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Thread: Bleeding front brakes produces just a little brake fluid.

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    Default Bleeding front brakes produces just a little brake fluid.

    I have read and read and read the posts here trying to figure out what to do next to try to get the brakes working correctly.

    Original problem: Front brakes were locking up after they were driven on for a little while, Right more than the left. Note: The 1976 280Z had been sitting outside at a mechanics garage for almost a year.

    What I have done so far: Cleaned and lubed the front brakes.
    I was able to get the front right brake brake line unhooked thaty goes through the proportinal valve and fluid seems to make it through there. I have been unsuccessfull getting the brake lines loose on the brake warning light valve.

    On the back drum brakes the emergency brake lever was pushing on the brakes and hence not allowing the hydrolic brakes to engage very well. I have temporarily unhooked the Emergency brake so that the hydrolics can do the braking.

    When I bled the brakes, I got good flow to the rear brakes however when I try to bleed the front the flow coming out is very little, even after bleeding them twice.

    Now I have to pump the brakes one time before they will engage and even then the stoping power is very week.

    Do the rear brakes have to engage before pressure is set to the front brakes? If so maybe I need to tighten the release wheel on the reer brakes a little?

    What do you all think? New front brake lines? Could the problem be in the Brake warning light valve (I think that is what it is called)

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    Also, I have adjusted the brake pedal back to 8". It originally was at 7'

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    Aside from a warning light, what that valve really does is meter the pressure balance between your front and back brakes. It is called a proportioning valve in some cases. The light works off it as an auxiliary benefit

    This is a problem with no easy answer I can think of. Your car is currently not safe, so my advice to you, is to start with the master cylinder and start looking for leaks, or a poor seal. Then work your way down the line. If you have an obstruction not allowing that to work, you will need to fix that soon.

    Be methodical and take your time fixing it. This site will be extremely helpful.
    1971 240Z HLS30-38691
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    You should adjust the back brakes using the star wheel to as tight as you can without dragging. The excess volume from your loose back brakes probably isn't allowing enough pressure to build up before bottoming the piston in the master cylinder. It's not good for the pistons in the rear cylinders to travel far in their bores either.

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    Ok, that makes sense. I was thinking it might be something like that. I will tighten the back brakes up with the star wheel.

    Also, I guess these cars basically have 2 proportioning valves.. one that is close to the master cylinder and one that is on the firewall?

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    You got me there...not sure what is on the firewall. Mine is on the fender near the MC. But I have a 1971.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    The other one he's describing on a 76 isn't a second proportioning valve. That's the the brake line pressure differential warning light switch.
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    Aha.. the Brake Line pressure differential warning lite switch. Do those get clogged up?

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    Good picture
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	76_280z Brake line Pressure differential warning light switch 1 of 2.jpg 
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    I would start by fitting a new master cylinder.

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    Check Master Cyl, then clean the Proportioning Valve, then completely remove the Bleeder screws in the calipers and make sure that there is not some crap clogging up the port. Tip: you can use some electric trimmer line to rod out the ports and hard lines to push out any debris.
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    Disconnect the front brake line at the MC and the brake lines at the calipers. Squirt a whole can of Brake Kleen through the lines. Blow air through the lines after. Reattach the lines and bleed. Also, check the pushrod in the booster to make sure its going all the way back. Sometimes it needs to be shortened a bit.

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    Ok, I have figured it out. In most all the reads about bleeding the the brakes it only mentions bleeding at the 4 tires. It never dawned on me that I need to bleed the Master Cylinder also. So with my son pumping the brakes, I attached a tub to the back tire part of the master cylinder and fed it right back in to the reservoir. Pumped off a lot of air. Repeated for the other resovoir. Brakes are working wonderfully!!

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