Brake Pressure Issue

[PoorMtnKid]

Hello Everyone

Been a while since I have been on here, but having an issue with my brakes so coming to the best minds to try and resolve the issue. Here is my set up:

• 280zx Front Disc
  280zx rear disc
  15/16 Master Cylinder

I went on a mission to do some maintenance on the rear cross member. I dropped the entire rear crossmember which resulted in removing the rear brake lines. After changing out the bushings, re greasing axels, replacing brake lines, etc I put it all back together. After doing a brake bleed(two party- one pumping one braking bleeder loose) I could get some pressure but only when pumping it a few times. If I step in the car and press on the brakes it goes basically to the floor. Give it 2-3 pumps and pressure builds AND holds. It does not continue to drop after pressure is built up.

After this I noticed some fluid on my transmission, turned out to be brake fluid and it was coming from the hard line that runs down the tranny tunnel to the rear. I assume it had a crack so I replaced it with a soft stainless steel braided line. After replacing this line I decided to get a vacuum bleed system. Continued to bleed the brakes as recommended(RR,LF,FR,FL) with the vacuum pump, same problem still persists. I checked the entire system and I do not see any visible leaks. I even did a "bench bleed" of the MC while in the car using the side ports and hose redirecting to the reservoirs and still the same problem is there.

The Problem : No pressure when first applying pressure. Give it 3 pumps and it has what I would consider somewhere between 1/2 and 3/4 pressure of what it has been in the past. This pressure will hold, I tested by putting a 2x4 against the pedal and seat and it stayed in place for over an hour.

Thoughts? Thanks

[bertvorgon]

Where is the brake bleeder on the rear caliper?

It sounds like you still have a lot of air in there.

[PoorMtnKid]

Calipers are mounted at 12 o'clock with the bleeder slightly in between 12-1.

[bertvorgon]

Not bad...I have taken my caliper off...get a block of wood that fits between the pistons....then you can have the bleeder totally vertical...bleed...tap with hammer to dislodge any air bubbles....pray.....

Has helped a few times, specially with a system that has had maintenance.

[PoorMtnKid]

Could this be accomplished using the vacuum method?

[bertvorgon]

When it comes to getting air out.....anything attempted can't be bad for the most part. Yes, the vacuum can be used the same.

Considering you say you have NO pedal until multiple pumps, you do have some significant air somewhere in the system.

If you bleed the front...does any air come out or is it solid fluid?

While I think of all my tricks, once I jacked the front of the car up to be way higher than the rear, then let a good "head" of fluid gravity flow out both bleeders, making sure the master is stayed on top of for topping up, and, that the rear is shut off as soon as solid fluid comes out.

[bertvorgon]

Also, who ever is pumping the brake pedal, do it nice and slow...rapid pumping can cause a type of cavitation in the master which does not help things at all.

[PoorMtnKid]

Yesterday I tried the gravity trick. Got the car higher in the front broke both rear bleeders open. Within about 2 hours it drained about .75 Qt all through the rear passenger. Barley anything came through the driver side.

While using the vacuum prior I could pull fluid through no problem. Thinking that side might have been slightly lower. I didn’t expect the fluid to flow so quickly through and it dried up. Going to try it again but not leave the garage and see what I can accomplish.

[bertvorgon]

Knowing that the passenger side flowed well, close THAT bleeder...which then forces the fluid to go out the drivers side. Once that flow is established, then you can do the bleed procedure.

The way the rear lines split to me, has always made a bias to one side.

[PoorMtnKid]

So I’ve tried everything and still am getting the same issue. Even swapped out a new MC with no luck. What is a typical sign that the calipers are bad? I have no leaks yet I’m getting only half pressure. And once again after sitting for a min or so the first pump basically goes to the floor and requires 2-3 brake pumps before it builds what little pressure there is.

I’ve tried gravity in which I’ve run through 2-3 quarts of oil between all 4 corners. I’ve tried the pneumatic vacuum. And I’ve tried the classic two party pump the brakes crack the bleeder method.

[bertvorgon]

That almost sounds like it is bypassing in the master, that is really the only thing left, based on your testing to this point.

[CP]

I am literally having exactly the same problem and have gone through the same steps including replacing the master cylinder. I used a pressure bleeder instead of a vacuum bleeder but all of the same results. I have finally just dropped the car off at a mechanic last night to have a look and will let you know what he comes up with.

[bertvorgon]

I watch with interest this thread. I too have had problems in the past, when I removed my rear calipers for rebuild and it seemed to take forever to get the "pedal" back. I know next time I will instantly cap the brake lines to stop any fluid flow.

In my case I held the caliper in my hand, wood block(S) in caliper, and had a hammer to tap the caliper to get air to my top bleeder, held totally vertical. I have flexible lines at the back, so that made it easy to remove and position.

[icehouse]

You guys bleed the master cylinder?

[CP]

Yup, more than once