koolaid_kid

iTrader: (21)

This is on my neighbor's 98 Accord. I got in it today with the engine not running. Pedal felt fine. With my foot still on the pedal, I started the engine. The pedal went almost to the floor. He told me he had been pumping the pedal to get it to stop when he drives it.
I had three thoughts:
1) Vacuum leak, causing havoc with the brake booster.
2) Bad booster.
3) Air in the system, with a possible leak since he said has been getting worse. But the MC is still full of fluid, and prior to starting, the pedal felt fine to me.
Any help would be appreciated.

35th SS

iTrader: (2)

bad/faulty brake booster.

koolaid_kid

iTrader: (21)

Or could it be a faulty master cylinder, which does not show up until the booster applies its multiplication factor?
I just don't want to go into parts replacement mode. I suspect one or the other, but not both.

Wesmanw02

iTrader: (4)

Master cylinder is bad. The only other thing that would cause that is a leak in a caliper/wheel cylinder/brake line, but you say the MC is full, so thats not it.

The problem isn't the booster. If the booster is bad you will lose assist, it will not cause the pedal to drop to the floor. You would just need a lot more pedal pressure to stop the car.

koolaid_kid

iTrader: (21)

That is what I thought as well. Since the booster's function is to, well, boost, it would make more sense that a faulty one would make for a more difficult (harder) pedal, not go to the floor.

koolaid_kid

iTrader: (21)

O.K., the master cylinder did not fix it. There aren't that many parts left. It does not have ABS, the rear cylinders do not appear to be leaking (nor is the master cylinder loosing fluid. Air in lines or booster. (Disclaimer, I did not bleed the brakes, he did.)
Any thoughts?

Wesmanw02

iTrader: (4)

Was the master cylinder bench bled first?? That is critical.

koolaid_kid

iTrader: (21)

IDK, he did it, not me. If not, how do I overcome his booboo?

Wesmanw02

iTrader: (4)

Not much you can do besides pull the master cylinder back out of the car and re-bleed it. Just about all reman/new master cylinders come with bleeder kits and instructions on how do to it. Basically you install the included plastic fittings into the ports, run the plastic hoses from the fittings to the reservior, fill the reservior with fluid, and work the pushrod until you don't see any more air bubbles in the hoses. Then the master cylinder is bench bled and ready to be installed. Then you have to bleed the rest of the system as usual.

There are only 3 things that will cause the pedal to go to the floor - a defective master, a leak in the system, or air in the system. Consider that when you diagnosis the car.