Brake Master Cylinder Questions

[twsutt]

Great! Now you tell me. Oh well, I guess that I'll probably get to re-do everything within three months. At least brake fluid is dirt cheap.

[twsutt]

Okay, so I took my time and properly bled the brakes - I was rushing things and kept letting the fluid drop down so low that I was allowing air to get back into the lines through the brake fluid reservoir.:lick: Everything seems good, pedal pressure is strong the brakes will even lock up if I slam on the pedal - something that was impossible before replacing the MC & booster. So, I took it out on a little ~130 mile test run and ran into a traffic jam on the last 10 miles of the trip. This stop-and-go traffic had my foot on the brakes more than on the gas pedal - and my brake pedal kept reaching further and further toward the floor. By the time I got home the brakes were almost gone.

I checked under the hood to find that the reservoirs, both front and rear, were empty. I jacked up the car, removed the wheels and checked all of the brake line connections and bleeders for leaking. The leaks are where the brake lines connect to the MC. I tightened the connections as much as I'm willing to - I'm afraid of stripping things out. But it still seems to be leaking. Is it adviseable to wrap teflon tape around the threads of the brake lines or will the temperatures/pressure be too great for teflon tape?

*For those of you that have experience with brake fluid; yes the leaking brake fluid completely removed the paint from the frame rail. I guess that Por-15 will be in my future.

[sblake01]

The problem with doing that is that teflon tape isn't designed to use on flare fittings and might actually keep them from seating properly.

[al'z]

Teflon tape will not do the trick. If you look carefully, you will notice that the mating surfaces of the brake lines to the MC match. That is, one is concave and one is convex. This is the "sealing point", not the threads (that happens with pipe thread b/c it's tapered). What you have is straight thread that are used to keep the mating surfaces tight and sealed with metal to metal contact.

Hopefully you did not strip the MC female threads. If you had to use a wrench to install the line from start to finish, you likely stripped it-sorry. If you were able to work the line by hand until the very end, you likely didn't tighten it enough-easy fix. To know if you have enough torque on the line nut make sure you are using a properly sized tubing wrench (this looks like a six-sided box-end wrench with a small part missing). After running the line by hand turn it with your wrench another fifteen degrees or so. This should not require full-strength on your part.

If you do this and it still leaks, remove the line and check the mating surfaces for rust pits, gouges or irregularities. You can usually get away with replacing the line from the MC to the proportioning valve if pitting is present.

Good luck.

[sblake01]

tubing wrench (this looks like a six-sided box-end wrench with a small part missing)

More commonly known as a flare wrench. Hope that's what you're using on your brake lines.

[twsutt]

I probably crossthreadded the connections. If so, I'll have to take it back to swap it out for another rebuilt MC. Besides, I just noticed that thay gave me a 13/16" MC anyway - not the 7/8" that it's supposed to have.

[Arne]

There's another possibility, considering that this is a rebuilt unit. I've seen a few rebuilts where the rebuilder forgot to re-install the cone-shaped flare seats in the ports. If that's the case, it doesn't matter how tight you get the fittings, it won't seal.

As for cross-threading, you are (unfortunately) much more likely to damage the threads on the line nuts, not the threads in the cylinder.

[twsutt]

Last weekend I finally got a chance to get under the hood and take things apart to see what is causing the leak. The brake lines weren't cross threaded as I had suspected - the problem appears to be that a small amount of rust formed on the end of the brake line fitting causing several small pits. I see that Black Dragon Auto has metric brake lines availble for next to nothing (http://www.blackdragonauto.com/ICATALOG/Z/full.aspx?Page=106).

Does anyone happen to know the length of the brake lines from the Master Cylinder to the Brake Switch Assembly? (I'm at work and my Z is in my garage.)

If I buy too long of a line, can I put the excess into a corkscrew?

Will my brakes be adversely affected by a few extra inches of brake line?

[Arne]

I see that Black Dragon Auto has metric brake lines availble for next to nothing (http://www.blackdragonauto.com/ICATALOG/Z/full.aspx?Page=106).

You should be able to get generic metric hard lines from most any auto parts house. No need to mail order it and pay shipping costs.

Does anyone happen to know the length of the brake lines from the Master Cylinder to the Brake Switch Assembly? (I'm at work and my Z is in my garage.)

Not off hand, especially for a 280Z. Not too long, though.

If I buy too long of a line, can I put the excess into a corkscrew?

Yes.

Will my brakes be adversely affected by a few extra inches of brake line?

No, no effect at all.

[trykflyr]

If you're going to bend that extra length, be SURE to use a tubing bender so you don't kink the line. Any sharp kink will cause problems and if you try to straighten it, you'll crack the line. A method for very short runs and tight bends is to fill the line with fluid, cap the ends, and then bend it by hand. You're essentially bending a solid rod and the tubing walls won't collapse. It's pretty astonishing how tight a bend you can actually get using this method. I've used it to bend aluminum hydraullic tubing in systems running 3000 psi and 30 gpm. Learned it in Battle Damage Repair school in the Air Force.

[mikewags]

Don't mean to Hijack the thread here, but in your experience; whats the average cost of a new brake master cylinder for a 1975 280z? Mine has surface rust all over it, and instead of cleaning and painting it; i've thought of getting a new one.

[twsutt]

mikewags,

A new master cylinder will run around $270. A rebuilt master cylinder could be as low as $38.