I had already attempted to bleed the master cylinder while still mounted in the car, by jacking up the rear car to level out the cylinder.  While this should have worked in theory, the pedal remained limp.  So I did it the correct way this time, completely removing the cylinder from the car and bench bleeding it.  I used a master bleed kit from NAPA, which comes with several different size ports to bleed a wide variety of domestic and foreign cars.  I actually purchased two of these kits, as the M Coupe’s master cylinder has three ports that must be bled, a product of its DSC and ABS setup.

Bench Bleed Master Bottom Bench Bleed Master

So bench bleeding complete, back in the master cylinder goes.  NOTE: Always lube the o-ring that creates the seal between the vacuum booster and master cylinder.  I failed to do this on my Spyder once, and I ended up wasting money on a brand new booster when is was just a dried up $2 o-ring.  With the lines disconnected, then reconnected, air is destined to be introduced into the lines, and worse, into the labyrinth that is the ABS manifold.  The only way to truly bleed these modern systems is to electrically actuate the various pumps, valves, and corresponding solenoids.  The dealer would normally do this with a very expensive proprietary computer system.  Fortunately for us mere mortals, some very smart tinkers have cracked the code and versions of this software are available online and via eBay.  I have just such a device, which runs on a $100 used Dell laptop I also found on eBay.  The program, called GT1, allows me to bleed (ventilate in BMW parlance) the system.  The system must also be pressurized in order to properly do this, which a Motive pressure bleeder does nicely.

GT1 Bleeding Program Pressure Bleeding Brakes

Rather than waste even more money on expensive brakes fluids (thus far I’ve ran through gallons of ATE, Motul, and Brembo LCF), I just picked up several liters of AutoZone brand fluid.  I would use the cheap stuff to just flush out and bleed the system, until I had a solid pedal.  I ran through the routine as I normally would, nothing out of the ordinary.  I was getting a decently solid pedal, that is until I cranked the engine and had vacuum assist.  At that point the pedal would begin to get softer, softer with every additional full-throw pedal engagement.  I was stumped.  I quickly inspected everything, but nothing jumped out at me.  I did, however, notice my PFC Z pads were getting rather thin.  They weren’t yet to the point where replacement was absolutely necessary, but I was concerned, given I had the Race School and a track weekend at COTA coming up.  So I decided to pull the pads, perhaps this would solve my pedal issue (though physics says otherwise.)

The results weren’t comforting.  The pads were all cracked right down the center, all of them.  This could have been any number of things, I’m no brake pad expert.  I suspect that they simply were over-used, given that the Z pads are intended for performance street driving, and I was using them very hard at some fairly quick tracks.

Cracked Pads Up Close Cracked Pads

Fortunately half my house has become a bit of a BMW/Toyota/Nissan parts store, and I had a set ofPFC 08 pads.  See, the E36 M3 using exactly the same brakes as the M Coupe, or rather the M Coupe uses E36 M3 brakes.  I had purchased the 08 compound pads for my M3, as they are PFC‘s new endurance race compound, making them great for DEs.  I also had a set of Bimmerworld’s titanium backing plates.  These thin metal pieces are shaped just like the pads and go between the piston and the pad.  Titanium doesn’t transmit heat nearly as much as steel, definitely not as much as aluminum, so it makes for a great shield against pad/rotor heat destroying dust boots, piston seals, and boiling the brake fluid.  In order to install them, the spring clip which fits into the piston must be removed.  This clip isn’t necessary for the brakes to function, it just reduces the likelihood of the brakes rattling or squealing.  The clip is simply riveted into the back of the pad, and can be pried out easily.

New and Old Pads New vs Old Pads

Clip Installed Clip Removed

The new pads were installed and everything torqued back down, just like I’ve done probably a hundred times.  I did another bleed, checked the pedal, cranked the engine, checked the pedal again…. still soft.  I was about to give up, but logic was saying that it couldn’t be air in the system, that fluid had to be leaking somewhere.  So I went around to every caliper, cleaning everything with brake cleaner, and allowing it to dry.  I then cranked the engine and pumped the brakes again.  I went around with a flashlight and closely inspected every line, connector, fitting, and of course the calipers for leaks.  That’s when I noticed that a couple of the bleed valves were wet with brake fluid.  Not only that, but there was a little wet spot directly across from the nipple on the inside of the fender liners on the back right and front right.  I cleaned everything meticulously again, then tried the brakes with the engine running another time.  I got out and inspected again, sure enough, wet with fluid.  Not a lot of fluid mind you, but then again it doesn’t take much when you consider just how little the pads are moving.

I tightened the two culprit bleed valves (aka bleed screws, aka bleed nipples) just a smidgen more, just in case they weren’t completely seated.  Then I tried the whole effort again, only to discover it was still a soft pedal and I still had fluid weeping from the valves.  About then is when I remembered that I had installed Speed Bleeder valves on this car (as I had on most of my cars.)  The Speed Bleeder is a simple idea, incorporating a check valve into the bleeder, so that air can not enter the system.  This should allow for easy one-man bleeding, as you can open the valves and just pump.  I decided to remove the two valves and replace them with a new set of Speed Bleeders I had on hand.  Sure enough, both valves were deformed, crushed at their tips.  Strange, as I only ever use a small (well what other kind of 8mm wrench is there) wrench to tighten the valves closed.  I was just about to begin the entire bleeding process over when my pessimism took over.  What if the other two remaining valves were similarly damaged?  Better to find out now than at the track, so I backed the other valves out; sure enough, crushed just like the others.

Speed Bleeder PackagingDeformed Speed Bleeders

I decided to do a little experiment, to see if it was me over-tightening them, or just a weak design (well really both.)  I installed four brand new Speed Bleeders, lightly tightening each of them.  Then I pressurized the system.  I pumped the brakes a bit, checked each valve for leaking, and leaking I found.  So I tightened them a bit more and repeat.  I did this a few times until I couldn’t see any more leakage.  At that point I backed all the bleed screws back out and inspected them.  As I suspected, each was slightly deformed.  Not nearly as badly crushed as the originals, but still deformed.  Not too confidence inspiring given that these were fresh out of the package.  That was it for Speed Bleeders, time to go back to the tried and true plain old bleeder valves.

I purchased a new set (plus spares) of bleed valves.  I didn’t go with the BMW OEM valves, as they use a rather small 7mm hex, which is easily rounded.  I used some Dorman valves in the same taper, pitch, and size as stock, but with an 8mm hex.  I added some brake thread sealant, which must be baked on at 200F for about ten minutes. New Bleed ValvesWith everything back together, I went back to bleeding.  Full of hope, I cranked the engine and pushed the brake pedal; Success!!  The pedal feel that I so longed for was finally restored.  The pedal remained solid, allowing for much easier heel-toe shifting.  The following weekend I was able to put the brakes through their paces at TWS during the Club Racing School, and they performed flawlessly.  Sure the new 08 pads squealed a bit, but the feel was so much better, it truly transformed the drive.  I could brake deeper, more consistently, with much more confidence.  I didn’t experience any fade the whole weekend, the first time I wasn’t on my back between sessions bleeding the brakes.  This just goes to show that sometimes it’s the simplest of things than can create the biggest and most complicated of issues.  I should have started with the simple to fix items when I began troubleshooting months ago, I would have saved myself a lot of time, headache, and especially money blown in brake fluid.  Let this be a lesson to others, you’re often better off sticking with OEM, especially when dealing with bleed valves!

Chad Morehead has an excellent blog on track day driving and tinkering.  This is reprinted with his permission.  

Visit his blog at www.eatsleeptinker.com