Anyone know of a very compact brake master that comes in a 15/16" variety? Needs to fit in the space shown in the diagram. As an example, I found the one pictured from a '87 Diesel Isuzu pickup -- supposedly comes in 15/16 according to rockauto.com but no one seems to be able to actually get it. They only seem to have the 7/8 version. I know I could do remote reservoir, but I'd like to find one where that isn't needed. Thx.
If I remember correctly, post 82 A & G cars (Malibu, Regal, Monte Carlo, etc.) are 15/16 (or metric equivalent). They are aluminum body with plastic reservoir.
Actually he will be able to tell the difference if he is installing this in a MGBV8 as his posting name might suggest. The difference will be a harder pedal and shorter stroke and is very noticeable unless he also has a remote booster for the brakes. At least that has been my experience with British cars.
Running the numbers (I've done a lot of this for my own selection), it takes 120 pounds of foot pressure to break 1000 lbs of line pressure with a 15/16" master, with a presumed 6:1 pedal ratio. Now keep in mind that that is max force and rarely used around town or even at the track. It's really only used in a panic situation. With a 7/8" master, it requires 105 lbs to achieve almost exactly the same line pressure. So that's a max difference of 15 lbs at the foot pedal. The reality is that you really operate at half that pressure for routine driving, perhaps less, so you would have to be pretty sensitive to tell that the 7/8" master was 5-7 lbs softer. I stand by my statement. He won't be able to tell the difference and in a weeks time it will be a moot point as muscle memory sets in. Additionally, it is widely recommended that you be able to develop up to 1200 psi of line pressure. The 7/8" master will allow this with the same effort that allowed 1044 psi with the 15/16" (that's 120 lbs of foot pressure), so it would be prefered. Now depending on his actual pedal ratio and slave cylinder sizing, this is all variable. I think you can use this as a fair basis of comparison. 1/16" is not a big difference.
I understand what you are saying but I still stand by my statement. I race a 1966 Marcos 1800 GT (an obscure British car) and had a brake pedal that was really hard... The pedal had almost no movement and required a lot of effort. I switched to the next size smaller Master cylinder and got a pedal that had more movement with less effort and thus had more "feel". I could modulate the brakes during threshold braking easier than I could before. My wife has a Triumph TR3a with a Toyota 5 speed transmission with a annular slave cylinder. Once we had the conversion finished she complained about not having any feel with the clutch...the clutch was, in her words, either engaged or not and nothing in between.... she was having trouble slipping the clutch as she accelerated from a stop. Once again I changed the master cylinder down a size to get "better feel" by having a softer pedal and longer stroke. The person I had re-sleeve the Master cylinder to a smaller size (a smaller size wasn't available in this case) predicted fairly accurately how much more travel the pedal would have between disengagement and full engagement. The wife is a lot happier with the new set-up than she was with the old set-up. So, not to pick a fight, but based on my experience with real British cars being used in the real world, the original poster may feel a difference. Between you and I, we will have to agree to disagree and that is also fine.
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