brake master cylinder
Melting Slicks
Joined: May 2002
Posts: 2,508
Likes: 0
From: Wisconsin
Yes, I'm making my own power bleeder out of an old MC top and an air fitting. I'm having a very similiar problem, except I have brakes for the last inch of travel and I get a good firm pedal with the engine off (no assist) but only that one inch with it on. And after a bleeder is opened I have to pump the pedal to get that inch back. I replaced the MC and bled everything. I'm going to try power bleeding and rebleeding the MC. Does it sound like a bad booster? The pedal gets easier to push with the engine on, it doesn't make sense to be the booster.
Thread Starter
Melting Slicks
Joined: May 2004
Posts: 2,084
Likes: 1
From: Aussie expat in Saudi Arabia
Righto guys, the day has dawned! I picked up a new booster yesterday and am going to fit it today, once the temperature drops below 50 degrees C!!
While I had my old one out, I pushed on the rod (that attaches to the pedal) and it was very soft and spongy and made some weird clicking noises :*****
The new booster I have, I can barely move the rod and no extraneous noise come from it when I do...
I'll let you know if it fixes my brakes
While I had my old one out, I pushed on the rod (that attaches to the pedal) and it was very soft and spongy and made some weird clicking noises :*****
The new booster I have, I can barely move the rod and no extraneous noise come from it when I do...
I'll let you know if it fixes my brakes
Team Owner
Joined: Mar 2002
Posts: 24,160
Likes: 78
Originally Posted by saudivette
While I had my old one out, I pushed on the rod (that attaches to the pedal) and it was very soft and spongy and made some weird clicking noises :*****
Team Owner
Joined: Mar 2002
Posts: 24,160
Likes: 78
Originally Posted by saudivette
While I had my old one out, I pushed on the rod (that attaches to the pedal) and it was very soft and spongy and made some weird clicking noises
Thread Starter
Melting Slicks
Joined: May 2004
Posts: 2,084
Likes: 1
From: Aussie expat in Saudi Arabia
Originally Posted by wcsinx
Hey! It just occurred to me that you have the opportunity to solve the mystery. Do you still have the old booster, or did you turn it in for a core? If you have it, would you be willing to saw it in half? Maybe that could shed some light on the mysterious sinking pedal-bad booster problem.
The diaphragm (yellow) was ruptured, the reaction plate (red) was corroded to almost nothing and the return spring was broken. When the push rod (purple) was being pushed, it had to travel (unassisted) all the way to meet the master cylinder push rod (blue), before any braking began to take effect. As the diaphragm was ruptured, it was left to the broken return spring to try and push the pedal back to it's "normal" position when you took your foot off the pedal. Does that make sense?
Thread Starter
Melting Slicks
Joined: May 2004
Posts: 2,084
Likes: 1
From: Aussie expat in Saudi Arabia
Originally Posted by wcsinx
Hey! It just occurred to me that you have the opportunity to solve the mystery. Do you still have the old booster, or did you turn it in for a core? If you have it, would you be willing to saw it in half? Maybe that could shed some light on the mysterious sinking pedal-bad booster problem.
The diaphragm (yellow) was ruptured, the reaction plate (red) was corroded to almost nothing and the return spring was broken. When the push rod (purple) was being pushed, it had to travel (unassisted) all the way to meet the master cylinder push rod (blue), before any braking began to take effect. As the diaphragm was ruptured, it was left to the broken return spring to try and push the pedal back to it's "normal" position when you took your foot off the pedal. Does that make sense?
In my case, I can see why the pedal was spongy and why the pedal went nearly all the way to the floor...
Race Director
Joined: Sep 1999
Posts: 11,361
Likes: 383
From: Plano TX
Yeah, I'm curious also if replacing the booster fixed it. I kind of felt like the guy reporting little green men... 
Wondering why the "rebuilt" booster would have that symptom... Maybe the rebuild was so crappy they didn't replace a rusted out reaction plate????
Wondering why the "rebuilt" booster would have that symptom... Maybe the rebuild was so crappy they didn't replace a rusted out reaction plate????
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Team Owner
Joined: Mar 2002
Posts: 24,160
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Originally Posted by zwede
Wondering why the "rebuilt" booster would have that symptom... Maybe the rebuild was so crappy they didn't replace a rusted out reaction plate????
Thread Starter
Melting Slicks
Joined: May 2004
Posts: 2,084
Likes: 1
From: Aussie expat in Saudi Arabia
I still need to bleed the brakes but even now are a zillion percent better. pedal doesn't sink any more and the faint hissing noise from under the dash has gone away...
Race Director
Joined: Sep 1999
Posts: 11,361
Likes: 383
From: Plano TX
Originally Posted by saudivette
I still need to bleed the brakes but even now are a zillion percent better. pedal doesn't sink any more and the faint hissing noise from under the dash has gone away...
Team Owner
Joined: Mar 2002
Posts: 24,160
Likes: 78
Originally Posted by saudivette
I still need to bleed the brakes but even now are a zillion percent better. pedal doesn't sink any more and the faint hissing noise from under the dash has gone away...
You should have mentioned the hissing noise in post #1. That's a sure fire sign of a bad booster. Glad it's working (better) for ya.
