I have a 1984 Accord. I am losing brake fluid but do not know where. The brake pedal goes to the floor. I have checked all four wheels, no leaks at the wheel cylinders, I do not see a leak at the master cylinder.
What am I missing?

 

it could still be the master cylinder. some leaks are hidden. i have never worked on an Accord that old before but doubt master cylinder's have changed much over the years.

 

You have probably checked this but trace all the lines with your fingers. It's an 84 could be anywhere. Sorry not much help.

 

Do you also have failed-booster symptoms? E.g., hissing sound, pedal feel not changing when you start the car?

I seem to recall that it is possible for the MC to leak fluid into the booster and then have it sucked into the intake manifold. Check the inside of the booster vacuum line for fluid.

Roy

 

Leaks in the 4 brake cylinders/calipers would have to leak OUT, so you'll find evidence of the leak.

Master cylinder is the only place where it can leak internally. It leaks back into the reservoir as it loses pressure. The classic description of a bad MC goes like this:
- Brakes feel nice & normal when you first apply them. Not soft.
- Pedal sinks smoothly to the floor while you're holding it, say at a red light.

 

A leaking MC will also allow brakes to be "pumped up" to hold, but pedal will gradually fall as fluid leaks by piston of MC.

good luck

 

He says he is "losing" fluid. I assume that means he has been adding fluid to compensate for the loss. If that is the case, a typical MC internal piston seal leak doesn't fit.

 

Yeah, that's true if he has to keep adding fluid.

A neighbor had one where it was leaking past the MC piston rod & filling up the vacuum booster. That thing can hold a lot of fluid before it starts leaking out.

 

Thanks for the advice from all. I think that I am going to replace the master cylinder. I will report back.

 

Carefully check the length of the pushrod, old vs. new mastercylinder. If they are different, there's a procedure (using a strange proprietary tool) to adjust the pedal pushrod. Hopefully they'll be exactly the same.