Just attended my first autocross in the Mini - had an absolute BLAST. For sake of argument, I'm an "intermediate" autocross driver. My question is this: what might be the most obvious weak point in my braking setup? Read on for details and symptoms:

-Stock 2006 MCS with JCW tuning kit only - all else stock MCS suspension, etc.
-17x7.5 Rota RBs
-Achilles ATR Sport at 42 psi all around
-EBC Green stuff pads in front (bedded over ~1000 miles, after good, solid, pressure bleed w/ super blue)
-stock pads in rear
-stock rotors all around (the front rotors are in good condition, but unfortunately I didn't turn them with pad replacement ::providing hand for slap:: )
-DSC OFF

Now for the two main symptoms:

1) "soft" pedal feel and
2) not much bite at all - having to mash the pedal deep - followed by a feeling of "weak" straight-line braking, and the ABS kicking in more often than hoped.

Regarding the "soft" pedal feel - I've read others describe the green stuff pads as "soft" compared to stock, along with others saying that that it's:

a) normal and provides for good modulation
b) not normal, and is due to improper bedding or unturned rotors

Compared to other cars I've driven, it just "feels" like there's not much bite, and that the only good braking is happening at the last 20% of pedal travel. Of course, it's not much further after that when I feel that numb pulsing. Other "sporty/performance" cars I've driven seem to bite strong further up top.

Either way, I know the Achilles are economy tires (oddly, the few online reviews put them in spitting distance of the Hankook Ventus V12s), so feeling the ABS so much makes me wonder if the brakes are doing their job, and it's the tires that are not up to the task. Still, it doesn't explain the lack of bite in the brakes and the pedal travel. Maybe I'm just not used to it.

OR

I'm just coming in too hot on every turn. I'm kinda willing to accept this as an answer since I'm new to Minis, but I did a few laps with a more experienced driver, and received positive feedback on my execution. Let's just say I graduated from "braking too hard and too late" a long time ago.

Hope this post is digestible - thanks in advance for any feedback!

 

If you're getting to the ABS, tires are a good start, doing anything with the brakes really isn't going to do much--your brakes are only as good as your tires.. But I think you're going to need to upgrade the brakes too, once you get a more track friendly tire, the R53 stock brakes just don't hold up well on the track (some will disagree with it, but I see very few with stock brakes these days.).

 

First, soft pedal almost always means you need do another brake flush.
Start there, you should have a firm pedal at the top.
I don't have any experience with those pads, but reading the info on EBC's website, I'm going to assume they are as good or maybe a little better than stock brakes. I don't think it's possible to overdrive the brakes in an autocross.
Its possible the brake pads aren't making good contact with the discs as you mentioned those are worn. If there is a substantial lip around the edge of the disc, that may cause some of the problem. You shouldn't ever turn discs. They have a Min. Thickness measurement etched around the hat. if the wear surface is thinner than that measurement, get new discs, and a reminder that cheap discs tend to warp. These are BMW brakes and the general rule of thumb I've found owning BMW's and working on them is that you have to replace the discs every second set of pads.

It's not tires, otherwise you'd hit ABS sooner.

Lastly,I'm assuming you have a manual and not an Auto trans. If auto, thats your problem.

 

"It's not tires, otherwise you'd hit ABS sooner."

I'm thinking tires with little grip are going to stop rotating sooner under braking than sticky tires would. In any event the tires need to go anyway so I'd start there.

 

I've heard of that before - another bleed would be a snap, but just curious, conceptually speaking - how do repeated flushes affect pedal feel? Something about thoroughly expelling old fluid - and its tendency to compress more than fresh fluid?

Agreed on the rotors - I did intend the new pads (without new rotors) to be a stop gap before a full BBK upgrade, but I certainly don't want to be barking up the wrong tree, especially if it's an expensive one.

 

Yup. Less grip = earlier ABS activation.

 

"good braking is happening at the last 20% of pedal travel. Of course, it's not much further after that when I feel that numb pulsing."

If the tires were so bad, the ABS would be coming on earlier in the pedal travel, not the end of pedal travel.
Maybe this needs to be clarified. By last 20% of pedal travel, do you mean the pedal is going all the way to the floor? Or is the pedal only going halfway to the floor? That should help narrow it down.

 

Soft pedal is from small air bubbles in the fluid. What method are you using to bleed the brakes? I've always used a pressure bleeder attached to the reservoir. Getting all the air out is the key. Old fluid and new fluid have the same compression. Old fluid just has more water in it which lowers the boiling temperature and can also cause corrosion in the brake system if left in too long. 2 years is recommended interval. 1 year or less if you do lots of track events.

BBK adds more unsprung weight as well as rotational mass which makes your acceleration slower and handling decreased. If you are only doing autocross, then BBK is overkill. Racing brake fluid, racing brake pads, and stainless brake lines should be all you need to do for your brakes (along with new discs) until you've converted your car to a full race car and are closer to 300HP and are driving on larger faster race tracks for extended periods of time.

 

Yeah - I knew that would be kinda hard to explain quantitatively. The best I can describe is that it sure feels like the pedal is close to the floor. It also feels like pushing it any more wouldn't do any better, though.

It's not like under hard braking I'm thinking "Oh ---- there's no braking power.." it's more like, "Hmm these brakes aren't much good until I'm mashing them"

 

If that's the case, then the brake flush isn't necessary. I'm leaning more towards new discs. If you have to mash the brakes to get the ABS to kick in, then the tires are working also.
But as the others mentioned, once you get the brakes working well, you're going to find that the tires will be the weak link.

 

I used the pressure bleeder, and flushed through maybe 80-85% of the can of super blue. Being used to the 2-man method over the years, it was a joy to use. But like I said, I only flushed through enough to see the fluid go from light amber to blue, then a little more. Less than a can.

I'm familiar with BBK consequences - I know it would only be more critical for longer, faster road courses, repeated laps and hard braking, etc.

 

I've read about the microscopic goings-on with new pads on old rotors and such - what's your take on how new rotors and a good flush would affect bite?

 

Then much of comes down to the pads...poor modulation.
The OEM pads are generaly not well liked cause they have an on/off feel...
not sure about EBC greens, but MANY folks have moved onto the reds..better feel in the new pad mix.
The greens seems to have half the sites say ok for auto-x, half say NO. A few say one or two times a year, you need better....so I'm guessing the pads MIGHT be kinda a partial feel issue....Perhaps the rotor is on a second set of pads and is thin too? Tires are pretty low end, but you own them, so WHY not use them till they need to get swapped....
Bleed again....good DOT4 or a race fluid....will take MULTIPLE pumps to flush the old stuff.....
Not a trackie, but sounds like a couple things could be done to "elevate" the car from the DD to more of a track spec car...

 

Yeah, I remember reading the different opinions on EBC greens. Now with the rotors, they're not scored or damaged, but they are definitely on their 2nd set of pads. I don't think I clarified that well enough.

How would rotor thickness affect brake/pedal feel, if the rotor surface was hypothetically perfectly new and smooth?

 

new rotors are thicker...
So they hold more heat, and resist warping....
BUT more importantly if a rotor is UNDERSIZED, the caliper may have trouble gripping it...a caliper has limits on how much the "pucks" can move and push on the pads/caliper...
A worn rotor with a new pad is usually ok...but as the pads get thinner..and the rotor wears more...can be an issue....
The OEM rotors are soft, and the OEM pads chew them up thickness wise....the oem pads usually leave a ridge around the uncovered edge....
With aftermarket pads+ Rotors, folks can get 2 or sometimes MORE sets of pads, but with OEM, one pad to one rotor is not uncommon....That is why they SHOULD be measure BEFORE installing new pads on an old rotor....lets face it...sometimes you could trash a nice $45-80 pair of pads simple because you did not install a new pair of rotors, that can be had for $30+ each, (check AMAZON, free shipping or rock auto)so $60-75 pair if you look around (like centric Premium or slight better their 125 series...high carbon content). Sure you can spend 3x the amount on rotors if you want...but entry level, OEM equivalent or slightly better is fine.

 

^Yes, great info!

 

In the past I've only ever replaced pads and rotors at the same time, or put new pads on old rotors. So you're saying that pads that have been "trashed" on old rotors shouldn't be reused on new rotors... they are cheap enough, I suppose.

 

One thing: warped rotors are extremely, extremely uncommon. What most people call warped rotors is actually pad deposits.

I switch pads for street and track, but I use fresh pads on new rotors, force of habit, the pads and rotors are mates for life. You can use fresh pads on old rotors, the key is properly bedding them in, and that was the one thing I forgot to ask you: did you bed the pads in, and if so, how did you do it? Many people will gently sand rotors with a fine grit sandpaper if changing pad compounds, then bed the new pads in. If you use pads from the same family (i.e. carbotechs) you don't need to sand the rotors when going from a less aggressive to a more aggressive pad, but if you went from stock to the EBC's, it's not a bad idea to do a gentle sanding. You're better off with new rotors though.

I don't autocross though, and what I need from the brakes is different from autocross. I still maintain the stock R53 brakes just aren't that good, there is a reason that the R53 JCW brakes are the stock R56 brakes.....

 

Yes, I completed the EBC bedding process - no sanding on the old rotors, and no hard braking for ~500 miles. After that, two rounds of 5 hard stops, waiting for the brakes to cool between rounds.

Bleeding was using a pressure bleeder to get rid of all the old fluid.

 

Oh heck y'all let's pour a little water on this cat.

Can we admit there may be more than one problem here? Do we agree that the symptoms ARE indeed a problem? I'll bite on that one most certainly.

Given: the OEM system is damned good, as I've autocrossed on R53 and R56 stock brakes for ten years, and I've always had more brakes than traction despite running sticky street and DOT-R Hoosiers.

Given: It is fair to expect that hard braking can occur without depressing the pedal past more than 50% of the available travel, and that the pedal should be firm, predictable, and controllable. This I offer again due to first hand experience in competition, where I heel/toe into 1st once in a great while (and on the street always) and therefore rely utterly on the ability to not only control all available brakes but also to do so in the narrow band of pedal travel which allows my foot to also be at the correct height for the throttle.

Given: For autocross the BBK is not necessary, as the heat capacity of those systems is not essential for the two or three short hard dabs of brake in a sixty second course followed by 10-20 minutes of cooling time.

So what I am hearing is two problems:

(1) the pedal feel is not inspiring confidence, due to long travel before significant braking force occurs, and
(2) the car is traction limited, with ABS appearing when braking at the limit.

Do I make sense so far?

Just to go out of order, I reckon we'll agree that the remedy for (2) is better tires, and that better tires are the cheapest overall opportunity for improved autocross performance in most cars (excluding the driver of course).

So how about (1)?

Restating the problem, the OP doesn't find the brake feel to inspire confidence, and reports more travel before hard braking occurs than he expects, and also that modulation of the brakes is difficult.

So wise advisors we have postulated regarding rotor runout, pad compound, pad break-in, air in the system, the specification of the brake fluid, and implicitly driver technique.

Call me a cheap b*stard but I'd take all that good advice and sort it by cost, and go from there. What I reckon I'd do is to rule out the fluid/bleed quality factor first by ensuring that the brake fluid is OEM spec and bubble free.

If that makes no difference at all, then what we're left with is rotor runout (improbable as the pulse that is symptomatic is not reported), pad compound, pad break-in.

That's a bit of a crap shoot in my view, as the parts named are reportedly of good quality - if we assume the products are not causing the problem then only pad break-in remains. That means two next steps are possible: (1) keep the products but reinstall them, in the hope that better break-in will produce the desired outcome, or (2) go back to baseline with OEM gear, which should presumably restore acceptable performance.

Pardon my babbling on - I am congenitally interested in problems and you've caught me with a few minutes to spare.

Cheers,

Charlie

 

Wow! Succinct summary. I'm on board with using different tires. As far as pedal feel, I'm certain there's no air in the lines - and as I mentioned, the braking was predictable and reliable all day long - it just felt like 80% of the pedal travel was worthless. As far as modulation goes, however, I didn't have any problem getting the car to "do" what I wanted - in other words, no surprises while braking - but as Charlie astutely put it, the pedal travel didn't inspire confidence (again, separate from tire traction inducing the ABS).

I have a feeling I'm leaning towards a new pair of rotors as Zippy mentioned, along with redstuffs, and maybe stainless steel lines and stiffer caliper bushings to firm up the feel.

Thanks Charlie and racingbmwm3 for the expertise weighing in - it was a good sanity check, as I have no problem replacing parts - it's just nice to know what to expect. And seeing how heel-toe action does require the brake pedal to be fairly deep, it makes sense.

 

That narrows it down nicely. The only question I have is regarding what is happening when the pedal is depressed. There are two scenarios - one consistent with the pads not being close enough to the rotors at the beginning of the pedal stroke, and the other where initial contact occurs near the top of the pedal travel but the increase in braking force is not proportional as desired.

In the first case rotor run-out could be the culprit (although some pulse is almost evident in this case). Do the brakes appear to start working at the top of the pedal?

In the second case steel lines might help, although I had them on the R53 and not on my current R56 which actually has BETTER feel.

Temperature can be very important too, particularly with non OEM pads that may be optimized for road race conditions rather than autocross, but I observe that you experience consistent performance across all conditions so I tend to deprecate that one.

New rotors and pads seems like a worthwhile effort if the bedding in procedure is clearly defined and can be followed, but I'm stubbornly caught on the outstanding performance that has been my experience so stiffening the calipers strikes me as potentially unnecessary.

Do report back in time please, 'cause I'm curious now.

Cheers,

Charlie

 

Bleeding the system first makes sense. If there is air in the ABS, that's really going to screw it up (and be tough to get out--may require a trip to the dealer). But, I still think your tires are limiting you.

The other is EBC's bed in process is different than what most recommend--drive first for 500 miles and then bed in? Never done it that way before.

I agree with all of the above, except I still don't feel the R53 brakes are all that good. The R56 yes, but they're a notch above the R53 brakes. May be good enough for autocross, but they don't hold up on the track.

The other possibility, and I'd only look at it after all else has been done, is the master cylinder. What happens when you depress the brake at a standstill--how does it react?

 

Excellent question. With both street driving and autocross, it seems that the "initial contact" you mention occurs far from the top. You know when you drive a dealer loaner or a car rental that (hopefully) has fresh brakes all the time? You hit the pedal, and it almost takes you by surprise how little pedal travel is required to grab the discs (disclaimer: the average car rental probably doesn't provide desireable response in autocross ). So in my situation, it definitely feels like the first scenario (although without the pulsing symptom). There is visible lip on the rotor - I can only assume (without pulling out my micrometer) that based on the recent records I have from the previous owner, the rotors are well beyond spec.

Any other feedback on caliper stiffening would be appreciated. I have heard that there's a noticeable difference, but then again, I don't want to solve the wrong problem.

 

The car's definitely not exhibiting any symptoms of a failing master cylinder.