9 replies to this topic

[farres_jr]

Hi!

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.

Edited by farres_jr, 20 April 2014 - 05:32 PM.

[bmtt4]

A friend who races a hillclimb mini had issues with a long/soft pedal which was traced to new alloy drive flanges, one had a slight out of balance/warp which was knocking the pad back into the calliper.  he found that the first pedal press was going long but the next press was giving a firm pedal.  

 

This may not be your issue but could be worth looking at as you seem to have ruled out a lot of the hydraulics.

[farres_jr]

A friend who races a hillclimb mini had issues with a long/soft pedal which was traced to new alloy drive flanges, one had a slight out of balance/warp which was knocking the pad back into the calliper.  he found that the first pedal press was going long but the next press was giving a firm pedal.  

 

This may not be your issue but could be worth looking at as you seem to have ruled out a lot of the hydraulics.

 

Thanks! We'll take a look ;)

 

Any more opinions?

[Captain Mainwaring]

Wheel bearings - end float in the hub.

[farres_jr]

Wheel bearings - end float in the hub.

 

Many thanks for the answer! How can I check/fix it?

[Captain Mainwaring]

Pop the wheel off - check for run out at the disk, give it a few turns and see what a DTI tells you, also pop a pinch bar in and see what gives.

[Captain Mainwaring]

Alternatively jack the car up (safely) - stick it in gear and let it run a bit, see what you can slide between pad and disk, though this may not be enough it there is a bit of end float on the bearings, you may need dynamic loads too.

[farres_jr]

Pop the wheel off - check for run out at the disk, give it a few turns and see what a DTI tells you, also pop a pinch bar in and see what gives.

 

 

Alternatively jack the car up (safely) - stick it in gear and let it run a bit, see what you can slide between pad and disk, though this may not be enough it there is a bit of end float on the bearings, you may need dynamic loads too.

 

Thanks!!! I'll try this week :)

[Lowlight]

I had a similar sort of thing in my Land Rover, the pedal was soft on first press then got better if you pressed it again until it felt fine. Turned out a piston seal wasn't seating right so the first push was pushing the piston in to the right place making the second push feel better.

 

Sounds like your problem is a bit more random; are there any high points in the system where an air bubble could be sitting?

[farres_jr]

I had a similar sort of thing in my Land Rover, the pedal was soft on first press then got better if you pressed it again until it felt fine. Turned out a piston seal wasn't seating right so the first push was pushing the piston in to the right place making the second push feel better.

 

Sounds like your problem is a bit more random; are there any high points in the system where an air bubble could be sitting?

 

Thanks! No, there are no high points. We removed the servo to avoid the only high point I had. We'll check piston seals...