1/8 to 1/4 bore Master Cylinder, does it matter?

[hockeyjerk1]

My MC is 1/8 bore on my 1/2 ton but I can get a really good deal on a 1/4 bore MC that is listed for a 3/4 ton truck. Does it really matter? Is anything affected by the larger bore? It will be mounted on a factory booster.

[Bigdav160]

The larger the master cylinder bore, the less pressure it exerts (actually multiplies) and the harder the pedal is to push down..

Power brakes usually have a larger bore MC than than manual brakes.

[Keith Seymore]

Originally Posted by hockeyjerk1

My MC is 1/8 bore on my 1/2 ton but I can get a really good deal on a 1/4 bore MC that is listed for a 3/4 ton truck. Does it really matter? Is anything affected by the larger bore? It will be mounted on a factory booster.

Yeah; it kinda matters.

Bore affects line pressure, which translates into pedal feel, pedal travel and pedal force.

If you start playing with the bore you could get into situations where you can't generate enough line pressure, or the pedal travel is affected such that you don't get good pedal feel until the pedal is too close to the floor, etc, or the pedal is too high/rock hard. The engineers chose that bore size for a reason, after extensive testing.

Probably best to just pony up the bucks and get the correct master cylinder - especially when dealing with a safety item.

K

[lolife99]

Don't you mean 1-1/8" and 1-1/4"?

[yellowbomber]

Yes he means 1-1/8 to 1-1/4. The 3/4 tons had a larger wheel cyl. bore too I believe and so it all evened out. By increasing the MC bore and not the wheel cyl bores, you will have less braking power. an 1/8" x 3.14 will be more loss than you realize at first.
I got a Raybestos or Bendix off Rockauto for under $35 as I recall. Good unit. I have gone new in the past for these old rigs but have actually found better quality in a well rebuilt one.

[mgchevyparts]

The 1 1/4" master is used with larger piston calipers, if you use it chances are it'll be too firm. True smaller bore (master) equates to higher pressure but it also means less volume. People automatically think higher pressure is better, the old "bigger is better" syndrome. Higher pressure is not necessarily better, what is better is MATCHING master bore size to caliper piston size. Smaller caliper piston(s) usually means smaller master size. Most D52 calipers, as used on 1/2 tons have a 2 15/16" piston which likes a 1" bore master for manual and a 1 1/8" bore for power, but small up/down changes can be made to fine tune the firmness/feel/pedal travel.
If I were you I would buy the correct 1 1/8" master

[hockeyjerk1]

Thanks for everyone's input, I'll stick with what is original to the truck which is 1-1/8