Philes' Forum by Vic Lucariello

I just got back from instructing at our Summit Point Driver School and Club Race, where I got the inspiration for this month's column. The inspiration [along with lotsa perspiration] came to me when my intermediate-group student completely lost his brakes and we did a little impromptu tour of the unpaved portions of the facility. Thankfully, we and the Bimmer escaped injury. The student said that his brake pedal had felt a bit 'mushy' or soft on the previous lap, then went completely to the floor just prior to our little nature tour. The student had the good sense to tell me he had lost his brakes and to drive straight off the racetrack [as per his previous training at our schools] onto an unofficial, unpaved escape road.

One thing that I relearned from this experience is to ask periodically, during a driving session, how the student's brakes are holding up!

The first thing I asked the student after we regained continence was when he had last changed his brake fluid.

If you have been reading this column for any length of time, you know that the DOT 3 and DOT 4 brake fluids found in virtually all passenger cars are glycol-based and hydroscopic. Hydroscopic means that the fluid has an affinity for water, which, while not particularly forthcoming from the skies as rain this summer, has been in bountiful supply as atmospheric moisture. As this moisture is absorbed by the brake fluid via the master cylinder reservoir vent, caliper and master cylinder seals, and even, some say, via osmosis through the brake hoses, the boiling point of the brake fluid/water mixture decreases.

If the operating temperature of the brakes reaches the boiling point of the fluid, vapor bubbles begin to form inside the calipers. The driver perceives this as a soft or 'mushy' brake pedal, due to the compressibility of the bubbles. [Hydraulic brake design is predicated on an incompressible fluid between the master cylinder and the calipers. Yes, Techies, I know that liquids are somewhat compressible, but they are virtually incompressible as compared with vapors.] If the brakes are not allowed to cool, vapor bubbles will continue to form until the volume of the bubbles exceeds the displacement of the master cylinder. At this point, the brake pedal goes to the floor! This is why we insist that your car receive semi-annual brake fluid changes if you attend driver schools. Of course, if you grossly overheat your brakes, even new fluid will boil.

Anyhow, to return to my saga, the student maintained that a shop changed the brake fluid two weeks prior to the Summit event. Since this particular student is one of our Chapter Tech Workers, I think we can accept this statement as fact. I suggested that the student bleed the brakes prior to the next track session, and catch the expelled fluid for me to examine.

Most DOT 3 and DOT 4 brake fluids are clear to light amber in color when new. As the fluid ages and absorbs moisture, its color darkens. Year-old brake fluidhas typically darkened to the point where it is quite easy to view the fluid level through the translucent brake fluid reservoir. With fresh fluid, it can be hard to see the level, especially in an older reservoir which has darkened a bit itself. This is how we know to question the brake fluid change date you indicate on your driver school tech form: If we can easily see the level, the fluid may not be a fresh as it should be or as fresh as you think it is.

The fluid the student showed me was hardly new in appearance. In fact, it was in a clear, iced-tea bottle and an onlooker thought I was being offered a drink of tea! The inescapable conclusion was that whoever changed the brake fluid did not take enough time and expend enough fluid to do the job correctly. Since I treated this subject in some detail in the May, 1999 Philes' Forum, I won't repeat it now. If anyone is interested in a copy of that column, let me know.

This is the second time this season [the first precipitated the May column] that a student thought her/his brake fluid had been properly changed, but something had gone wrong. My suggestion is that you buy yourself an inexpensive [< $50] pressure bleeder such as an Ezi-Bleed [advertised in the Roundel] and do the job yourself. The only other tools you will need are a 7 mm combination wrench [which may be in your Bimmer's tool kit], your lug wrench, a torque wrench, and a jack stand. [If your don't already have a torque wrench, please resign from the NJ Chapter immediately.] Sure, it is easier and faster to do the job if you have a lift, or at least 4 jack stands, a floor jack, and an impact wrench, but you can do as good a job as anyone with only the tools I mention.

If you choose to have someone else do the job, I strongly recommend you explain exactly what you are paying for and expect to be done. [Heck, show 'em a copy of the May column if you have to.] Bleeding the brakes is not the same as changing the brake fluid. Perhaps we can do a demo of what I consider to be a proper brake fluid change at the October tech session at Camptown Tool and Die. Interested in volunteering yourself and your Bimmer? Let me know. I love to watch my friends work! We'll even supply the tools. We'll even try to get Big Al [AKA: TBA] to demonstrate how not to wash an engine! I promise we won't let ol' TBA near your Bimmer.

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 A PHONE NUMBER WHERE I CAN REACH YOU DURING THE DAY ON WEEKDAYS. Also, please be patient, I try to return every phone call, but it sometimes takes a while. If you don't hear back from me within a few days, please call again. The best way to contact me is via e-mail.

Copyright 1999 - V.M. Lucariello, PE