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 Post Posted: Thu Jun 01, 2017 2:03 pm 

Joined: Tue May 30, 2017 4:47 pm
Posts: 1
swapped a rear GM 8.6 axle with disc brakes from a '99 Sierra into the rear of a '77 Malibu station wagon. Even with the metering valve removed from the Malibus combination valve don't have any stopping power, hard pedal, but slow to stop. From reading various threads on this forum guessing it's that the bore on the old Malibu drum/disc master cylinder isnt big enough and cant drive enough pressure for disc brakes on all four wheels. So go back to junkyard and get the booster and master from the Sierra the axle came from? The Sierra has a single reservoir master but the bore is 1/4" bigger....

 Post Posted: Thu Jun 01, 2017 4:06 pm 
Amateur Racer

Joined: Tue Jun 08, 2004 1:06 pm
Posts: 226
Location: Houston, TX
Usually a hard pedal is from a bad vacuum booster or your engine doesn't make enough vacuum to where your booster will not work.

If you master cylinder could NOT supply the volume, you would have a long pedal stroke and maybe go to the floor because it could not build pressure.

Smaller bore master cylinder build more line pressure than a larger bore master cylinder.

Usually with a rear disc swap, the only thing you will have to worry about is the stock drum brake side of the reservoir is too small and may run out of fluid. If this is the case, you pedal would most likely go to the floor.

With the information given, I can only guess its your booster.

David Schultz

 Post Posted: Thu Jun 01, 2017 7:32 pm 
MalibuRacing Junkie
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Joined: Sat May 15, 2004 7:26 am
Posts: 15822
Location: North Jersey
A disc/disc power master cylinder should have roughly 1-1/16" bore...


20k mile '80 Malibu, currently undergoing long term (aka no money) factory style install LS6 454, Cowl Induction, Legend LGT 700 5 speed. Full Global West suspension, 17" N90 wheels, 12" front/11" rear disc brakes, 9" 3.70 Auburn Pro posi.

"The older I get, the faster I was"

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