Brake Booster

[katsi]

OK, it's me again and I still am not able to build any pressure in the brakes system . But, I had a self proclaimed "Fiat Guy" come over to the house and take a look (he is a mechanic and bosts building many Spiders in the past) . Anyway, his diagnosis, which I have a hard time believing , is that the brake booster is bad. While, I am not in total disagreement with him on this, I don't quite believe his rationalle. He states that if the booster is bad then the knetic energy placed on the brake peddle will not get transferred to the MC . Thus, the system will not build any pressure and the peddle will continually go to the floor with only the spring tention as resistance . Personally, I believe that if this is fact, then any booster failure would result in total brake failure and I have a hard time believing that a car company would put something out there with such a possible catastrophic legal issue looming over the bottom line . Anyway, what are your thoughts? It seems to me that a brake booster is there to assist in the actual pressure needed for braking and a bad booster would result in more leg pressure and difficult braking. Am I right or am I wrong? My booster has NO brake fluid leaking. Also, it seems to me that if I did have a leaking booster than it would be a result of a faulty MC as the booster does not have any fluid goint to it . Anyway, let me know - Please .

[Snoopy]

In the german forum (sorry in german) i read that the right assembly an settings are difficult to do.
You have to set some screw in the exact position. If its wrong the car brakes very very bad or all the time...
My english is not good enough to translate it....

[kilrwail]

The only way a bad booster would kill the brakes would be if the primary metal plunger going into the rear of the m/c was broken. Not likely. Yesterday I solved the same problem you've been having by jacking the rear of the car as high as my jackstands would allow, then lowering the front (wheels removed) until the brake rotors were only an inch off the floor. I was able to watch the fluid coming out of the left front and I got two big bubbles (from the m/c) - likely the same out of the right front. Today I'll bleed the rears again, but my brakes are back to at least 80% of what they were before I began.

Of course, if your m/c has bad seals or other problems as Mark suggested, you must deal with that first.

[Kevin1]

If that diagnosis were right your brake pedal would go to the floor when the car was not running, too, as there isn't any vacuum then, either. I believe that your friend is mistaken.
No booter means no boost, it doesn't mean no brakes.

[mdrburchette]

Have you replaced the master cylinder? It's possible for one to be bad right out of the box. It's also a good idea, like others have suggested, to bench bleed the m/c. Do you have the actuating rod adjusted properly? Also, when you bleed your brakes, you need to make sure the axle is supported and start bleeding at the wheel farthest from the m/c. Hope you find your problem soon!

[So Cal Mark]

your "Fiat Guy" isn't too strong on theory. Have you verified that the mc is pumping fluid? Use a clear container with a hose on a bleeder. open the bleeder and pump the pedal. You should see fluid moving. Despite what Vicks claims, any new part can be defective

[narfire]

I'll second the bad MC out of the box issue. As mentioned I'm on my 3rd mc but this time I checked by cracking the lines at the MC and had someone pump the pedal,got fluid at the front line which is the single line to the rear but not the front lines. Popped the MC off the booster turned the acorn IN two turns and repeated. Then I got juice at the two rear lines which are of course the lines to the front brakes.
After jacking the car much like kilerwails method,pressure bleeded the brakes and got alot of air from the rear,brakes are better but not real firm yet.
Hang in there,brakes are alot better than packing a danforth anchor about and tossing that to stop.