tires and wheels I need some help with my brakes.

[Matt_P]

I haven't posted in a while, but I need some help with my brakes. My brake system is 100% stock.

What I replaced while restoring the car, or immediately before:

Hard brake lines, flexible lines with braided stainless, rear wheel cylinders, calipers, master cylinder. Drums and shoes were not replaced but had a lot of material left.

After reassembling the car, it drives great and the brakes work as they should. I can lock up the tires just fine.

Here's where the problems start. I take the 2002 to a BMWCCA 'autocross' at the BMW Performance Center, which actually is fairly hard on the brakes due to a drag race start that involves hitting 60 - 65 mph right before a 20 mph corner, and one other hard braking zone. The M cars were well into 3rd gear at the start, and I was redlining 2nd with my 4 speed and 3.64 rear. We get six runs (two sessions of three runs) and my brakes are faded into uselessness halfway through the 2nd run of both sessions. I locked up my rear wheels during a few runs despite the brake fade. On the way home, the car exhibits all the symptoms of a car that has overheated its brakes. They feel awful, with a soft pedal, bad initial bite, reduced stopping power. I had been running the no-name pads that came in the calipers, so that seemed like par for the course.

Due to the brake fade, I order some Carbotech Bobcats and get the rotors turned. I remove the front splash/dust shields for better cooling, as well as bleed the system and adjust the rear brakes. I bed the brakes in according to the Carbotech instructions, and let them cool completely.

When I drive the car after that, the brakes are TERRIBLE. I can't lock up any of the wheels, and can barely stop the car. After half of the pedal travel, there's not any additional braking force. I ask Matt at Carbotech if it is possible I glazed the pads while bedding them. He suggests I drive the car like that, if they're glazed they will get better with wear. 150 - 200 miles later, taking care not to overheat the brakes, there is no improvement. I scuff the pads and rotors with some emery cloth, which changes nothing. I try a different set of brake pads (a set of OEM Textars): No change.

At this point, I decide to replace the master cylinder, since it feels somewhat like a bad one, and the one I had did sit a while while restoring the rest of the car. There is no appreciable change after doing this.

I decide I've had enough of throwing parts at the problem, so I take it to a mechanic I trust that knows 2002s well. He thinks it is a brake booster problem, even though the booster holds a vacuum just fine. Specifically, he thinks it is a problem with the linkage inside the booster. I get another used booster, which holds vacuum and doesn't have any problem with the linkage, he installs it, bleeds and adjusts the brakes. Still no change. He mentions the rear shoes and drums look worn.

Hoping to drive the car to Eurofest and participate in the autocross, I pick the car back up the day before and replace the existing calipers with some rebuilt ones. Unfortunately this does not fix the problem.

Seeing as they're the only old parts left, I replace the drums, shoes, and parking brake cables, bleed the system, and adjust the rear brakes. Braking feels slightly better, but I still can't lock up any tires with the brake pedal. I can easily lock the rear tires using the handbrake.

That's where I'm at now, and I'm running out of ideas. At no point has the fluid level in the reservoir dropped, and I don't see any leaks. I plan to check inside the dust boots of the wheel cylinders for leaks, though I did not notice any fluid while changing the rear brakes.

Do any of you have any suggestions on what the problem might be?

[CJ_AZ]

My humble opinion:

It sounds like you boiled the fluid over. Try upgrading your brake fluid to a higher temp racing fluid and see if that helps. I had to do that when tracking my e36 - and also found out after going to SS lines and vented rotors. You can also look at cooling ducts for the front calipers to shave a few more degrees.

Also, get a pressure bleeder if you don't already have one.

HTH,

[Matt_P]

I use the Valvoline synthetic fluid (dry boiling point 500°), and have bled several gallons of fresh fluid through the system while troubleshooting this problem. While I probably boiled the fluid at the autocross, that does not explain my current problems I am having. I do have a pressure bleeder and have bled the system with that, and also with the old-fashioned method.

[jetboy]

damn. thats a tough one.

I assume you adjusted the lever arm going into the master cylinder? sorry I am at work and usually work on alfa romeo's and havn''t looked at this on an 02 - but it sounds to me - if it was an alfa, that your lever arm - part of the linkage form the pedal to the master cylinder has lost its adjustment, thus stomping on the pedal is only giving you a percentage- maybe 50% of what you think you should be getting.

this linkage can get torqued after hard use -

[Guest Anonymous]

I don't know if you mean synthetic to be silicone but if it is that is your problem. It doesn't compress as well as a stardard brake fluid hence your inability to lock them up. Just a thought...steve

[MatthewCervi]

That Valvoline synthetic isn't silicone. I've used it before and it works fine.

What about the rotors? Since they were turned are they still in spec?

Also, and I know it is extremely unlikely with SS braided lines, but is it possible that one of your lines has an aneurysm and is bulging out when you apply the brakes?

[Pastellbrent]

You may have a pushrod lenght issue. Because it was bent or the new master has a deeper hole, the booster is a little different, something like that.

I have personally seen SS brake lines that leak. The only way I would have known is that there was ATE Super Blue Fluid in the system which colored inside the clear cover.

The overall problem you describe is that of glazed brakes. If you have hardened and polished the rotors with heat there may be no saving them. This would have been evident when they were turned.

One thing I would try so that you can be sure that there is nothing in the lines acting as a brake bias valve keeping pressure off of the fronts. Take the lines off of the master and caliper and blow with shop air, do the same with the wheel cylinders.

I hope you get there.

Brent

[Matt_P]

You may have a pushrod lenght issue. Because it was bent or the new master has a deeper hole, the booster is a little different, something like that.

This, combined with the linkage note above is what I'm leaning toward. I know that the linkage is adjusted so that the pushrod engages the master cylinder at the beginning of the stroke, but it occurs to me that I don't know if it performs its full stroke (the bell crank at the top of the linkage could be slightly out of position, and the yoke on the back of the booster adjusted to account for this).

I don't think it's a kinked line or leaking flexible line, since the car doesn't pull at all under braking. That said, I will be checking all these things.

[Matt_P]

The overall problem you describe is that of glazed brakes. If you have hardened and polished the rotors with heat there may be no saving them. This would have been evident when they were turned.

I guess I should try new rotors as well, though I would be surprised at this point if they were the culprit. Is there any way to tell a glazed rotor visually?

[scottt]

Have you tried a set of stock brake pads ? I'm not familiar with Carbotech, but many track pad compounds need to be very warm before they develop a decent coefficient of friction. They may not be suitable for the street as those temps are rarely achieved.

[Matt_P]

Have you tried a set of stock brake pads ? I'm not familiar with Carbotech, but many track pad compounds need to be very warm before they develop a decent coefficient of friction. They may not be suitable for the street as those temps are rarely achieved.

Yes, I tried a set of Textar pads. Also, the Bobcat is Carbotech's performance street compound.

[c.d.iesel]

after all that..................

bottom lines:

replace the marginal rear drums and shoes .

max metal on the drum and max thickness on the shoes is key to rear drum performance - not - 'just ok stuff'

replace the front rotors and just use BMW JURID or TEXTAR brake pads.

Your Done. CUTTINGYOUR FRONT DISKS WAS A DEATH BLOW-

new thick metal rotors and thick new pads will shed heat and provide better stopping power than skinny rottors. Getting my picture?

new parts - especially if you expect the car to preform close to

it's new condition.

and your driving style has an effect on your brake performance - you might need to alter your technique abit.

[Lee]

Hi Matt.

After all I read, I still suspect some bubbles left in the brake system. How thoroughly has it been bled? How much fluid have you spent on the bleeding process (you could waste 2 quarts before you are satisfied). What method have you used?

First, have a friend push the brake pedal in repetition without stopping, while another continuously fills up the reservoir. This will equal to bench bleeding. Repeat for each corner. When you have such a problem, do not be shy to waste cheap fluid until you are satisfied with the pedal feel. Then pour the good stuff until it replaces the cheap one. Pump, pump pump. Do not be shy. I suspect you have bubbles everywhere.

Then, my next question is: is the ebrake adjusted to perfection?

Start by the basics. Then if nothing works, you can blame the rods and levers. And despite what people say, starting from the corner the further away means and does nothing, except if you want to save fluid Which is not your worst problem now. Pump. Pump. Pump.

[Matt_P]

after all that..................

bottom lines:

replace the marginal rear drums and shoes .

max metal on the drum and max thickness on the shoes is key to rear drum performance - not - 'just ok stuff'

Already done. It didn't fix the problem.

replace the front rotors and just use BMW JURID or TEXTAR brake pads.

Your Done. CUTTINGYOUR FRONT DISKS WAS A DEATH BLOW-

new thick metal rotors and thick new pads will shed heat and provide better stopping power than skinny rottors. Getting my picture?

new parts - especially if you expect the car to preform close to

it's new condition.

As mentioned above I have tried the TEXTAR pads, and I know heat is currently not an issue, as I am not overheating the brakes while backing down the driveway. The current problem is present even from a cold start.

I am going to try a new set of rotors, should I find nothing wrong with the linkage.

[Matt_P]

Hi Matt.

After all I read, I still suspect some bubbles left in the brake system. How thoroughly has it been bled? How much fluid have you spent on the bleeding process (you could waste 2 quarts before you are satisfied). What method have you used?

Very thoroughly, I have run as much as 2.5 liters through the system while bleeding it. I have used both a pressure bleeder and the pedal pumping method.

First, have a friend push the brake pedal in repetition without stopping, while another continuously fills up the reservoir. This will equal to bench bleeding. Repeat for each corner. When you have such a problem, do not be shy to waste cheap fluid until you are satisfied with the pedal feel. Then pour the good stuff until it replaces the cheap one. Pump, pump pump. Do not be shy. I suspect you have bubbles everywhere.

I really wish this was the answer, but I have bled the brakes at least 10 times while troubleshooting this problem, usually using about a liter of fluid, but sometimes as much as 2.5L until I was confident that there was no air left. I usually go around to all the wheels two or three times.

Then, my next question is: is the ebrake adjusted to perfection?

Start by the basics. Then if nothing works, you can blame the rods and levers. And despite what people say, starting from the corner the further away means and does nothing, except if you want to save fluid Which is not your worst problem now. Pump. Pump. Pump.

Emergency brake is adjusted as specified in the manual. Even when setting it to one or two clicks up, the brake feel is not improved and stopping power is still compromised.