No Brakes & run outta ideas

[BackDoorz]

Car is a 1976 280z with automatic transmission. I am the original owner. Been having brake issues off and on for about 2 years now. I will not go into all the details, but started out with wheel cylinder problems on the rear drums.

My current problem is no brakes. Pedal goes to the floor. The times that I have tested the car in the neighborhood, the brakes will stop the car, but are bottomed out leaving me no reserve at all.

The following have been replaced or repaired in the past 2 years:

- Both rear wheel cylinders. (These are not leaking.)

- Both front calipers and pads. (These are not leaking and the bleeders

are positioned to the top.)

- Master Vac (The check valve is operating correctly and reaction disk is

properly installed. The internal adjustable plunger has been adjusted

correctly for the master cylinder. It holds a good vacuum.)

- Master Cylinder (I am on the third one. All were properly bench bled.

Thought this was the problem, that’s the reason for three.)

- Proportioning valve has been cleaned.

- Brake warning light switch has been cleaned.

- Rear drum brakes are new and have been adjusted correctly.

I have bled the brakes many, many times using several methods. A vacuum pump, a Motive Products Brake Power Bleeder, and the good ‘ol way, with my wife inside the car working the brake pedal.

There are NO leaks anywhere in the brake system. When I bleed the brakes, I see NO bubbles at all and I bleed almost a pint of brake fluid through to each wheel. No brake lines are crimped.

Any suggestions, thoughts, or ideas will be greatly appreciated.

Brake hoses have been replaced with stainless steel braided.

Answer to madkaw:

I did your procedure that you did on your mustang early on.

Answer to Zed Head:

The brakes will pump up just a bit, but not like they should.

Answer to Darrel:

The push rod has been adjust correctly. I made my adjustments till I could tell that it was pushing in on the master cylinder when I re-bolted it. After that I gradually adjusted the push rod back in. Also the brake pedal moves only about a 1/2 inch or less before it engages the pushrod.

Edited September 5, 2014 by BackDoorz
Update answers to questions.

[Walter Moore]

I don't see any mention of the brake hoses. Have they been replaced? Old hoses get soft and swell when the hydrauilc pressure rises during braking.

I had a problem with hoses on my car. I had installed cheap "stainless braded" hoses, and could not get the brakes to work right. I ended up replacing everything with Nissan parts, including the hoses and that fixed the braking. I have always suspected that it was just the hoses.

[madkaw]

Walter makes a good point. Sometimes the rubber in the brake line becomes a check valve from deterioration .

Don't under estimate the ability for air to hide. I went thru all of your battles with a 69 Mustang. In the end, it was air trapped in the front brakes.

The only way I got the air out was removing the caliper and sticking a piece of wood in there to replicate the rotor. The wood thickness was enough to allow the caliper pistons beyond normal travel. When pushing the pistons back in I could watch the bubbles in the MC.

[Zed Head]

You didn't mention the basic test for air in the system, pumping the pedal. If you can pump the pedal up, there's air, if pumping has no effect there's an adjustment problem.

[Darrel]

When replacing the master, did you use the old rod or the new one?

[zKars]

I'm on side with Darrel. I'll be you don't have proper push rod engagement into the master.

You seem to have done everything else correctly.

[Marty Rogan]

I had a hard time bleeding brakes on my Z after installing the Toyota 4x4 calipers. Here is a copy of the post I did back then:

I feel your pain. I had one hell of a time bleeding my brakes after putting the conversion on.

Make sure you thoroughly bleed the master cylinder first. Then move to the right rear, left rear, right front, and then left front. I also had to crank up the rear drums a bit more.

If that doesn't do it, try this racer trick that Rick taught me. Once the brakes are bled all around, go to the right front, remove the outer brake pad, open the bleeder screw, then take a pair of lock jaw pliers and force the pistons in. Be careful not to push them past the seals. Put the pad back in and do this to the inner brake pistons. Then repeat on the left front. I was amazed at how much extra air I forced out of the calipers.

Once I got it bled correctly, the brakes are killer!

I also highly recommend installing SpeedBleeders on all 4 corners and the master. It will make your life much easier.

Hope this helps!

Marty

[BackDoorz]

Update on my current brake problem.

I took the front and rear brake lines coming from the bottom of the master cylinder out and insert two plugs. This was to determine if my master cylinder was bad. I had both reservoirs full of brake fluid. I started up the car and pressed on the brake pedal and the pedal moved just about a 1/2 inch. The pedal held firm and did not leak down. I re-installed the brake lines and started the car and the brake pedal went to the floor.

Now, was this a good test for checking out the master cylinder? If so, shouldn't I be seeing a leak some where? That is taking into account all the other things that I have done that is mentioned in my original post.

[Zed Head]

I like the test. It covers adjustment of the rod, overall play in the mecahnical , integrity of the MC seals under the extra pressure of the booster. Kind of narrows it down to something beyond the master cylinder.

I'm going to guess that because you've bled the brakes so many times that you think that there is no possible way that there is air in the lines (my comment in Post #4). My suggestion will tell you the truth though, whether you want to know it or not. If you can pump the pedal and it gets higher and firmer, there is air in there somewhere. I went through a whole weeks-long battle with air in the calipers.