Hey guys, I just rebuilt my engine and now that it's running and driving again my brakes are acting up. When I press the brake the first time the pedal goes straight to the floor and then on the second time the brakes have pressure on the pedal again. We just replaced the master brake cylinder but the problem remains. Looked over everything else and it all looks good. ABS light is on but the issue seems to be mechanical. Anyone have any ideas? Thanks, Zane.

 

It's likely air in the master cylinder and brake lines (and a lot of it). I'd suggest a full bleed using the old school "one person pumps brakes, other person twists your nipples" (you know what I mean!). For a master cylinder replacement, this makes sure you get the air out of the cylinder. Keep brake fluid at least halfway full in the reservoir so you don't reintroduce air.

 

Another "one in a million"...check to make sure the linkage where the brake pedal meets the master cylinder plunger is correctly installed. This month's Car & Driver had a freaky failure on their test Mustang Boss 302 where this linkage was installed incorrectly and broke, leaving them with no brakes during 60-0 brake testing. Fortunately no wreck, but makes you wonder...

 

I've bleed about a half gallon out of the lines thinking it was just air but I'm pretty sure we have all the air out. I'll check the brake pedal plunger but since the problem started before we replaced the "bad" master cylinder I doubt it's that. Thanks for the input. Still open for more ideas though.