So my brakes aren't working properly. Through some searching on the almighty Google it appeared to be the BMC, so I replaced it. Now I'm only having half of the original issue.Initially if I even touched the brake pedal it would sink to the floor and not come back up unless pulled all the way back causing the brakes to lock up and stop the car. I literally just finished the install of my BMC and the same thing happens except for when the car is off. Now it will get firm when the engine is not running but if I start the engine and push on the pedal it will go to the floor and not come up until pulled. Please help me figure this out TR.

 

Did you bleed the system...pass. rear 1st, drvr rear 2nd, pass. front 3rd and last but not least... Or did you not hook the peddle back up to the push rod maybe?

 

i'd almost say it is a combo of air in the lines and a dead/dying caliper.
when you replaced the BMC did you replace the booster as well?
the booster could be shot too. I've never experienced the check valve failing, so i'm not sure what symptoms that would give you, but you might as well rule that out too.

 

I've been told that if one shakes the BMC and you hear A LOT of shit in there rattling around, it's nearly shot.

 

Did you bench bleed the bmc before you put it in? Get it from advance?

 

I didn't bleed the calipers yet, after the install I hoped in and tested the pedal got the same BS jumped out slammed the door and gave the car the finger. Nope just the BMC I don't think any of my calipers are dying. When I started looking for the source of this problem I thoroughly inspected all four corners. Also my reservoir was full when I started the BMC replacement. I think I'll hunt down a check valve and hope that's the issue the booster is mad expensive. I already returned the old BMC as a core so I can't try that lol.Yep bench bled as per the supplied instructions. Advance is really my only option next to pepboys.I'm going to vacuum bleed the brakes tomorrow when it isn't raining. Any of you have a spare booster you could sell me if that's the problem? Hang on to it if you can I might have to buy it.

 

so you installed the new master cylinder and didnt bleed the brakes after?

 

Yeah, this. If you don't bleed the brakes.... they don't work.

Also boosters never go bad.

 

Seriously?

 

I know I haven't finished the job because the calipers haven't been bled. But the issue I'm having difficulty understanding is how they work fine when there is no vacuum but when vacuum is supplied they malfunction. Something I forgot to mention earlier is if I rev the engine the pedal moves up and down with the engine speed I.E. revs up pedal rises a bit back to idle pedal goes down, higher rev up pedal goes even higher.