Dodgy brakes

[robp]

I started this discussion on a Donington thread but I thought I'd start a new one here. 

I was at a trackday at Donnington on Monday.  I had a great time but around mid afternoon the brake pedal went to the floor.  I could pump up a little pressure but basically the brakes had had it.  On returning to the pits and after about 20 minutes the brakes were fine again with a firm pedal pressure.  This seems to be the symptons of boiling brake fluid.  The other thing to add was the rear brakes were really hot and the pads (despite being replaced fairly recently) were very worn.  It seems like the rear brakes were doing more than there fair share of work.  Out on the track I managed to lock the rear wheels a couple of times.  At no point had the front wheels locked.  In fact, no matter how hard I press the brakes, I cannot lock the front wheels.  Surely that's not right as the front should be doing most the work.

The brake system on my Westy consists of a tandem master cylinder, 4 pot front calipers and sierra rear calipers.  The is a adjustable pressure valve in the rear circuit which I had been winding to drop the pressure to the rear circuit.

Under heavy pedal pressure in the garage I could hear a slight clicking (?) from the front brakes so I thought I would investigate.  I removed the front calipers from the hubs.  It was a bit of a struggle to get the pads out.  The two rods that hold the pads in place were pretty much seized on to the pads.  The pads are worn down to about 30% original thickness but seem to have worn fairly evenly.  I cannot see what type of pad they are; Mintex, EBC, etc.   I pressed the brake pedal and all the pistons are moving freely.  I may try some new pads but not sure if I should try some more road biased ones that will work more effectively from cold or something like a Mintex 1144 as halfway house.  The EBC Green Stuff pads seem to have poor reports about ineffectiveness from cold so I wonder if I have those now.

I may get some new pads, clean up the brakes, put it all back together and see.  Could be a shagged front circuit on the MC.  I may remove the bias valve too (yes, it is on the rear circuit!).

[Grin-a-lot]

When was the last time you did a brake fluid change?  The fact that they failed, were allowed to cool and worked again suggests to me that overheating fluid is at least partly responsible.

I've had pedal to the floor issues on track and that was definitely boiling fluid (mainly due to small calipers admittedly).

If it was a purely mechanical problem, why would allowing the car to cool make a difference - unless there's some weird-ass dissimilar metal expansion issues going on (piston seizing when hot etc)

[fullpint]

Had a simular issue on my Fiat Coupe 20vt when on track (also a Punto GT) and it turned out in both cases to be the brake fluid boiling. Replaced the fluid and then sold the car before having a chance to test it under extreme conditions..
Brake fluid is one of those things we all tend to ignore   

[robp]

Yes, agree with the boiling fluid.  Brake fluid is about two years old.  I'll change it anyway.

What are people's opinion on why the fronts are not as powerful as they should be.  i.e. why, hot or cold, can't I lock the fronts under heavy braking?

[fullpint]

Go for a set of new pads mate, yellow stuff worked well on the coupe. Mk Indy (blade) is currently running yellow stuff pads and they lock up just fine 

[Lucky Ed]

Yellow stuff pads work well for me too, they are a bit wooden from cold but get better the hotter you get them! - they soon get up to temp, taking about the same time as getting your slicks hot, they just need a bit of persuasion

Your old pads may have gone hard, I've had it with bike brakes they don't get used very often, they soon go off - a new set makes one hell of a difference.

Good luck

[Krazyken]

Rob

I have plenty of EBC Race Brake Fluid in stock if you are interested, £10 per 500ml or £18 for 2.  This fluid coupled with Yellow Stuff pads will make a definite differernce to your braking, I have this set up and in over 200 track miles in a day never have any retardation or fade problems let alone a non existent pedal.

[robp]

Your old pads may have gone hard, I've had it with bike brakes they don't get used very often, they soon go off - a new set makes one hell of a difference.

Just changed the pads to Mintex 1144.  Wow, what a difference!  Ed, you were right, the old pads had had it.  Come to think of it, I've never changed them (in which time I've changed the rear a couple of times).  Original pads were EBC Green Stuff.  Probably good on a heavy car but many people don't like them on light cars.  I am now one of those!  The new pads are mega.  It's almost like I've just fitted a servo.  I only have to apply a fraction of the pedal pressure now.  I'll have to re-adjust the front/rear biasing again as with the lighter pedal pressure the rears aren't doing much now.

The next steps is to get some more testing done on road and track.  I will change the brake fluid too (so may take you up in your EBC offer, Ken).  Overall, absolutely delighted. 

[fullpint]

  Glad you sorted the brakes... Nice one...

[Lucky Ed]

Pleased it was an easy and relatively cheap fix - sounds like the results are impressive.

Trouble is you're going to be even harder to catch now