For those with the Trans Am style front brakes with the big four piston Kelsey Hayes ("Lincoln", although used on many other Fords of the era as well) calipers, what size master cylinder are you using?
I used a 1.125" Lincoln MkVII (and/or Mustang SVO) MC, Fox Mustang 4 cylinder style single diaphragm 9" brake booster (MustangSteve style), 3.7:1 pedal ratio, the above mentioned front brakes and Lincoln MkVII (and/or Mustang SVO) rear discs. Raybestos PG Plus brake pads front and back.
You would think the above setup would provide plenty of stopping power but they never felt that good. They stopped alright, but the pedal felt dead and the brakes didn't seem to "bite" (for lack of a better term). I suspected the brake booster was at fault (it seemed to work, but not very well), so I removed it, partly because I was curious how it would feel with manual brakes.
Removing the booster and connecting the MC to the original pin at the pedal increased the pedal ratio back to ~6.3:1 (vs 3.7 with the booster). The whole setup is now identical, leverage wise, to a stock 65-67 Mustang front disc setup, since the ratio between MC and calipers as wel as pedal ratio is identical. I therefore expected this setup to work at least reasonably well, pedal effort wise. ´
When I tested it yesterday it didn't take long to conclude that it wasn't the solution. I had to press the pedal all I could to slow the car down. Of course, I do have rear discs instead of (self energizing) drums like a Mustang with a stock disc/drum brake system, but I don't expect that to turn the brakes into impossible to operate.
I guess I could install a 1" MC to improve things (which would result in a 26% pedal effort reduction), but I still don't really understand why a "hydraulic leverage" (caliper piston area divided by MC area) like a stock Mustang disc brake setup would work so poorly. Any thoughts?
The easiest question to ask is if you are sure the brakes are bled properly?
Quote:
Originally Posted by Helmantel
For those with the Trans Am style front brakes with the big four piston Kelsey Hayes ("Lincoln", although used on many other Fords of the era as well) calipers, what size master cylinder are you using?
I used a 1.125" Lincoln MkVII (and/or Mustang SVO) MC, Fox Mustang 4 cylinder style single diaphragm 9" brake booster (MustangSteve style), 3.7:1 pedal ratio, the above mentioned front brakes and Lincoln MkVII (and/or Mustang SVO) rear discs. Raybestos PG Plus brake pads front and back.
You would think the above setup would provide plenty of stopping power but they never felt that good. They stopped alright, but the pedal felt dead and the brakes didn't seem to "bite" (for lack of a better term). I suspected the brake booster was at fault (it seemed to work, but not very well), so I removed it, partly because I was curious how it would feel with manual brakes.
Removing the booster and connecting the MC to the original pin at the pedal increased the pedal ratio back to ~6.3:1 (vs 3.7 with the booster). The whole setup is now identical, leverage wise, to a stock 65-67 Mustang front disc setup, since the ratio between MC and calipers as wel as pedal ratio is identical. I therefore expected this setup to work at least reasonably well, pedal effort wise. ´
When I tested it yesterday it didn't take long to conclude that it wasn't the solution. I had to press the pedal all I could to slow the car down. Of course, I do have rear discs instead of (self energizing) drums like a Mustang with a stock disc/drum brake system, but I don't expect that to turn the brakes into impossible to operate.
I guess I could install a 1" MC to improve things (which would result in a 26% pedal effort reduction), but I still don't really understand why a "hydraulic leverage" (caliper piston area divided by MC area) like a stock Mustang disc brake setup would work so poorly. Any thoughts?
The easiest question to ask is if you are sure the brakes are bled properly?
Yes, and the pedal is hard.
I don't know if i used the ultimate bed in procedure, but the pads have been on the car for a few years now. I didn't drive it that much, but the pads are certainly not new anymore.
If you look at the area 1" to 1.125" it's a 27% difference. Does not seem like it would cause this much difference.
I think of doing this swap as well, but have not investigated very deeply beyond the Calipers, brackets, etc...
I think some of the MC's had larger bowl for Calipers and smaller for Drums in back, and sometimes guys would set the lines incorrectly, any chance you have plumbed it wrong or have issues with the proportioning valve?
I think some of the MC's had larger bowl for Calipers and smaller for Drums in back, and sometimes guys would set the lines incorrectly, any chance you have plumbed it wrong or have issues with the proportioning valve?
The bowl size should have no impact on pedal effort or braking efficiency. Its just your back up fluid. Larger bowls are just a larger reserve for a system that will take more fluid to keep full. Major bandaid IMHO, because it will really only give you a little more time in the event of an actual failure.
OP: Perhaps I am tracking 100% to your first post. You have the K/H calipers up front and MkVII out back?
Your MC bore size needed is a function of the relationship (leverage) between the caliper/piston displaced volume (total) and the displaced volume on your master cyl. Its all about leverage.
I am (slowly) istalling cobra-PBR & MkVii-SVO disks on my '67. Its not together yet, but I am using a 1" manual master cyl from a crown vic. I decided to put it together with manual brakes before trying to deal with adding power.
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04 SVT Cobra, Torch Red (daily driver)
67 'vert 302,4spd,Red/Red (almost ready!)
67 Coupe 289,auto,black/black,deluxe (sold)
67 Coupe I6 to V8 conversion (sold)
This was mentioned to make sure the plumbing is correct. If a small bowl for rear drums is plumbed to a set of calipers that require more fluid than available it could have an impact on braking. I don't understand the band-aid comment, aren't the bowls sized to the OEM caliper and drum fluid requirements?
Quote:
Originally Posted by caveeagle
The bowl size should have no impact on pedal effort or braking efficiency. Its just your back up fluid. Larger bowls are just a larger reserve for a system that will take more fluid to keep full. Major bandaid IMHO, because it will really only give you a little more time in the event of an actual failure.
This was mentioned to make sure the plumbing is correct. If a small bowl for rear drums is plumbed to a set of calipers that require more fluid than available it could have an impact on braking. I don't understand the band-aid comment, aren't the bowls sized to the OEM caliper and drum fluid requirements?
Yes, the bowls are sized based on fluid requirements. My 'band-aid' comment is just stating that a properly functioning system should not use brake fluid. If you have an actual leak, a larger bowl is not going to help you.
The larger bowl is really just there to help give you enough capacity to effectively bleed the system. The extra few oz in the larger bowl will not save you if there is a real failure.
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mark
----------------------------
04 SVT Cobra, Torch Red (daily driver)
67 'vert 302,4spd,Red/Red (almost ready!)
67 Coupe 289,auto,black/black,deluxe (sold)
67 Coupe I6 to V8 conversion (sold)
I have the Trans Am style brakes on my 69.
I am using the 1.125 master from a Versalles/SVO with a master power booster.
I have Porterfield R4S pads and it works pretty well IMHO.
I would talk to a brake expert before you spent more time and money.
Talk to Shaun at Street or Track.
Yes, the bowls are sized based on fluid requirements. My 'band-aid' comment is just stating that a properly functioning system should not use brake fluid. If you have an actual leak, a larger bowl is not going to help you.
The larger bowl is really just there to help give you enough capacity to effectively bleed the system. The extra few oz in the larger bowl will not save you if there is a real failure.
The "spare fluid" in the reservoir also fills the system when the pads wear. New pads have maybe half an inch of friction material, so if you were to wear them down completely, the pistons would stick out by the same amount. The volume behind them needs to be filled with fluid.
The "spare fluid" in the reservoir also fills the system when the pads wear. New pads have maybe half an inch of friction material, so if you were to wear them down completely, the pistons would stick out by the same amount. The volume behind them needs to be filled with fluid.
Absolutely correct!
__________________
mark
----------------------------
04 SVT Cobra, Torch Red (daily driver)
67 'vert 302,4spd,Red/Red (almost ready!)
67 Coupe 289,auto,black/black,deluxe (sold)
67 Coupe I6 to V8 conversion (sold)
I have the Trans Am style brakes on my 69.
I am using the 1.125 master from a Versalles/SVO with a master power booster.
I have Porterfield R4S pads and it works pretty well IMHO.
I would talk to a brake expert before you spent more time and money.
Talk to Shaun at Street or Track.
Mine were reasonable but not impressive when I was still using a booster. Maybe the pads make the difference between yours and mine?
About 17-18 inHg at idle, IIRC and more when slowing down with the throttle closed. I did a bit of calculating, taking the booster diameter, estimated vacuum, pedal ratio etc. into account. With the booster, it takes a 100 pound force on the pedal to create a 1000 pound force on the MC, but with the manual setup it takes 160 pounds on the pedal. If course I expected that the required force would increase without a booster but hadn't calculated how much.
It still puzzles me how a stock manual disc setup with the same "hydraulic leverage" works well (I assume, never drove one)
Most calipers will easily lock up your tires at about 1200 PSI. Your 100 pound example is mathematically correct, but you might find that you're applying about 40 to the pedal and only getting 700 PSI. Generating 100 lbs with one leg is like going to the gym, and can seriously stress your paper-thin sheetmetal firewall.
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MC size question for Trans Am style brakes
