Basic brake bleed on older Z, reservoir-level not dropping

[Oceanzide]

Had I pulled the master cylinder first, I probably would not have posted the original post!  I'm just trying to bleed the brakes on my Z after replacing rear wheel cylinders. The peddle seems to get really firm after what seems a short distance, and I wasn't seeing any level change in the rear reservoir (after pumping). (I had loosened the dvr-side-rear bleed-valve and run a tube into jar with fluid.) So, having just bled the clutch, which didn't work until the master was primed, I assumed the problem would be a dry - possibly pitted - MC, but that doesn't look like the problem. 

So I'm still troubleshooting. Any voices of experience will be appreciated! 

Edited December 25, 2018 by Oceanzide
Including additional information

[Jeff G 78]

Front reservoir is for rear brakes and rear is for front brakes.  Are you getting fluid out of the rear bleeders?  Did you bench bleed the MC?  If not, do that first.  Put a 6" long hose from the front bleed port on the side of the MC and with the cap off, put the other end into the reservoir under the fluid line.  Crack the bleeder just enough to get flow and slowly pump the brake pedal.  Close the bleeder and repeat for the rear port.  Once done you can start bleeding the rear wheel cylinders starting with the driver's rear.  If you are not getting fluid, you have a blockage somewhere.  Either a hose has collapsed, you have gunk in a line, or there is something in the proportioning valve.

[Oceanzide]

Thanks Jeff.  i'll try that tomorrow. I'm a little worried about fluid running out the bottom of the bench-bled MC, during installation. I'll try using plugs temporarily...

BTW: I just updated my signature with year&model of the car. The early Zs had the big reservoir in front!   

[Patcon]

8 hours ago, Oceanzide said:

Thanks Jeff.  i'll try that tomorrow. I'm a little worried about fluid running out the bottom of the bench-bled MC, during installation. I'll try using plugs temporarily...

BTW: I just updated my signature with year&model of the car. The early Zs had the big reservoir in front!   

The way I bench bled a master was to use short sections of line from the bottom ports looped up and into the reservoirs. Work the master until no more bubbles appear

[Zed Head]

20 hours ago, Oceanzide said:

I'm just trying to bleed the brakes on my Z after replacing rear wheel cylinders. The peddle seems to get really firm after what seems a short distance, and I wasn't seeing any level change in the rear reservoir

Your symptoms seem to indicate that the brakes don't need bleeding, that you're done.  Or that the NP-valve is clogged.  With the bleed valve open in the back does any fluid come out of the hose when you press the pedal?   Make sure the bleed valve is fully open.  Won't hurt to blow a bunch of fresh fluid through the lines.  A speed bleeder valve helps a lot to just purge the system.  Pump the pedal and keep the reservoir filled.

[Oceanzide]

Thanks, all, for the help so far.  Today I reinstalled the MC and used Patcon's MC bleed suggestion with clear plastic tubes.  I was able to see bubbles in both reservoirs, but only the front one completed the fluid-loop with fluid completely filling the plastic tube. The rear tube never pushed out all the air, and the level in the tube only came as high as the level in the reservoir. Now, no more bubbles come out and as I press the pedal, the level in the rear reservoir goes up (even with plastic tube removed). I think it's time to look for seals.  Will a later rebuild kit include the same seals as were used in the early MC?

[Zed Head]

Probably easier and more effective to buy a reman MC.  The kits can be expensive, if you can find the right one, while a reman MC is fairly cheap.  The various brake and clutch cylinders go bad easily if they sit unused.  Might as well take yours apart before buying a kit, to be sure the cylinder isn't pitted.  If it's pitted, it's toast.

Here's the 1972 diagram showing how the front and back are "stacked".  One pushes the other.

[grannyknot]

Agree with Zed Head, the rebuild kits can be iffy and that's when you can find them.  The aftermarket MC's are good quality at a very reasonable price.

[Oceanzide]

Hi Zed Head, I'm not sure if you mean there are remanufactured MCs with the "F" mark in front? (Where?)

Hi grannyknot, I don't mind purchasing aftermarket if it looks like OEM. I'm just not finding an aftermarket MC with the "F" marking in front.

I'll probably end up getting the newer MC and swapping the lines underneath, but have not yet given up on the possibility to keep the OEM look/equipment.  Will probably get a quote to have mine "sleeved" & rebuilt  (, though expect that will be prohibitively expensive).

[Zed Head]

31 minutes ago, Oceanzide said:

aftermarket MC with the "F" marking in front.

 the possibility to keep the OEM look/equipment.  Will probably get a quote to have mine "sleeved" & rebuilt  (, though expect that will be prohibitively expensive).

Didn't know you were doing a restoration.  Actually don't even know what year you have.

Many ways to get it done.  Here are the Rockauto pages showing the difference between 71 and 73.  Add some detail and the resto guys will have answers.  If the MC is bad, the Master-Vac might be also.  Better check that too.  It's another hard to find part.

https://www.rockauto.com/en/catalog/nissan,1971,240z,2.4l+l6,1209158,brake+&+wheel+hub,master+cylinder,1836

https://www.rockauto.com/en/catalog/nissan,1973,240z,2.4l+l6,1209170,brake+&+wheel+hub,master+cylinder,1836

[Oceanzide]

Thanks Zed Head. My signature has model-year, also (now) VIN#. Checked out those Rock Auto links, I might take the 71 option, but for now I'll just see if new seals will solve the issue (if I can find them).  Actually, I'm still trying to figure out what's happening. I'm not seeing fluid inside car, so rear seal must be working. Pressure is being transferred forward to front piston, but not fluid, so floating/middle piston seems to be working. Is there a check valve that could "stick" and cause this?. i'd like to see a cutaway of the old-style MC, but my manuals only show the same cutaway picture as you attached above, which is for later model MC.

[Patcon]

4 minutes ago, Oceanzide said:

Thanks Zed Head. My signature has model-year, also (now) VIN#. Checked out those Rock Auto links, I might take the 71 option, but for now I'll just see if new seals will solve the issue (if I can find them).  Actually, I'm still trying to figure out what's happening. I'm not seeing fluid inside car, so rear seal must be working. Pressure is being transferred forward to front piston, but not fluid, so floating/middle piston seems to be working. Is there a check valve that could "stick" and cause this?. i'd like to see a cutaway of the old-style MC, but my manuals only show the same cutaway picture as you attached above, which is for later model MC.

Fluid won't show up in the car. It all ends up in the vacuum booster. Which ruins it. That's what ZH was alluding to