DeTomaso Mailing List: February 98, Message #57
     



From: 	tomas@fmcc.se (Tomas Gunnarsson)

Subject: Re: Power Brake Booster

Date: 	Mon, 2 Feb 1998 08:06:23 +0000



Jack Butler,BCH@HCIS.NET,Internet skriver:

> I have a 1972 pantera. With engine shut off and brakes bled the pedal is

> very firm. Start engine and the brake pedal is spongy. I also have a

> 1988 BMW M5. Two years ago the pedal got soft, same situation only with

> the engine running. I replaced the master cylinder and the problem did

> not go away. Called a tech rep and he said to replace the nitrigen

> assist ball. I did this and the problem was solved. The BMW is hydro

> assist but I assumed that it was a solid shaft from the brake pedal to

> the master cylinder. I was wrong. The shaft is split to creat brake

> pedal feel. I am wondering if the vacume booster on the Pantera is the

> same. You still have brakes but with considerably more travel. Has

> anyone taken one apart or had a similar problem. I can be reached by e

> mail or phone 502-444-6530



Jack,



The shaft is always split on a vacuum booster too. The pedal feel is created

by using a spring between the pushrod connected to the pedal and the booster

control valve. Without vacuum the spring bottoms out and the pedal rod pushes

the booster output pushrod directly without power assist.

I think all power brake systems feel like you describe: solid without vacuum,

mushy with vacuum. You probably simply have to rebleed. I had to do it

several times when I changed my master cylinder last year. Make sure you

build up brake line pressure first, then open the caliper bleeder. This helps

in flushing out air that gets trapped in the caliper hoses that make a high

bend in the wheel well.



Tomas



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