Hello all,
Recently I noticed by brake pedal getting a little soft, but nothing too strange. I just thought that maybe the pads were getting low (my first time replacing them) or maybe some air was in the brake lines, making the pedal feel soft. So I buy EBC GreenStuffs and some ATE Super blue fluid to change everything out. Did the swap, used the Harbor freight tool to change the rear pads, and everything went smoothly. I had the wife pump the pedal while I bled the brakes.. again no problems. However after I seat the pads according to EBC's instructions and put about 300 miles on the car, the pedal feels worse. Now it actually feels like the pedal is bleeding down when I hold pressure on the pedal, and to brake quickly I need to pump the pedal one time (not safe). In my past experience with BMW's I would first assume that the master cylinder is worn, or at least the seal around the piston inside the master cylinder. I'm 99.9% sure that this is the case, but I wanted to see if there was something particular to MINI's that I may be overlooking before I purchased a new Master Cylinder?
Any advice is greatly appreciated!
Thanks in advance
Josh

 

It could be the master cylinder, but before paying for that I'd try bleeding the brakes another time or two. It can be hard to get ALL of the air out.

Scott
90SM

 

If you allowed any air to get in by way of the reservior into the system then it could be air trapped in the ABS/DSC module. If thats the case then it takes pressure bleeding by a brake shop or dealership.

 

Check to make sure that on the rear pads the tension spring is in the piston slot. Sometimes they wiggle out when you put the caliper back on and you think its on there. Happened to me....

 

So your saying that you replaced the pads, bleed the system, everything felt ok and has gradually gotten worse? Air is air, if it is in the system and never was bleed out the pedal would have never felt ok, no matter where it is trapped at. I agree with you on your initial diagnosis of the Master Cylinder.

 

Well actually the brake pedal started feeling a little soft, this is what prompted me to replace the pads and bleed the system. I didn't really expect the pad-change to do much, but the pads were close to needing replacement, so while I was in there...

Anyhow I did change the pads, and I did bleed the system, and afterward the pedal feels a little more spongy.

Even this past weekend I bled the system again, and the pedal feels a little better, but the pedal still bleeds down (when I hold pressure on the brake pedal, the pedal will VERY slowly loosen and move toward the floor. Actually if I pump the pedal a few times it will get pretty hard. If I sit there and hold pressure on it, I will feel the resistance lessen in the pedal. Hope that makes sense. I'm no noob to brakes, I'm fairly certain that the master cylinder is the issue, but I just wanted to make sure that no one else knew of something special that ONLY pertained to MINI's.

Thanks for the advice!

 

You shouldn't have had air in the system in the first place, unless the system was opened. That said, air is extremely difficult to get out of the system. Even with the aid of a pressure bleeder, I have had to go around bleeders on the car multiple times.

 

I wouldn't be so fast with the master cylinder. I've had a similar problem with our race car. Pressure bled the system and had a firm pedal. But out on the track the pedal would go down to the floor. Replaced the master cylinder. Pressure bleed the system. and also pumped bleed the system. Firm pedal. But out on the track the pedal would also go to the floor.

We have not found the solution yet. But with the engine off The brakes are firm/hard and no loss of pedal.

But with the engine on and the brake booster is working the pedal almost goes to the floor. We think it might a vacuum leak. Or air in the ABS unit that we have not been able to remove. We have not hooked up to the service test equipment, but when the dealer does brake bleed the ABS unit it is cycled and you can hear the ABS working. This also might be part of the problem.

Are your brakes firm/hard with the engine off?
Does the pedal feel soft after the engine is turned on?

 

I am not an expert or officially a mechanic ...
but
When I bleed I turn the key on and if you have an assistant it is the gool ol pump 3 times and, hold , bleed.

WITH THE KEY ON
If you stomp on the pedal the ABS will cycle ... you can hear it.
not high tech but I have never had any issues bleeding ... and ALWAYS change the color fluid ..

So I do a bleed on all brakes, then a stomp bleed on all corners . then one more bleed.
This takes almost 2 quarts of fluid. to flush and bleed

 

Chad, don't act like you know everything.......


I'd start by doing a rebleed. Maybe with a new brake person. When bleeding i only use two words, UP and DOWN and the pedal person repeats when either task is complete. That way there is no miscommunication. If you have access to a good code reader (GT1ish) you can get it to activate the ABS module for you to get any possible air out of the ABS unit. I really only think this is a need to do if you know you bleed your fluid tank dry or you replaced the ABS unit. I think a rebleed is a cheaper option than master replacement.

p.s. i don't recommend stopping on anything in the car, throttle included.

 

What about cockroaches?

 

Depends on which floor mats you have:

All weather = stomp away

Carpet = High power vac

 

i'd say clean more often and tell the cockroaches to find they are not welcome.

 

What dot level was the brake fluid you put in?

 

dot 4 i hope

 

I definitely don't know everything.....and I definitely won't put a gurantee on a diagnosis over the net. At least not on this, hell I've even been wrong when working on a car first hand before, if you can believe that. What I did do was agree with his diagnosis based on HIS input.