240Z Brake Bleeding

[billf]

Hi all. I race in ITB, and not ITS (yet). My problem involves a Z that I've worked on for years...more than I'd care to admit to. I have changed all hydraulic brake parts, hardware and pads/shoes, and have not yet been able to successfully bleed the system.

With new master cylinder #1, I was left with a half pedal, very spongy and unpredictable pedal level. After bleeding with all known methods known to man, even power bleeder, I ended with the above described result.

After installing master cylinder #2 (thinking the first MUST be defective), I barely move fluid thru the lines, and the pedal is always on the floor. There is a small amount of free pedal felt, then the pedal can be moved to the floor with "minimal" resistance...ie: slightly more resistance than with the movement at the top (free Pedal). Fluid arrives at the wheel cylinder clear, and bubble free.

When changed over, the booster was undisturbed. Only the master cylinder and lines were touched.

Can anyone (or more) lead me down the trail to a functioning brake system?

My e mail address is [email protected] if any interest is in personal communication.

Anything would be appreciated.

Thanks in advance.

Bill Frieder

[terry]

Did you bleed the master?

[billf]

Yes, each time that it was changed, and then at the start of each cycle. My confusion starts when there is NO resistance...ie no spongy pedal, and no force behind the flow of fluid at each wheel cylinder.

Thanks for the thoughts.

Bill

[Tom Donnelly]

A bad brake booster might could do that. I had a booster give out on my old 280z and it was like no pedal pressure at all. But it only happened once in 20 years.

This was after I replaced the master cylinder, flushed the system, rebuilt the calipers, replaced a questionable brake line and replaced all the brake hoses.

The booster was "untouched". It turned out to have a pinhole leak. No apparent vacuum leak, just a pedal that was really mushy. Went to the floor and then caught like an on/off switch. I replaced the booster with a spare and the problem disappeared.

[irondragon]

Re 240Z brake bleeding:
Have you verified that the front calipers are not reversed?
I got a pair on the wrong way once and failed to notice that the bleeders were on the bottom instead of up top. No way would the system bleed till I got those bleeders up where the air was.
It's a dumb but easy mistake to make if you are in a hurry.
Best Regards - Bill Miskoe

[powerslide91]

I'm not sure of good suggestions, I have always thought the Zcar system was pretty easy to bleed. On my car I had replaced the system a few times and alwyas had pretty good luck. Sometimes when all the parts are new I would bleed it, then run is at low speed for a while to bed things in. I also think this helped rattle tiny bubbles that get caught in the parts loose so they collect. Then follow it up with another good bleeding.

Here is another random thought, are the rear wheel shoes adjusted up and making contact? On my car the adjusters were removed so I would adjust them by hand after each session to keep the pedal nice and high. If I skipped a session the pedal would get pretty low, and I guess if I kept letting it go it would run out of travel at some point. Just something else to double check since I would normally spin the adjusters back when replacing the shoes to make it easier to get the drums on and off.

I have heard of rebuild calipers not having the bolts that hold the caliper halves tight (though I have never seen that first hand). No matter, when I replaced the calipers, I always checked those bolts to make sure they would not spread under brake pressure.

Sorry all I have is some random suggestions to help you spend more time in the garage....

Jeff
- Zcar no more