Have to pump brakes

[73challenger_TN]

I have a problem. I have to pump my brake pedal a few times before they get any pressure.  I switched from a powerbooster to a new style manual master cylinder. I also changed over to chebbie disc brakes in the rear. I have a proportioning valve. I have bleed the brakes twice. It stops great when the pedal gets firm though so I don't think its the brakes doing it. Thanks alot!

[Chryco Psycho]

you have air in the system , are the calipers on the right way up , make sure the bleed screws are at the top

[Jacksboys]

air in the lines would have been my guess

[ntstlgl1970]

x3 air somewhere, could try bleeding the master cylinder too.

a less likely problem would be too long of a pushrod to the master (preload).

try bleeding first.....

[Aussie Challenger]

  My guess, was the master cylinder a new unit? if yes then as Chryco said calipers on wrong sides with bleeders facing down, swap them over.   

[73challenger_TN]

We figured it out. We screwed up the rear calipers putting them on somehow. We are going to replace them this week Thaniks alot

[73challenger_TN]

I replaced the calipers but now the brakes are squishy! I had a plug in the master cylinder to block off the back brakes and the brakes felt awesome! What could cause this? They are cadillac calipers by the way with a emergency brake.

[67vertman]

Air in the lines or calipers?  Did you check to see if the calipers need to be shimed to center pads?

Have someone hold the brakes, while you try and spin the rear wheels to see if you are getting good contact with the pads.

[73challenger_TN]

We couldn't spin it with the brakes held. Could the front brakes got air in them when we bled the back?

[Supercuda]

Guys, it's time to check the parking brake adjustment. With the GM caliper with the integral parking brake, it is necessary to cycle the parking brake several times, in order to set the correct travel for the caliper piston. The result of not doing this is a low or soft pedal, which firms up if pumped. When I replace pads on this style of caliper, I move the parking brake lever several times by hand, so that there is no question that I have the pads properly set. This is true with any caliper that uses this style of parking brake. You always have to turn the piston in when you service it, and turn it back out when the new pads are inserted. You also have to use your parking brake, or a low pedal will come to you as the rear pads wear.

[Bullitt-]

What's the condition of the rear brake hose?....Doesn't have to be cracked or leaking to be bad, they can balloon from an internal leak. .....  Also don't disks require more fluid, Do you have a master cylinder designed for 4-wheel disk?

[FJ5_440]

Guys, it's time to check the parking brake adjustment. With the GM caliper with the integral parking brake, it is necessary to cycle the parking brake several times, in order to set the correct travel for the caliper piston. The result of not doing this is a low or soft pedal, which firms up if pumped. When I replace pads on this style of caliper, I move the parking brake lever several times by hand, so that there is no question that I have the pads properly set. This is true with any caliper that uses this style of parking brake. You always have to turn the piston in when you service it, and turn it back out when the new pads are inserted. You also have to use your parking brake, or a low pedal will come to you as the rear pads wear.

This is quite a common swap for budget pro touring type cars.  You MUST set them correctly on install or you will never get them to feel right.

[73challenger_TN]

I took them off and ratcheted them. They are ALOT better but they are still soft until you pump them one time. I wish I would have just bought a wilwood setup now... It would have been a lot easier. I wonder if my master cylinder just isn't pumping enough fluid or maybe I still have some air in the lines? I read where a guy swapped these calipers on a toyota. He has the same problem so he put a residual valve on.

[Supercuda]

A residual pressure valve only masks the real problem, and wears out the rear brakes more quickly. You do not need to remove the calipers to ratchet out the pistons, and I am betting that you left some extra clearance between the pads and rotor, that you are still feeling. Leave them attached, and just cycle the parking brake lever on each caliper until you can't get any more adjustment. After you have done this, gravity bleed the rear system, making sure that you do not touch the pedal while the system is open. The volume of fluid required for disc brakes is not for the movement of the piston, but for the wear of the pads. As the piston is forced to move further out of the bore due to pad wear, the volume of fluid at the piston increases dramatically. This is why more volume is necessary. Regular, drum brake master cylinders can be used, but require constant vigilance to keep the master cylinder full.

[ntstlgl1970]

also to add to what supercuda mentioned, the pistons need to be aligned (the slot(s) in the piston) with the tit/tab on the inner pad, otherwise the piston won't sit flush against the pad and may cause other problems.