Travel in brake pedal issue/question

[LM7_67]

I've been working on swapping my front brakes to C6 vette units the past few weeks, and I got to bleed them tonight. I used a kore3 kit with a new 1" bore MC (switching from a 1 1/8") bore. The application I looked up for the MC was a '71 'vette with manual brakes I believe. Anyway, after bleeding the brakes, I have 2 - 3 inches of pedal travel with very little resistance and then it firms up abruptly. The pedal is slow to return to resting height through this section of pedal travel. To me, it feels as though the pin sticking out of the booster is not long enough to reach the MC so that loose pedal travel is the pin reaching the back of the MC. I already have the longer of the 2 pin sizes in there. Has anyone had a problem like this before? Ideas? Solutions? TIA!

[Ripped]

I think the best way to tackle this is step by step.

Make certain that you've bled the master cylinder properly.
If for some reason the master cylinder was pumped, when it was dry, there is a possibility that the piston seals might have been damaged.

What about the rear brakes? Is there any air in those lines?

Next make sure that the calipers are not reversed (ask me how I know) If they were reversed, there could be a lot of air in them.

When bleeding the calipers, have someone rap them hard with a fiberglass hammer handle to clear all the air bubbles.

Examine all your linkage including the pushrod, for slack.

You are using a smaller m/c bore, so it's not going to move the caliper pistons as fast, however it sounds like you have a lot of travel before you get 'bite'.

The baer (6 piston) calipers I have use the corvette pads and I have a 15/16 bore m/c. Everything works fine, no slack in the pedal, as you describe.

Also if the pedal feels mushy, make sure your firewall is nice and stiff, where the m/c mounts.

Hope that helps, good luck.

[LM7_67]

did some more investigating tonight... seems as though the rear brakes aren't applying at all. and the brake light is on. so I think there's just more air in the rear lines and the shuttle valve moved to set the brake light. once I get the air out of the rear lines, the pressure should equalize and the shuttle valve move back to its original position, right?

[Ripped]

It sounds like you have it.
Just remember to bleed the furthest from the m/c 1st, and maybe re-check the fronts.

Might be an idea to flush the brake fluid, while you're at it.

Good luck

[quarterbooty]

did some more investigating tonight... seems as though the rear brakes aren't applying at all. and the brake light is on. so I think there's just more air in the rear lines and the shuttle valve moved to set the brake light. once I get the air out of the rear lines, the pressure should equalize and the shuttle valve move back to its original position, right?

Reset the combination valve by holding the button on the metering valve down (if it's a disc/drum valve), or vent the high pressure side (i.e., the front circuit) to equalize the pressure. I've had success with the latter approach. Open a bleeder on one of the front calipers and pump the pedal several times until the brake warning light goes out. During this time, you should be pumping out the typical volume of fluid and the pedal should feel like you would expect it to during bleeding. When the valve resets (brake warning light goes out), close the front circuit and return to the proper bleeding order. Now the rear circuit should bleed like it is supposed to, which will let you get out the residual air.

[MCB Matt]

Quarterbooty has it right, follow his directions and open the front to equalize the pressure and you should be fine!

Matt