Too Much Brake Pedal Travel

[Keith1998M3]

My 1998 M-3 brake pedal has too much travel and is spongy. I installed big disks with 4 piston calipers (UUC). Otherwise the car is mostly stock. I understand that a larger bore master cyclinder would shorten the pedal travel and make the pedal firmer to pressure. Is there another BMW model that uses a larger bore master cyclinder that can be easily swapped with the M-3? Are there other non-BMW master cyclinders available that will do the job? What should I expect to pay for this parts conversion? Any sage advice will be greatly appreciated.

[SMOODY]

I would think that the standard master cylinder should still produce a firm pedal feel. Have you ruled out the following as possible causes?

Did you throughly bleed the system after the installation of the new calipers and that there is no air in the lines or in the master cylinder? Even a small bit of air can make the pedal spongy. Depending on the amount of air that entered the lines during the caliper install, it could take multiple bleeds of the system to remove all of the air.

Are the brakes spongy all of the time or only during spirited driving? If only during spirited driving, you may have some water contamination and the fluid is boiling. If so, bleed the system with a high quality fluid like ATE Super Blue.

Do you have stainless steel brake lines installed? They can help to reduce the sponginess of the brake pedal.

How many miles are on the car? Perhaps the current master cylinder has developed a leak and just needs replaced.

[Keith1998M3]

The big brakes came with stainless steel lines which I installed. I use Siuper Blue brake fluid. The pedal travel was immediately excessive and soft after installation. This does not feel like gradual wear on the master. I bled the lines at the time of installation and then, for good measure, had a BMW mechanic flush the system on two separate occasions about a month apart. This does not seem like an air problem. In fact, it was the BMW mechanic who told me he had had a similar problem and suggested a larger master.

[mlytle]

did you try calling uuc and asking the place you got the bbk from? if it is a symptom of the kit you wouldn't be the first with the problem......

[Keith1998M3]

Yes, I checked with the supplier (UCC). They said this is a known problem with their big brakes that can be fixed with a larger master cyclinder but they have not been able to recommend a stock BMW substitute.

[SMOODY]

Does UCC have ANY (not just BMW stock) recommendations for a larger master cylinder or do they just tell you what the cure is and leave it up to you to find a replacement?

I am surprised that a larger master cylinder is needed. Usually the upgrade kits are designed to work with the stock master cylinder with no change in brake pedal feel.

This may be the kind of question that you need to pose to the gurus at Roundel. I think that they can be reached at questions@bmwcca.org

[SMOODY]

Did you ever get any recommendations?

Just curious.

I also checked the e-mail address I gave for BMW CCA. It should have been techtalk@bmwcca.org

[Keith1998M3]

Thanks for the suggestion to check with Rondel's Tech Talk guru (Mike Miller). He was very prompt to respond to more than one e-mail and gave good advice. He suggested that, when the calipers are changed, there may be such a large quantity of air in the system that a simple bleed with not clear it. He suggest that the ABS valves needed to be cycled to clear the air from them system and that only an authorized BMW dealer is likely to have the computer necessary to do this. This would explain why the pedal was still soft, even after bleeding the brakes 4 times. I had the dealer bleed them and voila, it seems to have worked. The pedal is firm and does not seem to soften, even after several lapping sessions at the track. It seems I do not need a larger master cyclinder and am much happier with my big UUC brakes.

[SMOODY]

Thanks for the follow up. I am glad to hear that everything worked out for you and the gurus at Roundel were able to point you in the right direction.