

[pundit]

From looking at my rotors after nearly one set of pads and 40,000kms I'd say that they are already undersize. At least a 2mm lip each side... so machining is out.

[silver-e34]

yes the rotors are pretty thin and get flimsy on the brake lathe so you need to put special adapters on it to make it sturdier while being turned otherwise they will have nasty ridges so as long as you take your rotors to a professional you should be ok i have been able to turn my rotors 3 times before having to replace them :)

[KenB]

I'm getting close to doing my brakes also. They have around 80k miles on them. (still 15-20% pad left) There is a lip on the rotors so will replace them. I don't think its worth messing around with. They're relatively cheap from BMA.

[Ferret]

Hmm, the last german car I owned before the beemer was an '87 vw polo - *drumroll* without brake servo. (I loved that car!)

Brakes were critical on this car - but jeeze it could stop quick... untill I changed my disks/rotors. The old disks had huge ridges in them - looked like waves on the surface. I changed the disks and pads together... and immediately lost half my braking power.

My mother used to work in a garage at the time and I asked her boss what was going on - he checked I'd cleaned all the parts - grinned at me and asked if the old ones were ridged and scored badly?

Basically he ended up telling me that when the disks are ridged really badly - you've got extra surface area - I put the old disks back on and after a few hundred miles for the pads to bed in I had the same brake power again. Never bothered changing rotors since.

Just an interesting little story for your thoughts.

[genphreak]

Heh, maybe that's why stock discs have are flat but have circular ridge pattern on them- it could be this that ensures a good customer experience once the brakes are replaced at the dealer...

[632 Regal]

if they have deep ridges replace them, at $20.00 from BMA it's a no brainer. I bedded in the last set of pads/rotors and they warped and heat cracked the pads, had to do it again. This time i used the raybestos QS pads, which require NO bedding and its perfect...finally.


My brakes are getting low, I have been told that if I replace my pads and sensors that I should replace my rotors. I have never had to do this on any other car I have owned, but is this something particular to BMW's?

Do they just want more money out of me or is it a good idea.

[fkong777]

if they have deep ridges replace them, at $20.00 from BMA it's a no brainer. ......This time i used the raybestos QS pads, which require NO bedding and its perfect...finally.

$20?!!! really? what brand rotors were they? Maybe I'll just pickup new rotors if it is that cheap.

I do brakes on all my cars. it is pretty easy and parts are not that expensive. I like to change pads early so you dont groove the rotor with worn pads. It is a lot easier to just change pads

BTW I use akebone Euro ceramic right now.. Happy with it so far.. 80% less dust than Pagid.. I tried Pagid, Mintex, Ray.QS and now Akebono.
QS had low dust until they are half used then it dust like the rest of them.. Akebono so far have very little dust.. happy with it so far.

[632 Regal]

they were Opparts rotors, Bill R. mentioned some other brand a couple weeks ago that he has been using with good luck too.
$20?!!! really? what brand rotors were they? Maybe I'll just pickup new rotors if it is that cheap.

[MTV]

This shimmy under braking could also be your thrust arms - at what speeds does it occur ?

It usually occurs between 65-75 MPH. But there are times that there is no shimmy at all. I don't get any shimmy when I accelerate through the gears, only during this braking period. Could that still be the thrust arms?

I finished reading the rest of the posts and found varying opinions about turning or replacing the rotors. And it seems like it is a matter of preference, budget or driving style. At this time I am on a budget but did not know of the $20 rotors from BMA. If these rotors have good feedback I think that is the way I will be going. Does anyone have any feedback on the Opparts rotors? Thank you. :)

[632 Regal]

Im running them no problems at all.


It usually occurs between 65-75 MPH. But there are times that there is no shimmy at all. I don't get any shimmy when I accelerate through the gears, only during this braking period. Could that still be the thrust arms?

I finished reading the rest of the posts and found varying opinions about turning or replacing the rotors. And it seems like it is a matter of preference, budget or driving style. At this time I am on a budget but did not know of the $20 rotors from BMA. If these rotors have good feedback I think that is the way I will be going. Does anyone have any feedback on the Opparts rotors? Thank you. :)

[Zeuk in Oz]

It usually occurs between 65-75 MPH. But there are times that there is no shimmy at all. I don't get any shimmy when I accelerate through the gears, only during this braking period. Could that still be the thrust arms?
Thrust arm shimmy is usually felt between 45-55 mph, or thereabouts, and is usually worse under braking.

[Montreal525]

the proper way to do it is replace all 4 pads as sets and either replace the rotors if they are below spec thickness or have them turned at a machine shop but never install new pads without new rotors or at least turning you old ones

Ha... Done it couple time, on almost all my cars, with no problems... I have Brembo x-drilled rotors in front and just changed the front pads this summer. The rotors were well within specs and looked good. I didn't even take them off....

I believe it's all in the breaking period...

Jeff

[MTV]

Thrust arm shimmy is usually felt between 45-55 mph, or thereabouts, and is usually worse under braking.

Thanks for the info. I will keep an eye on it on my way home from work tonight. :)

[tdgard]

I change the rotors as a matter of course every time I do the brakes. When I bought my first BMW, I had the "well I've never done this on any other car" mentality. First time I took the rotors to a machine shop, they told me they could not turn them (which I DID do with every other car). This is because if you measure the new rotors with a caliper, they are built to spec. No extra metal to take off. Being stingy, I tested it. I found that I could never make it to the next brake change without developing a shimmy of some sort while stopping.

So based on lazyness, I now change the rotors every time on the front so I do not have to take the wheels off a third of the way through the second set of pads. It's amazing what spending a nominal amount of money will do to keep this from happening.

That being said, I let my rears go twice since I can not feel the effect.

[boardburton]

Where can I purchase these $20 BMA rotors?

[Blitzkrieg Bob]

http://www.bmaparts.com/

[rob101]

From looking at my rotors after nearly one set of pads and 40,000kms I'd say that they are already undersize. At least a 2mm lip each side... so machining is out.
2 mm?
thats HUGE!

[bmwalfa]

im looking at doing this to my car also, im thinking of putting drilled and slotted brembos on the front, and drilled in the rear, ive helped with a few brakejobs, and trust me, if your budget can allow, and you like to get into that gas, do at least drilled, also i believe a cooler pad lasts longer.
<br>
also check your rear rotors, it could be those that are warped, ive seen this happen on some larger trucks and suv's but i wouldnt rule it out for a bmw.

[632 Regal]

from what I understand which isnt much is the surface it heat treated and once cut the treating is gone. thats all I understand and dont know if its fiction or truth, the rotors are thin and excessive wear in a cut rotor makes sense, the hardness is gone.

[bsell]

My brakes are getting low, I have been told that if I replace my pads and sensors that I should replace my rotors. I have never had to do this on any other car I have owned, but is this something particular to BMW's?

Do they just want more money out of me or is it a good idea.

The money is somewhat of an issue but long-term customer satisfaction and ease of repair play a role also. Using brand new rotors removes any hidden issues with the old rotors popping up later plus the mechanic doesn't have to wait for the machine shop to finish turning your old rotors. I've had machine shops rush the turn job and leave grooves like an old LP record. Ever heard brake pads go 'clack, clack, clack' down the street? The grooves grab the pads and slap them around in their mounts, not good!

Change out your brake fluid while you are at it. You will be amazed at how much more abuse the brakes will take before they start fading. Remember, brake fluid absorbs water and water boils at 212 degrees which is way short of DOT 3 and 4 brake fluid. Plus the fresh fluid can help keep the rubber parts protected longer.

Brian

[Airborne001]

Thrust arm shimmy is usually felt between 45-55 mph, or thereabouts, and is usually worse under braking.

Sounds like my car, can the thrust arms be replaced without rebuilding the whole front suspension? Do you need any special tools (presses/pullers) to do the job?

[genphreak]

I've had machine shops rush the turn job and leave grooves like an old LP record. Ever heard brake pads go 'clack, clack, clack' down the street? The grooves grab the pads and slap them around in their mounts, not good! Brian Are you sure? New rotors come with grooves like a n LP record, straight from BMW...

[93 525 Paul]

Are you sure? New rotors come with grooves like a n LP record, straight from BMW...

Hmmm. I put Brembo rotors on the '93 and they didn't have grooves of any sort. They were a smooth machine finish (not shiny) and definitely not grooved (like you will get with the feed being too fast on a lathe.)

[bsell]

Are you sure? New rotors come with grooves like a n LP record, straight from BMW...

It depends on how deep they are and how agressive the pitch of the groove (how quickly the groove moves from the inside to outside).

Ideally, there should be a 'cross-hatch' pattern, which would feel omni-directional to the brake pads, and give a little texture to the surface to assist in seating the new pads.

Brian

[bsell]

Hmmm. I put Brembo rotors on the '93 and they didn't have grooves of any sort. They were a smooth machine finish (not shiny) and definitely not grooved (like you will get with the feed being too fast on a lathe.)

Was watching some kind of 'car' show on TV the other day where the guy recommended polishing the new disks with 600 grit sandpaper to make the disks 'shine'. This was supposed to help the pads seat better...

I know I ruined a brand new set of pads trying to get them 'seated' quickly without having turned or replaced the rotors. Smooth move Brian!

That is why I took my time with my 525's new brakes (all 4 corners). Gave them about 150 KM's of stop and go driving before I took the car up to highway speed and used the brakes stoutly.

The fronts seated pretty quickly. The back pads only contacted the middle half of the rotors until I got on them from highway speeds. I can't wait to try them on the Autobahn in January.:D

Brian