Brake pedal goes to the floor

minorv8 · Post by **minorv8** » Wed Feb 14, 2007 6:40 am

I have big 4-pot Brembos in front and VW/Seat single piston calibers in the rear. The master and servo are from Austin Metro. No problem whatsover.

Have you rebuilt your master cylinder ? Have you bled it ? In any case fitting a pressure limiting valve, preferably adjustable one, is very much to recommend, otherwise you may not get the brake balance set up properly.

v8viva · Post by **v8viva** » Wed Feb 14, 2007 10:34 pm

Master cylinder is brand new and it has been bled ok.The pedal is rocksolid once the fluid is restricted to the rear.I have ordered a bigger bore cylinder and will fit an adjustable pressure valve and failing that a bias pedal box is going in!!

Ian Anderson · Post by **Ian Anderson** » Thu Feb 15, 2007 4:19 pm

Do you have any run out on the discs?
Or are they some wierd setup with springs to retract the pads off the disc? (Don't laugh they do exist!)
Or when you were replacing parts did you "lose" the retained pressure valve?

If you do the disc will push the pad back to create an air space between pad and disc

You have to then move enough fluid to "fill the pistons" before getting clamping force. By then you could have run out of travel. I had the very same think (spring pads on a kart) they worked well until the pad wore then it was a big eye opener!

Ian

kiwicar · Post by **kiwicar** » Thu Feb 15, 2007 4:32 pm

Ian said
"Or are they some wierd setup with springs to retract the pads off the disc? (Don't laugh they do exist!) "

bonerville salt flar racers! go flat out for 4 miles on stuff the consistancy of ball bearings on carpet then hit pump the break peddle at 300mph while deploying a parachuteand try not to lock the wheels or turn the thing over, is it me?

It does sound as if your master cylinder is a bit small though.
Mike

Ian Anderson · Post by **Ian Anderson** » Thu Feb 15, 2007 5:18 pm

Try one or 2 of these
http://www.rallydesign.co.uk/catalog/ad ... 9eefdb2640

One if you have a single master cylinder - would that still pass MOT?

Two if you have a tandem master cylinder

Ian

kiwicar · Post by **kiwicar** » Fri Feb 16, 2007 9:27 am

it will only need a tandem/twin master cylinder and split system if it came from the factory with one, they came in mid 70's, a Viva probably pre dates the ruling.
Mike

v8viva · Post by **v8viva** » Sun Feb 25, 2007 9:32 pm

Problem sorted! Fitted a 3/4 bore girling master cylinder,did away with the servo and fitted an adjustable proportioning valve to the rear and it all works fine.Pedal is solid,brakes pull up very square even under hard braking and on the brake rolling road at work,they are recording:-
osf 220 kg/force
nsf 230 "
nsr 120 "
osr 120 "
Total braking effort is 690kg which seems acceptable for a vehicle weighing 1000-1200kg.
Thanks for all your help comments and i will be fitting a reverse swing wilwood pedal box in the near future to run a completely bias system
Gary