My new discs suck!

[BigBlockBabe]

I don't know what's wrong! I just switched to disc brakes using the spindles and proportioning valve from a 71 C-body like mine, a dual master cylinder attached to the pre-existing brake booster, and everything else new. The brake pedal doesn't seem to engage until it is half-way down. If I stomp on the pedal the car just slows... than stops. I've bled the brakes and m/c, the calipers are facing the right way, and I know the m/c works because it came of a working brake system.

Could it be that the 65 pedal/booster does not move the rod far enough? The original single cylinder m/c is considerably shorter than any dual m/c. The rod length has been adjusted so that it engages the piston as soon as the pedal is pressed.

Advise would be greatly appreciated.

[99 DeSoto]

Go to www.hotrodsusa.com and read Dean Oshiro's article on brakes. Dean knows everything!
jim

[Jims451]

It may be the pushrod, or the master cylinder uses a smaller piston diameter. I think you can get larger piston diameter master cylinders.

It's just basic physics, If the Master cylinder has a larger piston it will take less piston travel to build pressure, but you will also have to push the brake harder, but this may not be a big problem with power brakes or if you like a firm brake pedal.

[PRO]

Dont overlook rear brake adjustment and bleeding,(your sure the proportioning valve is plumbed right?)you possibly could have a bad booster,usually they have an external vaccum leak spray carb cleaner around the seam that mates the 2 halves while its runnug,if your rpm changes its bad if thats ok turn the car off and depress the pedal 3 times,it should have an assist "feel" to it at least this many times if it doesnt its bad.Then pull the master loose from the booster and look for brake fluid if its present its bad.If all this checks ok then jack up all 4 wheels and have someone in the car and start and put it in gear and slowly apply the brakes,what your looking for here is 1 or more wheels that are NOT engaging in unision or at all,hope this helps........PRO....

[BigBlockBabe]

PRO:
Everything checks out fine that you mentioned, but I haven't had a chance to check if all the tires are engaging, because the car is pretty big and I don't have enough jacks to raise it entirely but watching the car brake the tires seems to stop spinning at the same time. Wouldn't I feel the car pull when I apply the brakes if something wasn't engaging?

Could the pads be seeding, and therefore feeling weak?

Thanks for the help.