Rear Disc Brake Conversion Master Cylinder Question

[austinsnake]

Hi All,

I recently completed the rear donor drum to disc brake conversion on my MK3, using Richard Oben's North Racecars solution. The new axles, brackets, rotors, calipers and soft brake lines went on nicely, and the Factory Five Halibrand replica wheels bolted up as advertised.

I'm now ready to swap out the donor master cylinder for a 93 Cobra 15/16" bore master cylinder to support the rear disc brakes.

I had already ditched the proportioning valve, so I just have two questions related to the swap:

1. Does the front output of the Cobra master cylinder get split 1:2 to drive front left & front right brake lines? Is there a recommended part for this?
I assume the single rear Cobra master cylinder output goes directly to the single rear brake line.

2. The depth of the bore for the new Cobra master cylinder seems to be the same as the original donor one, so I'm thinking I don't need to adjust the rod depth coming out of the booster pump. Is that correct?
I don't recall how that was set up in the first place :-) That is, how far out the rod should be with respect to the depth of the master cylinder bore when the brake pedal is fully depressed.


Thanks!
Brian

[Jeff Kleiner]

The front port of the master cylinder goes to the rear and vice-versa. If the depth of the bore for the pushrod is the same as what came off you're good to go...this is assuming that you're using the same booster.

Jeff

[J R Jones]

Drum rear brake systems rely on a flow control check valve to keep the shoes from releasing too far from the drums. Without that device rear drum brakes are not efficient.
That check valve is not appropriate for disc brakes. It may have been part of the proportioning valve that you removed.
When you get to dynamic evaulation your combination of parts may require tuning with an adjustable proportioning device. Ultimately emergency braking is better with greater front brake proportion than rear brake proportion.
The brake pedal push rod should release from the master cylinder piston with just a bit of clearance.
jim

[austinsnake]

Thanks, Guys, that's helpful.

Yes, I'm using the same booster, and Breeze looks to have the needed adapters to connect the new MC to the front L & R brake likes and the single rear line, so a pretty easy MC swap.


Brian