Brake Pressure Issue

[icehouse]

When I bleed brakes I have the pedal pusher pump the brakes 3 times hold it then I release the pressure. Maybe try it that way. 1 pump per bleed screw loosen takes to long.

[bertvorgon]

That is what I do and NOT fast pumps!

[CP]

Even tried holding my nose at the same time...LoL to no avail.

[bertvorgon]

I hear yah...our cars can be very vexing at times.....I have had mine for 42 years now and a few times....TO THE MOON RALPH!!!!

[PoorMtnKid]

Haha same here. More than once. Twice off the car before installing and twice on the car after not getting any pressure built up.

[datzenmike]

Been wrestling with bleeding my rears also. Had both axles out of my 710 and I guess it siphoned out completely. Reservoir was empty but I filled it anyway tried several times, even a vacuum bleeder with no luck. Eventually it dawned on me to crack the bleeder on the master and nothing came out. Took 2 1/2 pumps to get a spray. Went back to each rear wheel cylinder and now huge volumes of fluid. Pedal is like a rock now.

BTW I had the brakes adjusted all the way tight so the wheel cylinders were not involved.

[PoorMtnKid]

Hoping to hear back from CP soon, have not really tried anything as its dreadfully hot here in Vegas right now. Might give it a try tomorrow morning early if I can get someone to come over to do the pumping action for me.

[CP]

Sorry have not replied sooner.I don't know if what we discovered is going to help. We have installed a disc brake conversion on the rear using I believe Maxima brake calipers. It was purchased locally as a kit. In any case, we had not had the parking brake hooked up to the external actuators on the calipers. The piston on this caliper rotates out to take up slack as the pad wears. I had tried rotating the piston out to minimize the clearance between the pad and the rotor. As it turns out, it was not out far enough. The reason for the soft pedal was pumping the caliper piston out to contact the rotor. This turned out to be the biggest issue although further bleeding of the brakes was required. So I don't know if this is going to help you.

[PoorMtnKid]

Interesting, my 280zx rear calipers also have the Ebrake lever and I also have never had the E brake cable hooked up. So from what I gather you are saying is the piston on the rear had too much play before contacting the rotor resulting in the soft pedal? Might have to investigate this tomorrow.

[CP]

I would have a look at the rear brake pads and see if there is any slop in them after the car has been sitting. If so you may have the same problem and you either have to rotate the piston out or put a shim in to take up the slack.

[slowerthantime]

I have been watching this thread with interest as I have a similar set up and same soft pedal. Rebuilt 280zx calipers front and rear, new lines, rotors/ pads and master cylinder. Wilwood proportioning valve.

After repeated bleeding I couldn't get a solid pedal. Tried a vacuum bleeder and had some success. After pulling a ton of fluid through the rear brakes, I got a big air bubble that I suspect was hiding in the proportioning valve. Pedal feels great now. Park brake is also adjusted and working.

[Byron510]

Admittedly I have also had a ‘hidden air bubble’ issue in a stack brake system. Twice on my green 68 I had it where I moved tones of fluid through the system before it was right. I wondered about the stock shuttle / pressure differential valve that is the brake pressure warning switch, or it one of the two stock, brass splitter boxes was the issue. In either case, it is frustrating, and I’m sure the issue was not the BMC, bench bless or not, it didn’t seem to be the source. That was years ago when I had the issues, and I had it happen twice on that car. I wish I knew when the solution was. It just eventually bleed through after walking away a couple of times. And maybe that was the key. Possibly that air bubble needed to move to a point where it is no longer trapped and can be moved through. Both times it happened only when the system was completely emptied for some time due to other work taking place.

Byron

[bertvorgon]

We found "tapping" some of the potential offending joints, brake bias, etc., sure helped. It is amazing how air bubbles can just sit in some spots.