rayL79

Will a dual master cylinder for a power brake car fit on my manual brake car and does it accept 2 1/4" lines? I'm trying to do a dual master cylinder conversion without changing a lot of lines or going to a proportioning valve.
Ray

Avispa

A correct 66 master cylinder has only one pressure port. You'll need a 67 master cylinder for a dual circuit conversion or a power brake MC.

rayL79

So my question is "Will a 1966 power brake master cylinder fit in my car?"

68hemi

A 1965/1966 PB master cylinder WILL of course fit your 1966 car but you will have to add a line since 65/66 PB cars are ALL dual cylinder systems unlike the manual brake cars that are single.. The 65/66 PB master cylinders are hard to find and EXPENSIVE hence the suggestion to use a 67.

rayL79

Thank you, that was very helpful. If the '66 power brake cylinder has two 1/4" outlets, my intention is to disconnect the 1/4" brake line that goes from the block to the rear brakes and connect it directly to the rear port of the new master cylinder, after putting a plug in the block where it came from. Does this sound reasonable? The 1967 master cylinders don't have two 1/4" outlets (one is smaller).
Ray

R66

You are correct with your routing. I ran a new line to a coupling at the existing tee just to maintain the original configuration should I choose to put the single cylinder back on. Probably wasted my time and money.

Grampy

The line from the block is not long enough the reach the dual master cylinder. You'll have to splice. I put a proportioning valve in as the splice point in my '66 with '66 power master cyl. I also ran new stainless lines while I was at it.

buns

Ports on the '67 master are 9/16 -18 and 1/2 -20. Adapters are available from Eaton/Weatherhead and Edelmann. Try these part numbers, one of which might be wrong. 7912 and 7908.

vark_wso

Is adding p/b booster & associated hardware part of your plan? Or, are you just considering trying to run this '66 p/b master cylinder, un-boosted?

uvettcha

My Vote is Boosted is so great over non Boosted........ask me how i found out..........Hi

larrywalk

I did this many years ago - adding a '67 Corvette master cylinder. Yes it will fit, but unless you want power brakes (I didn't), use the '67 manual brake master cylinder because it has a 1" diameter piston assy. Power brake master cylinders use a larger piston which will make your pedal forces way too heavy without the rest of the power brake system. Manual braking is fine!

Second point...
Since the '65 manual system had only one line out of the MC, I figured that it the pressure to both the front and rear brakes was the same. To make the hookups easier, my front brakes (1/4") line connected to the rear outlet of the MC, and the smaller 3/16" line to the rear brakes connected to the front outlet. (Edelmann makes adapter fittings.) Braking action has been exceptional.

Third point...
I saw no need for the differential switch below the MC (it's not really a proportioning valve anyway), besides I didn't have the electrical wiring for a dash "Brake" light. If either brake system failed, the failure should be apparent to me.

It's a nice change and improves safety if one circuit goes out!

buns

The '67 power and manual masters are the same. P/N 5458831.

68hemi

My advise for anyone that is fooling with their factory brake system is to contact someone like Master Power Brake. The will have what you need and know how it should be plumbed rather than finding out the hard way. You brakes are stopping a 3000 lbs. missile going down the road and you are possibly endangering yours and others lives.

zpletcher

Why bother if not power brakes. Has anyone ever heard of the single master cylinder failing? I have not.
jmho

larrywalk

In over 50 years of ownership of my '65, twice I've had a loss of brakes when one CALIPER failed. With a single master cylinder, loss of any caliper will result in all calipers losing pressure. Although the MC did not fail, losing that single circuit took out all brakes. Two hydraulic circuits gives you redundancy for loss of either, or any caliper.

rayL79

Thanks for all the very helpful posts, guys. What prompted this was my right front caliper all of a sudden started leaking and the brake pedal got soft and gave me a little scare. With a single master cylinder you could lose all braking...and we all know the emergency brake is not going to save your ***.

seivadmij

rayL79,
I know this post was a while ago. But I am looking into converting my 1962 to a dual reservoir system.
Did you have any issues using the 1966 Dual reservoir power boosted master cylinder in a manual application?

vettebuyer6369

Over 5 years later. Let’s start a new thread