Hey everyone I'm stumped. I found a upgradable brake kit to convert rear drums to disc but idk if I need new master cylinder & boosters? I have a 1978 Malibu Classic it came w the 3.8 V6. I had a 300+hp 4.3L V6 built so I wanna upgrade the brakes. Thanks in advance
1978 Malibu rear drum to disc conversion
- Thread starter Jay Clement
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You need a larger bore master cylinder and a disc/disc proportioning valve.
Hey Texas thanks. Any idea of the size bore I'd need? I'm planning on getting a set of moser dual piston disc for the rear and just run the stock up front. Or any way to direct me to find out the bore size I'd need?
You might want to discuss it with the folks you are buying the conversion from. The biggest bore stock g body cylinder I'm aware of is 1-1/8". My car is an 82 GP. It is front disc/rear drum. It was a diesel so it has the hydroboost system. The cylinder is the old style with the cast iron reservoir and metal top. I think there are later model cylinders with the big bore that have the aluminum body with plastic reservoir and top. I'm only just learning about this so I'm not an expert, but evidently some later 80's GM cars had a 'quick takeup' master cylinder'. It takes less pedal movement to be responsive. Look into those. With calipers in the rear, you have a lot more volume in the system so you need a cylinder that can move more volume or you end up with a pedal that moves too much and feels too soft. There is likely an aftermarket cylinder out there that also will fit the bill. Another way to 'tune' the system is to move the place where the rod from the booster connects to the pedal up some. Doing so gives you slightly less mechanical advantage (leverage) but more rod travel for the same amount of pedal movement.
Different G Body brake pedals have the rod attaching point at different locations relatve to the pedal pivot based on if it is a vacuum brake or hydroboost car.
Hopefully others will chime in with what they are using and how it feels. I think many G Bodies came with 7/8" or 1" bore cylinders so hopefully you will be fine with a 1-1/8" cylinder.
Just anecdotal, We put stock rear disc brakes from a 79-81 Firebird on my brother's 78 Z28. The stock master cylinder for that system is 1-1/8".
Hope this helps.
Different G Body brake pedals have the rod attaching point at different locations relatve to the pedal pivot based on if it is a vacuum brake or hydroboost car.
Hopefully others will chime in with what they are using and how it feels. I think many G Bodies came with 7/8" or 1" bore cylinders so hopefully you will be fine with a 1-1/8" cylinder.
Just anecdotal, We put stock rear disc brakes from a 79-81 Firebird on my brother's 78 Z28. The stock master cylinder for that system is 1-1/8".
Hope this helps.
i recently upgraded my brakes to c5 vette on the front and ls1 on the rear. i kept the stock proportioning valve and stock m/c that measures
7/8". after bleed the full system, i had a long, squishy pedal. it stopped but didn't feel right.
my next step was to swap in a m/c from an '86 mcss that i had. this was a quick take-up style that measured 24mm (15/16). the pedal feel was improved but i don't think it is right. i test drove it in the rain and tried several panic stops on a clear wet road, i was unable to get the brakes to lock. i believe this means i don't have enough brake pressure to the calipers. my next step will be to try a 1-1/8 mc, larger piston will generate more pres. i'll keep you posted
7/8". after bleed the full system, i had a long, squishy pedal. it stopped but didn't feel right.
my next step was to swap in a m/c from an '86 mcss that i had. this was a quick take-up style that measured 24mm (15/16). the pedal feel was improved but i don't think it is right. i test drove it in the rain and tried several panic stops on a clear wet road, i was unable to get the brakes to lock. i believe this means i don't have enough brake pressure to the calipers. my next step will be to try a 1-1/8 mc, larger piston will generate more pres. i'll keep you posted
You might also want to update the prop valve to a disc/disc type. Use one from an early 80s Toronado or Riviera from the boneyard or get an aftermarket replacement from someone like CPP or Inline Tube.
yes, I'm working towards that goal if necessary. baby steps. i want to change things one step at a time and verify I'm going in the right direction. I've spent many hours researching this and there is a lot of misinformation out there. I'm building this car in manner so my wife can drive it as a daily driver. last thing i want to hear is her bitching about the idiosyncrasies that i created. once i get the brake feel right, i'll address the proportioning valve issue if necessary.
Nice survivor! The rims add some understated flash. I always liked the Olds body line below the Landau windows, and your pinstripes highlight it. But I meant the '57 Carrera Panamerica...
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