Ecotec, Fastback, T-Top Build. (Page 21/21)
Lunatic OCT 12, 06:52 AM

Originally posted by longjonsilver:

i have found when attempting the conversion that there is a hole in the bottom due to a rust spot, that was not visible until i began cleaning it. Will this hole negate my vacuum?

How in the world did you get that snap ring off down deep in the hole of the cylinder?


edit: since the booster is in vacuum (it is in vacuum no?) couldn't i repair the hole by cleaning well with a wire brush and sandpaper and solvent, and then use JB weld? The vacuum will be sucking in the repair, not pushing it out. ;-)

I did mention to look for the nicest, cleanest booster that you could. And this is exactly the reason why.
We cannot have any leaks in the booster or else it will not work as intended.

A quick run down on booster operation.
The purpose of a brake assist unit is to decrease brake pedal effort without decreasing braking forces. This assist allows for less pedal travel and drastically reduces driver fatigue when operating. The vacuum brake assist uses engine vacuum and controlled atmospheric pressure to apply mechanical force to the primary master cylinder piston.

1) In the "released position", we're in a vacuum suspended mode. The vacuum port is open, the atmospheric port is closed and the return spring keeps the booster in the home position.
2) In the "applied position", the vacuum port is closed, and the atmospheric port opens. This happens only when the pedal is moving downward.
3) In the "holding position", the vacuum port and the atmospheric ports are both closed.

When the brakes are released, the booster returns to a suspended mode. To get there, the following happens.
-Foot pedal pressure is released.
-Vacuum port opens.
-The atmospheric port stays closed.
-Engine ingests the filtered air from the rear chamber.
-Return spring pushes the booster to the home position.

With where your hole is, you'll be losing vacuum and allowing in unfiltered atmospheric air. Both of which are not good. Remember, there are huge forces in the booster.

Take the rear shell to someone with a welder and weld the hole shut or find a better booster.

As for the circlip, I have a decent set of snap ring pliers. If you choose to use an awl or pick to dislodge the clip, there's a good chance that you'll deform the clip. You should always replace circlips, they almost always deform to some extent.

[This message has been edited by Lunatic (edited 10-12-2018).]