I've had this issue with my 96 accord where the brake pedal will go almost to the floor before it engages. It only happens immediately after the car is cranked, hot or cold. I replaced the master cylinder and it made no difference. I just realized I forgot to bleed the abs modulator so I did that. It didn't help either. This is my 16 year old daughters car so I MUST get it fixed quickly. Any help would be appreciated.

 

Did you bench-bleed the new MC? If not, it seems like you need to bleed a tremendous amount of fluid thru the system in order to work all the air from the MC.

It's also possible that the brake pedal pushrod length needs to be adjusted. Honda has a special tool for that. I'm not really sure if your problem can be caused by it being too long or too short.

 

I did bench bleed the new master cylinder. But I had this problem before I replaced it.

 

Yeah. The strange thing for me is why it would do this ONLY when youjust start it. I can't think of a reason for it to happen like that.

 

Today it did something really bad. The pedal went to the floor and there was NO pressure. I couldn't even pump any pressure. Of course after a few seconds the pressure returned. That was after I had drifted into a 4 lane! Fortunately nothing was coming.
And again, it happened right after I started the car and was pulling out of a parking lot.

 

That kills my next idea...
I was about to suggest checking all the calipers. If something pushes the pads away from the rotors, the pedal will go to the floor first time. But pumping WILL work. And I don'tknow what sort of problem would keep pushing the pads out.

Lack of vacuum at the booster would result in a very HARD pedal. It'll require plenty of muscle to stop the car, but the pedal won't go down.

How about old stale fluid back in the calipers? A long shot, because I'd guess you bled fresh fluid completely around when you installed the new MC. Did that bleeding exercise behave normally or was there anything unusual?

 

I did accidently pour a little fluid from the catch bottle into the reservoir when I was bleeding. I'm pretty sure I pushed it through the system though. I have gone through 1/2 quart on the master cylinder swap.

Just for the record, I replaced the front brakes 12,000 miles ago and just recently replaced the rear.
Maybe I should go through the system one more time. It's just a pain unless I'm sure it will help.

 

Well, if it were my car I'd bleed all wheels again. I wish I could say that I'mSURE it would help.

 

Are you losing any fluid? If the fluid is not being lost, the only explanation is a leaking MC. I know it's new, but that's the only place fluid can bypass to reduce pedal pressure. Assuming no air, as you press the brake pedal fluid is immediately bypassing, hence no pedal. A defective part is not unheard. Is this an OEM master cylinder?

good luck

 

Not losing fluid.