Hello,

I just got back from a track weekend yesterday and had a horrible time trying to get the brakes to work. The pedal was spongy and when I could pump it up a bit going into the braking zone I would have to stand on it in order to slow down the car even a little. After I went off in turn one because I couldn't slow down I went into the pits and pretty much ended my weekend.

I bled them several times. When this didn't work, I took the car to Viper, the shop in the VIR paddock, to have them bleed the brakes. There was no air in the lines or ABS and the feel did not improve. I have not noticed any fluid drop in the resevoir and there were no leaks found after a thorough visual inspection. After some thinking, both the chief mechanic and I concluded that the master cylinder was to blame.

Any thoughts? The car has 41,000 miles and has been tracked several times in the last year and a half. Thanks to anyone who can offer some advice.

Nick

 

What pads are you running? Stock calipers? Have your other track days been on VIR also or on other tracks? Which VIR course were you running? Have your other track days been at similar ambient temperatures, or cooler temps?

When you say "spongy" - does the pedal eventually stop when you stomp on it, or does it slowly continue to move to the floor?

How did the Viper shop bleed the ABS? I assume they have an appropriate BMW/MINI scan tool to do it?

 

1. Run the car at idle, and not moving
2. Pump up a good pedal on the the brakes
3. Does the pedal bleed back down after a very short amount of time, like in a couple of seconds? If so, this is a classic symptom of a Master Cylinder leaking internally.

 

I am running Hawk HPS pads on JCW calipers. I have driven the full course at VIR often and have driven when the ambient temperature was much warmer. The pedal does slowly move to the floor but at the same time I really cannot pump up the pedal to a "good" feel. My car has never really had a firm pedal like other cars i've driven. Usually if it's brake fade there's still a little stopping power left at the bottom end of the brake pedal travel. Now even when the car is cool I struggle to get it slowed down from 30 and the pedal does slowly reach the floor.

The Viper shop bled the ABS by:
1. pumping up the bleeder system to about 25 psi instead of the normal sub 15 psi.
2. cycling the ABS by doing a few hard stops in the gravel in the paddock and then returning to the shop to do another round of bleeds.

Viper is not equipped with the Mini service department's ABS pump cycling tool.

 

Gotcha. With that setup, you should have no problems (duh - you knew that).

I think I have similar pedal feel that you are having - like yours, my car has never had the "short throw, hard pedal" that some MINI owners brag about. I can't decide if it's getting worse over time or not. I'm close to swapping my master cylinder just to see if that makes a difference... I *think* mine will do the slow push down to the floor over time - tried it today, but it's so slow it's hard to tell if it's behaving as it should without another MINI for comparison.

That bleed approach probably will clear the ABS... though I'm not completely convinced that it will. The fluid (and any accompanying bubbles) doesn't move very far through the system during a pedal push in a sealed system... I'm not convinced that just making the abs activate will actually get all the air out of the ABS. Personally, I bought AutoEnginuity so I could do this. But that's overkill for most sane folks.

 

To be a little more clear on the pedal bleed down thingie.....

At the dealership now and just spoke with the tech on my mushy pedal and extended pedal travel with the bleed down after pumping a good pedal. He informs that it is is normal and we checked a few other MINIs on the lot for my satisfaction. The story is that some bleed down is normal and an artifact of the ABS. Specifically on the the pedal feel, it does stop some distance from the floor, if however, the pedal keeps going all the way to the floor....then it is the classic leaking Master, but it has to go all the way to the floor.

So, I am not getting a new master cylinder today, and I am stuck with a pedal that in my view, is mushy. Grrrr! I want that good high and hard pedal too, damnit!

 

Well, at least misery has company.

 

IMO, those are the results I would expect with Hawk HPS. Not really a track pad, far from it.

I faded those coming out of the driveway in my old Subaru and the brake feel was lacking.

- Andrew

 

OP - have you inspected the pads? Are they glazed? And visible deposits on the rotors?

 

I made a point to take the pads off and scuff them up in the paddock. No change.

andyroo, I do find it strange that this happened when I put the hawk pads on. However, the pedal is definitely mushy and I can't engage the ABS no matter what temperature the pads are. I don't think it's the pads.

Thankfully this is happening at the exact time the race car build is finishing up