77cutlassLS3

I have a 77 Olds Cutlass that I had a local shop do a 6.2L LS3 swap in. We upgraded the brakes with 13" C4 corvette fronts w/ dual piston C4 vette calipers and pads,rears are redrilled 84-86 Mustang w/ 82-88 Camaro calipers and pads. Because of budgetary constraints we used the stock brake booster with a 77-82 Vette master cylinder and proportioning valve. Since completion the brakes work descent but there is a significant pedal travel before they engage. Brakes will lock and stop the car but the pedal is almost on the floor before engaging. I have talked to several other people at car shows with LS swaps and all have the same problem. Is this because an LS3 doesn't produce enough vacuum? Looking for advice on a fix for this.

ls1nova71

iTrader: (4)

Low vacuum wont make the pedal travel longer, but it may make the pedal harder to push since there will be less assist, but that's not what you're describing. It sounds like you have too small of a brake master cylinder bore, but you could try adjusting the brake booster push rod at the pedal and see if that helps.

33willys

iTrader: (1)

Don't believe vacuum is your problem because you can lock them up albeit lots of pedal travel. Your problem seems to be adjustment. First, the rod from the pedal to the booster should be adjusted for about 1" (or less) of travel 'till resistance is felt. Next is the adjustment between the booster and M/C which should be about 1/16". I think if those two adjustments will bring your system up to par.

hookemdevils22

iTrader: (12)

OP's master is a 1 1/8" bore, while the C4 had 7/8". I agree that the push rod likely needs adjustment.

ijimmy

Agree with the master cylinder being your issue , what is your vacuum at idle ? ,Ill bet its sufficient . Strong vacuum will decrees effort , not travel , master cylinder bore size effects travel , as well as the placement of the the fulcrum on the pedal , I have several ls retrofitted vehicles , they all stop better than before the conversion , because I upgraded the whole brake system to handle the increased performance

77cutlassLS3

Thanks everyone for your advice. I will investigate the master cylinder bore suggestion. I'm told there is no adjustment to the master cylinder push rod and have been reluctant to try the pedal adjustment rod because it is very difficult to get to on this car. I think I will have to break down and try that also.

jozw30