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MC bore size questions
https://slantsix.org/forum/viewtopic.php?t=42358		 Page 1 of 1
Author:  Dakota_Don [ Fri Oct 22, 2010 4:37 pm ]
Post subject:  MC bore size questions
My MC went crap on my dart (15/16 bore) and all i could get was the 1-1/32 bore mc and they suck, soooo i was wondering.....If I went from a 1-1/32(26mm) bore MC to a 13/16 K-car(21 mm)then I will have more PSI but less volume and more pedal travel correct?

if I bought a MC adaptor and used an alu MC from the K car which has a 21 mm bore which is close to 13/16 bore but smaller then the 15/16.. will that be to0 small of a bore? Reason i'm asking is I need a MC and so far haven't found a 15/16 bore locally(carquest is looking).. But i have a good 87 K car MC FREE other then the adaptor..also I am not sure of the fitting sizes either..

My GM caliper bore sizes are 2.5 in or 63.5 . The 75 dart Caliper bore size is 2 19/32 or 66 mm.


Basically which MC would be a better match for my disc.. the 15/16 or the smaller 13/16?

Thanks

Don
Author:  emsvitil [ Fri Oct 22, 2010 4:51 pm ]
Post subject:  Re: MC bore size questions
Quote:
My MC went crap on my dart (15/16 bore) and all i could get was the 1-1/32 bore mc and they suck, soooo i was wondering.....If I went from a 1-1/32(26mm) bore MC to a 13/16 K-car(21 mm)then I will have more PSI but less volume and more pedal travel correct?
Yes

How far does the pedal travel now?

The new travel would be (26^2)/(21^2) * current travel or 1.53 times the current travel

Depending on current travel, you might hit the floor and not have enough braking..........
Quote:
if I bought a MC adaptor and used an alu MC from the K car which has a 21 mm bore which is close to 13/16 bore but smaller then the 15/16.. will that be to0 small of a bore? Reason i'm asking is I need a MC and so far haven't found a 15/16 bore locally(carquest is looking).. But i have a good 87 K car MC FREE other then the adaptor..also I am not sure of the fitting sizes either..

My GM caliper bore sizes are 2.5 in or 63.5 . The 75 dart Caliper bore size is 2 19/32 or 66 mm.


Basically which MC would be a better match for my disc.. the 15/16 or the smaller 13/16?

Thanks

Don
Which of the two calipers (GM/Mopar) are you using?


What you need to do is compare the ratios of the areas of the MC piston and calipers pistons (Add up the area of all front pistons (both sides); if sliding caliper multiple area by 2 for equivalant opposed cylinder caliper)

i.e. ((63.5^2)*4) / (26^2) = 23.86 for GM / 26mm combo
you can do the others......
Author:  Joshie225 [ Fri Oct 22, 2010 5:40 pm ]
Post subject: 
Isn't the K-car master cylinder meant for a diagonally split brake system? I'm thinking the front to rear ratio would be non-existent for a diagonal system.
Author:  Dakota_Don [ Fri Oct 22, 2010 7:24 pm ]
Post subject: 
I am using the GM calipers, the piston bore on them are 2.5 in, just a tad smaller then the 75 Mopar calipers.



if i cant use the K car MC then I will have wait to see what car-quest will find..
Author:  Dakota_Don [ Fri Oct 22, 2010 7:31 pm ]
Post subject: 
the rear wheel cly are the original 68s, so which bore MC would be a better match with my calipers? I was told the K car wont work cuz its for a power brake system,so that MC maybe out.. but is that what the adaptor is for? to use a power brake 2 bolt MC on the older 4 bolt MC mounting surface? plus i know i may need an adjustable rod..
Author:  Dakota_Don [ Fri Oct 22, 2010 7:42 pm ]
Post subject: 
Did some searching and the GM application that my calipers came from use a .875 bore or 7/8 MC (22mm)with pwr brakes which is very close to the mopar 15/16 bore..(24mm) and the 13/16 bore is 21mm with pwr brakes
Author:  slantfin [ Sat Oct 23, 2010 10:17 am ]
Post subject: 
Could you rebuild your original MC?
Author:  Dakota_Don [ Sat Oct 23, 2010 2:17 pm ]
Post subject: 
I could if i had it... sent it back as a core, the replacement mc had the 1-1/32 bore.. now my old mc is gone or on someone elses car..I did find a new one on the net.. but was hoping to get one locally or a newer easier to find upgrade..

and when I do talk to a counter person and ask them questions? they have no idea.
Author:  Dakota_Don [ Sat Oct 23, 2010 2:19 pm ]
Post subject: 
Quote:
I could if i had it... sent it back as a core, the replacement mc had the 1-1/32 bore.. now my old mc is gone or on someone elses car..I did find a new one on the net.. but was hoping to get one locally or a newer easier to find upgrade..

and when I do talk to a counter person and ask them questions? they have no idea.
oh the FWD MCs are out...and will not work
Author:  Joshie225 [ Sat Oct 23, 2010 3:29 pm ]
Post subject: 
If you want a 15/16" master cylinder ask for one for a '74 Dart with power brakes. The manual brake master cylinder has a 1-1/32" bore.
Author:  Dakota_Don [ Sun Oct 24, 2010 1:15 pm ]
Post subject: 
actually i tried different yrs and locally haven't had any luck..carquest is going to call some venders for me
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