axle/disc brake swap help

mdvana

New Member
May 30, 2017
1
0
0
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....
 

malibudave1978

Amateur Racer
Jun 8, 2004
226
0
0
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.
 

LS6 Tommy

MalibuRacing Junkie
May 15, 2004
15,847
1
38
North Jersey
A disc/disc power master cylinder should have roughly 1-1/16" bore...

Tommy
 

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