How do you tell if a master cylinder is bad? I am just at wits end with my brakes on this new car. Either that or the booster is working WAAAAY too good. The problem is there just isn't any pedal feel. My street car (280 with stock 7/8 and 280 Booster) has the nice gradually increasing resistance (motor running) all the way down.

The new car has a 15/16 on a 280 Booster. The booster holds a vacuum and the system is fully bled (and bled and bled). The brakes work good, but there is no pedal feel. With motor running, it is just gush all the way down and then BAM! the brakes engage--hard. With motor off, brakes are very hard.

I have gone through everything several times. My mechanic went through it and deemed it fit ("rears were out of adjustment a bit"). Something has to be wrong. Either that or this is the way they all are and my street car with its good pedal resistance is wrong. I don't think so. I'm going to take the spring off today and see where the pedal 'falls', in case it could be either of the rod adjustments, but you would think I would notice a short rod when the motor is off.

It's almost as if the booster works to good. It feels like a mushy massive land-yacht Lincoln or something, except when they do finally engage, they are stopping a 2000 lb car with R4S's. I need to be able to feel them! Somebody help!

steve

Steve:

I couldn't find the thread, but someone (somewhere) on the site has previously indicated that this situation is (or can be) caused by the little rod that fits between the booster and the M/C being not adjusted (in regard to length) correctly. I don't remember the specifics of correction but I believe "trial and error" was involved.

The only thing I really remember was that for me it was going to be important to never mix things up or change things in this area. Sorry I can't help more, but maybe someone else remembers more on the subject or can find a link to the thread.

I don't know if this help, but someone posted here recently that if the servo/booster pushrod is removed and a rubber disc inside the servo gets dislodged, then the symptoms are exactly as you describe. Nothing at first and then Bamm

beat me to it Bambikiller:classic:

heres a thread that mentions the 'reaction disk' in the servo. About half way down first page.

http://www.classiczcars.com/forums/showthread.php?s=&threadid=12572&highlight=rubber+disc

regards

Andrew

This is EXACTLY what mine is doing. It totally stands on it's nose. I was ready to do something drastic like take the guts out of the proportioning valve or something. My mechanic said it was because I turned the frontt discs and not the rear drums. He also said the rears were not adjusted properly. Right.

But there are still a few unanswered questions.

Thread moved: http://www.classiczcars.com/forums/showthread.php?s=&postid=86575#post86575

steve