How to check & replace your BMW front disc brakes and rotors

bluebee:
As a male, I would like to apologise for the many comments made by my gender denigrating your tireless efforts to get a job done right, the first time.

I'm just about to replace the front rotors and pads on my 03 525iT and am using you material as the most through and complete set of instructions I have seen on the net, including videos, blogs etc.

Your job obviously leads you to your extensive research on a subject with witch you have little knowledge, but I am grateful for you efforts and desire to share your data. I too do a lot of research before buying anything over $100, or before tackling new or infrequent jobs, like a brake replacement.

Thanks for the info., and ignore the macho "Just get the damn thing done" guys who would never admit to their mistakes.

Did the fronts on my 03 525iT, followed your instructions to a T. Car stops like a jet grabbing the wire on an aircraft carrier, even, straight with wonderful pedal feel. Obviously the Brembo rotors and PBR ceramic pads are most of the reason, but following your instructions made everything perfect. Only complaint, the big G's that occur now.
Thanks for all your research and posts to make it so simple and having the confidence for doing it right.

Originally Posted by Ted Milner

I would like to apologise for the many comments ... denigrating your tireless efforts to get a job done right

Thanks for the kind words. I don't think it has as much to do with gender as with the fact that most people have the confidence to just 'do the job' without looking up how.

I don't have that confidence - but - as always - our strength is our weakness.

The strength of many who "just know" how to do it is that they get the job done fast and easily - yet - their weakness is they often do it 'wrong' (e.g., a BMW brake job is nearly dry if you ask Bentley).

On the other hand, I might do it right (because of the extensive research), yet it takes me forever to get the job done.

In the end, we need both types of people to cover the weaknesses and to add up the strengths. That's what a TEAM is all about!

Originally Posted by Ted Milner

am using your material as the most through and complete set of instructions

Thank you for recognizing the fact that EVERYTHING that I could think of answering 'is' in this thread (i.e., all torque figures, specs, measurements, fluids, decisions, tools, tricks, mistakes, suppliers, costs, etc.)

Originally Posted by Ted Milner

ignore the macho "Just get the damn thing done" guys who would never admit to their mistakes.

Thanks. I think, since this was my very first thread on Bimmerfest, folks were unaware of my propensity to keep asking and looking for answers - so it threw them off at first.

Originally Posted by Ted Milner

Did the fronts on my 03 525iT, followed your instructions to a T.

Fantastic! It makes me feel good to know that the team helped someone else, simply by typing our experiences and by posting our pictures!

It's nice to know this thread (my very first on Bimmerfest) has helped others:
> E39 (1997 - 2003) > Brake Job Torque Specs

Re: wear limit on rotors

I know this is an old thread, but want to point out the following. The wear limit is the limit down to which the rotors can be turned before they should be replaced. Turning rotors instead of replacing them points to the fact that they are intended to be useful for the term of a standard brake job at and above that limit.

Moreover, think of how brakes work - unless your rotor surfaces paper thin, it will still perform its intended function (i.e. stopping the car).

However, below a certain point, the rotor will be more prone to warpage as their will be less material to disperse the heat, and less structural rigidity due to thickness.

Therefore, it's perfectly fine to use rotors down to the number printed, (and technically beyond). When they warp, replace them.

In general, while all of the research is valid (and interesting!) the average driver will not notice a difference between rotors of varying thickness, brakes at varying hardnesses, etc. If you drive casually and not spiritedly, your deciding factors will be NVH. Noise, Vibration, and Harshness. If you're not stepping hard on the pedal repeatedly to brake (as a spirited driver would) then you probably won't notice differences in fade and initial bite.

So interesting as it is, it might be overkill for your project. I *do* second that I don't trust mechanics with my car if I can help it, though. But note that even though your car was built by engineers, it was designed to be maintained by mechanics, so there is wiggle room in the tolerances by design.

Originally Posted by bluebee

That's EXACTLY my question!

Thinking more along these newly logical lines ...

The rear rotors start at ~20mm (0.787 inches) and the wear limit stamped on the rear rotor is 18.4 mm (0.720 inches in the Bentleys).

If the wear limit is 0.720 inches for a rear rotor, I'm assuming that means the wear limit really isn't a wear limit, it's a pad-replacement limit. The true it's-too-thin-now wear limit would be, I'm logically assuming, 0.720 inches minus whatever is normally worn off the rotors during the lifetime of a single set of pads.

Given I have 60K miles, I'm assuming that's two sets of pads in the rear, and given the rotor started off at 0.787 inches and it's now roughly 0.727 inches, that makes it about 0.030 inches per pad set.

That would mean the TRUE wear limit for these rotors is 0.720 minus 0.030 inches, which is 0.690 inches.

Does this make logical sense to you that, in summary, each set of pads eats up about 0.030 inches of rotor, and that you can put pads on the rears at 0.720 inches, so, the true minimum thickness, after those pads are worn, would be 0.690 inches?

Originally Posted by Richter12x2

The wear limit is the limit down to which the rotors can be turned before they should be replaced.

I agree.
I suspect that limit isn't a mechanical strength limit so much as a heat-dissipation limit.

Originally Posted by Richter12x2

unless your rotor surfaces paper thin, it will still perform its intended function (i.e. stopping the car).

I agree.
I suspect the danger is overheating, resulting in brake fade due to gassing.

Originally Posted by Richter12x2

However, below a certain point, the rotor will be more prone to warpage as their will be less material to disperse the heat, and less structural rigidity due to thickness. ...When they warp, replace them.

I disagree.

The topic of warp is well covered in this thread, but see this reference outside this thread for details:
- Let's discuss the truth about rotor "warp" (1)

Originally Posted by Richter12x2

the average driver will not notice a difference between rotors of varying thickness, brakes at varying hardnesses, etc.

I agree.
I suspect the only thing that will happen is that the rotors will not dissipate heat as well as they should - and - the result will be brake fade (I'm guessing so if others know better, please correct where I err).

Originally Posted by bluebee

The first thing I noticed was there was no grease on either the spring or on the two 7mm caliper bolts. Checking the shop manual that came with the car, it says not to grease them. I wonder how they slide without being greased. Anyway, I decided to clean them with brake cleaner but it didn't really do much. I don't know what you guys do so you can suggest something here.

Moving on to the measurements......

Checking the rotors with my fingernail, they seemed to be in good shape with respect to smoothness. My fingernail didn't catch too much on any particular grooves and all were smooth. So the rotor passed the smoothness test.

I borrowed a mic to see how fat the rotors were......

I checked ten places just like the Bentley manual said. Pretty much all were in the .760 to 0.777 inch range which seems a bit small for the specification (0.800 inches). I wonder how they got so thin as they seemed in good shape otherwise.

Checking for warps, I borrowed a dial gage. Hooking it to keep it from wandering was problematic so I ended up vicegripping it to the spring and letting it hang down onto the rotor as I spun the rotor by hand from the lug bolts placed back in the lug holes.

I checked in a few concentric circles and all were within 0.002 or 0.003 inch. I didn't see a warpage spec in the Bentleys that came with the car. Did I miss that? It didn't seem to be in the brake section (page 340).

Hi BlueBee,

I've done my brake lines, rotors, calipers, and boots on calipers, so I feel like a "pro," but still learning. I too wondered about the grease on teh slide bolts/bushings on the caliper. I did grease them but after several months, I'm getting a noise when applying the brake. I know that could be a million things. I even brought the car in for a free inspection and of course they said it was nothing and reseated everything.

Since brakes are almost new, I suspect the only thing is that the calipers are sticking because of teh grease. It was fine when I was in the hot TX sun but here in FREEZING ohio, i suspect the grease is gelling up or something. I'm contemplating either cleaning the 10 year old bolts/bushings or replacing them. (roughly $20 per caliper if I recall).

I also wondered how the calipers would operate "dry." But if Bentley says not grease, it's probably ok.

Update to follow when I get some warm weather to do the job (no garage).

Originally Posted by mjbennett9

I also wondered how the calipers would operate "dry."

It's the age-old question. In fact, cn90 has a good thread on it right here today:
- To Lube or not to Lube Brake Guide Pin

I just ordered new rear rotors and pads, and will install them tomorrow, the previous owner didn't replace the rear brakes, and I believe the car still has the original brakes in the rear.. The rear rotors were too far scarred to save......

The oem replacements will only be about $150.00 (plus tax, and some incidental stuff added..). I am going through CARQUEST.

Then I need a tire, one of my tires has seen better days.. my wife said, I should take advantage of having the car now and take a long wanted trip.. My health is so damned bad, I could not travel alone.. but would love to hit the road...

Originally Posted by retiredat44

I believe the car still has the original brakes in the rear.. The rear rotors were too far scarred to save......

The original brand for the rear pads is Textar, so, if they're NOT Textar, they're not original.
As for scarring, in this thread it is well pointed out that "grooves" need to be extremely deep to fail a rotor (by BMW specs).

Originally Posted by retiredat44

Then I need a tire

If you need "a tire", then you're best matching with what is on the vehicle.
See also the following, found by typing /tire F3 in the best links:
- How to logically choose tires by the numbers (1) (2) or by Bimmerfest user recommendations (1) (2) & where to buy your tires in the USA (0) (1) (2) (3) (4) (5) (6) & tire plant codes (1) (2) (3) & tire safety (1) & recommended tire pressures (1) (2) (3) & the claimed benefits of nitrogen gas (1) (2) & choosing the right BMW tire/tyre size (1) (2) & tire circumference, diameter, offset, & clearance calculators (1) (2) (3) (4) (5) & a torque conversion calculator (1) & tire terminology (1) (2) & wheel terminology (1) & BMW wheel specs (1) & BMW & replica wheel styles (1) (2) (3) (4) & the difference between cast vs forged wheels (1) & where to find the wheel markings for proper match mounting (1) & the best products for cleaning wheels (1) & how to choose the right size wheel spacers (1) (2) & where to go when you bend or otherwise damage your wheels (1)

You can most likely tell when rotors have been damaged, they will look damaged and feel damaged, then the measurements will back that up. I used to replace rotors on several cars I have owned in the past.. Including a large custom van, but my Hondas and Toyotas never needed brakes often. You can see damage when the grooves cut into rotors like a butter knife through butter.

I also try to use parts sales persons with experience in the car I am working on. I get their feedback. I use forum feedback and info, a mix of information. And tailor it it to my families driving style, weather, and terrain. I add my 56 years of mechanical experience with building cars. Repairing cars. A wide variety of muscle cars, passenger cars, and the college courses I took, experiences, and life experience and all the reading and studying, and friends who had different cars and also rebuilt their cars. I then determine the medium cost of what I can afford, and durability, safety, recommendations.

Then all that determines on the replacement parts. I then am satisfied I purchase quality parts, not the best, but not the worst. Knowing my family is safe and the car performs as per designed. After this I would not hesitate to place it on mountain roads, the autobahn, and that my family will be safe with quality parts, that will perform to their best, for the quality at that purchase price, and since we want safety and do not perform reckless stunts, nor abuse the car, or push it past the laws of the roads we drive on. I am confident, the car is safe, and if I do decide to give it gas, it will also perform equally as well in braking as designed. I did my due diligence in choosing replacement parts and assembling them.

I will not hesitate to drive anywhere legal and enjoy the drive. And know we can be as safe as BMW intended.

It came with vented brakes and I am replacing the parts with what came off. Same with tires. Quality.

It will be fun and safe to drive!

Originally Posted by retiredat44

I purchase quality parts, not the best, but not the worst

How do you know if one brake pad or rotor is better than another?

I just replaced my rear brakes with Zimmerman rotors and Pagid pads. $200.00 included all parts, brake fluid, bleeder kit,. etc..
There are vented, slotted, drilled. The old ones were to far gone to save, they still had meat, but the grooves were too deep.

2001 530i

Originally Posted by shaftdrive

How do you know if one brake pad or rotor is better than another?

Relying on the opinion of others is the primary source of info for most product evaluations on this forum. Search for your product in question. Virtually every topic & product has been covered, in depth. As with any product selection, it is all about the tradeoffs. If you want max performance (best combination of brake bite & feel), stay with the OE brake pads (Jurid fronts & Textar rears). But they generate more dust than Pigpen. If you want clean wheels, go with a ceramic (e.g. Akebono). You will give up some braking bite & feel. In theory, all braking distances should be near equal since ABS is the great equalizer. When it comes to rotors, they are essentially the same. You can pay more for no rust coatings or bling (slots or holes), but none of it makes any difference in braking performance. The well known brands (Brembo, Zimmerman, etc.) are highly regarded, but hey, it is essentially a chunk of cast steel.

Originally Posted by Fudman

But they generate more dust than a Pigpen.

Somewhere, someone mentioned that it isn't so much they generate more dust than any other brake pad... it's just that their dust is dark color and therefore it stands out on the wheel, versus a more neutral colored dust, which, if the theory is true, doesn't show up as much.
Not sure if that's true though ... and I don't know how to test it ...