Manual disc brakes vs power disc brakes questions

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ir3333 said:
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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I can get a 1&1/32 " diameter bore MC . Stock from aspen/volare. Thats as close to 1" as i can find.

Still asking what car do i get a 15/16" bore one from?
 
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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I am also thinking of dumping my booster for manual disk on my 73 Dart Sport. Can the master cylinder I have bolt to the firewall and use the other pushrods? If so where can I buy one??

Thanks!!!
 
moparmat2000 said:
I can get a 1&1/32 " diameter bore MC . Stock from aspen/volare. Thats as close to 1" as i can find.

Still asking what car do i get a 15/16" bore one from?
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...15/16 " was used on the early A body 4 piston Kelsey Hayes disc system
a cast iron master back then.
 
Scottd9990 said:
I am also thinking of dumping my booster for manual disk on my 73 Dart Sport. Can the master cylinder I have bolt to the firewall and use the other pushrods? If so where can I buy one??

Thanks!!!
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You need a manual brake pushrod. And can use the power brake master cylinder and attach it to the firewall. However i think there is a specific manual brake master cylinder for front discs without power brakes. Its bore is different i think its smaller If that all makes sense.
 
[ottd9990, post: 1971366728, member: 47458"]Ok, thanks Matt! I will try to find the parts.[/QUOTE]
Is your brake system stock. If so look at the chart 72bluNblu posted in post #11.

It shows V-L car line with 2.6" calipers and manual disc brakes as using a master cylinder with a 1.03" bore. That equates to 1&1/32" bore in fractional size. According to rock auto a 70s plymouth volare/aspen used a master cylinder in this size in aluminum. It is a 2 bolt master cylinder, and requires a 4 bolt to 2 bolt adaptor. The cheapest i have found these aside from making one myself was dr diff at $38

It shows a power brake master cylinder for V-L car lines as .936 bore. So A bodies used a smaller bore master on power brake cars, and a larger bore on manual brake cars.

I can only assume with power assist a larger bore master was unnecessary and made the brakes touchy. With manual brakes a bigger bore was necessary for the brakes to work properly without power assist.
 
15/16"=.937"

15/16" was the standard size for A-bodies with 9" drums and power disks. It was a common bore size across quite a few mopar platforms as well.

As far as "working properly", that's not the right way to put it. A-bodies work just fine with either a 1-1/32" bore m/c or a 15/16" bore master cylinder, manual or power. The difference is completely down to pedal feel and effort. The only reason the factory used one vs the other was a subjective decision about how the brakes should "feel" with each system. Either one will stop the car just fine.

Just buy an aluminum m/c from Dr. Diff. It's $95 for the 1-1/32" bore master and that includes the 4 to 2 bolt adaptor. It's an extra $30 if you want the 15/16" bore because Cass actually sleeves down the later m/c's from 1-1/32" to 15/16". Having used both, I prefer the 15/16" bore and that's why I pay more to have them. But that's just my opinion.

Mopar Aluminum Master Cylinder Kit
 
I was going to get a 1&1/32" aluminum MC off rock auto for about $27 and the adapter kit off ebay for $38, and call it good.

Its nice to know theres a 15/16" special bore one avail though
 
Unfortunately, I've never seen a new "parts store" 2-bolt 1 1/32" bore (Aspen/Volare) master cylinder that wasn't cast iron.
 
79 Aspen/Volare or 80s diplomat / fifth ave / fury. Just looked on rock auto. Your right, the new ones appear to be cast iron. The cardone remans however appear to be original aluminum pieces.
 
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72bluNblu said:
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.



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.
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I never said all cars need a 1.125 bore MC. I merely stated what worked for me. If that doesn't fit with your thoughts, who cares? You have a habit of pouncing on other posters, as if you're the only one who is right. Not the first time you've done it to me. I don't agree with you. I know what worked for me. You didn't see me puffing about how wrong you are. If you don't like what I think, state your opinion, and move on.
 
ir3333 said:
..."somethings wrong" was a bad choice of words.
smaller pedal ratio would certainly increase the length of pedal travel.
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You're right. It was a bad choice of words. And my car is not a C body. If my car is so wrong, why did the factory use the larger MC with the larger calipers? Again, I never said mine is the only answer. I just resent know it alls from assuming I'm wrong .
 
whew..glad i retracted my mistake but i did not say you had a c body and i did not say your car was wrong...i said something is wrong.
i did not realize the correct master was 1 1/32" for the 2.75 callipers but i think
it should work fine.... i have used both 1" and 15/16" masters with 2.75 callipers on A bodies and like them because they develop more pressure than the 1 1/32" with less leg pressure,but have a bit more pedal travel.
As was mentioned your pedal ratio may not allow a master cyl with a smaller piston.
 
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ir3333 said:
whew..glad i retracted my mistake.
i did not realize the correct master was 1 1/32" for the 2.75 callipers but i think
it should work fine.... i have used both 1" and 15/16" masters with 2.75 callipers on A bodies and like them because they develop more pressure than the 1 1/32" with less leg pressure,but have a bit more pedal travel.
As was mentioned your pedal ratio may not allow a master cyl with a smaller piston.
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Well, since I have a Dart also, I think I will crawl under both cars, and look into the pedal ratio. Maybe I will find a difference.
 
I bet the flip flopping of the master cylinders in this chart has something to do with the bracket and linkage setup on A bodies behind the master cylinder changing the pedal ratio. Notice the V-L power disc brake MC .937" bore is the same as V-L 9" drum brake cars, however the V-L with manual discs use a 1.031" or 1&1/32" bore MC

Now look at B-J-R-W car line manual disc with 2.75" calipers. Its listed as 1.0" bore. This setup is mounted to the firewall no progressive linkage. B-J-R-W car line with power discs on 2.75" calipers uses a 1.031" or 1&1/32" bore MC with power brakes.

Not sure in the V-L but the power brake linkage behind the booster may slow down, or speed up the rate the piston moves, it may act like a force multiplier. kind of like a lever and fulcrum arrangement does.

downloadfile-5.png
 
furyus2 said:
I never said all cars need a 1.125 bore MC. I merely stated what worked for me. If that doesn't fit with your thoughts, who cares? You have a habit of pouncing on other posters, as if you're the only one who is right. Not the first time you've done it to me. I don't agree with you. I know what worked for me. You didn't see me puffing about how wrong you are. If you don't like what I think, state your opinion, and move on.
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I "pounce" on misinformation. And in addition to saying a 1.125" master cylinder worked for you, you also suggested that a 15/16" master cylinder won't push enough fluid to run 2.75" calipers on an A-body. And that is misinformation. It's actually wrong. I know that because I've run that exact combination, and it works great. I also never said a 1.125" master cylinder wouldn't work. I said it wasn't needed, and it isn't. And on an A-body I don't think a lot of people would be happy with the pedal feel a 1-1/8" master cylinder would give, but that's my opinion. And as I've said several times, any master cylinder from 15/16" to 1-1/32" will work just fine on an A body, anything in that range will stop the car just fine. The difference within that range basically comes down to pedal feel, and that's an opinion.

What works on a '64 Fury and what works on an A body aren't necessarily the same thing. The fact that the brake pedal hit the floor on your '64 Fury with a 15/16" master tells you everything you need to know. On an A-body a 15/16" master cylinder works great. The differences in the braking systems between an A-body and your '64 Fury are apparently too great for that information to be relevant.
 
Ok i got some good info from asking these questions, thank you to all that answered. I appreciate the charts, and i copied them. I also appreciate those who did this mod and shared what master cylinder they used, how the pedal feel was etc, etc. I am sorry if this started an argument over this so at this point i'm out.
 
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DoctorDiff said:
Unfortunately, I've never seen a new "parts store" 2-bolt 1 1/32" bore (Aspen/Volare) master cylinder that wasn't cast iron.
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BTW i just got 2 new volare aspen 1-1/32" MCs from rock auto. They were supposedly remanned, however all the parts including the reservoirs are new castings. These were closeout for $12.27 each so i bought 2 of em. One has an aluminum body, one has a cast iron body. Both of the ones i recieved have a groove in the back of the piston for a manual brake pushrod o ring retainer. Plus the threaded holes for the brake lines on these are not metric, but are standard SAE thread.

I still need to buy the 4 bolt to 2 bolt adaptor firewall adaptor. The doctor diff one looks to be the best quality made one. The mopar perf one looks like its just hacked out of a 1/4" plate of aluminum.
 
Do those masters have the residual valve in the port for the rear brakes? or will you have to put one in line?

Gary
 
moparmat2000 said:
Not sure.
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Well I read all this hoping to learn something, I didn`t. I have 4 wheel discs on my 68 fastback. Willwood fronts, and an ebay bought special build dana 60, w/ probably chevy discs on it. I haven`t bothered to figure it out yet.. I ran new brake lines, an installed a 1987 diplomat master cyl., its alum., on an offset 1/2" thick spacer for head clearance, (raised port heads.) I had to machine the lower fin off the drivers side valve cover to get it off and on, and used flexable lines on the master cyl. just in case I needed to swing it out of the way, I don`t. The car stops fine, but takes a hair more leg pressure than I`d like, but it`s not bad. I`m thinking about adding about 1/2" length to the brake pedal arm for more ratio, and using a real brake pedal as it has a 4 speed pedal in it now. anyway, anybody ever extended their pedal arm ?? sorry for all the lead up ! P.S.- I lengthened the pushrod 1/2" to make up for the 1/2" offset spacer, works well. opinions welcome.
 
I wouldn't mess with trying to change the pedal ratio. That '87 diplomat has a 1 1/32" bore master cylinder. Swap it out for a 15/16" bore m/c and you'll have a much nicer pedal.
 
moparmat2000 said:
Bob what diameter are your front caliper pistons?
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not sure, they were on an aftermarket front end I picked up that was really worth the money. only thing I did was install it and build strut rods for it.-------72 blue, not sure it`s worth the effort at this time, but what alum. Chrysler master cyl has the 15/16 piston ? mine does not have that big of a piston as you said, might have forgot what I did use !?? I know it`s under and inch.
 
The rule of thumb is increasing to a larger bore master, while leaving the calipers a stock diameter = harder pedal, and decreased clamping force at the wheels.

Using a smaller bore masterwhile leaving the calipers a stock diameter= softer pedal and increased clamping force at the wheels.

I am going to use a 1&1/32" bore master which is stock bore for A body manual disc brakes, however i increased my caliper piston size from 2.60" to 2.75" using cordoba big brakes. Instead of making the master cylinder bore smaller, i increased the bore size of the calipers effectively accomplishing the same thing. I will see how this goes, and may decrease the master bore size in the future if i feel the pedal is too hard.

As a side note dippy M body calipers use the larger 2.75" diameter pistons, and the rotors and brake pads they use are the same part numbers as an A body.

15/16" bore master cylinder can be found by speccing out a mid 70s A body with power disc brakes.
 
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