Factory Power Brake Fun (not really)

[dibbons]

I noticed awhile ago when I pressed the power brake pedal on the '65 Formula S that the idle speed would change. Then I noticed the idle speed was not changing when pressing on the brake, but the idle was then rough and the power brake assist was no longer available. Took an extreme effort compared to before to bring the vehicle to a complete stop.

I used my home-made smoke machine today to see if I could find the exact source of the problem. However, no smoke could be seen emanating from either the booster cannister or the fender mounted reserve tank.

Then I decided to test the line using a vacuum gauge/tester (which is what I should have done in the first place). Using that test device on the hose that normally connects to the intake manifold resulted in a complete inability to provide a vacuum in the system (needle on gauge while pumping pretty much stayed on/near 0).

Later, I plan on plugging the hose at the intake manifold (to disconnect the booster completely) and drive around the block to verify the brake pedal effort is exactly the same with the hose either on or off.

 

[cudamark]

A rough idle indicates it might be a vacuum leak in the booster. Pull the vacuum source hose off the intake and plug the intake nipple. The idle should be good now. If so, you have a leak in the booster system somewhere. Probably the booster itself as those were trouble prone on the early A's. I'd also check the extra vacuum hoses that go to the vacuum reservoir and the reservoir itself too.

 

[dibbons]

Update: Drove around the block with the power brake booster hose disconnected; found the same brake pedal effort either way, with the hose on or off. No booster boost at all.

 

[Mike69cuda]

I used to do this test with a vice grips. Clamp hose flat till you find the offender.

Upgrade to a dual master cylinder when you replace booster.

 

[lemondana]

I would have yours rebuilt, rather than get a generic unit that might not fit. Chinese in other words.

 

[cudamark]

If you need boosted brakes, I would recommend the '67-72 booster and master cylinder. The original Bendix booster with remote reservoir is a trouble prone setup and some parts are getting very hard to find, not to mention someone that knows how to rebuild one.