i upgraded my crummy 9" manual drums to power front disc/rear 10" drum. sounds great right? except the boost is insane. i take the boost off and i have great pedal, but with it on there is no resistance all the way to the floor. the brakes work great, but there is no feel to them. it also labors my poor 225, and it sometimes stalls. conversion was from a 73 scamp. i'd just go back manual, but my wife is going to drive the car occasionally, and that just won't fly. can anybody tell me what i did wrong here?

It might be that the booster itself is bad.

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65 Dart station wagon slant 6 - now under construction
47 Dodge Custom 4 Door sedan
87 D100 Short Bed slant 6

Retired USAF 1966-1986
Retired US Postal Service 2004-2014

i might have thought that, but it's the second booster. the first did it too, both brand new

It should cause any issues with the running. Get a vacuum gauge. Excellent tool to have with a slant for tuning too!

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'72 Duster 198 stock cam, 3:23's Hookers on jack stands for 8 years in the driveway
'79 Maxivan 360 Offy Qjet Comp RV cam/rusting in the driveway.
93 D350 160HP Cummins Auto Dually Clubcab needs a injector pump
2005 Golden Couch Buick

What size (piston diameter) master cylinder are you using? I usually see "large" bore (1 & 1/16") units for power disc brakes. Did you use the complete pedal linkage from the donor car? The only design that I'm familiar with on A-bodies is the Midland-Ross booster which had a "multiplier" lever as part of its mounting bracket. The lever increased M/C travel while decreasing mechanical advantage at about a 2:1 ratio. Lastly, I believe there is also a choice as to what size pistons you can get on the front calipers, which also affect the overall hydraulic ratio.

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63 Valiant Wagon
225 - 4 bbl

i bought all new parts where i could, what they had in the system for a '73 scamp (donor car), took what i could from the scamp. bought a new rod for the extra distance. from what i had read beforehand it was supposed to be a straight bolt-on, and everything bolted on. i guess i should have investigated a bit further :/