More disc brake questions

[moparmat2000]

From Dr. Diff site:

Master Cylinder/Caliper Bore Size - Quality Body Shop Drivetrain

Master Cylinder/Caliper Bore Size

All else being equal…

• Increasing the master cylinder bore diameter yields a shorter, harder pedal stroke with decreased clamping force at the brake pads.
• Decreasing the master cylinder bore diameter, yields a longer, softer pedal stroke with increased clamping force at brake pads.
• Increasing the caliper bore diameter, yields a longer, softer pedal stroke with increased clamping force at brake pads.
• Decreasing the caliper bore diameter yields a shorter, harder pedal stroke with decreased clamping force at the brake pads.

Based on this information above, a stock A body caliper piston is 2.50" diameter, and a stock A body manual master cylinder is 1-1/32" diameter bore. This is factory setup.

Cordoba brake pistons are 2.75" diameter. So according to this above information from DrDiffs website, if i use an aluminum 1-1/32" bore master cylinder in a manual brake config, which is the same as stock A body manual disc, along with 1/4" larger than stock A body piston calipers off a cordoba it should yield a softer pedal, with a firmer clamping force.

 

[ir3333]

Based on this information above, a stock A body caliper piston is 2.50" diameter, and a stock A body manual master cylinder is 1-1/32" diameter bore. This is factory setup.

Cordoba brake pistons are 2.75" diameter. So according to this above information from DrDiffs website, if i use an aluminum 1-1/32" bore master cylinder in a manual brake config, which is the same as stock A body manual disc, along with 1/4" larger than stock A body piston calipers off a cordoba it should yield a softer pedal, with a firmer clamping force.

i think stock A body single piston callipers are 2 5/8",a 1 1/32" master will probably be fine.
As stated,i have used 1" master with 2 3/4" callipers ('73-4 E body pin style) and loved the brakes ...everything was new.This was on a '70 Duster

 

[moparmat2000]

i think stock A body single piston callipers are 2 5/8",a 1 1/32" master will probably be fine.
As stated,i have used 1" master with 2 3/4" callipers ('73-4 E body pin style) and loved the brakes ...everything was new.This was on a '70 Duster

Regardless, the point i was trying to make is that going by the above information, i am enlarging the caliper piston size, and keeping a 1-1/32" manual master cylinder. A 1-1/32" master IS the same bore as stock A body manual disc brakes. According to this information it would yield a softer pedal with a firmer grip at the calipers.

This is the information i needed. I was thinking of going power brakes, but if this gives me a bit of a power feel without the weight, cost and space useage of a booster, then i'm all in. I screen shot that info and stored it in my phone.

 

[72bluNblu]

O.K. 72bluNblu Just a FYI you said that you changed to 1.12 Tbars and the front would lock before the rear, Yes now you don't have the weight transfer to the front so you need to put the valve in the front line to reduce and balance the braking force!! It's not just for the rear. It's when some guy doesn't fully understand or care how it works, that's when he gets out of control and crashes into someones car that does.

You don't want ether end to lock first, all 4 at the same time!! Front locks first and it understeers, pushes, plows,
wont turn. Rear locks first oversteer, rear comes around, spins out, but you can control it if you know how to drive. Understeer is very hard to get under control, once you get off the brakes the car is still sliding if you are in corner usually it's to late to recover.

I'm well aware of how it's supposed to work. But even in a perfectly balanced car the odds of all 4 wheels locking at the exact same time during street driving are pretty much nil. Just look at any auto racing. When they overbrake it's almost always a single wheel locking, not even both front or rear. If you're not going perfectly straight on dry, level ground on pavement that's in good condition it's not going to be the same every time. And if you're running drums out back it's a crap shoot, the auto adjusters aren't perfect. Sometimes they're different by a tooth and one wheel will lock first, sometimes they'll both be a little tighter or looser. And I would NEVER reduce the pressure to the fronts. Ever. Increase the rear braking to match, absolutely. Dialing down the front is just increasing your stopping distance, that's 70-80% of your braking you're turning down.

Truly if you're doing it right you should be threshold braking and not locking any of the wheels. Bottom line is know your car.

Based on this information above, a stock A body caliper piston is 2.50" diameter, and a stock A body manual master cylinder is 1-1/32" diameter bore. This is factory setup.

Cordoba brake pistons are 2.75" diameter. So according to this above information from DrDiffs website, if i use an aluminum 1-1/32" bore master cylinder in a manual brake config, which is the same as stock A body manual disc, along with 1/4" larger than stock A body piston calipers off a cordoba it should yield a softer pedal, with a firmer clamping force.

You can't necessarily compare the A-body and Cordoba systems for pedal feel. Remember that E-bodies that had manual brakes and 2.75" caliper bores used 15/16" master cylinders, they used 1 1/32" for power systems. And Cordoba's used 1-1/32" m/c's and had standard power.

Stock 73+ a-body calipers were 2.6". Not sure if that's 2-5/8" rounded off or not, some of the re-popped ones are spec'd at 66mm which is 2.6". I prefer the 15/16" master cylinder myself even with the 2.75" bore calipers. Anything from 7/8" to 1-1/32" will work.

 

[moparmat2000]

Thanks everybody for all the information , and great conversation. These 1-1/32" dippy masters are going to work just fine on both apps. A little softer pedal on mine with the larger piston calipers, and as advertized on the 69 notch since its 85 dippy brake pistons are closely sized to 73 dart calipers.

Thanks Guys
Your the best.

 

[moparmat2000]

Stock 73+ a-body calipers were 2.6". Not sure if that's 2-5/8" rounded off or not, some of the re-popped ones are spec'd at 66mm which is 2.6". I prefer the 15/16" master cylinder myself even with the 2.75" bore calipers. Anything from 7/8" to 1-1/32" will work.

Stock bore manual disc brake master cylinder for A body is 1-1/32" so this is why i am interested in the dippy master. Its the same bore as stock A body. This takes some guess work out of my equation. Caliper pistons being slightly larger than stock A body, it should soften the pedal , and make the calipers grip tighter. Sounds like a win to me.

Isnt the 15/16" master supposed to be for A body power disc brake cars? Trying not to get confused now.

I guess i will go with what i got, and try it. I may like the pedal feel, i may not.

Thanks again for all the info guys

 

[72bluNblu]

Stock bore manual disc brake master cylinder for A body is 1-1/32" so this is why i am interested in the dippy master. Its the same bore as stock A body. This takes some guess work out of my equation. Caliper pistons being slightly larger than stock A body, it should soften the pedal , and make the calipers grip tighter. Sounds like a win to me.

Isnt the 15/16" master supposed to be for A body power disc brake cars? Trying not to get confused now.

Yes, 15/16" was used on the stock power brake A-bodies. But they were backward from the other body styles, E-bodies for example used 15/16" for manual and 1-1/32" for power, exactly opposite from the A's. Has to do with the pedal ratio change going to the power booster, the linkage was different for A's than the other body styles.

 

[brian6pac]

There is a lot of good info flying around but bottom line is get the balance as close as possible. The Abody is no where close to a Bbody and the suspension is totally different. my car is set up and the adjustable valve is right beside my seat, some times with the heat changing things a 1/2 turn will fix it.

 

[moparmat2000]

Yes, 15/16" was used on the stock power brake A-bodies. But they were backward from the other body styles, E-bodies for example used 15/16" for manual and 1-1/32" for power, exactly opposite from the A's. Has to do with the pedal ratio change going to the power booster, the linkage was different for A's than the other body styles.

Exactly. Its because of the A body power brake linkage being the force multiplier. B, E, C body cars did not have linkages like this, because there was enough room under the hood to not need it.

But since i am going manual discs. The dippy master is sized the same as manual disc brake A bodies. It will be bolted directly to the firewall just like a stock A body cast iron manual disc master cylinder. No multiplier linkages.

Those brackets and linkages were only needed to bring the brake booster up high enough to clear the LH valve cover on a V8 A body, that crazy **** wasnt needed on B,C, E body cars. Since they had enough room under the hood, The linkage from those went straight in from the pedal into the back of the master, or booster in an inline fashion.

 

[72bluNblu]

Exactly. Its because of the A body power brake linkage being the force multiplier. B, E, C body cars did not have linkages like this, because there was enough room under the hood to not need it.

But since i am going manual discs. The dippy master is sized the same as manual disc brake A bodies. It will be bolted directly to the firewall just like a stock A body cast iron manual disc master cylinder. No multiplier linkages.

Those brackets and linkages were only needed to bring the brake booster up high enough to clear the LH valve cover on a V8 A body, that crazy **** wasnt needed on B,C, E body cars. Since they had enough room under the hood, The linkage from those went straight in from the pedal into the back of the master, or booster in an inline fashion.

Sorry, but no, that's incorrect. B & E bodies absolutely had a linkage system. It was different from what the A's used, but it was not a straight through set up, even on the small block cars. This is the booster and linkage from my '72 Challenger. The linkage was on the cabin side of the firewall, but the booster did mount higher than the manual m/c. If you look at the gasket, you can see the opening for where the manual m/c would be, below the booster input. The reinforcing plates were different for power and manual brake B/E cars but the gaskets used were the same. You can even see the bumps in the gasket for the other set of holes in the firewall where the manual master cylinder would mount (above and below the lower studs).

Regardless, it doesn't matter, you're going to be running manual brakes. I ran the exact same set up on my Duster for awhile with the exception of using 11" rear drums (same bore diameter wheel cylinders though, so, same pedal effort). IMO the 15/16" is a better choice for the master cylinder bore. The 1-1/32" will absolutely work, but it's not what I would choose even for $12. You'll have a higher pedal with a shorter throw than what I had in my Duster when I was running the same calipers and rotors as you're going to run. You don't need to compare different body style cars because there are people here that have run the same brake set up with 15/16" or 1" m/c's (ir3333), and both of us recommend 15/16" or 1". That doesn't sound like much of a difference, but if ir3333's math is right the 1-1/32" master cylinder will take 6% more effort than a 1" m/c and 18% more than a 15/16". Your car, your choice. Just trying to put the info out there.

 

[moparmat2000]

I stand corrected. They had those little devils hidden behind the firewall. I will give the 1-1/32" bore MC a try. If i dont like how it feels, i can always step down a bore size to 1" or even smaller to 15/16"

 

[BillGrissom]

Some trivia additions to the discussion:

I recall I used standard SAE tube nuts for 3/16" tube on the MC from a 1995 Breeze I used. It had the normal inverted flare ports. Otherwise, a Breeze uses metric hardware. I think metric brake parts start with the "bubble flare" fittings and tubing, starting in the late 1990's in U.S. cars. BTW, the tubing is "6 mm", but I found it interchanges w/ 3/16" tubing, and I double-flared some, but the threaded ports don't interchange.

My 65 Newport C-body has a factory booster w/ drum brakes. There is no linkage like in post 35 photo of a 72 Challenger. The pedal rod goes straight into the booster. I have changed the booster twice. There is a plate that bolts to the firewall, which the booster attaches to, with a 4-bolt pattern but a different pattern than a 74 Dart booster I had. Other than that, the two boosters were almost identical - same diameter Midland-Ross, except the cylinder thru the base-plate was a different diameter.

 

[famous bob]

Some trivia additions to the discussion:

I recall I used standard SAE tube nuts for 3/16" tube on the MC from a 1995 Breeze I used. It had the normal inverted flare ports. Otherwise, a Breeze uses metric hardware. I think metric brake parts start with the "bubble flare" fittings and tubing, starting in the late 1990's in U.S. cars. BTW, the tubing is "6 mm", but I found it interchanges w/ 3/16" tubing, and I double-flared some, but the threaded ports don't interchange.

My 65 Newport C-body has a factory booster w/ drum brakes. There is no linkage like in post 35 photo of a 72 Challenger. The pedal rod goes straight into the booster. I have changed the booster twice. There is a plate that bolts to the firewall, which the booster attaches to, with a 4-bolt pattern but a different pattern than a 74 Dart booster I had. Other than that, the two boosters were almost identical - same diameter Midland-Ross, except the cylinder thru the base-plate was a different diameter.

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I don`t remember which master cyl. I got, manual, or power, but my late 80`s one had a smaller bore and piston than those mentioned above. very close to what I`d really like !

 

[moparmat2000]

I opened up my rock auto master cylinder boxes today. There is a reciever groove in the back bore of the master cylinder piston for the pushrod O ring on both master cylinders. Also for the life of me i cannot see what is remanned on these. Neither of the body castings are chrysler castings they are brand new aftermarket castings, and the reservoir plastics look new as well. One body casting aluminum which i will keep for my car, the other casting is cast iron. This adds a little weight but is still lighter than a full cast iron unit. I will keep that one for my sons car.

 

[moparmat2000]

After getting home from work i also looked into the brake line threads on the master cylinders. These are SAE, and will thread into 73 to 76 brake lines, not sure if 72 back are different threads. According to rock auto this master cylinder part number goes from 1977 to 1989.