Weak brakes

[black gold man]

Rear brake adjustment. Adjust by hand if auto adjusters not working.

Raise rear tires you should feel slight drag on the drum when you rotate

the wheel by hand with properly adjusted rear brakes. And a firm pedal.

[Zed Head]

Still not clear what "weak" means, or "light" or "very little resistance." If the pedal has very little resistance it must be going to the floor. Right?

Just trying to help you describe the issue.

[Lani Kai]

Well, before I replaced the MC and re-bled it, the pedal didn't quite go to the floor, and would firm up after a few pumps. Pedal felt fine immediately after bleeding, but with the engine running it goes to the floor and pumping doesn't build up resistance. I can hear the idle speed change as when I step on the brake pedal though.

[EverRude]

I suspect, you suspect the booster. If engine idle changes when you press on brake I suspect booster as well. The booster uses engine vacuum to increase braking power. When booster develops leak the vacuum leak affects how the engine runs. More you press pedal the bigger the leak and greater more noticible effect on engine.

Good luck.

PS check our your photographs. Really beautiful work. Have any like that of your Z?

[Zed Head]

I agree with ER on the idle speed change indicating the booster leaking vacuum. Is there a hissing noise also?

The pedal going to the floor could indicate air still in the lines or a leaking cylinder, most likely the master if you don't have fluid leaking from the wheel cylinders or calipers.

Or as bgm suggested, your rear brakes are out of adjustment and you're just pushing the wheel cylinders way out of their bores. The calipers are self-adjusting but the back drums are not. Does the parking brake handle come way up or does it set tight and low? If it comes way up, you can try setting and releasing it several times. Otherwise, a screwdriver through that little hole on the drums, or remove the drums and turn the wheel.

It sounds like you have the same problems you started with. Bummer.

[Lani Kai]

I suspect, you suspect the booster. If engine idle changes when you press on brake I suspect booster as well. The booster uses engine vacuum to increase braking power. When booster develops leak the vacuum leak affects how the engine runs. More you press pedal the bigger the leak and greater more noticible effect on engine.

Good luck.

PS check our your photographs. Really beautiful work. Have any like that of your Z?

Thanks for the compliments; I don't have any photos of the Z yet because it's still mostly stripped down, but I definitely will once it's finished.

I agree with ER on the idle speed change indicating the booster leaking vacuum. Is there a hissing noise also?

The pedal going to the floor could indicate air still in the lines or a leaking cylinder, most likely the master if you don't have fluid leaking from the wheel cylinders or calipers.

Or as bgm suggested, your rear brakes are out of adjustment and you're just pushing the wheel cylinders way out of their bores. The calipers are self-adjusting but the back drums are not. Does the parking brake handle come way up or does it set tight and low? If it comes way up, you can try setting and releasing it several times. Otherwise, a screwdriver through that little hole on the drums, or remove the drums and turn the wheel.

It sounds like you have the same problems you started with. Bummer.

I didn't notice a hissing noise, but the thing about idle change makes sense. Are there common problem spots, assuming my new booster isn't defective?

I'm guessing the pedal becoming light with the engine running seems to indicate that the main cause doesn't lie with the booster; it's only exacerbating the symptoms because it puts more force on the brake system.

The parking brake comes up pretty high; I'd say to about 60 degrees? I read about the auto-adjust feature in the FSM so I will try that out later today, as well as a manual adjustment if necessary.

[ZCurves]

I concur with Zed Head and EverRude - looking more like the Booster. But I wanted to add my suggestionz as well.

After all of this work that you have done, I strongly suggest the following (in addition to changing out the Booster).

Here we go.

• Check the Vacuum Check Valve. Many modern Nissans use the same check valve - the Z has a big rubber spacer over it. You might find one off of a wreck.
  
• Check the rubber line going to the Check Valve and then on to the Booster. It should be snug, if not RTV it.
  
• Check the movement of the Caliper Pistons AND Rear Cyl. Look for binding.
  
• Clean,Lube and Properly Adjust the E-Brake Adjusters. There should be significant drag if you are doing this by hand. Remember, the drag will be nothing when a 1000+ lbs is sitting on it.
  
• Remove and clean out the Proportioning Valve.
  

The last one is almost always overlooked. Most of us know that it is there, but few have removed it and cleaned it out. You will be absolutely amazed at what comes out of it. More than likely the Plunger is seized up with years of crud. I urge you to take the time to clean it out. If you choose to accept this task, be gentle with the flared fittings -they are soft like the others on the MC. I am attaching a .pdf for your viewing/rebuilding pleasure:).

[Arcspark80]

I know if the check valve is installed in the wrong direction it will affect your engine rpms. did you make sure to install it in the proper direction?.. Im having brake issues myself with my pedal not building up enough pressure to stop. Just saw the thread about adjusting the rear brakes. Im gonna try that, because I know my e-handle goes up pretty high and doesnt actually seem to be working as well as it should.

[Z train]

Odds are the adjusters are frozen.