I am at my wit's end with these brakes!

[KDMatt]

Quick Update:

I'm not sure, but I might be on to something now.

I plugged off the outlets on the master again, and started to give it another round of bleeding, and I'm noticing that when it's sealed off, closed up, and plugged off, the pedal still has a bit of squishy give to it.

It's been so long since I've had 'normal' brakes, I can't remember how much give is normal in the pedal, but I feel like with the master cylinder isolated and blocked off (and properly bled, well theoretically) there shouldn't be any movement in the pedal, or at least very, very little, yet I still get some.

I was having these symptoms with the original master that was in the car, and while it does seem a bit unlikely that the rebuilt unit I have in there now would also be bad, I'm having trouble ruling it out entirely. It was a relatively inexpensive rebuilt unit from Autozone, and at this point I'm not above casting some doubt on it.

What are you guys' thoughts? How much 'give' should my brake pedal have with nothing attached to the master cylinder?

[hr369]

Brakes should be very firm. No squishy feel.

Get another master. I got a good one from rock auto.

[alternativez]

Try this, not second-guessing, just being thorough. think zen and the art of brake bleeding; patience is key: all tubing blown clear from both ends with dry air, no moisture in lines, system all assembled, engine off, fluid in reservoir (don't let it run empty while bleeding), cap loose but covering to keep contamination out, all adjustments to rear shoes, attach clear plastic tubing to each caliper and wheel cylinder bleeder, place tubes into clear, clean glass jars to collect fluid. Open all bleeders and allow fluid to passively move through system and drip out of the tubes. This can take several minutes. If the fluid doesn't eventually drip out without pressing the pedal, there is a blockage. A blockage, such as caused by dirt, air, crushed or corroded tubing, fittings misaligned or so tight they crush the tubing at the fitting, minute crud inside the caliper or cylinder, etc. sometimes the blockage is small enough to be forced out with pedal pressure, but usually must be removed by immaculate disassembly and cleaning. Then, if fluid has passed through all corners, it will bleed. Now, with enough clean fluid in each jar that the brakes can't suck air, close all bleeders only snugly, have your helper pump the pedal slowly, firmly, all the way down about 5 or 6 or some divine number of times, then hold and continue pressing the pedal firmly while you open one bleeder only enough to release fluid, not loosely. You should start getting a strong flow of fluid without even the tiniest air bubbles or spurting. It sometimes takes several times of pumping and purging and refilling the res, and then even a couple of times around the system to get all air out. If the pedal is released before the bleeder is quickly closed it would suck air, but if the tubing now has no air in it, it would only draw fluid, but make sure it can draw no contamination. The first couple of times I open the bleeder, I usually try to close it quickly just before the pedal has gone all the way to the floor, then repeat with that wheel until it is clear and the pedal feels firm. The job of the helper is significant. Over the years my wife has found that she needs to use both feet because it requires more strength, persistence, and endurance than one might expect, and communication...follow the rule of farthest first. Any time a brake system has been disassembled, it takes more effort to clear and to bleed than it does after only changing pads and shoes. When you get this done, you will have a great, pretty much all new, brake system! It's going to feel great! Good luck! Patience and persistence; this is one "simple" job that itself demands perfection. And, yes, new and reconditioned parts aren't always 100% functional as we should be able to expect. Sorry for such a long post.

Edited May 18, 2013 by alternativez

[KDMatt]

Brakes should be very firm. No squishy feel.

Get another master. I got a good one from rock auto.

I'm going to bleed the master one more time before I say for certain one way or the other, but yeah, I'm kind of feeling this.

I might shoot a quick video to go along with this too, just so people can really get a sense of how much play I'm getting in the pedal. I really want to be 100% sure that the master isn't functioning properly before I order ANOTHER one.

Also, I'd be tempted to go with another provider if I do indeed need to replace the master cylinder again. MSA is almost prohibitively expensive, but I'm curious to hear thoughts on Black Dragon? $100 is steeper than the $40 I paid at Autozone, but a definite improvement over the $270ish at MSA.

@ altnernativez: Thank you for the words of encouragement and Zen approach to bleeding! I concur with the note about "gravity bleeding," and I will definitely give this a shot. Thing is, at the moment, the master cylinder is isolated and plugged off, so there's nothing to bleed again just yet!

Also, I'm thinking of using some couplings and a T-fitting to bypass/remove the check valve -- I get the sense that most of us car savvy drivers don't really need it anyway, and it's just one more thing that complicates stuff. Hell, I might even get rid of the stock proportioning valve and get an inline one for the rears -- it should certainly make things a lot simpler if I decide to do a rear disc conversion ... assuming I can get all of this working again... :x

Also thinking, at this point, Speed Bleeders might be a worthwhile investment. Yes?

Thoughts and opinions, as always, are appreciated.

Edited May 18, 2013 by KDMatt

[alternativez]

Isn't the check valve there, as we used to call it, the "anti-backfire" valve, for the purpose of preventing gases and fumes from going to the booster? It should apply negative pressure, or vacuum, to pull from the booster to the intake manifold, thus you will only have the assist if the engine is running or if the booster has some residual vacuum just after the engine is turned off, (but you don't need the boost for bleeding). You don't want the fumes to reverse and go to the booster by installing it backwards or by eliminating it. In such case, the booster will not maintain its assisting function, and it will deteriorate from the oil and gas fumes from the intake manifold from whence the vacuum is drawing. Also, I suggest for the present to keep the stock prop valve, as it should work properly as the system was engineered. Then, when you upgrade to a stronger rear setup, you might insider changing it. I suggest first getting your system functioning 100% before modifying it. Back to the bleeding, I've worked on all sorts of vehicles in my life, and still, I get frustrated once in a while with bleeding a system after I've opened the lines. Also, the fluid itself, when agitated slightly, will contain small air bubbles which have to consolidate and be expelled. That's why it may take the slow, repeated process and a very firm pressure at the pedal and good timing when opening and closing the bleeder. I just went through that same frustration with my work van after it was rear-ended by a texter, and I had to replace some hard and soft lines and calipers. I, too, was at "my wit's end" after several tries and running out of time. A friend's advice was, "you prolly just need to bleed it again." It helped that it had sat a few days, and then it finally bled and is working fine. That last time, even though I again bled all twice around, the only one where I found air was the right rear, and it wasn't much, but it only takes a small amount of air anywhere in the cylinders or lines to cause a spongey pedal and uneven braking. Again, sorry for the long post. This is the sort of thing that works best if we could get together in the garage. Writing about it takes as long as doing it! Ha! Be sure to post your outcome. Good luck!

[black gold man]

I will say it again adjust rear drums until you can spin the tire less then half rotation .

Open rear bleeders before hand to let rear cylinders retract in. Then bleed after adjustment.

Edited May 20, 2013 by black gold man

[KDMatt]

Hey guys, sorry it's been a while since I posted.

I decided to shoot a video to better illustrate what's going on. Hopefully the running commentary along with the visuals will help inform the issue here. I'm thinking master now? Let me know what you folks think.

Thanks again for the help.

[240260280z]

Nice video.

It looks like you may just have to adjust the rod between the pedal arm and the booster in the cabin (free play).

Do the correct brake pedal height settings first to ensure the pedal is in the correct location.

You may also have to set the rod into the master cylinder correctly. Some masters have different cone-shaped indentations where the push rod presses into the master so a stock set up may need to be optimized to compensate for the difference between an after market copy of a copy of a copy and the original equipment.

[beermanpete]

To expand on what Blue said, there needs to be free play in two places, between the pedal and booster, and between the booster and the master. When pushing the pedal gently with your hand you should be able to feel two distinct times when free play is taken up as the pedal is depressed.

As for the squish, the reaction disc is a compliant joint in push rod (within the booster) that is part of the booster valve that controls the amount of assist. It is a rubber disc about 1/4 inch thick. You might be feeling that compress a bit. Keep in mind that the pedal ratio (~4:1) will exaggerate the motion. Have you checked to make sure the reaction disk is in its proper place? This is a somewhat common problem that trips people up from time to time. Also, once the master starts to move the piston seals have to move past the ports between the cylinder bore and the fluid reservoirs. This will account for some of the pedal travel and could have a progressive feel at the ports gets smaller and restricts the fluid flowing back into the reservoir.

Edited May 31, 2013 by beermanpete

[Travel'n Man]

I am wondering how you found a master cylinder for 40.00 (did I read that right?).

If you are thinking about changing/upgrading your rear brake system and proportioning valve you may really want to ditch the $40.00 problem and move to a 15/16th Master or a 1" Master to take care of your future braking needs. That would be one piece of your future braking needs finalized................just a thought. I do use speed bleeders that work great. For plugs I use the brake male fitting that is inline with the flare that are filled with JB Weld for plugs - they work great and make a nice seal so things do not leak at all. Keep us posted.

When you engine is running are you getting any better vacuum?

Edited May 31, 2013 by Travel'n Man

[LeonV]

If the master was truly dead, the pedal would slowly drop to the floor...

[KDMatt]

@Blue: Alright, I'll do the gymnast thing again and get my head under the dash to adjust the pedal a bit better. Question though: How do I check the rod going into the master? Would that really cause the pedal to feel THAT funny??

The note that I forgot to make in the video is that as I go down the line of brake fittings, the squishiness/sponginess gets progressively worse as I connect more and more things.

@ Pete: Alrighty! I've read up on the reaction disk, and while my symptoms are quite different from what most people experience, I'm really not above ruling that out either. Is there a way to make sure it hasn't slipped out with the booster still on the car??

I could yank the thing out I guess, but I really don't want to! Taking it apart looks like a nightmare!

@ Travel'n Man: Yep! It's a Fenco rebuild from Autozone: Fenco Reman/Master Cylinder (Brake System) (M51658) | 1976 Nissan/Datsun 280Z 6 Cylinders H 2.8L FI | AutoZone.com

If I could find the paperwork on it, it does have a lifetime warranty, and I could always make them deal with this instead of me!

I'm curious about the 15/16" and 1" master. Do you have any links I could read up about that on? I've toyed with the idea of going with discs in the back at some point in the future, but never took steps to actualize that. It would certainly fit within the Z -mantra of "Well since I'm replacing <x thing> anyway I might as well do..."

I'm already going to lose the check valve, and probably go with an aftermarket/universal proportioning valve, just to keep both circuits truly isolated from each other and keep things nice and simple.

@ LeonV: That's what I thought too... I guess now I'm not so sure? I don't think it's totally "dead" as it does at least move fluid, but it certainly doesn't feel rock solid. At this point I'm just guessing!

... also, have I mentioned lately how much I hate flare fittings? haha