If i understand the problem, the fronts are engaging beflre the rears -
usually calipers need much more fluid than wheel cylinders - think of the
relative piston area - so I am surprised it is not the other way around.
One thing you have not mentioned is the bias bar, between the pedal arm and
two piston pusrods, which I assume you have and is usually the means to
adjust relative piston travel front to rear.
My GT6 set-up uses two girling clutch masters - 5/8 bore with a Tilton bias
bar between them. The "front" master cylinder piston travels more than the
rear given the greater fluid needs of the calipers vs wheel cylinders, so
the bias bar goes from being tilted one direction to the other as the front
master piston travels much further. I have thought about going to a 3/4
bore for the front and leaving the rear the same, to push 50% more fluid to
the front ("pi" r squared) with the same piston travel.
----- Original Message -----
From: "Robert D. MacKenzie" <dodo@texas.net>
To: <fot@autox.team.net>
Sent: Tuesday, May 20, 2008 12:02 PM
Subject: [Fot] Dual Tilton Brake Masters on MK1 Spitfire
>I have having some issues with a Tilton dual brake master cyl installation
>I
> started over the weekend on my Spitfire Racer
>
> I bought two used 1 inch Tilton masters with all the correct
> brackets/mounts
> with remote reservoirs plus two Wilwood proportioning valves to be
> installed
> on my Mk1 spitfire, replacing the original single circuit master.
>
> The cylinders were rebuilt using the correct Tilton kits. I made up new
> lines from the master outlets to the valves and then into the existing
> brake
> lines.
> Everything went well until the final bleeding process began.
>
> The 1st time I tried to bleed the front first then the back. The front
> brakes felt fine with good travel and pedal feel. But when I tried to
> bleed
> the backs the system would bind and I had a very high pedal effort. When I
> blend the backs with the fronts open they worked fine by themselves. When
> everything was closed the system will bind with very high pedal effort but
> no brakes. Not good.
>
> I then tried bleeding both systems at the same time, and that seemed to
> work
> until I closed off all the speed bleeders and the system would bind again.
>
> I believe that the master cyl providing pressure to the front brakes
> caused
> the pistons to press the calipers closed before the rear ones can apply
> the
> rear brakes. Making adjustments to the proportioning valves does not seem
> to make any changes. I also tried adjusting the bracket connecting the
> two
> pistons to the pedal to push one in earlier than the other but that did
> not
> make a difference. Swapping the cylinders or the valves side to side made
> no
> difference. I believe each individual component is working right, just
> not
> together.
>
> Before I go much further I have some basic questions:
>
> Are two 1 inch masters the way to go? Do I need to run a smaller
> cylinder
> on one side or the other? Do I need two valves or will one suffice as
> the
> other will always be open?
>
> Any help/advice will be appreciated.
>
> Thanks
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