dual MC dilemma

[62Tbird]

I am almost done with my 65 disc brake swap on my 62. Before I bench bleed the MC, I mocked up this dual MC to my rebuilt original brake booster.

https://www.tbirdhq.com/pc_product_deta ... E24B40929F

^ This is the brake MC I purchased.

When I am installing the MC onto the factory brake booster, there seems to be a lot of preload from the pushrod to the master cylinder. I adjusted the pushrod by turning the adjuster bolt all the way in and still get excess preload on the MC.

I contacted the supplier and he suggested using the factory spacer between the MC and booster. Only issue is my setup does not have a spacer. Prior to this disc brake swap, I installed a rebuilt unit and confirm there was no spacer used and my 62 was working adequately with the previously installed MC.

I am stumped at this point, only things left is bench bleed MC, plumb in adjustable prop valve, bleed system and go for some test drives.

Any help is appreciated. Thank you.

[stubbie]

You could probably use something like this.
https://fatfourcustoms.com/shop/s2k-clu ... er-spacer/

[Steverino]

Hey @62Tbird, I'm gathering parts for my conversion and wondering how things ended up with yours. So far I have 66 calipers, spindles, rotors, & backing plates. I guess I still need the lower control arms and of course the master...

Are you satisfied with how everything works now? What did you end up doing to make the master cylinder work? Does it clear your brace okay?

Thanks in advance for any advice...

[Rusty57]

You are correct to be concerned with preload on the MC. There should be a very small amount of slack between the pushrod and the MC when everything is in the “home” position.

The piston in the MC has to return all the way to the stop. This opens the ports from the wheel cylinders so the fluid is returned to the reservoir and allows the brakes to release.

Another point consider is that normally in a power brake setup the pushrod is actually 2 pieces. There is one piece that is connected the the brake pedal arm typically with some type of threaded clevis. It includes the valve that controls vacuum to the booster.

There is second push rod that seats into the end of the one connected to the brake pedal. The other end of this second pushrod seats into the cavity in the end of the MC piston.

Both of the those pushrods need to be the correct length for the system to work properly. Depending upon your mixture of parts you might need some custom length pushrods.