I have a 98 Civic with rear drums that needs a new master cylinder and booster. Currently it has a 13/14" but it's dust and needs to go. I have a spare 15/16" that I want to throw in it but I figured I'd ask here if anyone thinks I might run in to problems before I do.

Anyone see a problem with doing this? I'm pretty sure it's just going to give me less pedal travel.

 

use the correct one, they only cost a few bucks for a rebuilt one from an autoparts store.
I believe the 15/16" may have different threads for the brake lines too.

 

Using a 15/16 MC will leave you with a rock hard brake pedal.

 

Rebuilt ones are seventy bucks that I could save. I don't think it will give me a "rock hard" pedal, I guess I'll find out though. I did a rear disc swap in my 94 (with 15/16" master cylinder) and I noticed some difference in pedal travel but nothing extreme. I think the same will happen with the drums, maybe a little stiffer.