Brake pedal too soft!!

[Olly P]

Did a session at the ScoobyZone trackday at Castle Combe, and 2 corners in, the brake pedal went to the floor.
Its got new Mintex 1155's on the front, new standard pads at the rear.
Black diamond grooved discs (on their second set of pads)on the front and standard Subaru discs on the rear.
Goddrich braided hoses all round.
Home made master cylinder stopper. (not ideal but its better than nothing.)
The fluid was completey changed after a track day at Keevil about 3 weeks prior to this. (brakes were vague and soft at best, was being outbraked by everything)
I've done the searches and checked what people have suggested:
The calipers are the right way up.
The wheel bearings are fine.
The hub nuts are done up.
No particular bedding in method (never needed it before) probably did about 300miles on the new pads before the SZ trackday at Castle Combe.
Have bled them again this morning.....no change to the amount of pedal travel.

What could have happened at Combe to make the pedal go to the floor?
And is there anything I can do about the amount of travel on the pedal?
Cheers in advance.
Olly

[Broxi]

Possibly the seals in one of the calipers or the Master Cylinder.

if you get all 4 wheels off the ground, engine running and have some-ones foot on the brake, try turning the wheels, see if any of them will move, you might have to use a wheel wrench on one of the nuts, to get even pressure, if one turns or turns easier than the others check its seals.

other than that, id check the seals in the Master Cylinder.

I had a similar problem on a Cavalier, turned out to be a seal in the caliper.
did not seem to be any leak, but one wheel would turn a bit with the wheel wrench on it the other would not. I bought a caliper repair kit changed the seals Bled the Brakes and peddal was solid yet again.

Derek

[Olly P]

Thanks Derek, I'll try that.
How would I check the master cylinder seals?

What happens when the seal on the caliper goes?
I thought it just allowed crap into the piston which would eventually seize.
Are you saying that the seal is leaking fluid or what?

[Agent Smith]

what fluid you using??

could be that causing the prob........sounds to me like its boiled.....then again moisture may have got in the fluid container...

[bob]

Would not say the fluid boiled...As the pads were smoking the answer lies there...Soft peddle usuall = air in system or brake fade due to overheated pads. Remove pads, sand down and bed in. Quick bleed of the system would not go a miss...

[Agent Smith]

does it mention that the pads were smoking?

[bob]

I was there....:wink:


does it mention that the pads were smoking?

As the pads overheated and were smoking the heat from this will transfer to calipers and Fluid. The fluid will then overheat and brake peddle becomes soft. But the underlying cause would be Pads and disks..Seen this many times after the Exmoor runs where we would all stop and watch our brakes on fire...:eek:
Small disks and single pots are just about U/S when keeping up a hard pace. A few bends and they start to overheat and as calipers are not alloy they tend to hold the heat.

[Olly P]

Sorry forgot to mention the pads were smoking. But Bob was the one who pointed it out to me.
It would appear that I probably glazed the pads.
It was the second corner so no real chance of boiling the fluid.
The pads were smoking when I came back, which is strange considering I had only done one lap and half of that was at a crawl. This would indicate that the pads weren't bedded in properly so were only braking on the high points of the disc.
I also checked the one way valve on my brake kit and was suprised to find that I could blow through it the wrong way.
So another bleed with some help has improved things alot as there was air in the rears for sure.
I've also been doing some bedding in procedure as suggested, which has improved the initial bite.
Feels alot better.
Also the early Scoob has some weird 2 stage servo which means the pedal will always be softer at the top.