[geezajob]

I've recently upgraded my R34 brakes to 6-pot 343mm APs with DS3000s.

Now they stop very smart from cold, almost too sharp, squirming under heavy braking.. but that's OK.

The thing is, after 1-2 laps of Elvington airfield, they're knackered, with the pedal going very spongey, and needing pumping to get them to work. The old brakes lasted longer than that !!!

I've had them bled since, just to check there's no trapped air, but it still happens.

Any ideas ?

 

[Joss]

Could it be

the Fluid boiling?

 

[geezajob]

yeah, that's what it would suggest.. but what's the point of larger discs (which you'd think would dissipate heat quicker and have greater heat capacity) if they don't last as long as std. brakes ??

They've used 5.1 fluid. Should I consider using Castrol SRF for example which boils 100 degs higher.

What happens with other AP 6-pot owners ?

 

[TOKYO]

What about

them stopper thingies under the bonnet I've heard about.

I think Henry had some for sale at the last Grasshopper and I believe Abbey and SVS have 'em as well.

Mind you I think all the tuners have got 'em.

glen

 

[Simon]

It does sound like the brake fluid, did you have it changed when you uprated the brakes? Maybe the new fluid is not up to the job. I'd say it would be worth a try to change to SRF.

I guess it could also be your brake hoses expanding, might be worth changing these for braided ones at the same time.

Stopper things? are you refering to the brake support brackets that stop the master cylinder flexing? I would think they would only make a difference to the 'overall' feel of the pedal, in this case I think it's obviously heat that is causing the brake to 'go spongy'. But again, they're not expensive and probably worth a try.

 

[geezajob]

Yep, they changed the fluid, and fitted braided hoses at the same time.

SRF it is then !

 

[Peter]

Motul RBF600 is almost equivalent of SRF at a fraction of the cost. I've done numerous track days now with it in without any problem. I just give them a good bleed before each track day. Gary (GTart) can supply.

The DS3000s are an agressive pad so I'm sure you'll have built up a lot of heat although my brake fluid boiled last year at Silverstone and I completely lost all foot braking. You may have just suffered with some major fade.....?

Have you tried DS2500s? They are very effective pads, kinder to your discs and wheels.

The Cusco master cylinder bracket is pretty good and does firm things up not that it will solve your current problems.