Car - 1997 Honda del Sol S
Brakes - 1998 Honda Civic EX
MC - 1997 Honda del Sol S (13/16")
Brake Booster - 1997 Honda del Sol S

I recently upgraded to 10.3" front from a 98 Civic EX. All parts were functioning as normal previous to their removal from the car. I did all the work myself (removal and re-installation).

When I went to bleed the brakes after the install, I couldn't get them to bleed. Turns out my MC was bypassing (noticed a leak at the rear ball bearing seal). So I replaced it today. Bleeding went well, got all the air out of the system. Pedal seems firm. I star the car, and it falls flat.

My brake pedal will maintain pressure when the car is off. If I mash it ALL the way down, I hear a "groan" noise. When I start the car (AKA, apply vacuum to brakes), the pedal sinks to the floor. My car also gets a slight idle fluctuation when I vigorously pump the brakes.

Is this the brake booster?

 

the idle fluctuation is normal, as long as it isn't too severe. did you try pumping the brake pedal with the engine running?

 

Yes, that's where I get the idle fluctuation.

When the car is running, I can't stop the car. The pedal is just SUPER soft. Even though it's completely firm and feels normal with the car off.

 

damn that's weird. i didn't think brake boosters ever went bad but that's what it sounds like. you have the one-way valve on the hose right?

 

Yeah, I've got the one-way check valve. And I know it's working (and installed the right direction), because if I flip the hose, the brakes feel stiff when the car is running, but still can't stop the car -- ie, the brakes aren't getting vacuum.

 

do you have a service manual? maybe run through the flow chart for 'pedal sinks to floor' and see where that takes you.

edit: have you tried rolling the car while the engine isn't running and pressing the brake to see if they're working? i'm thinking maybe the master cylinder needs to be bled.

 

I'm taking it to a shop to have it put on a vacuum pump tomorrow morning. Hopefully, we'll figure out the issue and go from there.

My previous MC was bypassing, so maybe there's just a HUGE air pocket. I did all the leak and function tests in the service manual and passed with flying colors ... just can't brake.

 

what happened with this? did you get it sorted?

 

Turned out it was the fault of the new master cylinder.