Oceanzide

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

    Recommended Posts

    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 by Oceanzide
    Including additional information

    Share this post


    Link to post
    Share on other sites

    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.

    • Like 1

    Share this post


    Link to post
    Share on other sites

    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!   

    Share this post


    Link to post
    Share on other sites

    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

    • Like 2

    Share this post


    Link to post
    Share on other sites
    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.

    Share this post


    Link to post
    Share on other sites

    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?

    Share this post


    Link to post
    Share on other sites

    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.

    image.png

    Share this post


    Link to post
    Share on other sites

    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).

    Share this post


    Link to post
    Share on other sites
    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

    Share this post


    Link to post
    Share on other sites

    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.

    Share this post


    Link to post
    Share on other sites
    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

    Share this post


    Link to post
    Share on other sites
    2 hours ago, Oceanzide said:

    Thanks Zed Head. My signature has model-year, also (now) VIN#. 

    The sig only shows up to other people if they're signed in.  Guess I missed it, I read the posts and only sign in if I want to say something.

    Seems like you might just have a piece of seal stuck in your rear orifice.  Ha ha.  Couldn't resist.  But it seems possible, based on the picture, below.  That would give front pressure only.  This picture is from the 1970 FSM, available from the site's Download area.

    Pretty easy to remove the MC and look around.  The MC is easy to take apart also.

    image.png

    Edited by Zed Head

    Share this post


    Link to post
    Share on other sites

    Thanks for the pic! I have two old Chilton manuals that cover 240 to 260 and 240 to 280, also a Clymer covering 240 to ZX - none of them shows cutaway of early MC (To be fair, Clymer shows the most accurate diagram of early Tokico MC.)  Where did you find this pic?

    Re: "Rear Orifice" (not to be confused with PC virus "Back Orifice") If that's the little plunger under the "dome" on the end of the rear piston, then that was the problem! It wasn't a stray rubber fragment, though... It appears these parts are anodized aluminum, and the anodization was chaffed off the plunger right behind the rubber seal. So that's where some sort of corrosion developed and the plunger was stuck/glued about 2mm away from being closed. 

    Am able to bleed MC now - what a relief!

    Hopefully the vacuum booster is OK. I stuck my finger inside and felt the rubber which seemed very pliant but not wet.

    Thanks to all for the help and suggestions.

    Share this post


    Link to post
    Share on other sites

    I meant the hole that the fluid passes through when the piston pressurizes it.  Not clear (to me) what plunger you're describing.  Sounds like you had already taken it apart, unless you work really fast.

    Here's the link to the site's file collection area.  Lots of good things in there.  Clickable menu on the right side.

    https://www.classiczcars.com/files/

    Share this post


    Link to post
    Share on other sites

    There's a check-valve built into the (front of) rear piston. It's supposed to close when applying brakes. When pedal is released, if there's less pressure in front of piston, fluid can move from slotted part of piston (reservoir) forward, past the front seal (of rear piston). This was stuck  open.

    I tried to dismantle the front&rear orifice, but don't have a bench or vice and was never able to unscrew the large fittings.

    Thank you for the that link Zed Head - I'll check it out (later, when not constrained to phone GUI).

    Share this post


    Link to post
    Share on other sites

    Thanks for getting back with the results.  Looking at the diagram and thinking hydraulically I can't see how the valve sticking open would block pressure from the rear system.  Unless the seal was sitting over the orifice, blocking it, and the fluid was just passing through the open valve to pressurize the front system.  Seems like an open valve should have just acted like a single piston system.

    Anyway, sometimes just taking things apart and putting them back together has results.  Carry on.

    Share this post


    Link to post
    Share on other sites

    I have the same issues as well i think. Im trying to bleed my bmc off of my 76 280z and only seem to be able to bleed the rears but the fronts will not. The reservoir at the rear which sends fluid to the front brakes doesn't seem to move any fluid at all. Is that what you had a problem with too? I bought a rebuild kit and installed correctly to the best of my knowledge. Do you guys recommend i take it apart agian and check everything and try to do a bench bleed? Even the rear brakes seem to take forever to bleed out the air bubbles. 

    Share this post


    Link to post
    Share on other sites

    What happens at the bleed screw?  Does the pedal go to the floor when you have a front bleed screw open?  Or does it stay high like pressure is building?

    Describe what's happening, in detail.  Probably a clue in there.  Also, where you started.  Why did you decide to rebuild the MC?

    Share this post


    Link to post
    Share on other sites

    Sorry I actually ended buying a brand new one to save the trouble in the future just as a matter of precaution. I think it ended up being my rebuild kit not sealing right or something. 

    Share this post


    Link to post
    Share on other sites

    Create an account or sign in to comment

    You need to be a member in order to leave a comment

    Create an account

    Sign up for a new account in our community. It's easy!

    Register a new account

    Sign in

    Already have an account? Sign in here.

    Sign In Now