Brake diaphragm failure in my 57?

[Highsider]

After replacing my master cylinder and 7.5” booster this past fall, only 140 miles ago, I have a dead brake pedal. At first, I could make my passenger fly out of his seat when I tapped the pedal. The brakes were nice and powerful. Now, they are like decent manual brakes.
I found this explanation and potential cure on the NAPA site. You guys have any input?


Yes, the Edelbrock carb may be causing a rich fuel condition and no, I don’t have a charcoal filter inline.

[Speedbumpauto]

A quick test of the booster is to step on the brake pedal firmly and start the engine. If it's healthy, the pedal should fall about an inch or so when the engine starts. If it doesn't, then you need to follow those procedures, especially if the booster is downhill from the carb.

[Highsider]

Thank's Speedbump.

No pedal movement when doing the test.
Yes, it is beneath the driver's floor.

[OrrieG]

FWIW this thread is helpful. Something I did not know I needed and will correct.
Posted via Mobile Device

[Speedbumpauto]

Yea, me too. I had a buddy whose truck we did and his failed in a very premature fashion. We just blew it off as a bad part, the seller replaced it and we moved on. This made me start thinking. Mine isn't running yet and it's EFI, but I'm absolutely going to plumb in a filter. To top of the diaphragm thing, I'm running a vacuum booster pump due to more camshaft than a sane person would use so could have been a double whammy!

[Highsider]

I wish I had known this.
I got the truck home Aug 2012 and drove it wishing it had/figured it should have stronger brakes.
Has the MII kit w/discs.
Finally put the new m/c & booster in late fall...then, over a short period of time the brakes felt weaker & weaker.

[Speedbumpauto]

Beauty of forums like this. Even if it's a little tardy, we still get to learn stuff.Whoda thunk....but from the late 50's on, we all had boosters that were uphill so no harm there.

[entourageguy]

I had heard of a bad batch of the chinese boosters.

[Highsider]

Originally Posted by entourageguy

I had heard of a bad batch of the chinese boosters.

But, it sits 18" below manifold level without a charcoal canister and if the rubber parts are "Chinese" non fuel resistant,
I guess I am putting one in. Even NAPA refers to it..

[Rude Dude]

If exhaust is routed to close to brake booster and you cant touch the booster with your hand then the rubber diaphram is heating up certain failure assured.

Originally Posted by Highsider

But, it sits 18" below manifold level without a charcoal canister and if the rubber parts are "Chinese" non fuel resistant,
I guess I am putting one in. Even NAPA refers to it..