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Dual Circuit Brakes

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BBH

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I just wanted to ask for some advice ……

As part of my 1961 BT7 re-build I am taking the opportunity to move to a dual braking system, and to this end I plan to install a dual circuit pedal box with balance bar so I can have independent front and rear master cylinders. At the rear I am using the standard drum brakes, whilst at the front I have upgraded to thicker BJ8 disks and type 16 callipers.

The big question is whether I need a servo in the system. My initial thoughts based on some advice I had was to do this but I am not too sure and would value folks experience, especially if they have a not too dissimilar set-up regarding:


  1. How important is having a servo with the set-up I am planning?
  2. If I go without a servo what size master cylinders are recommended for the back and the front?
 
You do not need a Servo. Since you're keeping the drum rears, you're not really changing the specs of the system.

Your BT7 came with a .625" Master cyl which works without a servo. You merely need to add another .625" master to drive your rears. The rears are already setup with the proper size wheel cylinders to give the proper proportional force between the front discs and rear drums.

You could start with the balance equal between the two masters, though you'd have the option of changing the balance if your new fronts took more force to operate.
 
One of the racer posters here gave me a simple method to get pretty close on the front/rear balance:

With the car on jackstands...
Have the assistant press on the brake pedal while you turn the wheels by hand.

You're looking for a balance adjustment where the front wheel is just stopped solid and you can still turn the rear wheel but feel the brakes dragging.

I did this with my 4-wheel disc setup and then verified it on the road. Once you get it adjusted, seems to require no further adjustment.
 
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