cosworth caliper problem

[corsair66]

I have fitted 3 door Cosworth 4 pot calipers and 285mm discs to my car and I have used a .875 master cylinder with remote servo. When you apply the brakes the pistons move out and clamp the pads but when you take your foot off the pistons retract off of the pad by less than 1mm. When you reapply there is a small amount of pedal travel. Now all is bled correctly no air and I have rebuilt the calipers with new pistons and rubbers (which they did not need as it turned out!). A friend has suggested that the size of the master cylinder piston may be pulling fluid back when you release the brakes and therefore pulling the pistons back as well. Strange but it sort of makes sense. Never had this happen in 40 years of playing with cars. Anyone with any ideas out there? As a temporary solution I have made up some ally shims between pad and piston but with wear it will come back. Paul

[Col-ashtonmobile]

hi mate , give me some more info on the servo , i,ve had a problem before with a pedal changing pressure ( was very dangerous ) and it was the servo ..

[corsair66]

Newly purchased Lockheed remote servo 2;1 ratio. Cheers, Paul

[Col-ashtonmobile]

my first thing to do would be make up a new pipe and bypass the servo and see if that makes any difference...

[corsair66]

Just what I thought after your first post, thanks. Do you think dropping to a 5/8 master cylinder would be ok and run without a servo? I also have discs on the rear, usual Sierra calipers/Fiesta discs. Paul

[Col-ashtonmobile]

i always fit 3/4 mimimum , i,ve actually got a 1 inch on my escort with ap 4 pots up front and sierra discs on the rear and it stops good as its heavy on the front

[corsair66]

With a servo? Paul

[Col-ashtonmobile]

no servo mate ....

[corsair66]

Thanks for your help. Paul

[Col-ashtonmobile]

lets us know how you get on mate

[corsair66]

Bit of a long wait for this but finally got rid of the servo and everything works properly Plus a problem I also had with my engine hunting on a light throttle has been cured. Did not think that was down to the servo but there must have been an air leak in the servo, so double whammy! Thanks. Paul

[Col-ashtonmobile]

Well done mate dont hesitate to ask if you need any advice we,ll always try & help