Philes' Forum by Vic Lucariello

Hello, Bimmerphiles! I hope you are all enjoying the Summer and have signed up for our September Lime Rock Driver School.

I haven't written much about 2002's lately, so I dug up some stuff from an old c olumn that you '02 Philes might be interested in.

A common problem on 2002's is a sticking brake pedal. Some folks have reported that everytime they apply the brakes they have to pull the pedal back up by hand to get them to release! The 2002 has a rather complicated linkage attached to its brake pedal. The linkage begins at the bottom of the brake pedal, within the infamous pedal box, and ends at the brake booster, which is under the hood.

On many cars, the pedal box has been perforated by corrosion, and water/road sal t corrode the brake pedal pivots within the box, resulting in the sticking pedal that Frank described. This same problem will also cause the throttle to stick open, since a pivot for the throttle linkage also resides in the pedal box. Nea t, eh? [Ever wonder why we insist upon getting in your car and fully depressing the gas pedal before letting you on the track at Lime Rock?] The only permanen t fix for a perforated pedal box is replacement. However, gaining access to the box by pulling up the carpeting, then lubricating the offending pivots, may tem porarily treat the symptoms.

Another, less likely, spot for the brake pedal linkage to bind or stick is right behind the brake booster. Thankfully, the linkage is reasonably accessible at this point and can be lubricated.

Another common problem is an alternator lamp which insists on glowing, even afte r the alternator and regulator have been replaced. Some likely causes this prob lem include a loose or slipping drive belt, a missing or frayed alternator groun d wire, misaligned alternator due to deteriorated rubber mounts, and loose conne ctions at either the alternator or regulator. Many times, the three-wire conn ector at the back of the alternator is loose. I guess that the combination of 4 -cylinder engine vibrations and many, many miles will tend to fatigue and loosen the push on-style terminals. Sometimes, removing the connector and cleaning an d slightly crimping the female terminals is all that's necessary to restore a charging system to good performance, hopefully prior to wholesale parts replacem ent!

Returning from those antediluvian times, here is something for you owners of mor e modern Bimmers.

Mark Bukachevsky had an interesting question regarding brake bleeding/fluid chan ging on ABS [Antilock Braking System]-equipped bimmers. Mark wanted to know how much fluid is required to do a fluid change on ABS cars. Before I tell you wha t I told Mark, perhaps a bit of prose on ABS is appropriate.

The Bosch ABS used on the Bimmers I've seen comprises an electro-hydraulic modul ator installed in the brake lines between the master cylinder and the individual brake calipers, a control computer whose location varies, and a speed sensor f or each wheel. During braking, if the computer determines that a wheel is about to stop turning [incipient lock-up], the modulator is commanded to isolate the appropriate caliper from the rest of the brakes, and reduce the hydraulic pressu re to that caliper until the offending wheel speeds up a bit, at which time the modulator increases the pressure, again causing incipient lockup, etc. The cycl e is repeated several times a second until either the car's speed drops below so me minimum value [eg: 10 mph], or the driver releases the brake pedal. The puls ation the driver feels in the brake pedal while the ABS is active is the result of this cycling.

Unlike some other, less sophisticated ABSs, the system is capable of controlling simultaneously any combination of wheels. Moreover, it has self-diagnostics wh ich runs a checking routine each time the car is driven. A failure sensed eithe r during initial power-up or during subsequent operation will result in the inst rument panel "ABS" lamp to illuminate. All ABSs I'm familiar with are designed to "fail safe" in that even a total failure of the ABS should not affect normal braking action.

Anyhow, returning to Mark's question, I feel that both the bleeding/flushing pro cedure and the required amount of fluid are different for ABS-equipped vehicles.

Since the ABS has more tubing and wetted components than a regular hydraulic sys tem, I think that more fluid is required to do a proper flushing/fluid changing operation. I have found that 1/2 pint of brake fluid does the trick on non-ABS vehicles, and twice this amount, or 1 pint (approx. 120 ml), is appropriate for ABS.

Many folks change their brake fluid by bleeding the brakes and repeatedly refill ing the master cylinder reservoir until clean fluid flows from each bleeder scre w (don't forget the bleeder screw on that clutch slave cylinder, now!). While t his works, I feel that a better approach is to replace all the fluid in the rese rvoir with new fluid before you start the bleeding operation. Do this by suckin g out the old fluid with a turkey baster, Mityvac hand pump (available from J.C. Whitney, et al, for about $20), or other means.

Incidentally, before you begin working on any power-assisted brake system, be su re to repeatedly depress the brake pedal while the engine is stopped. This will exhaust any residual power assist and decrease the likelyhood of highly pressur ized fluid causing personal injury. More importantly, make sure that the vehicl e is properly supported on jack stands, and that you have your eye protection on . Ask me how I learned about not getting brake fluid in my eyes!

There is only one difference I can think of between ABS and non-ABS when it come s to the fluid changing operation. There are areas within the ABS modulator tha t only contact pressurized brake fluid when the ABS is operating. Therefore, th e fluid changing procedure described above will not entirely flush out the modul ator. In most cases, this is not cause for concern, however, if you have a car whose brake fluid is really old and discolored (ie: the fluid looks like coffee! ), I suggest you change the brake fluid, take the car out and operate the ABS, t hen run some more fluid through the system.

Anyone wishing to contribute to Philes' Forum should contact me via the info on the masthead. I'm interested in tech tips, repair/maintenance questions and/or tips, dealer horror stories, product evaluations, etc. Please call before 8 PM , and if you leave a message, PLEASE INCLUDE YOUR WORK PHONE NUMBER. Also, plea se be patient, I try to return every phone call, but it sometimes takes awhile. The best way to contact me is via e-mail.

Copyright 1997 - V. M. Lucariello, PE