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Thread: Help! Lack of Brake pressure

  1. #1
    www.project240k.com khughes's Avatar
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    Default Help! Lack of Brake pressure

    Hi Guys,

    desperately need some advice!

    Today, i got the front brakes back on (i had taken them off, cleaned them up, seals are okay etc.). Previously i have removed the rear brakes, and again cleaned them up and seals are okay.

    I have bled all the lines, running about a litre total through the complete system, so it is free of gunk etc. as much as i know.. The brakes were still very spongy even after 10 minutes of pumping!

    As soon as you turn the car on, there is absolutely no pressure!

    we even tried pulling the master cylinder apart and put it back together (it was sticking a little initially, but seals etc. look ok). At first we tightened the locking screw on the master cylinder in before the pedal was depressed and we could therefore not pump the brakes, but by screwing it out, depressing the pedal, screwing it back in, we now get full movement.. bled the master cylinder after this too..

    Now this introduced another problem, we can bleed the front brakes fine, but the rear ones arn't getting enough pressure.. they seem to pump a bit of fluid, and then suck most of it back..

    still have absolutely no pressure when the car starts (and why does pumping the brakes affect the car's idle?)

    Anyone got any ideas? could it be the mastervac / master cylinder unit be stuffed? if so can you get reseal/diaphram kits? or is there a newer unit i can buy cheaply? (looks like PBR make a replacement master cyl) are they the same as 240z's or 240C's or something?

    bugger, i though the car would be almost ready to go this weekend
    Last edited by khughes; 05-22-2005 at 04:16 AM.
    07/74 Datsun 240K GL Hardtop KHGC110 - #5497 (longest 240k project in history?)
    1970 Datsun 240Z HS30 #212

    www.project240k.com - project details on all my cars

  2. #2
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    Quote Originally Posted by khughes
    ...........(and why does pumping the brakes affect the car's idle?)(
    using up Vacuum (which comes from the intake manifold) by repeatedly activating the MasterVac.

    good luck fixing the problem
    (BTW, I don't think the MasterVac is the problem or it would affect both front AND rear brakes.)

  3. #3
    Alfa to Zed Ricklandia's Avatar
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    Quote Originally Posted by khughes
    ...(and why does pumping the brakes affect the car's idle?)
    The idle issue is most likely related to the Vacuum booster. Check the line for leaks, if not that, it might be the booster itself. As for the Master cylinder, no leaks anywhere? (wheels cylinders?) Just to be sure, in what order did you bleed the brakes?
    1973 240Z - Red/4 Spd w A/C - HLS30-134739
    1990 Alfa Romeo Spider - Black

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    www.project240k.com khughes's Avatar
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    well, after looking around the z part of the forums.. looks like i am going to have to check the following:

    - reaction disk in booster is in place
    - bench bleed Master Cylinder
    - put the right brake on the right side (doh! bleeder valve goes on top )

    I guess if these fail, i need to start looking for a new booster and possibly M/C? i noticed http://www.datsport.com/510_brake_bo..._cyl_assy.html have one for $390 (youch) for the 1600, i hope they arn't that expensive normally!
    07/74 Datsun 240K GL Hardtop KHGC110 - #5497 (longest 240k project in history?)
    1970 Datsun 240Z HS30 #212

    www.project240k.com - project details on all my cars

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    www.project240k.com khughes's Avatar
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    Quote Originally Posted by Ricklandia
    The idle issue is most likely related to the Vacuum booster. Check the line for leaks, if not that, it might be the booster itself. As for the Master cylinder, no leaks anywhere? (wheels cylinders?) Just to be sure, in what order did you bleed the brakes?
    there certainly isn't any huge puddles of fluid under any of the brakes (and i pumped it for quite a while!) and there doesn't seem to be any visual leaks in the M/C though i am really confused as to why the rears no londer work like they did (but could this be down to not bench bleeding it? or maybe i didn't put the retaining screw in at the right split second?)

    I bled them, Front right, front left, rear right, rear left (after doing the master cylinder on the car)

    The booster line does look pretty ratty, so i will check that out in the morning (is there an easy way to check this?)

    Bambikiller240, thanks i guess i need to have a search around to understand how the inlet manifold pressure works, i wouldn't have thought it would have that much of an affect!
    07/74 Datsun 240K GL Hardtop KHGC110 - #5497 (longest 240k project in history?)
    1970 Datsun 240Z HS30 #212

    www.project240k.com - project details on all my cars

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    Alfa to Zed Ricklandia's Avatar
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    Quote Originally Posted by khughes
    (snip) I bled them, Front right, front left, rear right, rear left (after doing the master cylinder on the car)
    S.O.P. for bleeding brakes is always start with the brake FARTHEST away from the M/C - so it would be passenger rear, driver rear, passenger front, driver front.
    1973 240Z - Red/4 Spd w A/C - HLS30-134739
    1990 Alfa Romeo Spider - Black

    "Beer is living proof that God loves us and wants us to be happy." - Benjamin Franklin

  7. #7
    www.project240k.com khughes's Avatar
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    ah okay, thanks for that, i will do that after i pull out the M/C to try and bleed that properly
    07/74 Datsun 240K GL Hardtop KHGC110 - #5497 (longest 240k project in history?)
    1970 Datsun 240Z HS30 #212

    www.project240k.com - project details on all my cars

  8. #8
    www.project240k.com khughes's Avatar
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    woohoo! we now have something that resembles brakes! flipped the calipers over (so the bleader is on the top, bled the master cylinder again, and bled the whole car (furthest first )..

    bench bleeding the M/C didn't seem to work so well, so i took it all apart again and poured fluid into it as i reassembled it.. (though i ended up with about 2L of brake fluid in my clothes )

    but after that, the rear seems to be getting a good split of pressure, haven't tested on road yet, but certainly works alot better than they did before!
    07/74 Datsun 240K GL Hardtop KHGC110 - #5497 (longest 240k project in history?)
    1970 Datsun 240Z HS30 #212

    www.project240k.com - project details on all my cars

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