[grivera]

Thinking about converting to manual brakes as I have a low vacuum situation in my 66 due to cam. The car has has 4 wheel disc brakes - fronts look like factory A body and rear I assume are the Eldorado calipers. What is the recommended MC if I go manual? Any particular model/year to use and how about the rod that pushes the MC piston?

The car currently has the 1/4” brake line to the rear - is a particular year MC needed to accommodate this line?
Do I retain a proportioning valve? I believe the current one is for a disc/drum car so if I would put correct in.

Pics of current set up below.

[jwcfbd]

what about adding a vacuum canister and keeping your power brakes?

[grivera]

In research phase right now to determine what route to go - nothing is off the table. For this thread I want to limit to manual brake conversion.

[Schurkey]

Virtually every car with (front) disc brakes, or 4-wheel discs has a power booster.

Disc brakes have very little self-energizing action, and what little they have reduces as the pads wear.

Manual disc brakes are not a great idea. Either the pedal effort is too high, or the brake pedal travel is too long. Neither is good.

FIX THE ENGINE to recover your vacuum. Or add a suitable vacuum pump. Or replace the vacuum booster with Hydroboost.

[64speed]

That looks like a drum/drum master

[Scarebird]

Originally Posted by Schurkey

...Manual disc brakes are not a great idea. Either the pedal effort is too high, or the brake pedal travel is too long. Neither is good...

This is nonsense.

A lot of factory cars had manual disc in the 60's till the mid 70's; Corvettes, Camaros, Firebirds, and especially Mustangs. I have hands-on converted several vehicles to disc or factory disc with a manual master.

Example A: 1968 Firebird Sprint with manual drum. Friend bought the car with 69 style OEM conversion kit in the trunk. We fitted it out and left the drum master in place to test - it worked perfect: effort and balance excellent.

Example B: My 1971 Lemans. Original power disc car, refitted with 4 disc (large bore front, Eldo rear). Used 1974-80 1/2 ton GM truck master with reworked pushrod, excellent results - pressure less than clutch and a bootfull will lock all 4 up easily.

One nice thing about manual in addition to simplicity and size is that the braking result is far easier to modulate - light push equals light slowing.

Unless you are a 80 pound woman in heels, manual will work quite well.

OP: that booster is trash - a dual 9" will work down to 9 in Hg.

Manual masters for that era caliper require 1" bore masters, 7/8" is for Metric calipers. And keep the 1/4" rear line - too much frictional loss with 3/16" says Bernoulli.

[65madgoat]

7/8" master cylinder and go smaller (3/16") on brake line to the rear is my advice going manual. Manual works great when set up right.

[rasilverbird]

Originally Posted by 65madgoat

7/8" master cylinder and go smaller (3/16") on brake line to the rear is my advice going manual. Manual works great when set up right.

Wilwood told me to go with a 1.125" for manual discs. They don't work so well

[Scarebird]

Originally Posted by rasilverbird

Wilwood told me to go with a 1.125" for manual discs. They don't work so well

What calipers are in front?

[65madgoat]

Originally Posted by rasilverbird

Wilwood told me to go with a 1.125" for manual discs. They don't work so well

That is odd and wrong. That size is for boosted brakes.

For manual, you go 7/8" or 15/16" usually.

[Skip Fix]

I went a click smaller than 1" for my race car manual 4WD. Started with the Strange 1&1/16" MC way too much pedal effort!
Mid 60s after 64 Vettes had 4WD and lots were manual and the 1" MC that everyone copies for disc kits.

[Formulajones]

Corvettes we're built in The 10's of thousands with 4 wheel manual disc brakes starting in 65 and continued the trend with manual into the mid 70's. Power was an option.

I did 4 wheel manual disc on the Vega and simply used a manual 4 wheel disc master for a Corvette, just pic a year. It's a 15/16 bore and I plumbed in my own adjustable proportion valve. Very easy

[grivera]

Originally Posted by Formulajones

Corvettes we're built in The 10's of thousands with 4 wheel manual disc brakes starting in 65 and continued the trend with manual into the mid 70's. Power was an option.

I did 4 wheel manual disc on the Vega and simply used a manual 4 wheel disc master for a Corvette, just pic a year. It's a 15/16 bore and I plumbed in my own adjustable proportion valve. Very easy

Thanks - how did you like it?

[Skip Fix]

Just T the fronts and an adjustable prop valve in rear.

[grivera]

Originally Posted by Scarebird

This is nonsense.

A lot of factory cars had manual disc in the 60's till the mid 70's; Corvettes, Camaros, Firebirds, and especially Mustangs. I have hands-on converted several vehicles to disc or factory disc with a manual master.

Example A: 1968 Firebird Sprint with manual drum. Friend bought the car with 69 style OEM conversion kit in the trunk. We fitted it out and left the drum master in place to test - it worked perfect: effort and balance excellent.

Example B: My 1971 Lemans. Original power disc car, refitted with 4 disc (large bore front, Eldo rear). Used 1974-80 1/2 ton GM truck master with reworked pushrod, excellent results - pressure less than clutch and a bootfull will lock all 4 up easily.

One nice thing about manual in addition to simplicity and size is that the braking result is far easier to modulate - light push equals light slowing.

Unless you are a 80 pound woman in heels, manual will work quite well.

OP: that booster is trash - a dual 9" will work down to 9 in Hg.

Manual masters for that era caliper require 1" bore masters, 7/8" is for Metric calipers. And keep the 1/4" rear line - too much frictional loss with 3/16" says Bernoulli.

Great info- thank you

[RocktimusPryme]

Real world experience because I have a similar setup.

I have a manual full disc setup. Mine is all Right Stuff gear but that’s basically stock A body equipment anyway.

I’m fairly certain the supplied master from my front disc kit is a 1” bore. I had it when I originally had disc/drum. When I converted the rear to discs as well I changed to a disc/disc combination valve but did not change the master.

I don’t love the pedal effort. It stops fine but if I need to stop in a hurry I’m putting all my leg into the pedal.

So I would definitely go smaller than 1”. It seems 15/16” bore might be the sweet spot based on what I’ve heard others say. I’ve been meaning to make the swap myself but I hate messing with the lines on that combo valve. It’s only a minor issue so I haven’t talked myself into the battle.

[AG]

I used a Wilwood 1" master on my brother's LeMans with manual D52 fronts and drum rear and the brakes are excellent. I like the feel of manual brakes.