The black 928 street car - 6 liter with an issue with brakes
07-12-2014, 04:28 PM
#1
Rennlist Member
Thread Starter
The black 928 street car - 6 liter with an issue with brakes
My friend has a braking issue. one that i havent seen or felt before. take off driving, brake pedal firm as normal. push down on slow down after releasing gas, and nice pedal and slow down... but if you release and then press again, it goes, all the way to the floor!! I mean ALL the way. then, all you hear is squeeking rear brakes being engaged, seemingly nothing up front.
if you pump the pedal, it all comes back. hold the pedal down. it doesnt push in. push and release while sitting still. no problem.
Im thinking its something to do with the vacuum brake booster or master cylinder.
but , if the booster was really doing something under vacuum, for which it seems to be doing, wouldnt it be filling up with fluid? it doesnt seem that it is.
Im puzzled.
MK
if you pump the pedal, it all comes back. hold the pedal down. it doesnt push in. push and release while sitting still. no problem.
Im thinking its something to do with the vacuum brake booster or master cylinder.
but , if the booster was really doing something under vacuum, for which it seems to be doing, wouldnt it be filling up with fluid? it doesnt seem that it is.
Im puzzled.
MK
07-12-2014, 07:18 PM
#2
Nordschleife Master
It'll only go down to the floor if the master is failing or fluid is leaking out somewhere.
The booster fills with fluid when the seals on the master have failed.
There might be two problems at once like a flakey master and a vacuum leak.
The booster fills with fluid when the seals on the master have failed.
There might be two problems at once like a flakey master and a vacuum leak.
07-13-2014, 02:18 AM
#3
Rennlist Member
Thread Starter
if the master was failing, why does it feel fine for a push of the pedal and then if i push it again, it goes all the way to the floor?
didnt see any leaks, so master?
way too early for my smart elec comment
07-13-2014, 10:53 AM
#6
Nordschleife Master
so, there would have to be leak into the vacuum booster, so i should see some fluid gone with a few pedal to the floor exercises?
if the master was failing, why does it feel fine for a push of the pedal and then if i push it again, it goes all the way to the floor?
didnt see any leaks, so master?
if the master was failing, why does it feel fine for a push of the pedal and then if i push it again, it goes all the way to the floor?
didnt see any leaks, so master?
You can check for leaking into the booster by threading a piece of rope in through the vacuum port. It's not unusual to have some wetness at the tip. It is unusual to have an inch of brake fluid.
Trending Topics
07-13-2014, 07:52 PM
#8
Rennlist Member
Thread Starter
When you push the master the cups go forwards and either the fluid is going into the lines or slipping past the cups. The usual sequence is for the first pump to be bad and the second to be good. That's because on the second pump people push hard (in a panic?) and the cups seat along the walls. This situation is unusual.
You can check for leaking into the booster by threading a piece of rope in through the vacuum port. It's not unusual to have some wetness at the tip. It is unusual to have an inch of brake fluid.
You can check for leaking into the booster by threading a piece of rope in through the vacuum port. It's not unusual to have some wetness at the tip. It is unusual to have an inch of brake fluid.
the fact that this has a good pedal first , is puzzeling. a quick note. sitting idle, i cant get this phenom to happen. only while driving. the decel miust put more vacuum in the booster and be causing the issue. very strange. only on the second push is the problem showing itself.