Hi Mark,
I presume that you are using one of the in line master cylinders with the
plastic tank.
Based upon what you have said in your message I don't think you understand
the theory of operation of that master cylinder.
In short, if either the front or the rear system develops a leak those
master cylinders isolate the leaking system and allow the other to continue
operating.
If you are sure that air has been eliminated from both systems you need to
centralize the "shuttle" in order for both systems to operate.
To do this open one bleed screw and press down hard on the pedal, this will
push the shuttle to one end. Close the bleed screw.
Press down on the pedal then have an assistant slightly open a bleed screw
of the other system. Do this very slowly. You should feel a "bump" in the
pedal as fluid seeps out of the bleed screw and the "shuttle" centralizes,
release the pedal and close the bleed screw as soon as this occurs.
The idea is that you are moving the "floating" shuttle" to the mid
position. On the original systems there was a brake fail indicator light
which went out when the "shuttle" was centralized making this process a
little easier.
Hope that helps,
Michael S
On Thu, Oct 31, 2013 at 1:52 PM, mark henderson <markhenderson3376@gmail.com
> wrote:
> I have a rear brake issue with my '58 Sprite. The Bugeye has the stock
> .875" rear wheel cylinders and we have installed a 1967 Sprite/Midget
> tandem master brake cylinder and front disc brakes. The problem is; we can
> turn the rear brake drums by hand when the front brakes lock up. We have
> sealed all leaks and bled the system thoroughly, no air remains in system.
> We have adjusted rear brakes shoes as tight as possible. We backed off
> pedal stop to try to increase piston travel in master cylinder. When we
> bleed front brakes first then check rear brakes, drums are locked.
>
> My summation is that the new master cylinder is not pushing enough fluid to
> the rear brakes before the fronts lock up. When the front brakes lock, the
> piston cannot go any further into the cylinder to push any more fluid to
> the rear brakes. Bleeding the fronts first and then checking the rears are
> locked seems to prove this. I have gone thru the math to see if the
> original .875" cylinders require a lot more fluid than the .75" cylinders
> of the 1967 Midget and they will require more volume of fluid to travel
> equal distances but not a lot.
>
> Short of replacing the rear brakes with later Midget/Sprite backing plates
> and wheel cylinders, does anyone know of another fix for this? Has anyone
> done this swap before with only the tandem master cylinder and front disc
> brakes swapped over. My old Lucas/Girling books show no wheel cylinder with
> smaller bore that will fit the Bugeye backing plates. Thank you for any
> thoughts. Regards, Mark
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--
Michael Salter
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