Brakes need help

[1972 CST]

When I bought my 85 shortbed it came with the 1 inch wide rotors and small brakes in the back I just switched to 1 1/4 rotors and bigger brakes in the rear I was wondering if I need to switch my master cylinder?
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[spencer_41188]

you will notice the brake peddel will travle farther then befor but as long as it dont hit the floor and you still need pressure ie wont stop and the peddel has hit the floor

get some floor/firewall to peddel mesurements, with engine off have a friend crack a bleeder to releave pressure so the peddel will bottom out mesure between peddel and floor/firewall then close the bleeder and with the engine on (to make the booster work) have your friend mesure the peddel with all your effort pushing on it ... i would get a bigger bore master if its less then a 2" or 3" diffrence but thats your call how far do you wana push the peddel that stopes you?

[1972 CST]

I got two master cylinders from the part stor one has a big Piston and one has a small one my truck already had a big bore in it so should I put the bigger one back in ?
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[spencer_41188]

with the small bore you will have a longer stroke but more pressure peddel is easyer to push

with the big bore you will have a shorter stroke and less pressure and the peddel is harder to push

if you are NOT running a booster the small bore is the better choice
and if you really wont a touchy peddel go with the small bore

all depends on what your doing with the truck and how you wont it to feel

to me touchy peddles remind me of a ford ... cant stand it and never get use to it

both will work but its your call