"HELP" Power brakes very touchy
The car has always had the 340 as it is #'s matching. The new rod that goes through the firewall needed to be adjusted as it was set too long. The pedal, when pushed, has about 2 in of travel before the brakes come on. So in other words the brakes hit hard after the 2 in of travel is taken up. If I continue to hold the brake pedal, it holds solid and does not go down any further. The brake pedal feels good when pushed and holds with about 6 or 7 inches to the floor, (it does not go to the floor) I should also tell you that I have not adjusted the rod between the booster and the master.
Yeah I think your P-rod may be a lil short. It's really hard to tell from here tho.
I can give you a definitive test tho.
Just back the nuts off the M/C about a quarter inch and then slide a couple of 1/8th metal spacers in the gaps near the studs, then tighten the nuts and go for a spin up and down the driveway so to speak.. If it's way worse, then we're on the right track. Easy does it!
If I'm right, make the P-rod Two full turns longer, remove the spacers, and bolt it tight. Then another road test. If it's now better than it was yesterday, then we're on the right track. If you you get the idea to adjust some more, then one turn atta time. If the pushrod gets to be too long, then if you shine a light down into your reservoir, you will see the shine of the power-piston, in the C-port. A hint is Ok, maybe even up to half covered; but ideally the port should be dark. Don't use a useless LED flash-light for this test. I only use clear brake-fluid.
I should warn you, that if the pushrod gets to be much too long, and you press real hard down on the pedal like you would in a panic stop, this circumstance can BREAK the plastic-control valve in the booster. When this happens, the pedal will be like an ON/OFF switch, with almost no ability to modulate it.
Personally;
1) I don't like the dual diaphragm boosters. I have never been happy with how they work. Nor have I been able to make them work satisfactorily, with a low idle-vacuum.
2) I don't like the feel of a bigger than 1inch bore.
3) I really do like the 15/16ths M/C, with a big F-body booster, which is what I ended up using in my combo; which is; 3.55s, a manual-trans, and a 367 that pumps 185 or more psi cylinder pressure at 11.3Scr .
4) the F-body Booster that I finally snagged, (third booster I tried), is still working down to 9inches of idle vacuum, once it has been evacuated, which only takes couple of seconds of run-time, with my 4-speed combo. Once the car is moving, the vacuum never gets that low again.
5) yes the 15/16ths M/C does have a lil more pedal travel, which I like, but the ability to smoothly modulate the brakes, while simultaneously trying to work the other two pedals is well worth it.
