The rear brakes must be adjusted right in order to get the brakes to
bleed out satisfactorily. Why this should be more important in MGB than
in other cars I can't say, but spend the time to adjust them before
trying to bleed again. Question--how far up does handbrake pull (or did
it pull before you started this job) in order to lock the rear wheels?
3-4 clicks is what the book says the handle should lift if brakes are
You installed the MC, then filled and tried to 'bench bleed' it?
Since you are working at an awkward position and are probably trying to
be ultra careful about spillage, I am guessing that the MC still has some
air in it. If you have plastic threaded bleeder screws, try attaching
clear hose to them to re-direct the fluid back into the MC. You can then
press a lot of fluid through the MC and watch it carefully for any sign
The brake light comes on (imagine that--somebody has one that
actually works) when the pressure in the front and rear lines (systems)
differ. There's a little shuttle thing inside the sensor that gets
pushed to one side by uneven pressure, and that causes a switch to switch
on the light.
If you are not getting pressure in the rear system because of 1)air in
the MC, 2)air in the rear system or 3)out of adjustment rear brakes, #1
and #2 can definitely cause the light to come on and #3 might cause it.
But don't despair. When you walk away from the project tonight it may
be in complete frustration. When you return tomorrow, the bubble may have
found its way out of its own accord. Doesn't seem reasonable, but has
been known to happen.
BTDT on all the above.
On Sat, 31 Aug 2002 14:20:08 -0700 (PDT) Zach Dorsch
> Help, I am getting very frustrated with my car. 1973 MGB dual line,
> non-servo brakes. I asked a few weeks ago about a replacement for a
> master cylinder, so I decided to order a new one from LBCarco.
> To recap, front brake lines started leaking somewhere, checked
> connections, nothing, but the line was wet. I replaced the front
> lines. So far so, good, only when I hit the brakes gradually the
> pedal slowly goes to the floor without really stopping. However if
> I stab the brakes the car squealed (sp) to a stop. Okay figured
> master cylinder, so I replaced it today.
> Went ahead and attempted to bleed the brakes with a friend that has
> helped me bleed the brakes before.
> I first put the MC in without the lines connected and put in a
> little fluid and pumped until the fluid came out of the fittings (to
> prime the MC). I then hooked up lines and proceeded to bleed like
> normal, only something was not quite right. I had to depress the
> pedal about two inches to get it to brake. I don't think this seems
> right but I tested it around our block. I could lock up the brakes,
> but it took an incredible amount of pedal effort and that is when
> the brake warning light came on. I figured that I had not bled them
> the right way, so I tried again.
> For some reason when bleeding back brakes the pressure goes down and
> does not return? Could the rear brake adjuster affect this? Any
> other ideas?
> Thank you
> Zach Dorsch
> (I have posted this to the bbs as well, so I apologize if you have
> already read my note)
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