Manual disc brakes vs power disc brakes questions

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moparmat2000

moparmat2000

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I have a disc brake question but need to lay out what i have, and what i am concidering.

I have the disc / drum setup off a 79 cordoba. This has the 11.75" rotors and 2.75" calipers, and 10x2.5" finned drums in the back.

I have a 74 dart power booster, and would need the 79 cordoba master cylinder to port enough fluid to make the cordoba pistons work.

The dart master cylinder as well as the cordoba one are both cast iron and extremely heavy. This is probably the reason for 2 additional support struts off the power booster to the firewall and inner fender. I also have put this car on an aluminum diet, trying to shed some nose weight.

I was looking into the aluminum master cylinders off a 79 dodge D150 pickup. This truck uses the same rear wheel cylinder part number as the 79 cordoba, but has 3.18" diameter piston calipers.

If i use the dodge truck master with the 74 dart power booster, will the brakes be too touchy? If this is so, will it offer enough assist by itself if i run the dodge truck master cylinder as a manual brake master cylinder with my cordoba brakes? Is the dodge truck master cylinder ports SAE or metric thread? Will it accept a regular A body manual brake pushrod? If not where can i get one that fits? I know there is an adaptor bracket for this conversion.

Reason i mention this is i have driven 4 wheel manual and power drum cars, and power disc brake cars before, but not manual disc brake cars.

I know it would be much simpler without power brakes to work on the car. Anybody do this before? I want to decide before i spend any money rebuilding this booster.
 
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I have 2 manual disc cars, both stock A bodies, and both stop fine. I have no trouble locking them up if need be. I think power brakes are overkill until you get up around 4000 pounds or more. More room in the engine bay w/o the booster, no worrying about not having enough vacuum to work the booster if you have a lumpy cam, one less thing to break and go wrong. If you do decide to go just manual disc you will need a manual disc pushrod, because the pushrod setup is different between a power brake and manual brake setup - disc or drum. PM me if you need a pushrod.
 
I have manual std disc/drum and It's not really that much different than the power....to me. I put a brand new cast iron master on my car and it is leaking fluid down my firwall and bubbling my paint so I will be switching to the aluminum.
 
airgrabber said:
I have 2 manual disc cars, both stock A bodies, and both stop fine. I have no trouble locking them up if need be. I think power brakes are overkill until you get up around 4000 pounds or more. More room in the engine bay w/o the booster, no worrying about not having enough vacuum to work the booster if you have a lumpy cam, one less thing to break and go wrong. If you do decide to go just manual disc you will need a manual disc pushrod, because the pushrod setup is different between a power brake and manual brake setup - disc or drum. PM me if you need a pushrod.
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Did the pushrod ends change at all when mopar went from cast iron to aluminum on the master cylinders? Reason i ask is i have access to a lathe and a bridgeport at work and can make my own adjustable one.

Also from what i understand manual disc brake vehicles use a different master cylinder than power brake ones. Does a manual brake master cylinder use a larger bore than power?

I am assuming the dodge truck master cylinder will have a larger bore because of the 3.18" front caliper pistons, if so this may work fine as a manual brake master with the cordoba brakes.

Any thoughts? Agree? Disagree? Other options?

Thanks in advance
Matt
 
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Manual brake setups use a "pushrod retainer" (basically a 1/4" piece of small vacuum hose), that fits on a groove machined at the end of the pushrod. The master cylinder has a corresponding groove in the back of the piston, and evidently not all m/c's have this groove. I guess the pushrod can fall out if the brake pedal is pulled back too far. I can't remember if my power brake pushrods are lacking this groove, but that may explain the different m/c applications.
 
fshd4it said:
Manual brake setups use a "pushrod retainer" (basically a 1/4" piece of small vacuum hose), that fits on a groove machined at the end of the pushrod. The master cylinder has a corresponding groove in the back of the piston, and evidently not all m/c's have this groove. I guess the pushrod can fall out if the brake pedal is pulled back too far. I can't remember if my power brake pushrods are lacking this groove, but that may explain the different m/c applications.
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A friend of mine said on his GM applications the manual and power master cylinders had different sized pistons. Maybe because of more pedal effort required with manual discs.
 
Yep, and the factory applications seem to be all over the place IMO. My cars either have or will have manual brakes, and I've used the 1 1/32" m/c's pretty much across the board. I like the extra pedal throw, and ability to modulate the brake pressure. The bigger bores, for me, we're just too stiff. I've also standardized my stuff to 2.75" calipers, and mostly 10" rear drums.
 
I have the 2.75 calipers with the larger rotors on my 64 Sport Fury. I ended up with a 1 1/32 bore MC. I had a 15/16 bore MC onIt, but it didn't move enough fluid. will need the adapter for the 4 bolt to 2 bolt mounting on the aluminum MC. Works fine without a booster. If you want to use the truck calipers, order a MC for a truck with a manual brakes. Probably will need to be at least 1 1/8. Maybe larger if available. I have a push rod on this car without the rubber retainer. Never fell out in 20 years. It's stopped by the brake light switch. I made my own adjustable pushrod.
 
I have been changing all of my cars over to manual brakes. After running my '74 Duster as is with the factory manual disks and master I decided it was far better than the power set up for brake feel and modulation, and not that much worse for actual brake effort. Worth the trade off. I've run my Duster with the stock master and stock disks, the stock master and 11.75" disks, and currently run it with Dr. Diff's 15/16" aluminum master cylinder and his 13" cobra style disks with 11x2.5" drums in the back. That set up works great.

I also recently changed my Challenger over from power disks to manual. It had the stock power master cylinder with 11.75" disks and the 2.75" calipers. I switched it over to Dr. Diff's 15/16" aluminum m/c like the Duster. The 15/16" m/c moves more than enough fluid, the pedal is impossible to hit the floor with. It does have a little more travel than a 1-1/32" m/c, but I find that gives a lot more ability to modulate the brakes and it reduces the amount of "leg" needed a little. Not much, the feel and modulation factor is why I run the 15/16" not the force needed on the pedal. I also run 11x2.5" drums on the back of the Challenger.

Dr. Diff also machines the back of the m/c piston to work with the manual push rods. It's probably not 100% necessary, but it keeps everything working as it was intended. The only beef I have with his m/c's, and it's not his fault, is the gaskets that come with the m/c from the factory. By the time you're done bleeding the brakes they'll start leaking, I think they only last for one or two tightening cycles on the caps. I just replace them with Dorman caps and gaskets, those work fine.
 
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Here's a chart showing the stock m/c sizes from a '73 factory manual. The only one it doesn't show is the stock A-body KH disks, which used a 1" m/c.

***EDIT***

Sorry, I screwed up my description of the bore to pedal effort. Like I always do. :BangHead:

So, the smaller m/c bore will require more force to push down, it has a higher line pressure (smaller surface area on the piston). BUT, since it moves less fluid, there's more travel. Which is why it's confusing. It feels "softer" because it travels more, but really it takes more pressure to push.

The larger m/c bore takes less pressure to push because of the larger piston area. But, because it moves more fluid, it doesn't travel as far, so, you get a higher pedal that gets harder faster because of the shorter travel distance.

Why the B/E body m/c bores are flip flopped from the A-body m/c bores I'm not sure, but since there is some mechanical advantage from the lever for the booster it may be that the levers are different between platforms, I never checked from one to the other despite having both A and E body boosters and hardware at one point. I sold my A-body booster set up so I can't compare them anymore.

At any rate, I like the 15/16" M/C with manual disks, the pedal effort isn't bad and the slightly longer travel makes it easier to modulate the braking force. But that's just my opinion.

factorym:c.png
 
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It looks like the 1&1/8 is 1979 dodge truck.

1&1/32" or 1.0313 is 79 volare, 1980 mirada

What does the 15/16" diameter one come off of ?

Based on the chart that 72bluNblu provided, the pickup master may be a bit much at 1&1/8" bore for its 3&1/8" diameter caliper pistons, however the mirada, volare one at 1.03" diameter bore with 2.75" piston calipers will prob work better with manual or power.

Also are the fittings on these aluminum wonders metric or SAE?
 
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72bluNblu said:
I have been changing all of my cars over to manual brakes. After running my '74 Duster as is with the factory manual disks and master I decided it was far better than the power set up for brake feel and modulation, and not that much worse for actual brake effort. Worth the trade off. I've run my Duster with the stock master and stock disks, the stock master and 11.75" disks, and currently run it with Dr. Diff's 15/16" aluminum master cylinder and his 13" cobra style disks with 11x2.5" drums in the back. That set up works great.

I also recently changed my Challenger over from power disks to manual. It had the stock power master cylinder with 11.75" disks and the 2.75" calipers. I switched it over to Dr. Diff's 15/16" aluminum m/c like the Duster. The 15/16" m/c moves more than enough fluid, the pedal is impossible to hit the floor with. It does have a little more travel than a 1-1/32" m/c, but I find that gives a lot more ability to modulate the brakes and it reduces the amount of "leg" needed a little. Not much, the feel and modulation factor is why I run the 15/16" not the force needed on the pedal. I also run 11x2.5" drums on the back of the Challenger.

Dr. Diff also machines the back of the m/c piston to work with the manual push rods. It's probably not 100% necessary, but it keeps everything working as it was intended. The only beef I have with his m/c's, and it's not his fault, is the gaskets that come with the m/c from the factory. By the time you're done bleeding the brakes they'll start leaking, I think they only last for one or two tightening cycles on the caps. I just replace them with Dorman caps and gaskets, those work fine.
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To reiterate, when I changed ONLY the calipers to the 2.75 bore size, the 15/16 MC that was on the car working for several years, would not move enough fluid to properly operate the brakes. Yes, the pedal did hit the floor. I changed to the 1 1/32 bore, and instant pedal, worked great. End of story.
 
moparmat2000 said:
It looks like the 1&1/8 is 1979 dodge truck.

1&1/32" or 1.0313 is 79 volare, 1980 mirada

What does the 15/16" diameter one come off of ?

Based on the chart that 72bluNblu provided, the pickup master may be a bit much at 1&1/8" bore for its 3&1/8" diameter caliper pistons, however the mirada, volare one at 1.03" diameter bore with 2.75" piston calipers will prob work better with manual or power.

Also are the fittings on these aluminum wonders metric or SAE?
Click to expand...

The fittings on Dr. Diff's m/c's are SAE, you don't need to make any changes to the brake lines. They're from the later "cloud" cars if I remember right. You can buy them in 1-1/32", which is what they are originally. Cass actually sleeves them down to make the 15/16" version. And like I said, my Challenger runs 11.75" disks and 2.75" bore calipers, the 15/16" works great.

furyus2 said:
To reiterate, when I changed ONLY the calipers to the 2.75 bore size, the 15/16 MC that was on the car working for several years, would not move enough fluid to properly operate the brakes. Yes, the pedal did hit the floor. I changed to the 1 1/32 bore, and instant pedal, worked great. End of story.
Click to expand...

Except it's a '64 Fury. What's the pedal ratio? The original m/c in that car was a single pot with a 1" bore. There's a lot more to it than just the size of the m/c bore and the piston bore, the piston travel, pedal ratio, and size of the rear wheel cylinders are part of that too. When I converted my old '55 Dodge Coronet to a dual m/c and disk brakes I needed a 1.125" bore master, even 1-1/32" was barely enough to keep it off the floor. But that doesn't mean that all cars with disk brakes need a 1.125" m/c.
 
Not sure what the pedal ratio is. I imagine it would be the same for all A body cars from 67 to 76.

I did put my power booster with support brackets on a bathroom scale and got 11 lbs. The old iron master cylinder added another 10 lbs to it. If the new master weighs in at about 2 lbs then i got a 19 lb savings, and an uncluttered firewall.

Now i just gotta figure which MC i need that will work with my 2.75" calipers. 72bluNblu chart shows a 1.03" bore master for use with power brakes and 2.75" piston calipers on B-J-R-W car lines, but shows a 1.03 bore piston MC on the V-L car line with 2.60 piston calipers with manual brakes. Now if we can find the pedal ratio of these different car lines, and compare that to the A body pedal ratio, i'd have a definitive answer.
 
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Just an FYI

V-L = A body
R-W-S-X = B body
B-J = E body
P-D-C-Y = C body and Imperial
 
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Either will work fine. Looks like you figured out that the V-L line is A-bodies. It's just the codes the used in the factory manual.

The B-J-R-W line includes Challengers, and it shows the manual disk m/c at 1". Mines 15/16" and is no where near bottoming out on the floor on my Challenger, even with the 2.75" bore calipers. So, you can use either a 15/16" or 1-1/32" m/c, it will just be down to what you prefer as far as pedal feel.

modelchart.jpg
 
Thank you to everybody who responded to this thread. This helps me with my diet plan for my 67 barracuda. So far my math shows as this.

Dry shipping weight 1967 notchback sport coupe with V8 2,855 lbs

Top off all fluids including fuel
3,016 lbs

I removed , power brakes, oem starter, oem alternator, iron heads, iron intake, copper brass radiator, iron bell housing, iron cased A833 gear box. 459.53 lbs

Add manual brake lightweight MC, denso starter, denso mini alt, aluminum heads, aluminum intake, aluminum radiator, aluminum bellhousing, aluminum cased A833 O/D. 234.4lbs

The net difference puts me at 2792 lbs with all fluid capacities full.

This figure doesnt take into concideration that i added disc brakes which are heavier than the front drums, will be adding a 1&1/4" hollow swaybar on the front, and a solid 7/8 sway bar on the rear, subframe connectors, four 1/8" thick torque box plates, beefier 2×3 boxed lower radiator support, and caltracs. In this regard the weights gonna go back up maybe 50-75 lbs i'm thinking.

I am also thinking of ditching the lead acid battery for Li battery once pricing comes down. I can drop off roughly 45lbs, for a 5 lb Li battery a net weight savings of 40 lbs.

Although i do have a spare manual box, I dont plan on ditching the power steering as i'm using C body pitman and idler arms for a faster ratio, and will be dialing down the pressure in the pump for a better road feel. I may go with a lighter borgeson power steering box later.
 
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furyus2 said:
To reiterate, when I changed ONLY the calipers to the 2.75 bore size, the 15/16 MC that was on the car working for several years, would not move enough fluid to properly operate the brakes. Yes, the pedal did hit the floor. I changed to the 1 1/32 bore, and instant pedal, worked great. End of story.
Click to expand...

something was not right with your brakes.I have always used 2 .75" piston callipers with 15/16" or 1" bore master and my a bodies all stopped effortlessly with about 2 1/2" of pedal travel.
i don't know about moving enough fluid...the pistons only move about .003 - .005
 
Which car line uses a 1" bore aluminum master? Wasnt the fwd cirrus , stratus car line the one with the 15/16?
 
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ir3333 said:
something was not right with your brakes.I have always used 2 .75" piston callipers with 15/16" or 1" bore master and my a bodies all stopped effortlessly with about 2 1/2" of pedal travel.
i don't know about moving enough fluid...the pistons only move about .003 - .005
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Maybe being his fury is a C body, maybe it has a different pedal ratio than A and B body stuff. I dunno just posing the question.
 
moparmat2000 said:
Maybe being his fury is a C body, maybe it has a different pedal ratio than A and B body stuff. I dunno just posing the question.
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..."somethings wrong" was a bad choice of words.
smaller pedal ratio would certainly increase the length of pedal travel.
 
Can i assume correctly that a 15/16 or 1" will give firmer pedal feel / higher fluid pressure because of a smaller bore as compared to a 1.03" bore, or is it the other way around.
 
smaller bore master = softer pedal and longer travel but more pressure.
...a 1 1/8" master will take two legs to stop / lock the wheels and the pedal will be
rock hard after an inch of pedal travel.
 
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