soft pedal with LS1 brakes- HELP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[TMat]

Here's my situation- I have a 69 camaro which I have put LS1 brakes all around, with a new manual (non-power) 15/16" bore MC . After rolling the car 20 feet the brake pedal goes soft, but if you pump it, it comes back up.

I checked the runout of the rotors and found the driver rear has about .015. This is using the rotor from the driver side and then swapping the pass. side rotor to the driver side and checking the runout. I got .015. I replaced the axle. I still have excessive runout.

Last summer I swapped my rear gears for 3.08 with an open diff, at the same time I changed the brake system. Could the carrier be causing the problem, or do I have the wrong size MC? Any ideas would be helpful.

[bowtie65]

Man Trev, I thought you figured that problem out. That sux!

[chicane67]

Sounds like seeping air into the system... or you still dont have all of it out yet.

Diff wont effect it.

Possible worng master... but 7/8 to 15/16 is right in the ball park for that system (manual).

[paul67]

Is that the same master cylinder bore as the original should have been for the calipers if so ,then check how far the rod moves in the master comperd to a car running those calipers as you might not be moving enough oil until you do then the next pump.

[Hammered]

This is a good resource for these type problems: http://www.mpbrakes.com/technical-support/troubleshooting-disc-05.cfm