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

[Zed Head]

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.

Edited December 28, 2018 by Zed Head

[Oceanzide]

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.

[Zed Head]

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/

[Oceanzide]

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).

[Zed Head]

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.

[fairladyz432]

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. 

[Zed Head]

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?

[fairladyz432]

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.