Brake Issue, Need Answers


Pro Stocker
May 27, 2003
New York
Im sure some of you have read this on another forum but the answers have been slow and I need a fix.
I replaced everything in my 81 Malibu. Master, calipers, proportioning valve, rubber lines and wheel cylinders. The wheel cylinders are 1" bore that came with the Torino 11" drum brake in the Moser 12 bolt rear.
I also replaced the booster with a generic dual diaphragm instead of the single that came on the car.
Ive bled the master and the whole system multiple times. The pedal is still soft and goes almost down to the floor. The car is not running. Repeat ! Its not running.

Two weeks ago I finished doing the complete brake system on my 83 Malibu wagon. Again, this car is also not running. The pedal is much harder and doesnt go down as far as the pedal in the coupe. Not even close.

I spoke to someone in tech support at Master Power Brakes. The guy there said that the issue is probably the fact the wheel cylinder bore is 1" and the original rears were only 3/4". He said I would need a bigger bore master cylinder. At least 1 1/8 instead of the original 1".
Guys on the forum said thats incorrect.
Other replies said I might have the wrong pin in the booster. Too long and its not letting the correct amount of fluid into the lines for the rear.

Anyone else have a problem like this ? Im sure someone on MR put in a Moser rear with the Torino drum setup.
Im posting this question all over the place guys. I need to get this solved.

LS6 Tommy

MalibuRacing Junkie
May 15, 2004
North Jersey
I think you need more volume, too. A large bore will give you a harder pedal, but it will move more volume of fluid. MP Brakes knows what they're doing. They spec'd a 1-1/8" bore master for my 4 wheel disc power brake setup. The car is not on the road, but they tell me that is their standard setup.