The BMW Brake FAQ

22 Mar 2015 | Author: | Comments Off on The BMW Brake FAQ
BMW

Introduction

If you asked me what I like most about the BMWs I drive, there is no doubt that I would answer the brakes. The brakes are the main reason I own my cars, one of the reasons I won’t sell the cars, and the most important safety system in my car. BMW brakes have helped me stay alive.

That’s not bad for a system that was designed some time in the late 1970’s!

This article discusses many aspects of the brakes in your BMW. It was formerly known as the E28 Brakes FAQ, regarding the 1982-88 5-series. All of the information here relates to the E28. However, much of it also applies to all the other BMW models.

While each model uses somewhat different suspension geometries and brake technologies, the design goals are the same – to provide a nimble and responsive suspension with exceptional brakes.

Most of the information herein is directed to owners that are interested in learning more about their car’s brakes. If you are using your BMW like a conventional automotive consumer, this FAQ is for you. If you are using your BMW at the racetrack (BMW CCA driver schools, for example), you may require further suspension analysis and more advanced solutions to brake problems due to the additional stresses you place on your car.

But start here so that you can rule out the obvious trouble spots.

Due to changes in the laws regarding what materials may be used in brake pads, brake technology has advanced. Nonetheless, BMW owners (and owners of every other make and model) have discovered that today’s advanced brakes can be considered analogous to a double-edged sword. They perform beautifully. However, the rotors can warp and cause the steering wheel to shake.

If you want to avoid repeat visits your mechanic to resolve your brake problems, read this FAQ. I believe it is the most accurate information, to date, regarding BMW brakes. If you find anything in this FAQ that is incorrect or misleading, I would appreciate it if you would contact me so that I can update this article.

My knowledge of the E28 stems from about ownership of one 1983 E28 since 1988 that, had driven nearly 320k miles before being prepared as a dedicated ice racer, and ownership of a 1987 E28 since 1994. Both eta engines. I am a do-it-yourselfer, and my experience is from driving and working on these cars, and from the advice of particularly outstanding BMW CCA friends.

If you have corrections, updates, or any additional information that you feel can improve this FAQ, please send e-mail. If you wish to reproduce any part of this FAQ, all I ask is that you get my permission first, and PLEASE mail me a copy of your periodical where my FAQ appears to the address at the end of this page.

FAQ Questions

The 82-88 5-series, as well as the E34 and E39 5-series and the E30,E36, and E46 3-series, while popular cars amongst BMW people, all have the reputation for developing a shimmy upon braking. This shimmy becomes more noticeable over time and mileage. There are many proposed solutions, but no one except BMW AG has spent the research dollars and time to figure out the best solution, and in my opinion, they have found it.

There has been some conflicting information on the Internet and amongst some aftermarket parts suppliers about the best solution. The intent of this FAQ is to clear up some of these questions.

In a nutshell, why does the front end shimmy upon braking?

This is a two-part answer: first . these cars’ suspension was intentionally designed to be responsive and nimble, unlike large American sedans which allow heavy weight to rest on the front wheels. As a light suspension, it is more prone to transmitting vibrations through the steering wheel. In the 3-series and 5-series, these vibrations are caused by deteriorating components in the suspension.

As these various components wear, the evidence of their wear becomes apparent through vibrations in the steering wheel most noticeably upon braking, and particularly between 50-65 mph (80-105kph). Second . the other half of the problem rests with the material used in the brake pads and how it interacts with the rotors. In the mid-80’s, asbestos was outlawed in the USA.

After the BMWs of that era had already been designed and produced, BMW had to search for a semi-metallic pad for replacement parts (scheduled maintenance), because they couldn’t sell the asbestos pads once the asbestos law went into effect. The asbestos pads were originally selected because they were able to generate acceptable levels of heat, while it was much more difficult to reach similar specifications with semi-metallic pads.

In time, the additional heat generated caused the rotors to warp. During this period, BMW issued many updates. They used a number of rotor and pad manufacturers, including Textar and Jurid.

They did this until they felt they got the proper pad-rotor combination. It was fairly common for dealerships to replace set after set of warped rotors and ruined pads in some customers’ cars (dealers can fish for an answer, too). The rotors were often replaced free under the 12-month parts warranty.

Unfortunately, although this problem was known while the E34 and E36 were still in development, these cars exhibit the same problem to a lesser degree. The E46 and E39 have been reported to have the same susceptibility to shimmies, but the underlying suspension components are stronger that older models. Again, replacing brakes with new ones won’t solve the problem (for too long) unless the suspension is in good shape.

What parts should be replaced?

If you experience the symptoms mentioned above, your rotors are most probably warped. If you get the shakes at different highway speeds even prior to braking, you definitely have one or more worn suspension components. Whether or not your need to replace suspension parts is a question based on the car’s history, age, and mileage. You should not blindly replace the brake components without examining the rest of the suspension.

It is common to need additional suspension work in addition to the brakes, particularly on cars with over 100k miles.

Replace all four rotors and pads with stock pads. From a dealer. They’re relatively inexpensive ( cheaper than American and Japanese cars!!). So do all four.

ALL FOUR . The labor is so bloody easy that you won’t be sorry. Besides, after you do it, and you’ve insured the rest of the suspension is working, you’ll be really happy. REALLY.

All service bulletins from BMW on brake replacement recommend replacing front and rear rotors as well as pads when servicing brakes.

Brake Replacement Parts list:

Front pads (1 set – usually Jurid 506EE for older E28s)

Rear pads (set)

Factory spin-balanced rotors x 4

Front left brake sensor

Rear right brake sensor

Hex key screws x 4 (provide month/year of your BMW mfg.)

1-2 quarts brake fluid (per mfg. spec.)

As I said, the brake job is quite easy. At this point, I don’t see a reason to go into excruciating detail about the procedure for replacing brakes, particularly because the Bentley, as well as the BMW shop manual, are very clear on this.

Why can’t I simply turn the rotors?

Warped rotors cannot be turned (cut). The excessive heat that has caused the rotors to warp changes the composition of the metal so that they cannot be cut properly, and the problem returns virtually immediately. New rotors from a BMW dealer, with a BMW CCA discount, are so inexpensive, particularly on the older BMWs, that it is economically foolish to turn old ones.

Another comment on turning rotors – when you buy new rotors from BMW, they have a coating on the brake surfaces. Clean them before installation. Take some brake cleaner and clean off both surfaces of the rotor (where the pads make contact).

Then, upon assembly, don’t touch the surfaces with your greasy hands.

I’m trying to get the old rotors off, and I’m afraid of stripping the hex key that holds them on. What should I do?

Whatever you do, don’t strip the hex key bolt that holds the rotor to the hub! Use a fine dentist-type tool to clean out the vertices of the hex key, so that a hex socket can be completely inserted into the screw. Give it a shot of Wurth Penetrating fluid if you’ve got it. Then (I do this before I remove ANYTHING else), with someone pressing the brakes (or handbrake, if rear), apply a firm torque to the screw.

These screws shouldn’t be too tight, although dirt and corrosion can make it more difficult. If you strip it, get the easy-outs. I have successfully removed these screws with easy-outs.

It requires patience. Otherwise, drill out the head of the screw and remove the rotor. If all else fails, a sledgehammer (seriously) can be used. One or two whacks to the backside of the rotor (be careful not to hit anything else) will, in fact, remove it.

Remember, it is only a set screw. The wheel bolts firmly attach the rotor to the hub.

Is there some trick to removing the rear rotors on a BMW?

On the rear wheels, the inside of the rotors act as a drum for the emergency brake shoes. You must loosen the emergency brake so that the shoes back away from the inside walls of the rotor. Loosen the emergency brake, left and right side, by loosening both nuts at the emergency brake handle. Further, the emergency brake’s internal adjusting nuts are accessible through the lug holes in the hub.

Then remove the rear rotors.

Should I flush the brakes?

You should ALWAYS be flushing the brakes once per year. Read your car’s owner’s manual for manufacturer recommendations. And check out the article, Bleeding your BMW’s Brakes, and Fabricating a Brake Bleeder Pressure Kit for more information on how to build your own brake bleeder.

Can I use a pressure bleeder to flush the brakes?

In most cases, you can. In certain models, you have to. A couple other CCA members have developed a home grown tool for this purpose, since so many commercially available bleeders are inadequate to the task.

Read the article mentioned in the last question.

Any other nebula to consider, Mr. Enginerd?

Yes, I’m glad you asked. Make sure you torque the wheels to 85 ft-lbs. No more, no less. Believe it or not, this torque spec. insures the proper heat dissipation between the brakes and the wheels.

This means every time you get new tires, every time you have the wheels rotated, every time you put on the snows, make sure the monkeys at the tire shop use a torque wrench to put on the lug bolts, not an airgun.

I replaced the rotors and pads with the OEM stuff you suggested. It’s only 5k later, and they’re warped again. Why??

This is a sign that you didn’t find the root cause of the problem. Yet. Assuming that they warped in less than 1 year and you got them from a dealer, the rotors are under warranty. You can replace them for free.

But you have to examine the other components in the suspension, one by one. Clearly, one must examine each bushing, each tie-rod assembly, and the shocks. Bushings should be checked for hairline cracks; specifically look at the lower control arm bushings and thrust arm bushings. These can be disconnected in order to examine them.

Tie-rod assemblies, track rod, and idler arm (in the E28) should be checked for play, and can be checked by hand. Ball joints (in lower control arm or thrust arm) can be checked by the bar-under-the-wheel test, usually, and should also be checked for visible signs of boot deterioration. Shock diagnosis is difficult, since the bounce-test is useless.

Often, the type of driving and mileage must be considered, as well as how tires wear, how well the car tracks at high speed, and how much the car leans on cornering. My first E28 lasted with shocks until 150k, my newer one seems to need them after only 80k. Finally, a four-wheel alignment should be performed so that the rear wheel alignment can be measured (there are no adjustments here) and the front wheel alignment can be measured and adjusted.

In my older E28, the front strut bearings were a serious culprit, in addition to the shocks. This made sense, since worn-out strut bearings are not able to properly hold the strut in place upon braking, and the result was a couple of BADLY shaking strut assemblies.

One other thing – don’t forget that your wheels and tires are also suspension components, and MAJOR ones. I have used both the stock 14 rims and aftermarket 15 rims. Some have used +2 and even +3 sizes. The difference in road feel between 16 and 18 wheels is dramatic, and unless you live in a part of the world with perfectly smooth roads,you may find that larger wheels can exacerbate brake problems. Wheels must not be dented or out-of-round.

The same is true for tires. I have seen worn tires make a car feel like it was on its last leg. You may need to purchase new tires to fix brake problems, but that’s the subject of another FAQ.

Whatever you do, don’t be a cheapskate when considering tires. A poor choice may cost you a lot more money down the road.

I consider this to be fact; others say it’s subjective, so standard disclaimers apply. First, with the CCA discount, the price can’t be beat. Second, all parts (excepts bulbs and brake pads) come with a 12-month, unlimited mileage warranty. As long as you have a valid receipt from a dealer, they will allow you to replace warped rotors – for those do-it-yourselfers, the only cost is your time to do the labor. You should not take advantage of this policy, but use it when necessary.

I would check with the dealer, at the time of purchase, what procedure they use to replace rotors under warranty. BMW policy requires dealers to replace them for you even if you bought them at another dealer, but some dealers will give you a hard time, so don’t count on their cooperation. One year I went through 4 sets of rotors until I isolated the worn suspension part that was causing the problem (see previous question).

I have known the service departments of some dealerships to have similar experiences. Since I posted the first version of the FAQ, I confirmed that Eurasian can also get the Jurid pads at reasonably competitive prices as compared to BMW dealers (with a 20-30% CCA discount). I would ask specifically for the model 506EE pads.

Also, see the next question for a discussion of stock vs. aftermarket rotors.

C’mon, what’s the difference between the stock rotors and the same rotors from an aftermarket?

Well, aside from the warranty, which is important, the stock rotors are spin-balanced at BMW after the OEM manufacturer (Brembo, Ate, Balo, etc.) ships them to BMW. Some manufacturers claim to spin balance their rotors, but they may use less reliable clip-on or glue-on weights, whereas BMW shaves metal off the rotor to achieve the proper balance.

My experience is that from a reputable BMW dealer with an aggressive parts department, you can buy rotors CHEAPER from the factory. The aftermarket dealers that advertise in Roundel have been, in EVERY case, MORE expensive (to my surprise as well), and there is rarely a warranty with their products.

OK, now I’m replacing suspension parts. Do polyurethane bushings help?

Not really, unless you are planning to modify the springs, struts, and sway bars. Some people have claimed to use the 750iL bushings successfully, but my feeling is that the car, in its stock form, wasn’t designed to run with these, and these stiffer bushings will put more stresses on the rest of the suspension, which were not designed to work with them. Also, on the later E28 models (87-88) some have claimed that only the 750iL bushings will work.

I am still investigating this.

Needless to say, any new bushings WILL help, if your existing ones are worn. The stock bushings are very cheap – the labor is difficult, unless you can remove the ball joint without damaging it, and have a workbench to carefully press out the old bushings and press in the new.

OK, I’m using the stock pads and I’m happy. But the stock pads generate a lot of brake dust. Can I use dust shields?

General consensus has been that using dust shields are the WORST thing you can do for the health of your suspension. While they do appear to keep the dust off of the wheels, some people have claimed that the heat from braking isn’t dissipated properly, and some have empirical data of amazingly fast rotor warpage with their use. More frequent use of a good wheel cleaner is the best solution.

I happen to prefer P21S, due to its overall excellent design and environmental-friendliness (it won’t kill your cat, it won’t ruin your glasses, it won’t destroy your brakes). Admittedly, it requires a bit of elbow-grease. But, like Zymol Wax, the results speak for themselves.

There has been some speculation about the negative side effects of Armor All’s QuickSilver wheel cleaner, but I don’t know much about that, except to say that anything corrosive should not be sprayed near any brake components. Period.

What about cross-drilled rotors?

If you’re doing driving schools monthly, you’re probably in a different realm of brake pad/rotor/fluid than most of us. You’re possibly using Cool Carbon pads, and maybe even racing brake fluid. In this case, cross-drilled rotors may make sense for you to dissipate gases and to prevent brake fade. You might even install air ducts to provide extra cooling to the brakes.

But if you’re not pushing the envelope with this type of driving, cross-drilled rotors are a waste of money. Better spend it on some driving school to learn how to drive. I’ve also seen some instances of stress fractures developing in cross-drilled rotors that eventually ruin the brake pads.

I don’t know if the manufacturers of these parts really know what they’re doing.

Speaking of driving habits, can my driving habits cause my brakes to warp?

This is a tough question, because I have some firm opinions here, which all may not agree with. I don’t believe in automatic transmissions, because I believe they relinquish much car control to mechanisms that don’t have eyes. I feel that with automatics, one must use the brakes much more often since they have less control over the drivetrain.

Some people claim that braking with the engine (ie. downshifting) is wrong because brakes are cheaper to replace than a clutch. Well, one of my E28s had gone 220k miles before requiring clutch replacement, and I downshift all the time. Some people claim brakes are cheaper to replace than a clutch, and while this may be true, it’s a safety issue. I’d much rather replace a clutch than play detective with my front suspension.

Determining worn suspension parts can be an expensive, frustrating, iterative process.

My point is that you shouldn’t ride the brakes. You should be aware of your driving so that you don’t use the brakes until you need to. That may sound simplistic, but if you think about it, and practice it while you drive, you can drive smoothly and preserve your brakes for when you actually need them. Short, firm braking, combined with downshifting, allows far more cooling than riding the brakes for a hundred meters before a stoplight, tollbooth, etc.

Your brakes need the time/air to cool. I also don’t sit with my foot firmly on the floor at a stoplight, pressing the pads against hot rotors, but this probably isn’t an option on an automatic.

Can I attend driving schools at a race track with a BMW, or will it warp my brakes?

The answer to this is completely subjective. My answer would be yes, but to be fair, the stresses on your car during a school are quite high, so you shouldn’t complain when things break. As Richard W. says, schools do wonders at exposing weaknesses in your car.

You can surely commence rotor warpage during a day of spirited driving at a school.

Are BMWs the only cars that warp rotors?

No. In fact, due to asbestos being outlawed by the US government, all cars now use non-asbestos pads. One reason that this wasn’t as much of a problem with American cars is that they would die long before the rotors warped. On my old E28, they warped after 130k miles. Another reason is that these other cars are designed to provide very soft rides, which usually means very heavy front suspensions, which masked out many vibrations until the vibrations were quite serious.

Now, with CabForward designs and more nimble suspensions, I commonly hear about those new Chryslers warping rotors in only 25k miles of driving!

Steve, are you this anal retentive with all your automotive repairs?

Yup. 8^)

In my E28 M5 the factory replaced the front bushings with 750 hydraulic bushings. With the larger wheels and tires which are stock on the M5 (225/50/16ZR tires), this is the only thing which prevented the shimmy from recurring every 8k miles (on a new car, with nothing worn).

There is available a spun stainless steel hub cover, which redirects air flow, and GREATLY reduces the incidence of rotor warpage. These can be obtained from Carl Nelson at CNPR 1-800-466-8184.

For track use, if you wish to engage in spirited driving, and do not want warped rotors, Cool Carbon Pads are a MUST, IMNSHO. They are the only way I have avoided the problem. At a BMWACA drivers school at Laguna Seca, the Instructor asked me why my rotors weren’t warped, as all the other E28 M5’s he had been that day were.

For the answer, see above.

Front Brake Upgrade Kit Addendum, courtesy of Mark Magee :

The stock E28 brakes are excellent. They even stood up to track use at Sears Point. However, they are entirely inadequate for track use at Laguna Seca (Laguna has a tremendous amount of elevation change.

Turns 2, 5, 8, 10, and 11 require a significant amount of braking – four hot laps can cook the stock brakes).

I went with a Dinan front brake upgrade kit. It uses 850i rotors and pads, but not the same calipers. I believe the 850i calipers are two piston, whereas the Dinan calipers have one piston each (I have heard that Dinan no longer sells the kit I have, but has replaced it with two other kits).

I highly recommend this setup. Changing pads, crossdrilling rotors, etc. gave less improvement, with greater side effects (great track pads are often noisy on the street and may not work well at low temperatures; the cross drilled rotors warped very quickly).

I also have stainless steel braided teflon hoses, which improve pedal feel. And I installed air ducts from a company called Berlinetta. These ducts are specific to the E28 M5 air dam (shared by the iS) and seem to provide an extra measure of cooling. *Fresh* brake fluid with a high boiling point makes a big difference.

The brake upgrade required a wheel upgrade. The stock TRX wheels do not accommodate the big brakes (besides, TRX tires are lousy). The original M5 wheels (16×7.5, 20 mm offset) fit.

850i wheels (16×7.5 10 mm offset) fit. But both require trimming or bending back the inside lip of the rear fender (the factory trimmed the M5 fender; B-Line body shop recommended bending because it leaves all the metal in place). The tire to use is 225/50 16 . This is almost exactly the same diameter as the stock tire (BTW, the Tire Rack catalog has some useful tire information, including a formulas for calculating diameter, wheel offset, etc).

Other 16 wheels may or may NOT fit the Dinan brakes. I highly recommend a test fit with any oversized brakes. The wheel offset is very critical with the E28 chassis. More than 20 mm means rubbing against the front strut.

Less than 10 mm means rubbing against the rear fender (the offset numbers change with wheel width; consult the Tire Rack catalog for formulas). The opening inside the rim is critical also. The distance from the Dinan brake caliper to an M5 wheel is on the order of 1 mm.

Dinan sells big wheels for the E28 chassis. I think they are 17×8, and can be fitted with 235/45 17 (if I remember correctly). These wheels are rather pricey, and require spacers in the front (to keep the wheel away from the strut) and fender adjustment in the rear.

I chose not to go for that size because 16 tires are cheaper and more plentiful. For example, I don’t believe the Yoko A008 is available in 17.

A word of caution about wide tires. The recirculating ball steering in the E28 is famous for numb on center. A sloppy front end (due to wear of ball joints, tie rod ends, etc.) combined with extremely wide tires will make matters significantly worse.

(Someone told me that E28 M5 brakes can be fitted on a regular E28. I have not explored this. I do know that the front strut [inserts] are different, so I was skeptical that this is a bolt on task).

1997, 2002, 2004 – Steven J. Bernstein All rights reserved.

Comments to: garageboy.com

Steven Jay Bernstein

updated Monday, 23 February 2004 2:23:11

Tagged as:

Other articles of the category "BMW":

Twitter-news
Our partners
Follow us
Contact us
Our contacts

dima911@gmail.com

Born in the USSR

423360519

About this site

For all questions about advertising, please contact listed on the site.


Car Catalog with specifications, pictures, ratings, reviews and discusssions about cars