Brakes are fine unless you REALLY-MUST-STOP- NOW.

[PaulF]

Hi All,

New to this excellent forum and have a brake question. I have a 1969 Camaro RS with 350 and a 4 speed. I just finished installing DSE rear 3" lowering springs with Delrin bushing/shackle kit, Viking double adjustable rear shocks, SpeedTech tubular upper/lower control arms, Viking double adjustable front coilovers, Unisteer rack and pinion, rebuilt tilt steering column, The Right Stuff 8" dual diaphragm vacuum assist with 1 1/8" master cylinder, Baer SS4 front 11" disc brake kit, Baer Iron-Sport 11.6" rear disc brake kit, 18x9.5 Vintage Wheel Works 2 piece type V40 rear wheels w/ 275/40-18 Hankook V12 tires, 18x8 VWW V40 front wheels w/ 245/40-18 Hankook V12 tires.

The original plan was to retain the 15" rallye wheels which is why I went with the smaller brakes, but I ended up buying 18's anyway. I find the car stops infinitely better than the original 4 wheel manual drum brake setup. HOWEVER, the car won't lock 'em up in a panic stop situation. Will a smaller diameter master help this issue, or did I simply make a mistake going with a 8" dual diaphragm booster? I'm not sure what cam is in the engine, so not sure if it just low vacuum, but even after driving and letting off the gas while in gear, shouldn't it make enough vacuum to function properly? Any ideas would be awesome. Thanks.

paul

[Mr Nick]

That 8" booster sure isn't helping, but you may have a couple other issues too. I had an 8" booster for a few weeks because it was needed at the time for clearance issues. I then was able to make a 9" booster fit (both dual diaphragms) and the brakes were noticeable better.

What pads are you running?

You also need to throw a gauge on there and find out your vac readings at idle minimum. Try disconnecting the vac booster line, and take it for a drive. If it feels the same or pretty darn close, that booster isn't offering much assist. (don't forget to plug the vac line!)

[Rod]

agreed with Nick, what do you have for vacuum? do you have a big cam, if so that's the problem, once we know the vacuum reading, we can go from there

[PaulF]

Thanks guys. I'll measure idle vacuum and see where I'm at. I do get decent assist initially, then when the pedal is about halfway down it gets super firm and I can't seem to get anymore braking force. I'm running the pads that Baer supplied with the SS4 kit. I'd rather not buy another booster, but if 8" isn't enough for 4 piston calipers, then I need a larger one. I can't locate the piston area for these calipers, so I'm just guessing on whether this booster set up is sufficient.

[Apogee]

The dual-8" booster should provide similar boost to the OE single 10.75" unit and most likely isn't the problem. Low vacuum levels could explain some of the issue, so an accumulator may be justified or an auxiliary vacuum pump if it's really bad. I don't know what the piston area is on the SS4 caliper off hand, however my guess is that you're running the wrong MC for your components and that a 1" bore MC would be a much better choice. How did you choose the 1.125" bore MC? Stepping down to a 1" bore alone will provide ~25% more pressure with the same pedal effort. The standard Baer pads are pretty decent pads and also not likely to be the issue.

Stepping up to a dual-9" booster would be a good way to get another 25% boost, but I'm still leaning towards the MC as your primary issue with respect to low brake torque, followed by your vacuum levels leading to the inconsistency at the pedal.

Tobin
KORE3

[PaulF]

Thank you Tobin! That is super helpful information that gives me the direction that I need. I appreciate your expertise! I just ordered a 1" MC. Thanks again Tobin.