PDA

View Full Version : Brake problem-Pedal going down before any


Gobbracing
07-19-2007, 08:53 AM
Have any of you experienced this? Please help.
I have to push the pedal further before I get a response (pressure).
And it gets even worse when autocrossing.

My MSP has 65 0000 miles with all new calipers, hoses and nothing leaks.
Me and my mechanic have flushed the system 3 times now with no change.
I use Motul RBF600 brake oil. I removed the ABS fuse since I run in STX.
We were going to change the master cylinder last night but got a bad rebuilt, so we put back the old one and we're back to square one.
I replugged the ABS last night and the pedal was exactly the same after driving about 40 miles.

So now we're wondering if the master cylinder really is the problem or maybe the proportionning valve in the ABS.
orng1
07-19-2007, 11:00 PM
I'd guess master cylinder also. At a stand still does the pedal feel like it's getting softer as you hold it down?
Brian MP5T
07-19-2007, 11:02 PM
Master...
JRTritsch
07-19-2007, 11:08 PM
Generally will get some leakage with a bad seal on the master... but since you have had everything apart so much it may be hard to tell. What method are you using to bleed?
Brian MP5T
07-19-2007, 11:13 PM
Get speed bleeders. They KICK ASS!
Gobbracing
07-20-2007, 07:48 AM
I'd guess master cylinder also. At a stand still does the pedal feel like it's getting softer as you hold it down?

Yes. That's what's happening.

I picked up a low-milage used master cylinder last night and I will be installing it this morning. I hope it works. Fingers crossed.

BTW. Which brake system oil do you guys use in your MSP. Me since I autocross and lap, I use Motul RBF600, but I'm wondering if it damaged my master cylinder. Right now I'm gonna use regular braking oil to be safe until I'm sure about which one to use.
Gobbracing
07-20-2007, 07:52 AM
What method are you using to bleed?

By gravity when I'm alone and I start from the furthest wheel to the closest one. When I have help it's the usual pump and hold technique.
Brian MP5T
07-20-2007, 11:18 AM
By gravity when I'm alone and I start from the furthest wheel to the closest one. When I have help it's the usual pump and hold technique.

Two people I hope..
Gobbracing
07-20-2007, 05:31 PM
Master cylinder is changed and the pedal is back with the help of a friend.
Now to see if it will past the test this Sunday at the autocross in Sanair.

Running STX with a co-driver (lady class)
Gobbracing
05-07-2008, 04:51 PM
Fixed the problem by changing the brake booster vacuum hose.