Master cylinder bore sizes and pedal hardness?

Master cylinder bore sizes and pedal hardness? - 09/26/08 04:41 AM

I want to get a harder, firmer brake pedal. Which master cylinder is going to accomplish this: the larger bore, or the smaller bore?
Car in question is a 1968 B-Body with front discs, rear drums, and an aluminum late model MC with a 1 1/16" bore (1.063").
A MC from a 1995 Dakota has a 15/16" bore. Will using this MC provide for a harder pedal? Will it even bolt up correctly?

Thanks guys.

Posted By: DoctorDiff

Re: Master cylinder bore sizes and pedal hardness? - 09/26/08 04:49 AM

A 1 1/8" bore master will provide a hard pedal.

Posted By: SuperCommando

Re: Master cylinder bore sizes and pedal hardness? - 09/26/08 03:18 PM

What do you think I'll get if I try the 15/16 bore MC?

Posted By: Anonymous

Re: Master cylinder bore sizes and pedal hardness? - 09/26/08 04:56 PM

Quote:

What do you think I'll get if I try the 15/16 bore MC?

a softer pedal with more travel and if it's manual brakes, a push rod that can fall out.

Posted By: SuperCommando

Re: Master cylinder bore sizes and pedal hardness? - 09/26/08 05:08 PM

Quote:

a softer pedal with more travel and if it's manual brakes, a push rod that can fall out.

Dang. Okay scratch that idea. GregZ, incidentally it was an aluminum master cylinder (1 1/16" bore?) I bought from MagnumHP a few years back I was thinking about changing. Not that it wasn't working okay, I just heard a harder pedal could be achieved with a different bore. It always felt like there was some slack in the pedal I had to take up before the binders would start biting...

Posted By: John_Kunkel

Re: Master cylinder bore sizes and pedal hardness? - 09/26/08 09:25 PM

A larger bore MC might firm your pedal and will shorten the pedal travel but will need more leg power to stop the car.

Slack in the pedal can be caused by a too short pedal pushrod or loose rear brake wshoe adjustment.

Posted By: RapidRobert

Re: Master cylinder bore sizes and pedal hardness? - 09/26/08 11:41 PM

Quote:

A larger bore MC might firm your pedal and will shorten the pedal travel but will need more leg power to stop the car. Slack in the pedal can be caused by a too short pedal pushrod or loose rear brake wshoe adjustment.

With the bore size you currently have you shouldn't be having excessive travel. If your rears shoes are up??? you might buy an adjustable pushrod & extend it a bit longer than the one you have in there now. This might take care of you & if you dont lengthen it to where your covering up the fluid return port in the bottom of the MC it will take up some travel/free play & you're good.

Posted By: SuperCommando

Re: Master cylinder bore sizes and pedal hardness? - 09/27/08 07:00 AM

Quote:

Slack in the pedal can be caused by a too short pedal pushrod or loose rear brake wshoe adjustment.

Very very interesting. Incidentally I did have to install new rear drum wheel cylinders lately because my last set started leaking. Guess I'll have to re-check the adjusters on my rears.

With regard to the MC pushrod length: the car was originally equipped with front 10.5" drums and the corresponding drum brake MC. Having switched over to discs, I installed the late model aluminum MC but merely re-used the old pushrod from the drum brake MC. Was I supposed to get a new pushrod, or possibly an adjustable one?

Posted By: MoparSam

Re: Master cylinder bore sizes and pedal hardness? - 09/27/08 10:30 AM

That MC pushrod will work just fine. Like others have said try adusting the back brakes.

cheers,

Moparsam