Brake pedal stroke question .

[chimp koose]

I have just determined that the master cyl I was sent has a 1" bore , not the 7/8" I was expecting . I have a question about designing pedal arms . Does the stroke of the pedal need to be able to bottom the piston in the master cylinder?  This cyl has     1 1/4 " of travel making the pedal need a 8 3/4" stroke to bottom the piston in the bore . I realize it will come nowhere near that travel in normal use but should it have that capability ? Trying to make a 90 degree pedal set up in the T .

[chimp koose]

Looks like I found the answer . That seems like a lot of travel but if it needs it to be right so be it . I may need to swing my pedal from closer to the dash than the firewall to get a decent arc for the pedal swing . I thought I ordered a 7/8" master but got a 1" instead . checking the application on the 7/8  , its for a 82 Rampage . 1 7/8" , 5/8" caliper /wheel cyl as compared to my            2 3/8"/7/8" on the T . May have to re think that one .

[enjenjo]

A 1" bore is in the ball park for the caliper/wheel cylinder sizes you have. You might consider changing the pedal ratio a bit. I have gone as low as 5 to one without needing excessive pedal effort

[chimp koose]

Thanks for the reply . I came up with the 7:1 ratio from measuring some manual brake pedals a long time ago . I really need to get this right on the first try as I don't want to butcher my firewall later . I may go through the firewall and use a remote reservoir instead of the 90 degree master . I have not cut anything yet , still doing the head scratching . How much pressure do I need to properly stop with disc and drum brakes ? I would like to know I can actually lock up the wheels even though that isn't the shortest stop . It lets you know you didn't leave any stopping ability on the table when you are done .

[enjenjo]

The master cylinder you have is a Rampage power brake master cylinder. The recess for the pushrod in the piston will likely be shallow. The manual break master cylinder is listed as .875", and will have a deep pushrod bore. That was a fairly common master cylinder for Mopars so should not be hard to find. The piston travel will be about the same.

I am assuming a GM metric caliper. With manual brakes the original master cylinder bore size was .875".

[chimp koose]

Enjenjo , I ordered what I thought was the right 7/8 " bore master cyl . what I actually ordered was a 78-81 Chrysler master cyl from something like a caravelle . I took the piston out and it is 1" . It has a deep hole for a pushrod . Are you saying that a 7/8 bore would work fine ? I checked the piston sizes of the rampage brakes and they were much smaller than the ones on my T so I thought that maybe there would be an issue if I used the 7/8" master . I guess I should have checked what M/C was used for the GM caliper in the first place . What were the GM metric calipers used on ? I thought they were on gen3 Camaros ? I would rather use the 7/8" M/C if I could so I can maybe use a 5:1 pedal ratio as you have suggested . That would shorten the stroke of the pedal by over 2"