Replacing brake rotors (1 Viewer)

[Jay H]

Hey, do you normally replace all four (car) brake rotors at one time, or is it OK to do it in pairs (2 front/2 rear)?

I know they tell you to replace the pad when you change the rotors, but I know my front rotors are more worn then the rear ones.

Jay

 

[Kevin P]

Pairs is fine - do both fronts at a time, or both rears at a time, but you don't have to do all 4 at once, especially since the fronts tend to wear out faster. Of course, if all 4 need work, then doing them all at once will save you some time/money.

KJP

 

[Todd Hochard]

Are the rotors below the minimum thickness? Are they warped? Is that why you are replacing them?

It's fine to replace just the fronts or the rears. No need to do all four. As a rule, I've always replaced both of the fronts, or both of the rears, though. Otherwise, you can end up with a pulling problem under braking.

Todd

 

[Jay H]

The rotors aren't warped (original BMW rotors on a '97 328i with only 43k miles on it) but it is officially below "BMW spec" on them Which was about 1.5 years ago. Knowing BMW dealers (who want like $950 to change them.. yeaaah right, when I can buy plain rotors (not slotted or any fancy stuff, I don't race) for $180 and do it myself! I have already changed my brake pads before and I know how to do the rotors so I just ordered a set of 4 rotors and the holding bolt on them. I also ordered some anti-squeel compound since I have to remove the calipers anyway, might as well use some of that and some brake cleaner.
I figure in the spring when I change from snows to regular tires, I'll change the rotors then.
Jay

 

[Armando Zamora]

Yeah, I performed my first ever brake job just a few weeks ago. My car needed new rotors and pads badly.

It wasn't that difficult of a job with the right tools and instructions. I ended up replacing the pads and rotors on all 4 corners. I did the fronts one week and the rears the following week. However, as mentioned, you don't need to replace all 4 corners at one time. Doing them in pairs is fine (i.e., fronts or rears). Gonna bleed my brakes this weekend.

 

[Jay H]

I am going to be bleeding my brakes too, but I've been reading a bunch about the new brakes with ABS, supposedly there is some added steps to bleed the brakes equiped with ABS which makes me wonder.. I'll have to dig up some of the info I've gathered on bleeding ABS equipped brakes..

The prices of slotted rotors are almost double the standard solid rotors and the cross drilled ones are even more, which is why I went with the standard $44/$38 dollar ones front/rear (individual prices)

Jay

 

[Armando Zamora]

Jay,

I fared pretty well with my setup. I went with slotted rotors for the front and plain rotors for the rear with Mintex Redbox pads all around (hoping to keep the brake dust down). The entire package set me back aproximately $250. The rotors are also coated with cadmium to keep the rusting down on the edges and hub. Of course, these are for a Passat. May explain why the parts are less expensive than those for your Beemer.

 

[Andrej Dolenc]

Supposedly when you have the dealer bleed your brakes, they can hook up your car to the computer and activate the ABS system, flushing out whatever brake fluid is in there. Most DIY'ers apparently don't worry about that all that much as long as you get on the brakes enough to activate ABS here and there. Not perfect, but a whole lot cheaper than having the dealer do the work.

Andrej

 

[Todd Hochard]

Wow. I find it very odd that the rotors are below minimum thickness with only 43K on them. For reference, my '95 Accord EX has 115k, and I'm about 1/2 way to the min thickness. They've been re-surfaced once, too.
My '80 Z28, which sees plenty of hard stops (some from 120+mph), have about 60% remaining, after only 25K miles.
I just find it odd that the rotors are gone already at 43K miles. Do you know this, or were you told?
Todd
P.S. You're not a "two-footed" automatic driver, are you?

 

[Jay H]

I doubt they are under any minimum thickness but for the first 4 years of so, when I drove to work, it's all city kind of driving. Within the 9.5 miles to work on the highway, there are like 7 lights so it's really stop and go, constantly to and from work. I'm sure I could drive quite safely for many more miles but I am going to change the two fronts come spring.
What is the absolute minimum thickness BTW, given that there is no warpage, or is it basically run them down until they warp when they are thin?
And nope, not a two footed driver.. Well, actually I am a two footed driver as I drive and I have two feet, but I only use one foot while driving an auto tranny.
Thanks everybody, BTW... Happy driving.
Jay

 

[Todd Hochard]

The minimum thickness would be stated in the service manual. It's based on a number of factors, all safety related.
They should last you to 100,000 miles or so, easily. BMWs have good brakes, that don't work as hard as other makes (e.g. undersized Ford discs), too, so that helps extend life even further. I'd really be surprised if they are "really" below spec per the manual.
I just asked why, as I see no point in replacing parts that aren't "used up," unless they are being replaced with higher performance parts (in the case of rotors- bigger ones).
My suggestion- take a look at the pads, change them if they need it, and resurface the rotors if they are gouged. Otherwise, leave them, and spend the money on something Obscure.
Todd

 

[Jeff_Krueger]

Just had to replace the rotors on my car, even though one side was gouged due to a cracked pad both rotors were really too thin. The car only has 80,000 miles but I suspect that the last couple times the rotors were resurfaced the Brake place just put them on the lathe and let it run until it ground a ton of material off. The car couldn't have possibly had more than three brake jobs total (I bought the car used with 27,000 miles).

My guess is that if your rotors are already getting thin they are probably grinding too much material off when they resurface them.

 

[Steve Schaffer]

Although it is virtually unknown for Japanese makes, I have seen rotors wear thin just from normal brake use on German cars without the pads going down to bare metal.

Maybe the German makes use harder pads and softer rotor metal, I don't really know, but it's something I've seen on a few German cars traded in at the Toyota store where I work.

I have never seen rotors on a Toyota wear significantly. Get gouged when the pads go to bare metal or warp from dumb driving habits, but never wear thin.

 

[brentl]

Jay; take this from a friend!

Get the proper rotors for the car!!

I know you don't drive it alot since you prefer your bike, but spend the money.

If you wanted cheap repairs you should have bought a Cavalier!

Brent
Just an opinion from a guy that tends to drive shitboxes because that's what he can afford.

It's like getting a winter tire/rim package and putting $20 hub cats on.

Dad mode OFF!

 

[Jay H]

Yo Brent, I bought the stock rotors from Bavarian Auto, not Dr. Nick Riviera (Hello everybody!!)... There is nothing wrong with plain ole OEM rotors, unless you are racing and see alot of track usage where you may want to have more cooling to keep the brakes cooler, my car stops very nicely, quite nicely indeed, not as good as my MR2 (115ft 60-0) but still very nicely.
I changed the brake pads around 28k miles, that definitely needed to be changed, at least the fronts. Plus the stock brake pads spit out brake dust like there is no tomorrow. I replaced it with some pads from a company called Repco "MetalMasters" and so far it is 50 times cleaner and brakes as good as ever.
Todd, hmmmmmm, maybe I'll spend the money (and my xmas bonus) on a new Marmot Hydrogen +30°F 800 Down sleeping bag.. 1lb 10oz of ultralight sleeping bliss.. Is that obscure enough?
Jay

 

[AjayM]

Even if you are concerned about performance don't buy slotted or drilled rotors, at least for most cars. The gains are non-existant (or associated with other changes) and the risks are very high (ever wonder how well a cracked/broken rotor stops a car).

Andrew

 

[Andrej Dolenc]

The minimum thickness of the rotors should be stamped on the rotor hat itself.

I'd also suspect whether the pads & rotors were in fact worn down. I did the first pad / rotor change on my '97 M3 at around 75k miles. Pads were pretty much toast, rotors were still above minimum thickness but replaced them anyway since we were doing a major suspension overhaul. The car has seen plenty of hard driving and autocross racing.

Andrej

 

[Todd Hochard]

Jay,
Most BMWs come with TUV-compliant pads from the factory, which require graphite. That's where a lot of the dust comes from. Replacement pads in the US aren't required to have it.
I'm not sure what the benefit of graphite in brake pads is. It's used as an anti-seize, but I'm not sure that's a good thing pertaining to brakes.
I agree with Ajay- drilled/slotted rotors for the street are a fantastic scam, IMO.
Are you actually going to sleep in that bag?
Todd

 

[AjayM]

I agree with Ajay- drilled/slotted rotors for the street are a fantastic scam, IMO.

Drilled rotors are a fantastic scam all together, most race teams now use slotted rotors and usually you will only see 3-4 slots in the rotor to give "bite" to the pedal, they will also use pads that have as much leading edge as possible (I believe that's the correct term). Either way a hard driving race team will replace the rotors before every race anyways so they don't have to worry about longevity. But drilling holes (Porsche, Ferrari, the really expensive Brembo's -think in the $400/rotor range- all cast the rotor with the holes in them, so no drilling) into a piece of cast iron will weaken the rotor by quite a bit, you are also removing surface area for the pads to work, and you are removing mass from something that should have mass to absorb heat. Drives me nuts seeing people buying them and thinking they are somehow improving something other than the bling factor.

Andrew

 

[brentl]

Sorry Jay, I thought you were getting something a little "off brand"

Brent