brake pedal to the floor at 100 mph !


D

dave benson

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Jul 24, 2008
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my rally car has been developing a strange problem over the last two rallies were with no warning, or for any reson i can find the brake pedal goes to the floor, i still seem to have rear brakes but no fronts !

my brake setup is off an mb6 282 fronts/262 rears, standard discs/calipers, ds3000 pads front ds2500 rears, braided hoses, hydraulic handbrake, adj. bias valve, castrol srf fluid lines setup so front lines and rear each fed from the master cylinder

before yesterdays rally i changed the master cylinder and front discs, but still have the problem

could it be the servo ?

mira rally 2012 big spin - YouTube check out six corners in !
 
Never had any issuses of loosing the pedal completly during a stage, but with mg zs 180 front brakes (different caliper but same size piston) and got so fed up with the poor pedal regardless of what i did i. have been running the 262 front brakes off my daily ek4. I assume the only way to go is a bias pedal box, but id rather not personaly.
 
is this not a case of brake pad knock off where during extended long straightsetc the pads rattle off of the discs and actually push the callipers pistons back. thus making you need to pump the brakes to get them back into place. are you using slotted or vented discs by any chance?
 
Gorbash12346 said:
is this not a case of brake pad knock off where during extended long straightsetc the pads rattle off of the discs and actually push the callipers pistons back. thus making you need to pump the brakes to get them back into place. are you using slotted or vented discs by any chance?
Click to expand...

Had this badddddd on a motorbike once when i had a tank slapper at 120mph+

Went for the breaks afterwards aand there was nothing, i had to pump like crazy! :nerv:
 
Gorbash12346 said:
is this not a case of brake pad knock off where during extended long straightsetc the pads rattle off of the discs and actually push the callipers pistons back. thus making you need to pump the brakes to get them back into place. are you using slotted or vented discs by any chance?
Click to expand...

the discs were new prior to this event, no grooves,so should be nice and straight didnt change the pads

not sure if its pad knock off

pedal doesnt feel right, its very spongy despite a brand new honda master cylinder and being bled to death !

could the servo cause this ?
 
dave benson said:
my rally car has been developing a strange problem over the last two rallies were with no warning, or for any reson i can find the brake pedal goes to the floor, i still seem to have rear brakes but no fronts !

my brake setup is off an mb6 282 fronts/262 rears, standard discs/calipers, ds3000 pads front ds2500 rears, braided hoses, hydraulic handbrake, adj. bias valve, castrol srf fluid lines setup so front lines and rear each fed from the master cylinder

before yesterdays rally i changed the master cylinder and front discs, but still have the problem

could it be the servo ?

mira rally 2012 big spin - Yo

uTube check out six corners in !
Click to expand...


Did you fit the 1" madter cylinder off the mb6 ? If you didnt then that will be your problem, however if you have fitted it then it sounds to me like one of the seals in the mastercylinder cannot hold the pressure and the fluid is slipping past. Hope this helps
 
dave benson said:
the discs were new prior to this event, no grooves,so should be nice and straight didnt change the pads

not sure if its pad knock off

pedal doesnt feel right, its very spongy despite a brand new honda master cylinder and being bled to death !

could the servo cause this ?
Click to expand...

or it could be the pads, because you did not change them they will have worn to the old discs there fore they will take a while to bed in properly. We have found this on a few cuatomers cars and ended up changing the pads too.
 
Gorbash12346 said:
is this not a case of brake pad knock off where during extended long straightsetc the pads rattle off of the discs and actually push the callipers pistons back. thus making you need to pump the brakes to get them back into place. are you using slotted or vented discs by any chance?
Click to expand...

This used to happen to my wildwood 4 pots on long journeys (around 100 miles) with no brakes being used, it's very possible that racing would speed this process up
 
dave benson said:
what clearance ?

genuine mb6 cylinder

feels like it is slipping pressure past the seal, but it is only 3 days old !!!
Click to expand...

Sorry forgot to write a reply.

Its between the servo pushrod and the master cylinder 0-0.4mm at 20in.hg vacuum applied .
 
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