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MC Bore Size: 1 1/8 vs. 1 1/32 #913750 01/25/11 04:34 PM 01/25/11 04:34 PM
Joined: Dec 2007 Posts: 284 Louisiana K kzinge1 OP enthusiast
kzinge1 OP enthusiast K Joined: Dec 2007 Posts: 284 Louisiana	I have the SSBC disc brake conversion on the front of my 69 RR and 10.5" drums in the rear. I am not using the booster that came with the kit. I am running the Strange 1 1/8" bore master cylinder right now and the brake pedal is too hard and the car doesn't stop well enough. Will the Strange 1 1/32" bore master cylinder be right for this combo or do I need to go even smaller than that? Last edited by kzinge1; 01/25/11 06:25 PM.

Re: MC Bore Size: 1 1/8 vs. 1 1/16 [Re: kzinge1] #913751 01/25/11 05:44 PM 01/25/11 05:44 PM
Joined: Feb 2003 Posts: 1,024 In the twisties R RokketRide super gas
RokketRide super gas R Joined: Feb 2003 Posts: 1,024 In the twisties	The pedal effort will be inversely proportional to the area of the MC piston. So taking 1-1/8 as a baseline: 1-1/16 would be 12% less pedal effort, 15/16 would be 44% less, and 7/8 would be 65% less.

Re: MC Bore Size: 1 1/8 vs. 1 1/32 [Re: RokketRide] #913752 01/25/11 06:22 PM 01/25/11 06:22 PM
Joined: Dec 2007 Posts: 284 Louisiana K kzinge1 OP enthusiast
kzinge1 OP enthusiast K Joined: Dec 2007 Posts: 284 Louisiana	Quote: The pedal effort will be inversely proportional to the area of the MC piston. So taking 1-1/8 as a baseline: 1-1/16 would be 12% less pedal effort, 15/16 would be 44% less, and 7/8 would be 65% less. So in that case, should I go smaller than the 1 1/32 Strange? Is there a minimum bore that this disc brake kit would require? Last edited by kzinge1; 01/25/11 06:25 PM.

Re: MC Bore Size: 1 1/8 vs. 1 1/32 [Re: kzinge1] #913753 01/25/11 08:32 PM 01/25/11 08:32 PM
Joined: Dec 2007 Posts: 284 Louisiana K kzinge1 OP enthusiast
kzinge1 OP enthusiast K Joined: Dec 2007 Posts: 284 Louisiana	Anyone know anything about this stuff?

Re: MC Bore Size: 1 1/8 vs. 1 1/32 [Re: kzinge1] #913754 01/25/11 08:33 PM 01/25/11 08:33 PM
Joined: Oct 2005 Posts: 8,867 Ontario, Canada S Stanton Don't question me!
Stanton Don't question me! S Joined: Oct 2005 Posts: 8,867 Ontario, Canada	Keep in mind that less effort means more travel ... you still have to move the same amount of fluid !!! That said, the most common m/c for a brake conversion seems to be the 1-1/32". A lot depends on caliper piston size as well. The least pedal effort will be achieved with a small m/c bore and a large caliper piston. Determine the size of your pistons versus the mid-70's Mopar calipers. If yours are the same or larger then the 1-1/32" m/c should be fine but if yours are smaller then you'll want to go smaller on the m/c as well.

Re: MC Bore Size: 1 1/8 vs. 1 1/32 [Re: Stanton] #913755 01/25/11 08:56 PM 01/25/11 08:56 PM
Joined: Dec 2007 Posts: 284 Louisiana K kzinge1 OP enthusiast
kzinge1 OP enthusiast K Joined: Dec 2007 Posts: 284 Louisiana	Quote: Keep in mind that less effort means more travel ... you still have to move the same amount of fluid !!! That said, the most common m/c for a brake conversion seems to be the 1-1/32". A lot depends on caliper piston size as well. The least pedal effort will be achieved with a small m/c bore and a large caliper piston. Determine the size of your pistons versus the mid-70's Mopar calipers. If yours are the same or larger then the 1-1/32" m/c should be fine but if yours are smaller then you'll want to go smaller on the m/c as well. I believe I have 4 piston calipers, if I remember correct. Should be bigger than factory. Do you know what the bore size was of the mid-70s Mopar MC's?

Re: MC Bore Size: 1 1/8 vs. 1 1/32 [Re: kzinge1] #913756 01/25/11 09:00 PM 01/25/11 09:00 PM
Joined: Jan 2003 Posts: 25,750 Rio Linda, CA John_Kunkel Too Many Posts
John_Kunkel Too Many Posts Joined: Jan 2003 Posts: 25,750 Rio Linda, CA	If "the pedal is too hard and the car doesn't stop well enough" I'd say the problem isn't the MC size. With a booster it should stop well if the parts are properly installed. Have you checked to see that the rear piston in the MC is fully returning? The INTERNET, the MISinformation superhighway

Re: MC Bore Size: 1 1/8 vs. 1 1/32 [Re: John_Kunkel] #913757 01/25/11 09:03 PM 01/25/11 09:03 PM
Joined: Feb 2003 Posts: 1,024 In the twisties R RokketRide super gas
RokketRide super gas R Joined: Feb 2003 Posts: 1,024 In the twisties	He isnt using a booster.

Re: MC Bore Size: 1 1/8 vs. 1 1/32 [Re: RokketRide] #913758 01/25/11 09:32 PM 01/25/11 09:32 PM
Joined: Dec 2007 Posts: 284 Louisiana K kzinge1 OP enthusiast
kzinge1 OP enthusiast K Joined: Dec 2007 Posts: 284 Louisiana	Yep, no booster.

Re: MC Bore Size: 1 1/8 vs. 1 1/32 [Re: kzinge1] #913759 01/25/11 09:40 PM 01/25/11 09:40 PM
Joined: Feb 2005 Posts: 28,312 Cincinnati, Ohio Challenger 1 Too Many Posts
Challenger 1 Too Many Posts Joined: Feb 2005 Posts: 28,312 Cincinnati, Ohio	Quote: Yep, no booster. Maybe that's why... I think you would need different petal linkage/ratio and MC bore size with manual verse power brakes. It's best to call the guys you bought the brake kit from.

Re: MC Bore Size: 1 1/8 vs. 1 1/32 [Re: kzinge1] #913760 01/25/11 09:57 PM 01/25/11 09:57 PM
Joined: Nov 2003 Posts: 36,040 Lincoln Nebraska R RapidRobert Circle Track
RapidRobert Circle Track R Joined: Nov 2003 Posts: 36,040 Lincoln Nebraska	As said I'd call/email them & see if the pedal ratio and or the bore size is OK w you not using the booster live every 24 hour block of time like it's your last day on earth

Re: MC Bore Size: 1 1/8 vs. 1 1/32 [Re: kzinge1] #913761 01/25/11 10:00 PM 01/25/11 10:00 PM
Joined: Jan 2003 Posts: 30,998 Oregon A AndyF I Win
AndyF I Win A Joined: Jan 2003 Posts: 30,998 Oregon	Most of the aftermarket 4 piston calipers have less piston area than the stock Mopar single piston calipers. So to work correctly, you need a master cylinder with a smaller bore size. (you also need to reduce the wheel cylinder size out back to get things back into the correct ratio but that is another can of worms) Bottom line is that you can't just randomly change parts of the brake system and expect the stuff to work correctly.

Re: MC Bore Size: 1 1/8 vs. 1 1/32 [Re: Challenger 1] #913762 01/25/11 10:01 PM 01/25/11 10:01 PM
Joined: Dec 2005 Posts: 1,462 Mrytle Beach SC J johnscudashop pro stock
johnscudashop pro stock J Joined: Dec 2005 Posts: 1,462 Mrytle Beach SC	Bigger isn't always better. I have Manual disc brakes on mine. and the 1" bore or higher had a much harder pedal. I got a wilwood master part# 260-8556-p with a 7/8 bore and it stops great ,with much better pedal effort 6438543-100_1433.jpg (171 downloads)

Re: MC Bore Size: 1 1/8 vs. 1 1/32 [Re: kzinge1] #913763 01/25/11 10:39 PM 01/25/11 10:39 PM
Joined: Jan 2007 Posts: 7,664 IN A ahy master
ahy master A Joined: Jan 2007 Posts: 7,664 IN	Quote: I have the SSBC disc brake conversion on the front of my 69 RR and 10.5" drums in the rear. I am not using the booster that came with the kit. I am running the Strange 1 1/8" bore master cylinder right now and the brake pedal is too hard and the car doesn't stop well enough. Will the Strange 1 1/32" bore master cylinder be right for this combo or do I need to go even smaller than that? Was your car originally manual or PB? Reason I ask is the PB pedal linkage setup gives less leverage. If you are running the PB pedal linkage without booster that's your first and biggest problem. The MC size would be secondary.

Re: MC Bore Size: 1 1/8 vs. 1 1/32 [Re: ahy] #913764 01/25/11 10:44 PM 01/25/11 10:44 PM
Joined: Dec 2005 Posts: 1,462 Mrytle Beach SC J johnscudashop pro stock
johnscudashop pro stock J Joined: Dec 2005 Posts: 1,462 Mrytle Beach SC	OK, I see. I thought you were running manual brakes. A 1 1/32 or 1 bore would sound like it would be better for your application. 6438672-100_1434.jpg (174 downloads)

Re: MC Bore Size: 1 1/8 vs. 1 1/32 [Re: johnscudashop] #913765 01/25/11 11:05 PM 01/25/11 11:05 PM
Joined: Dec 2007 Posts: 284 Louisiana K kzinge1 OP enthusiast
kzinge1 OP enthusiast K Joined: Dec 2007 Posts: 284 Louisiana	The car originally had manual brakes so the pedal ratio should be right. The SSBC kit came with a booster, so I didn't reuse the MC. I thought it wouldn't be right without the booster. I did call them before I did this to ask what MC I needed and they provided no help and I ended up getting the Strange 1 1/8 bore. I definitely don't want to throw parts at it because I will end up wasting money on something I don't need. I do know that I have a hard pedal and, from what I've read on here, that means the bore of the MC is too large. Now I need to figure out the right size before I spend another $100 on a MC.

Re: MC Bore Size: 1 1/8 vs. 1 1/32 [Re: kzinge1] #913766 01/26/11 12:27 AM 01/26/11 12:27 AM
Joined: Oct 2005 Posts: 8,867 Ontario, Canada S Stanton Don't question me!
Stanton Don't question me! S Joined: Oct 2005 Posts: 8,867 Ontario, Canada	Quote: Was your car originally manual or PB? Reason I ask is the PB pedal linkage setup gives less leverage. If you are running the PB pedal linkage without booster that's your first and biggest problem This is incorrect. The actual pedal and linkage is the same for both power and manual brakes. The leverage change is accomplished with a mechanism that is actually part of the booster assembly (if you notice, the booster rod is actually higher up on the firewall than the manual rod - as a result of this mechanism). If you were to try to use that mechanism with a manual m/c it wouldn't mount properly and I doubt you'd find a pushrod to fit.

Re: MC Bore Size: 1 1/8 vs. 1 1/32 [Re: Stanton] #913767 01/26/11 12:50 AM 01/26/11 12:50 AM
Joined: Oct 2005 Posts: 8,867 Ontario, Canada S Stanton Don't question me!
Stanton Don't question me! S Joined: Oct 2005 Posts: 8,867 Ontario, Canada	Ok ... it looks like the SSBC calipers have 2 - 45mm pistons for a total area of 4.92 sq.". The mid-70's Mopar calipers have 1 - 2.75" piston for a total area of 5.93 sq." Given that most of the manual brake upgrades using those Mopar calipers use the 1-1/32" m/c bore the caliper bore to m/c bore ratio is 14.3:1. In your case, using the 1-1/8 bore m/c, your ratio is 9.94:1. In other words, its taking almost 50% MORE effort to apply your brakes. To get close to the 14:1 ratio you'd have to go to a m/c with a bore of 15/16". NOTE: all of the above calculations are for comparison only and DO NOT take the rear wheel cylinder volumes into account.

Re: MC Bore Size: 1 1/8 vs. 1 1/32 [Re: Stanton] #913768 01/26/11 01:14 AM 01/26/11 01:14 AM
Joined: Jan 2003 Posts: 30,998 Oregon A AndyF I Win
AndyF I Win A Joined: Jan 2003 Posts: 30,998 Oregon	If that is a dual 45mm piston setup then the braking force is 17% less with the SSBC system than with the stock 2.75 piston. So that means you have to press harder to get the same brake force. A MC with 17% less piston area will get the pedal force back in line, but now the rear brake bias is off.

Re: MC Bore Size: 1 1/8 vs. 1 1/32 [Re: AndyF] #913769 01/26/11 01:50 AM 01/26/11 01:50 AM
Joined: Oct 2005 Posts: 8,867 Ontario, Canada S Stanton Don't question me!
Stanton Don't question me! S Joined: Oct 2005 Posts: 8,867 Ontario, Canada	Andy, your 17% difference would only apply if both systems were using the same size m/c bore i.e. 1-1/32" but since his is currently 1-1/8", he has to decrease the bore size significantly more than 17%. He has to decrease his current bore size about 30% - from 1-1/8" (.99 sq") to 15/16" (.69 sq"). A $40 adjustable proportioning valve will solve the front/rear bias issue.

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