'67 Pwr Brake Failure - Air leak sound under dash

[Victor E.]

Hi ... a long time NCRS member but my first post. I have done a search and not found this issue addressed, so starting a new thread.

I have a 1967 Power Brake roadster (427/400, but I don't think that matters). Yesterday I was coming to a stop light and realized my brakes were not stopping as normal. Still stopping, but gradually and only with hard pedal. It does not appear to be a fluid leak issue as the fluid reservoir is full, and brakes still stop with a hard pedal. At idle, I noticed an air leak noise under my driver dash WHEN DEPRESSING the brake pedal. When I got home, checked engine compartment fittings for possible leak, but heard nothing in the engine compartment when depressing the pedal (or otherwise).

In inspecting under the dash, it seems like the noise is coming from the push-pin area near the firewall, so am assuming there may be a vacuum leak in the booster near the firewall (booster at push rod?). In looking at rebuild kits available, I am only finding '66 and earlier for PWR brake cars, and '68 and later. There are individual parts for the booster available, but have never pulled a booster and understood it's inner workings ... so am hesitant to pull it, open it up and diagnose without some guidance.

Also, in Service Manual, no rebuild noted ... only replacement of unit. No exploded views of booster in assembly manual or otherwise.

I hate to just purchase a new booster if this is something that can be fixed with some simple wrenching and a seal replacement.

Anyone have a recommendation?

Thanks,
Vic

[Frank D.]

Re: '67 Pwr Brake Failure - Air leak sound under dash

There are a few tests you can perform:

1. With the engine OFF, pump the brake pedal to deplete any vacuum reserve, then,
2. With your foot on the brake pedal, start the engine, the pedal should depress about 1" after vacuum has established.

Next..

1. After the engine idling for a time and your foot OFF the brake, turn the car off.
2. You should get 3-4 vacuum boosted "pumps" before the pedal gets hard, that's your vacuum reserve

If either or both of the tests fail you prob have booster issues but the FIRST thing to check is the vacuum valve (plastic) that holds the rubber line in front of the booster....you can blow into it and air should pass one way and not the other...if that fails you might have a cheap fix by replacing it.

The booster rebuild instructions are in the '67 Chassis Manual IIRC but Karps Power Brake Service or Booster Dewey can rebuild the unit correctly....and have the parts. I've never rebuilt one personally.

[Keith B.]

Re: '67 Pwr Brake Failure - Air leak sound under dash

you could take a mity vac type tool and see if you can pull a vacuum on the booster and see if it holds

[Don H.]

Re: '67 Pwr Brake Failure - Air leak sound under dash

Victor,
Welcome to the forum! If there is a problem with your booster do not replace it (if it is original), have it rebuilt and re-plated.
Good luck,
Don H.

[Victor E.]

Re: '67 Pwr Brake Failure - Air leak sound under dash

Thanks all ... I was either going to fix it myself if easy, or have it rebuilt/restored. Will definitely run through Frank Dreano's diagnosis series to see what I find. I don't have a vac tool, but may look into it. Very much appreciate the quick and helpful responses. Thanks all.