I think you mean 15/16" ;)
That said, I fully agree; this conversation should absolutely continue until we have an extensive amount of qualitative data from members documenting their experience for each bore size per the type(s) of brakes they're running.
Keep in mind though,
@motorhead55,
@furyus, and myself all experienced excessive pedal travel with 15/16" bore masters w/o power assist. Both
@furyus and myself confirmed this happened with FMJ calipers, while
@motorhead55 refers to a "disc conversion." I assume this may have been a conversion to FMJ single-piston calipers, but since B-body and A-body calipers are equally on the table as a possibility, we can't be 100% sure. Feel free to confirm/deny,
@motorhead55, if you're around. It'd help the documentation efforts).
All three of us experienced a low pedal with a 15/16" bore.
@furyus claimed no pedal, while
@motorhead55 and myself had what we deemed a "pedal," but with excessive pedal travel and a spongy feeling that could
easily be classified as "no pedal." Personally, I felt I couldn't get enough pedal feel to reach the threshold or lockup braking points, resulting in a very unnerving tactile sensation.
In other words, it's likely we all experienced the same thing, and at least two of us are confirmed to have used the same setup.
What's more,
@furyus also reports having used the 15/16" bore master
with +73 A-body calipers, and this specific combination worked, but
not when this combo was changed over to the "larger rotors and calipers," which I'm assuming means FMJ parts (with "larger rotors," what else could it be?). Also,
@gtx6970 reports success with the "non-power assisted A-body disc brake conversion" with a 15/16" master, so that's two people running 15/16" successfully, but
specifically with A-body calipers.
All the data seems to be pointing to 15/16" bore masters working with non-power assist cars running A-body calipers, but excessive pedal travel with FMJ calipers. I'm really quite curious now about the respective fluid capacity of each caliper.
As for the books: I'd like to see
exactly what Condran states in the book to see if there's a "gotcha" in there that hasn't been noted, or if his claim is clearly an error. I haven't read the book myself, but out of curiosity, I Googled it and happened across this page:
View attachment 1438108
This isn't conclusive by any means, but note that neither of the caliper choices or knuckles are FMJ. The FMJ 11.75" rotors are also omitted as an option.
What's more, Condran specifically recommends, on this page, 15/16" masters for
power disc setups, and 1" for "standard" (I assume this means "manual") discs, going so far as to recommend increasing the bore size to 1-1/32" "to make the pedal firmer."
(He also recommends the "'79-up aluminum unit" I'm running now, but doesn't specify what the aluminum 1.031" master has over the 1" that makes it that much firmer - unless it's simply a poor choice of words; perhaps the goal was to point out that the aluminum units perform the same as a 1" bore steel master?).
According to this chart, all of these recommendations assume the user has B/E pin-type calipers and no other. Neither FMJ or A-body calipers are investigated, and - as per those warnings above - he was obviously not open to any other alternate combinations when he wrote the book. (Side note: I wonder if this bias originates from the same source where Ehrenberg's (hotly contested) argument over FMJ spindle geometry comes from, but that's a whole 'nother can of worms).
If he claims somewhere else in the book that 15/16" is appropriate for non-power disc applications, he's contradicting his own table in the same book. But before I assume this as the case, I'd love to see a copy of the page (or the wording) that you read,
@69charger440. Obviously, we can't really assume anything without comparing his exact words from one page to another.
-Kurt
) that specifically noted 7/8" bore.
