brake problems

[paygie94]

my 84 ford f250 6.9 started having weak brakes, then just recently started getting brake fluid inside the cab coming off the brake pedal. replaced master cylinder tonight and now im really getting a puddle inside the cab and I cant get any pressure to the calipers or the rear brake cylinder and have no brakes at all now. what am I doing wrong? help please.

 

[hallgren87idi]

maybe the vacuum booster took a crap? the one went out in my '80 ford fairmont, and when i pressed the brakes they would hardly work and it would make the car run like crap. i dnt know how to test it but that would be my guess, idk

 

[chris142]

Have you been adding brake fluid? Normally a bad master wont fill up the booster like that unless you have been refilling the master a whole lot.

 

[paygie94]

yes, I kept adding brake fluid to it.

 

[dirtbiker]

We just had the same scenario with our 79 powered 6.9. In researching it, a lot of what I read suggests that often times the booster and the master fail at the same time. The seal in the booster fails, and the vacuum from the booster sucks fluid past the master cylinder seals. Brake fluid is corrosive and exacerbates the diaphragm failure inside the booster unit. It is common enough that they sell re-manufactured booster/master assemblies, at very reasonable prices.

 

[chris142]

Adding fluid to the system filled up the brake booster since the master cylinder was bad. now you need a booster and a master

 

[riotwarrior]

Brake fluid is corrosive

Say what?

If that was the case then why would it work so well with so many different types of materials? Let me look at this ...Aluminum for master cyl, oh and plastic too, then steel for brake lines, rubber for seals and flex lines, so forgive me I'm just not seeing the fact as you put it?

Yes it will remove paint nicely but in regards to corrosive, I'm just not seeing that.

Please explain/prove this so I can learn about this nature of brake fluid.

Thanks

 

[mblaney]

I believe that EPDM is typically used for brake fluid compatibility; brake fluids (DOT 3, etc - not the new synthetic stuff) does not play well with petroleum based rubbers (buna-N and nitrile). The booster must have seals that are not compatible.

http://www.efunda.com/designstandards /oring/oring_chemical.cfm?SM=none&SC=Brake Fluid#mat

 

[dirtbiker]

I can't find the Bendix TSB I found last week when I was going through it, but it stated that (specifically) the diaphragm and valving in the booster are damaged by brake fluid. They cited that as the reason that often times the push rod seal begins failing, causing the booster to pull brake fluid past the master cylinder seals, and that the brake fluid in the booster causes a failure of the booster diaphragm. Since I received my new booster/master unit from a place that does not require a core (Amazon), it sounds like an autopsy is in my future.

 

[Bashby]

Careful taking the booster apart, there is a big spring under tension.

 

[dirtbiker]

Thanks. I am going to clamp it and slowly release it.

 

[chris142]

Why are you taking the booster apart? There's no user serviceable parts in there. Any auto parts store will have a new booster and master ready to go at a very reasonable cost

 

[thx997303]

Some people aren't content knowing what the problem was, but also how and why the problem occurred. I usually do the same thing if I don't have to return a core.

I'm naturally curious.

 

[dirtbiker]

You got it, thx997303. I already sourced and installed a booster/master. Since I do not need to do anything with the core aside from throw it away, I want to see if the failure appears to have occurred in the manner suggested in the TSB. Kind of a forensic experiment.