Braking problems
Turbo Mini Forums

Good morning!
As I've told in my introduction post, I've been building my race Mini for two years. Last weekend I raced it for first time. Everything went perfect but I had problems with brakes.

First, I'm going to list the components:

Minispares GMC227 yellow tag master cylinder with repair kit fitted as KAD told me. Motul RBF600 fluid. No servo.
- Front: KAD 4-pot vented calipers, 7,75" vented discs, C-STR987 carbometallic pads from Minispares.
- Rear: Minisport Minifin drums. No brake limit valve.
Everything is new.



The problem is sometimes the pedal is extremely soft and sometimes is hard, as I would like to be. It's not when hot or cold, it seems random.

After bleeding a lot of times, KAD told me to fit the master cylinder repair kit as some master cylinders are not in perfect condition when new. We bleed again, with Gunson Easybleed and with the traditional method.

The brake pedal is usually soft. Sometimes it goes harder after pressing it 5 or 6 times, but not always. Sometimes it's hard at first time.

If the problem appeared when hot, I would have thought about pads or fluid. But it appears when cold too.

I can't understand this situation so any suggestion will be appreciated.

I'm racing again in two weeks and I would like to finish the race because everyting is perfect except the brakes. Last race I only did 12 laps due to braking problems.

Many thanks and best regards from Barcelona!

Albert

Pd. sorry for my english. If you don't understand anything, I'll try to explain better.

If the pedal is always soft that would indicate air in the system, carefully check around all brake line joints, whilst getting somebody to press hard on the pedal, you might find a tiny weep of fluid coming from a joint, failing that take off the calipers and hold them so that the bleed nipple is at the absolute top and try again

I would say

strip and check the rear brakes, look for anything that might be sticking, and as a result puting the pedal at a different place in its stroke and changing the leverage so it feel's harder.

Also check the front wheel bearings and drive flanges for play, I have had the cheel bearing nut work loose so the disk can float about, push the pads back and put the pedal at the wrong point in the stroke.

bleed and re bleed, a tuiny bubble in the caliper can heat up expand and make the pedal soft, then cool be ok etc. It is worth proping the pedal down overninght with a peice of wood between the steering wheel and pedal. it seems this will force air past the seals.

I agree, rear pistons sticking is the most likely cause.

Also the yellow tag master cylinder alone has no real bias front to rear. As standard it had a proportioning valve. without this you will have too much rear bias. I'd suggest fitting a bias valve in the rear line.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph