Bleeding rear brakes

[restore]

I'm trying to bleed the rear shoe brakes on a "71". It was sitting for over ten years and the master cylinder and rear wheel cylinders pistons were frozen, I have honed and rebuilt each. I am  trying to use  a hand  vacuum pump to pull the hydro fluid from the master cylinder but it will not work. My question is: will the pump pull the fluid past the proportioning valve between the rear wheels or must it have pressure from the master cylinder? I am concerned about the proportioning valve also being frozen .Does anyone have any ideas or experience with a vacuum pump in this application?

[SteveJ]

I've never had any luck vacuum bleeding the brakes on either of my Z cars. If you don't have someone to help, here's one way you can do it:

1. Get a long tube.

2. Put one end in a jar of brake fluid.

3. Attach the other end to your bleed screw with a good run going up before the tube goes back down into the jar.

4. Make sure the reservoir is full.

5. Loosen the bleed screw.

6. Pump the brakes a few times.

7. Look for air bubbles in the tube.

8. Check the fluid level in the reservoir and top off as necessary.

9. Repeat steps 6-8 a few times.

10. Tighten the bleed screw.

11. See if you have a firm pedal.

12. If not, repeat steps 5-9.

[restore]

It's a "71"

[Zed Head]

You already said "that".

 

Press on the pedal with the bleed screw open and see if anything comes out.  They all work the same, master cylinder > brake lines > wheel cylinder.  People have reported clogged NP valves.  It's documented on this forum somewhere.  You can take them apart and clean them up.

 

I installed speed bleeders on mine so that I could push a lot of fluid through easily.  Same general concept as SteveJ's method, but easier to set up (for me anyway) and doesn't pull fluid back once it's left.

[Zed Head]

Forgot to say, you can only generate about 15 psi of pressure using a vacuum setup.  Much more pressure possible using the pedal, even without the booster.  Use the pedal to break crud free and push it through, then the vac system to bleed it.

[restore]

I'll try that. I'm not familiar with speed bleeders. You make it sound like a check valve. How do they work and where did you get them? My 71 is somewhat different from the 76 NP valve shown in the diagram. From the master cylinder the front and rear lines go into a pressure equalization switch and from there a line goes to the proportioning valve located above the right rear axle. It's that valve that I think is causing the problem. 

Rick from kansas

[rossiz]

speed bleeders are wonderful things - they replace your stock bleed screw and have a little one-way ball & spring valve in them.

you back 'em out a quarter turn then just pump the pedal and it spits out the old fluid and won't let air back in. i've used them on my bikes for years - they make bleeding a one-person operation.

 

i'm pretty sure summit has 'em - just do a google search for "240z speed bleeders" and you'll find them easily.

[Zed Head]

Here's a pretty good thread on the NP valve.  Post a thread with "NP Valve" in the title and you'd probably get some more ideas.

 

http://www.classiczcars.com/topic/45461-parts-for-oem-np-valve-and-brake-indicator-switch-unit/

 

Here's another that mentions speed-bleeders and gunk in the valve - http://www.classiczcars.com/topic/43220-brake-problems/

 

Forgot to say, if you know the thread size, some auto parts stores carry speed-bleeders.  Baxter Auto does, Russel is the brand I think.  I can't remember the thread size.  Pretty sure I just took a bleed screw in to be positive, and matched it.

Edited July 6, 2015 by Zed Head

[SteveJ]

You already said "that".

He accidentally posted that in this thread. He meant it for a private conversation.

[jfa.series1]

You may be right on track with a suspect proportioning valve.  Mine was frozen and prevented fluid from reaching the rear brakes.  All became better when I replaced it with one from a friend's parts car.

[Zed Head]

He accidentally posted that in this thread. He meant it for a private conversation.

I figured so.  I was goofing off...

[EuroDat]

If the master cylinder and rear wheel cylinders pistons were frozen then your NP valve is most likely full of gunk and could even be seized marginally operating.

My brakes worked find and just passed a roadworthy test when I replaced the MC and the wheel cylinders. I cleaned the NP valve and the switch. They were both full of sediment and sludge, but cleaned up ok and thats a couple of years back and no problems since.