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15/16" or 1 1/32" bore master cylinder?

Yes the Master was bench bleed, so what. Are the wheel calibers bleeders at the very top so air can escape? If not and can't correct it you can unbolt the calibers from the rotors and bleed them that way, putting wood block where rotor would be. If the bleeders are on the bottom, then swap left to right. And yes most "of us people" have gotten in a hurry or a brain yawn before.
edit: sorry was trying to delete this post after rereading the above better
 
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Since you have the MC to try, i would change just the MC, and see if it improves. For the rear, i would add in an adjustable prop valve. That way you don't have to keep changing wheel cylinders if you're not happy with them.
 
I ordered a Raybestos MC36412 (1-1/32" bore) and will try it.

Also found the 7/8" rear cylinders (Raybestos WC37236; fits 10" or 11" drums) too. Spec is for a '71-77 B-series van, though some of the suppliers on Rock Auto specifically note for the "3/4 ton model," e.g., B350.

Wound up getting sold old stock Brakeware 33605's (for $3.19 a pop! :) ) that specifically noted 7/8" bore.

-Kurt
 
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Have the same low pedal issues using a 15/16 master cylinder with my 66 satellite disc conversion, the brakes go very low to the floor but stop the car. I am going to switch to the 1 1/8 master and see if the situation changes.
Thanks for the information as this is a great forum.
John
 
I just put disc on my 62. I used the quick bleeder or speedy bleeders for the first time. It worked really well. Made it a one man job.
 
Have the same low pedal issues using a 15/16 master cylinder with my 66 satellite disc conversion, the brakes go very low to the floor but stop the car. I am going to switch to the 1 1/8 master and see if the situation changes.
Thanks for the information as this is a great forum.
John
Had same issue,low pedal, went with "the rite stuff" adjustable push rod, no more issues
 
whatever happened? Did any of you get things sorted? I'm having similar issues - sponge pedal city. Was using 15/16" MC, now 1-1/8" and it's better, but still no hard pedal. Going to get some speed bleeders and also add a 2 psi residual valve for the front discs. I'm running Wilwood forged Dynalite 4-piston up front and stock drums out back with smaller 7/8" rear wheel cylinders. Mine is a Power Brake car.
 
whatever happened? Did any of you get things sorted? I'm having similar issues - sponge pedal city. Was using 15/16" MC, now 1-1/8" and it's better, but still no hard pedal. Going to get some speed bleeders and also add a 2 psi residual valve for the front discs. I'm running Wilwood forged Dynalite 4-piston up front and stock drums out back with smaller 7/8" rear wheel cylinders. Mine is a Power Brake car.

My current configuration retains the FMJ front discs with single-piston calipers, 11" Budd drums in the back with B-body spec rear pistons, no vacuum booster, and a Dorman M99294 aluminum FMJ master cylinder with a 1.031" (might as well be 1") bore.

The pedal is still slightly spongy for my liking, but it has good feel and you can either threshold brake or lock them up if you want. Also, the FMJ aluminum-and-plastic master is a LOT easier to pressure bleed and doesn't turn to rust from brake fluid oozing out the top.

There's just not as much pedal feedback as I'd like. However, I think that's just the feeling of unassisted disc brakes in general rather than the master bore diameter itself.

Case in point, I've forever had the same complaint with bicycle disc brakes - both hydraulic and conventional cable discs - over bicycles with rim brakes (regardless of whether they're linear V-brakes, sidepulls, or dual-pivots - bicycle mechanic here), so I dare say it's a case of the tactile feel of a disc caliper applying its mechanical advantage to a braking surface. It is probably why vacuum-boosted brakes came onto the scene - folks used to the self-energizing feel of 4-wheel drums receive a similar tactile feeling from a booster.

-Kurt
 
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I have a 66 Satellite with the non power assisted A body disc brake conversion.
15/16" bore master from a later A body and the car stops fine.
The pedal isnt rock hard by any means but the car stops pretty good / maybe similar to my other one which is 11" manual drum brakes

I think the biggest advantage for the change to the disc brakes they will not fade if you have multiple panic stops in a row
 
Not sure if all that will work ok together but it's a big package of parts!
Agree, Cranky. Thought my set up
was kind of wonky with Ford/Jeep
front and rear. But each are inclusive.
 
EDIT: I accidentally wrote 5/16" instead of 15/16" for the master cylinder bore. It was pointed out to me, and I edited it below.

I value everyone's input on here, as it's a safe bet I know less than almost any member. But that said, I do think some of this discussion is trying to reinvent the wheel. And that's the purpose of this post. Let's not reinvent the wheel. The information is already out there.

Tom Condran, in his classic book Performance Handling for Classic Mopars, strongly suggests running a 15/16" bore master cylinder for manual brakes and the typical Mopar parts front disc conversion, with either size caliper piston up front. He also notes that it might be necessary to use the 7/8" bore wheel cylinders to prevent the rears from locking up before the front discs. This seems to be the issue Kurt was having, the front brakes were not locking up (I don't remember if he mentioned his rears locking).

There is another good book, Chrysler Performance Upgrades, by Frank Adkins, that goes into this a bit. I haven't read Richard Ehrenberg's "Disc-o-Tech" article in a long time, but it might discuss it as well.

I realize that this thread started in 2017. Who cares? The whole point of these forums is for people to learn, and that includes reading discussions from years earlier. Correct, concise information should always be the goal to help the current and future members gain knowledge. No one wants to read through pages of meandering guesswork in search of the truth if the truth is already out there.

The said, future readers shouldn't be wondering about whether it's safe to use a 15/16" bore master cylinder with a front disc conversion. It is, when it is incorporated as a component of a properly designed brake system. If you're using a manual disc conversion using (the proper) Mopar parts, as outlined by Tom Condran's book, then you have a proper designed brake system. Thus, the 15/16" bore master cylinder is recommended. Yet, everyone has his own taste, or preference, and he might prefer a different feel in the brake pedal. In that instance, he can try different bore sizes in different master cylinders and find one to his liking. But let it be known, using a 15/16" bore master cylinder is safe and preferred by more than just Cass at Doctordiff.

Thanks for not sending hate mail my way.
 
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I value everyone's input on here, as it's a safe bet I know less than almost any member. But that said, I do think some of this discussion is trying to reinvent the wheel. And that's the purpose of this post. Let's not reinvent the wheel. The information is already out there.

Tom Condran, in his classic book Performance Handling for Classic Mopars, strongly suggests running a 5/16" bore master cylinder for manual brakes and the typical Mopar parts front disc conversion, with either size caliper piston up front. He also notes that it might be necessary to use the 7/8" to prevent the rears from locking up before the front discs. This seems to be the issue Kurt was having, the front brakes were not locking up (I don't remember if he mentioned his rears locking).

There is another good book, Chrysler Performance Upgrades, by Frank Adkins, that goes into this a bit. I haven't read Richard Ehrenberg's "Disc-o-Tech" article in a long time, but it might discuss it as well.

I realize that this thread started in 2017. Who cares? The whole point of these forums is for people to learn, and that includes reading discussions from years earlier. Correct, concise information should always be the goal to help the current and future members gain knowledge. No one wants to read through pages of meandering guesswork in search of the truth if the truth is already out there.

The said, future readers shouldn't be wondering about whether it's safe to use a 5/16" bore master cylinder with a front disc conversion. It is, when it is incorporated as a component of a properly designed brake system. If you're using a manual disc conversion using (the proper) Mopar parts, as outlined by Tom Condran's book, then you have a proper designed brake system. Thus, the 5/16" bore master cylinder is recommended. Yet, everyone has his own taste, or preference, and he might prefer a different feel in the brake pedal. In that instance, he can try different bore sizes in different master cylinders and find one to his liking. But let it be known, using a 5/16" bore master cylinder is safe and preferred by more than just Cass at Doctordiff.

Thanks for not sending hate mail my way.

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:

img_6130-jpg.jpg


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
 
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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
Excellent discussion, Kurt. Without reading his whole book, one can easily misunderstand what that chart is saying. So it’s very understandable why you have many questions about it. I can try to explain more later tonight when I get more time.

And thanks for correcting me about the 5/16” vs 15/16” bore lol. Is there a way for me to edit it, so as not to confuse everyone?

I will be back later to address other issues from the book.
 
Good stuff!

FYI, there should be an "edit" button on the bottom left of each post, but - if I recall correctly - it is on a timer with this forum software for some inexplicable reason. This makes it really difficult to fix older threads where Photobucket ate everything :(

-Kurt
 
This is an interesting thread. I have 3 manual brake cars. All of them now have 11.75" stage 2 disc kits with single piston calipers and 15/16" aluminum master cylinders from Cass. On all 3 cars I also went 1 size smaller bore on the rear cylinders. Previous to this, I used 11" front discs, 1 1/32" masters, and stock rear cylinders. Personally, I like the 15/16" masters better as far as pedal feel. On 1 of the cars I thought I had an issue like is being talked about with to much spongy pedal travel. After about a month of many, many bleeding sessions, it finally got better and has been good since. Must have been a slight air bubble somewhere I guess. On my Duster I had to add a Willwood adjustable valve on the rears to prevent them from locking up first.
 
These days it seems to be easier to get verbal help than actual parts.

Would like to order a pair of SCE gaskets. Ship date ... May 5th !!!
 
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