Pulling my hair out!

[Backnzagain]

Hey Gary, I didn't mess with the rod when I removed the old mc, so I guess the reaction disc should be okay, right? I've bled and bled that mc I don't know how many times. Used a jar of brake flued with a hose attached to the bleeder screw till the bubbles were gone. This would suck if I have to buy another mc.

[Carl Beck]

Ok - so once you bled the MC.... did you then proceed to bleed the brakes again? To assure that you have now cleared any air from the lines...

Carl B.

[Backnzagain]

Yup, I've gone through the whole process several times. After using the hose to assure there's no bubbles, I go to the calipers and I have the same set up there. Always keeping it topped off, then I check for pressure at the mc with the hose removed. It just kinda oozes out. Same at the calipers, just fluid pours out, no pressure. Can it be a bad mc if the rear bleeds fine and has pressure??

[John Coffey]

Maybe a dumb question, do you have the brake lines reversed? A some point (Z to ZX?) they switched the front and rear ports on the Z MC.

[Darrel]

Carl,

I have a '73, if I wanted a 15/16" mc I can get the 79 zx mc direct replacement except having to adjust the rod length. Didn't the earlier 240 have the front and rear reserviours reversed from the later 240's?

[DatsunZsRule]

Was the original Master Cylinder a NABCO? Reason I ask is because two different kinds were available. NABCO and TOKICO.

There was no interchangeability of repair kits or parts between the two so possibly that could be your issue to.

Good luck,

[Carl Beck]

Carl,

Didn't the earlier 240 have the front and rear reserviours reversed from the later 240's?

Yes - 70/71 (Series I and II up to Aug. 71 Tokico) had the larger reservoir for the front brakes in front, while the 72/73's (Tokico - from Sept. 71 forward) have the larger reservoir in the rear. The 70/71's had the bleeder valves on the inside toward the engine, while the 72/73's had them on the outside under the fender. Huge difference in price between the two also (at least the last time I bought them).

Hummmm.... the distance between the brake line fittings is closer on the 70/71... and they are wider apart on the 72/73.... If you tried to interchange them, I don't believe that the brake tubing would line up properly... so you'd know something was wrong.... as you tried to force them into a new location...

( as I recall, I made that mistake once...)....

FWIW,

Carl B.

[Carl Beck]

Was the original Master Cylinder a NABCO? Reason I ask is because two different kinds were available. NABCO and TOKICO.

There was no interchangeability of repair kits or parts between the two so possibly that could be your issue to.

Good luck,

As I recall the OEM Brake M/C was TOKICO on the 240-Z's and NABCO was OEM on the 280ZX's. Checking the Parts Catalogs that seems to be the case as well.

FWIW,

Carl B.

[Nigel1943]

What way are you bleeding the brakes? Pump the pedal up with the bleed nipples shut until you get a hard pedal and then release the pressure thro the nipples. Is the pressure regulating valve and pressure differential switch in good order? What were the symptoms that made you change the M/C in the first place?

[madkaw]

I had this same thing happen on a 69 mustang I was fixing up. I put all new parts on the brakes, calipers,master cylinder,proportioning valve. I must of went thru a gallon of brake fluid trying to get it bled. I finally tried reverse bleeding which actually worked.

I removed the front caliper, this was the passenger side front, and put a block of wood in the caliper to duplicate the rotor but allows greater movement of the puck. I pushed the brake pedal so the puck comes out.

Then i removed the lid on the MC and slowly pushed the caliper puck in and I could see the tiny fine airbubbles coming to the top.

Now my situation was different for the fact i was having problem getting firm pedal on the first push. But i wasn't getting a good squirt out of the front calipers when I bled them, so in that way it was similiar. I replaced my MC 3 times convinced that was the cause. I have done brake jobs for years and never had this situation ,but all it was was air in the lines.

I wish you luck-I feel your pain brother

[Backnzagain]

Hey guys, thanks for all the responses. John, I'm sure the lines aren't reversed. I made sure when I swapped the mc I had it right. The new mc is identical to the one that was on there. I don't remember if it was nabco or tokico. I also rechecked this morning following the lines and making sure they are indeed hooked up to the right reservoir. I don't mind dumb questions at this point. I'm sure its something simple just because its driving me so nuts.

Nigel, I am bleeding them exactly as you described. I'm not sure what shape the valve and switch are in, is there a way I can test them? Here's the reason for the replacement in the first place. When I would stop at a light, the pedal would feel like it should, would go down just a little as the car came to a stop. But as I sat there the pedal would slowly push in, real slow actually. The first thing I did when I noticed this was inspect the whole system for leaks. Nope, dry everywhere. Once the pedal was down as far as it was go, I was still held stopped. I could pump them to get the pedal back up, but only for it to do the same thing and slowly go down. Do you think I was wrong in assuming it was the mc? My maiden voyage with the new mc I could feel a considerable difference. The pedal and brakes felt just like they should. But the further I drove the stiffer the pedal got until I was forced to pull over because the front brakes had totally locked down. To get back home I bled at the mc to release the pressure and drove her home. Does this help anybody with more ideas? I'm about to take another stab at it. I was thinking of driving it till I got them like that, get home and try to bleed at the calipers, well as fast as I can get the wheels off! What do you guys think?

[John Coffey]

But the further I drove the stiffer the pedal got until I was forced to pull over because the front brakes had totally locked down.

Pushrod length, pushrod length, pushrod length! You need to shorten the pushrod that sticks out of the booster because its not letting the piston in the MC retract far enough. Take the MC off and shorten the pushrod by one or two turns, being careful not to pull it out of the booster and causing the reaction disk to fall out.