Brake problem! Help!!!
Team Owner
Joined: Oct 2000
Posts: 38,897
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From: Washington Michigan
The 1967 dual master cylinder (casting #5455509, stamped "DC"), used for both manual and power brakes, has a 1" bore. As Jim and Mike noted above, a 1-1/8" bore master cylinder requires noticeably more pedal pressure to develop the same line pressure as a 1"-bore cylinder.
Pay no attention to the hacks who tell you to reverse the connections for "better braking"; the front caliper pistons (1.875") are larger than the rear caliper pistons (1.375"), and the larger front pistons require more fluid displacement than the rears for the same amount of piston/pad travel. The dual master cylinder is designed with more fluid capacity in the front portion of the bore in order to accommodate that requirement. That's how proportioning is accomplished without a separate valve - the difference in caliper piston diameter automatically (hydraulically) places 65% of the braking effort on the fronts and 35% on the rears under all conditions.
OEM-type organic pads also require less pedal pressure than semi-metallic "performance" pads to generate the same level of braking force, and they won't eat your rotors.
Pay no attention to the hacks who tell you to reverse the connections for "better braking"; the front caliper pistons (1.875") are larger than the rear caliper pistons (1.375"), and the larger front pistons require more fluid displacement than the rears for the same amount of piston/pad travel. The dual master cylinder is designed with more fluid capacity in the front portion of the bore in order to accommodate that requirement. That's how proportioning is accomplished without a separate valve - the difference in caliper piston diameter automatically (hydraulically) places 65% of the braking effort on the fronts and 35% on the rears under all conditions.
OEM-type organic pads also require less pedal pressure than semi-metallic "performance" pads to generate the same level of braking force, and they won't eat your rotors.
Race Director
Joined: Feb 2007
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From: northern california
C2 of Year Finalist (track prepared) 2019
Thread Starter
Instructor
Joined: Jan 2007
Posts: 109
Likes: 1
From: Huntsville, AL
The 1967 dual master cylinder (casting #5455509, stamped "DC"), used for both manual and power brakes, has a 1" bore. As Jim and Mike noted above, a 1-1/8" bore master cylinder requires noticeably more pedal pressure to develop the same line pressure as a 1"-bore cylinder.
Pay no attention to the hacks who tell you to reverse the connections for "better braking"; the front caliper pistons (1.875") are larger than the rear caliper pistons (1.375"), and the larger front pistons require more fluid displacement than the rears for the same amount of piston/pad travel. The dual master cylinder is designed with more fluid capacity in the front portion of the bore in order to accommodate that requirement. That's how proportioning is accomplished without a separate valve - the difference in caliper piston diameter automatically (hydraulically) places 65% of the braking effort on the fronts and 35% on the rears under all conditions.
OEM-type organic pads also require less pedal pressure than semi-metallic "performance" pads to generate the same level of braking force, and they won't eat your rotors.
Pay no attention to the hacks who tell you to reverse the connections for "better braking"; the front caliper pistons (1.875") are larger than the rear caliper pistons (1.375"), and the larger front pistons require more fluid displacement than the rears for the same amount of piston/pad travel. The dual master cylinder is designed with more fluid capacity in the front portion of the bore in order to accommodate that requirement. That's how proportioning is accomplished without a separate valve - the difference in caliper piston diameter automatically (hydraulically) places 65% of the braking effort on the fronts and 35% on the rears under all conditions.
OEM-type organic pads also require less pedal pressure than semi-metallic "performance" pads to generate the same level of braking force, and they won't eat your rotors.
Recap: Questions: A. Which MC you recommend? 1" or 1 1/8"
B. Booster clicking noise?
C. Rod adjustment (Pedal to Booster)?
Many thanks again, John!
Team Owner
Joined: May 2005
Posts: 31,497
Likes: 1,313
From: Huntsville AL
The master cylinder on the car now is a generic replacement for a 1967 to 1970s style MC. The bore on that MC is 1 1/8 inch. It has a single metal cap that covers both resevours, with two seperate wire clamps that hold the cap in place.
Sounds like Danny found part of the clicking noise. We may need that spring washer and retainer clip for the clevis after all.
JohnZ: Is there any issue with the fact that the longer push rod does not have the tip on the back end or the o ring like your picture shows?
Jim: I am also inclined to go back to the old 1 inch bore MC. Danny said that the brakes were better with that MC, but the car pulled to the right. I think we have the pulling issue resolved. That MC is a strange looking thing. Has a single metal cap covering both resevours, and line holes on both sides of the MC. I guess it is sort of a universal MC so you can hook up the lines on either side.
Danny: Changing the MC back ain't that hard. We can bench bleed it, install it on the car, then do a final bleed of the brakes like we did last night. An hour or so should handle it. We would need to put the old short push rod back in as well. Your call. I am available this evening after 5 pm or so.
Sounds like Danny found part of the clicking noise. We may need that spring washer and retainer clip for the clevis after all.
JohnZ: Is there any issue with the fact that the longer push rod does not have the tip on the back end or the o ring like your picture shows?
Jim: I am also inclined to go back to the old 1 inch bore MC. Danny said that the brakes were better with that MC, but the car pulled to the right. I think we have the pulling issue resolved. That MC is a strange looking thing. Has a single metal cap covering both resevours, and line holes on both sides of the MC. I guess it is sort of a universal MC so you can hook up the lines on either side.
Danny: Changing the MC back ain't that hard. We can bench bleed it, install it on the car, then do a final bleed of the brakes like we did last night. An hour or so should handle it. We would need to put the old short push rod back in as well. Your call. I am available this evening after 5 pm or so.
Team Owner
Joined: Mar 2003
Posts: 26,118
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From: Greenville, Indiana
Just in general, I don't trust anything rebuilt from Auto Zone.
It's been stated several times here there was no lack of braking power with the first master cylinder. The only problem was the right rear wheel apparently locking before other wheels. The only way that could be related to the master cylinder is if the front piston in the MC is blowing by and not providing pressure to the front wheels along with another problem of fluid distribution and/or lack of friction at the left rear disc. I'd guess the new pads fixed your "pulling" problem.
Either put the first MC back on and see what you get or get another MC from another source.
It hasn't been established yet if there is even any braking going on at the front wheels. Is there? Maybe you could find an emptly parking lot and run the car backwards and then apply the brakes, hard. That should make the front wheels slide if you have brakes on the front end.
It's been stated several times here there was no lack of braking power with the first master cylinder. The only problem was the right rear wheel apparently locking before other wheels. The only way that could be related to the master cylinder is if the front piston in the MC is blowing by and not providing pressure to the front wheels along with another problem of fluid distribution and/or lack of friction at the left rear disc. I'd guess the new pads fixed your "pulling" problem.
Either put the first MC back on and see what you get or get another MC from another source.
It hasn't been established yet if there is even any braking going on at the front wheels. Is there? Maybe you could find an emptly parking lot and run the car backwards and then apply the brakes, hard. That should make the front wheels slide if you have brakes on the front end.
Last edited by MikeM; Jun 17, 2009 at 01:15 PM.
Team Owner
Joined: May 2005
Posts: 31,497
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From: Huntsville AL
OK, progress has been made.
Danny got another 67 style MC and we put it on this afternoon. Bench bled the MC, then bled the brakes. Then went for a ride.
Car is significantly better. I would say it is about 99% where it needs to be now. Every now and then it seems to lose some clamping force toward the end of the braking period. Not much, and not everytime.
I suggested that Danny drive the car for a while and see where it is. If it hasn't changed any, we may try bleeding one more time.
All in all, a productive afternoon.
Thanks to everyone for all of the good advice.
Danny will keep us all posted.
Danny got another 67 style MC and we put it on this afternoon. Bench bled the MC, then bled the brakes. Then went for a ride.
Car is significantly better. I would say it is about 99% where it needs to be now. Every now and then it seems to lose some clamping force toward the end of the braking period. Not much, and not everytime.
I suggested that Danny drive the car for a while and see where it is. If it hasn't changed any, we may try bleeding one more time.
All in all, a productive afternoon.
Thanks to everyone for all of the good advice.
Danny will keep us all posted.
Thread Starter
Instructor
Joined: Jan 2007
Posts: 109
Likes: 1
From: Huntsville, AL
Yes!!! I am happy for the good news! Thanks to Ed McComas for his great help. And also thanks to all of you who gave priceless input. I am going to drive it and see what happens. At least I do feel safe in the car again. You guys are a great help on this forum, and I am very grateful....danny
