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brake booster

2K views 8 replies 7 participants last post by  lust4speed 
#1 ·
I have a 10" booster am rebuilding my engine I purchased stud girdles and now I hear the valve cover may not fit due to the stud girds I either may not be able to use them or remove the existing booster for a smaller one, I read its possible to not even need a booster. I have discs on the front reg rear brakes. So any info on this subject would be appreciated . 65 gto
 
#9 ·
I ran the 3" tall valve covers with my original brake booster which on a '67 is 10-1/2". Marked the bottom edge of the valve cover where it would contact the booster and then set the cover on the workbench and set a 1/2" pipe across the marked edge and whacked the pipe a couple of times with a big hammer until edge showed about a half inch dent. That allowed some clearance both at standstill and under acceleration when the engine lifts up a bit.

Some of our GTO club members have tried different sized boosters. Only booster that provided the same amount of assistance was the dual 9" booster and driving their car I'd say it was pretty even to the stock booster. The 8" dual diaphragm came up a little short and produced a somewhat harder pedal. The dual 7" was down enough where it just about wasn't worth the purchase.

Power brake master cylinders are usually 1-1/16" bore which produces more fluid with shorter pedal travel and with a good working booster stops great. Manual brake cars usually require a 15/16" diameter master cylinder and the smaller bore gives more leverage with the cost of additional pedal travel. My '67 GTO also has two mounting holes on the brake pedal arm with the bottom hole for power assist and a top hole supplying more leverage for manual brakes. Manual disks are going to require much more effort. Going from your daily driver to your Pontiac with manual brakes isn't a big deal since you automatically start applying more push if the car isn't slowing fast enough. Make sure you have your safety belt on when getting back into your daily driver after cruising around all day with manual brakes because the first stop is going to be abrupt.

My drag car has 4 wheel manual disk brakes and one good thing is it always stops the same even if engine stops. My street car would loose vacuum assist and I'd be fighting the high ratio master cylinder and the extra resistance of the dead booster diaphragm.
 
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