whaler

Due to my safety-oriented nature, I'd like to add a dual MC to a 64 Coupe. Due to my budget build nature, I'm going to retain drum brakes. I believe I can use a 77 - 82 Corvette manual brake MC.

Questions:

1) Do I need a different pushrod (if one comes with the MC from the autoparts place will it fit, or does the one in the 64 reach?)

2) Someone told me the pressure from a disk-based MC is too low, and I need higher pressure for drums. Is this true, and what are those things you put in line that increase the pressure?

3) I expect there is no distribution block. Any advice on where to cut the existing lines to minimize flaring (double flares I assume)?

4) Are there any other MC's that you'd recommend that would make this easier?

Any other thoughts would be appreciated. Other than "you should go to disk"...

Thanks as always!
- Paul

KC John

You will need a residual valve in both the front and rear lines, and I would go with a 1" or even a 15/16" bore on the MC.

Just ask the part house for a Chevy dual reservoir for a mid to late 60's Impala MC. I don't think they came with disks until sometime in the 70's, that will give you the right one for what you want to do. It will probably have the right bore and come with built in residual valves, but ask to make sure.

jim lockwood

Paul, there's some small amount of truth to what Someone told you, but I don't think Someone fully understood the situation.

Your single circuit master cylinder, assuming it's original to the car, has a 7/8" bore. If you install a master cylinder with a larger bore, you will notice the need to push harder on the brake pedal to achieve the same stopping effort. Depending on how much larger the bore of the new master cylinder, the increase in pedal effort could be substantial.

Some examples:

For a M/C with a 15/16 bore: 15% greater pedal effort needed

For a M/C with a 1" bore: 30% greater pedal effort needed.

So, in my opinion, your first goal might be to look for a dual circuit M/C with a 7/8" bore. I don't know if one exists or if one ever did.

If you must use a a M/C with a larger bore, you can mitigate the increased pedal effort in at least two ways:

1. Install shoes with lining that has higher-than-stock coefficient of friction.

2. Install all new wheel cylinders with bores that have proportionally larger areas to match the increased bore area of the new master cylinder.


Good luck with your conversion. It's worth while and worth doing well.

Jim

Too Slow '90

If your brakes are power I believe the dual master cylinder will hit the underside of the hood if it is stock. Don't find out the hard way!

Roy

toddalin

1. The pushrod will reach.

2. If you are referring to residual pressure (i.e., when you let your foot off the brakes), drums like 10# whereas disks like 2#.

3. You can use your existing front distribution block but remove the rear line and plug this hole on the block. The removed line is what is routed to the rear of the dual M/C.

4. As noted, try to find a small bore, dual M/C from a non-disk car that already has the correct residual valves built in (maybe a Camaro as it is of similar weight). If you end up using a Corvette M/C, you will probably have to add 10# residual valves to the front and rear lines.

As Jim noted, the pedal effort is increased with a larger bore M/C. But, the pedal stroke is decreased.

I run front disks and rear drums and use a '70s Corvette manual dual M/C and have the 10# residual valve (and proportioning valve) plumbed in the rear line. Even in this case, the pedal effort did increase considerably, but it is still tolerable.