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  1. #1

    Default Considering swapping Master Cylinders again -- Rear Discs

    Did a 5 lug swap YEARS ago in my '79 Zephyr, and my brakes have never felt quite right. I'm considering swapping my master cylinder but thought id see what the experts here think first. My pedal sometimes feels okay, but if I need to stop fast the pedal feels kind of "dead" and it doesn't react like it should. If I'm stopping slowly it generally feels okay. I can't lock my brakes front or rear. Heres my combo:

    94/95 GT front spindles/calipers/rotors
    94/95 GT 8.8 with stock discs and calipers
    gutted prop valve
    Jegs adjustable prop valve (currently fully open to the rears to help me out)
    Started with the 94/95 GT master cylinder and pedal was too stiff, now have the 1985 Lincoln Town Car Master Cylinder (1" bore)
    Stock 1979 Zephyr brake booster
    *I did NOT adjust my pushrod length as per the LMR instructions when installing master cylinders, I didn't even know that was a thing to do when I was 18 and doing the swap in ~2008*

    I'm not interested in swapping boosters if I can help it.

    My car sat for about 4 years and upon getting it going again I found both rear calipers frozen, so I replaced them. My fronts were fine.

    I'm 95% certain my brakes are bled well, as I used the Motive pressure bleeder and ran it until fresh fluid came out and no bubbles on all corners. the only thing that gives me pause with regards to by brakes being bled well is that the pedal feels inconsistent. As I said sometimes if I stop slowly the pedal feels pretty good, but if I suddenly need to jam on the brakes it almost always lets me down and feels like I cant really stop if I need to.

    I'm considering swapping in the 94/95 Cobra master cylinder with a 15/16 bore to give me a bit softer pedal.
    '79 Z7 w/sunroof, first car, 302, 5-speed, 8.8 Rear Disc
    '68 Cougar 302 4v Auto
    '84 Jeep Grand Wagoneer
    '03 F250 V10
    '04 Volkswagen Golf 2.0
    '07 Hyundai Entourage

  2. #2

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    I had a similar issue with my brakes. I also did a 5-lug and disc brake swap on my car. Adjustable prop valve set all the way to the rears.
    You mentioned that you did not adjust the pushrod, I would try that first since it's free. That helped my situation. I also moved the adjustable prop valve too and that also helped.
    Full disclosure, i am running a hydroboost because the modular engine leaves no room for a vacuum booster. So i have a completely different master cylinder than you. But other than that it's basically the same- reservoir, pushrood, gutted stock prop, adjustable prop, etc.

    Someone with more experience with the Fox master cylinders will respond, Smaller bore may help as well.
    79 Zephyr, 4.6L 4v/4r70w swap, with team z front and rear suspension, 8.8 and upgraded brakes and coil overs. Running Holley Terminator X Max.

  3. #3

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    Quote Originally Posted by massacre View Post
    I had a similar issue with my brakes. I also did a 5-lug and disc brake swap on my car. Adjustable prop valve set all the way to the rears.
    You mentioned that you did not adjust the pushrod, I would try that first since it's free. That helped my situation. I also moved the adjustable prop valve too and that also helped.
    Full disclosure, i am running a hydroboost because the modular engine leaves no room for a vacuum booster. So i have a completely different master cylinder than you. But other than that it's basically the same- reservoir, pushrood, gutted stock prop, adjustable prop, etc.

    Someone with more experience with the Fox master cylinders will respond, Smaller bore may help as well.
    I have my prop valve located on the firewall near where the rear brake line goes through the firewall. Where was yours before and where did you move it to that helped?
    '79 Z7 w/sunroof, first car, 302, 5-speed, 8.8 Rear Disc
    '68 Cougar 302 4v Auto
    '84 Jeep Grand Wagoneer
    '03 F250 V10
    '04 Volkswagen Golf 2.0
    '07 Hyundai Entourage

  4. #4

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    I meant that i adjusted the prop valve by turning the knob.
    79 Zephyr, 4.6L 4v/4r70w swap, with team z front and rear suspension, 8.8 and upgraded brakes and coil overs. Running Holley Terminator X Max.

  5. #5
    FEP Member 86MustangGtRob's Avatar
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    Feb 2012
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    Mississauga Ontario, Canada
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    432

    Default

    I have the 94-95 master with Brembo fronts and rear turbo coupe discs. The pedal feel is quite nice, especially on the road course at 120 miles an hour.

  6. #6

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    I have the same issue with mine. I have all the same stuff as you, Z7, except I have the '94-5 booster. Stops great in normal driving, but panic stops are very lacking. I have my adjustable proportioning valve WIDE OPEN to the rear too. It doesn't seem like I'm getting anything from them though. It's been my assumption that I must have air somewhere in the rear circuit. Or I was thinking maybe the line through the inside of the car is pinched off in a way that isn't obvious by looking at it or something. I've replaced every other line on the car. Bad adjustable proportioning valve? Maybe. Some issue with that stupid one-of-a-kind banjo fitting thing over the rear axle? Possibly. I got sick of fighting with it and am just letting it ride for now. Really frustrating though. I've bled gallons through my system and no help at all.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  7. #7

    Default

    I had issues when mine was "wide open to the rear" as well. I started adjusting it more towards the front and it improved things. Makes no sense lol.
    79 Zephyr, 4.6L 4v/4r70w swap, with team z front and rear suspension, 8.8 and upgraded brakes and coil overs. Running Holley Terminator X Max.

  8. #8

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    Quote Originally Posted by ZephyrEFI View Post
    I have the same issue with mine. I have all the same stuff as you, Z7, except I have the '94-5 booster. Stops great in normal driving, but panic stops are very lacking. I have my adjustable proportioning valve WIDE OPEN to the rear too. It doesn't seem like I'm getting anything from them though. It's been my assumption that I must have air somewhere in the rear circuit. Or I was thinking maybe the line through the inside of the car is pinched off in a way that isn't obvious by looking at it or something. I've replaced every other line on the car. Bad adjustable proportioning valve? Maybe. Some issue with that stupid one-of-a-kind banjo fitting thing over the rear axle? Possibly. I got sick of fighting with it and am just letting it ride for now. Really frustrating though. I've bled gallons through my system and no help at all.
    Interesting, and disappointing. You have the booster everyone says you NEED to make the brakes feel right and you're still having issues. I'm going to check my pushrod length today and see if that plays much of a role in my problem. Really disappointing when I met someone with an aero mustang and a 5 lug swap but kept his rear drums and was actually jealous because I knew his brakes felt right!
    '79 Z7 w/sunroof, first car, 302, 5-speed, 8.8 Rear Disc
    '68 Cougar 302 4v Auto
    '84 Jeep Grand Wagoneer
    '03 F250 V10
    '04 Volkswagen Golf 2.0
    '07 Hyundai Entourage

  9. #9

    Default

    I checked my pushrod length and it was slightly too long. Slightly meaning ~1/8". I fixed it and installed my master cylinder and honestly it feels worse. I'm going to try bleeding again, but i don't think that's my problem. If that doesn't change anything then I'm going to install a slightly smaller bore master cylinder to test out and see what happens from there.
    '79 Z7 w/sunroof, first car, 302, 5-speed, 8.8 Rear Disc
    '68 Cougar 302 4v Auto
    '84 Jeep Grand Wagoneer
    '03 F250 V10
    '04 Volkswagen Golf 2.0
    '07 Hyundai Entourage

  10. #10

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    I'm running 94-98 Cobra brakes on all 4 corners (slightly smaller caliper pistons than 99-up) with the 94-98 master cylinder and stock 300k mile 86' brake booster.

    Pedal feel is spot on and braking power is ridiculous. Light pedal modulation is excellent and panic stops are a non issue. This thing will make your eyeballs fall out. Adjustable rear proportioning valve is mounted where the stock valve was located (it's been deleted) and there's a lot of adjustment left for rear bias.
    Jeremiah

    1986 Mustang GT 5spd, 3.27's
    PimpXS ECU/Android Single DIN Touchscreen
    SN95 Cobra Brakes/SN95 Front LCA's/Axles/S197 Wheels
    1998 Explorer Engine/Stock HO Cam 281rwhp/326rwtq

  11. #11

    Default

    Quote Originally Posted by Two86fiveoh's View Post
    I'm running 94-98 Cobra brakes on all 4 corners (slightly smaller caliper pistons than 99-up) with the 94-98 master cylinder and stock 300k mile 86' brake booster.

    Pedal feel is spot on and braking power is ridiculous. Light pedal modulation is excellent and panic stops are a non issue. This thing will make your eyeballs fall out. Adjustable rear proportioning valve is mounted where the stock valve was located (it's been deleted) and there's a lot of adjustment left for rear bias.
    Well you have a different setup than I do. You have twin piston calipers up front and a larger bore master cylinder. If I had your front calipers on my car my pedal would be slightly softer than it is now, and vice versa if I had my current brakes and your master cylinder in my car they would be harder than they are now. I'm glad your setup works for you, though. A lot of it is preference, too. Some people like a firmer pedal and some people like a softer pedal. Something is up with my setup though cause it's not right.
    '79 Z7 w/sunroof, first car, 302, 5-speed, 8.8 Rear Disc
    '68 Cougar 302 4v Auto
    '84 Jeep Grand Wagoneer
    '03 F250 V10
    '04 Volkswagen Golf 2.0
    '07 Hyundai Entourage

  12. #12

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    Master cylinder bore is smaller on the Cobra's than the GT's. Mine is a 7/8" bore.
    Jeremiah

    1986 Mustang GT 5spd, 3.27's
    PimpXS ECU/Android Single DIN Touchscreen
    SN95 Cobra Brakes/SN95 Front LCA's/Axles/S197 Wheels
    1998 Explorer Engine/Stock HO Cam 281rwhp/326rwtq

  13. #13

    Default

    Brake pedal feel/effort is about the same as stock.
    Jeremiah

    1986 Mustang GT 5spd, 3.27's
    PimpXS ECU/Android Single DIN Touchscreen
    SN95 Cobra Brakes/SN95 Front LCA's/Axles/S197 Wheels
    1998 Explorer Engine/Stock HO Cam 281rwhp/326rwtq

  14. #14

    Default

    Quote Originally Posted by Two86fiveoh's View Post
    Master cylinder bore is smaller on the Cobra's than the GT's. Mine is a 7/8" bore.
    Oh yeah, I didn't realize your master was from a cobra too as you just said it was a 94-98 master cylinder. That's the master cylinder I want to try as well so hopefully it won't feel much different than yours.
    '79 Z7 w/sunroof, first car, 302, 5-speed, 8.8 Rear Disc
    '68 Cougar 302 4v Auto
    '84 Jeep Grand Wagoneer
    '03 F250 V10
    '04 Volkswagen Golf 2.0
    '07 Hyundai Entourage

  15. #15

    Default

    This is on my 1993 Coupe but should apply.

    Revision 1
    Stock 94-98 SN95 front calipers / rotors
    Stock 94-04 SN95 rear calipers / rotors
    Stock 95 GT MC
    Stock 95 GT Booster

    Revision 2
    Stock 99-04 SN95 front calipers / rotors
    Stock 94-04 SN95 rear calipers / rotors
    Stock 95 GT MC
    Stock 95 GT Booster

    Revision 3
    Stock 94-98 Cobra front calipers / 94-04 Cobra rotors
    Stock 94-04 SN95 rear calipers / rotors
    Stock 95 GT MC
    Stock 95 GT Booster

    Revision 4
    Stock 94-98 Cobra front calipers / 94-04 Cobra rotors
    Stock 94-04 SN95 rear calipers / 94-04 Cobra rotors
    Stock 95 GT MC
    Stock 95 GT Booster

    In all instances that car has had and has great brakes. I also have the proportioning sided of the stock combination valve gutted and a manual proportioning valve installed on the rear brakes. You need to adjust the proportioning valve such that the rear brakes just lock up before the fronts. You need to adjust the booster rod so there is a 0.015" to 0.020" which allows for complete release and no dead pedal. I cannot stress how important it is to get the air out of these systems but we all know that.

    If it was me I would suspect the booster (or some kind of vacuum loss) or the MC. This could be because under light to moderate braking the booster has enough vacuum assist but under heavy braking there is not enough, the booster has a leak, or the MC is fine under light pedal pressure but under high pedal pressure the pistons are bypassing fluid.
    http://vb.foureyedpride.com/attachme...1&d=1418488062
    '83 351W TKO'd T-Bird on the bottle

    http://vb.foureyedpride.com/attachme...2&d=1418488063
    '93 331W Mustang coupe that beat your mom's LTD

  16. #16

    Default

    Quote Originally Posted by Aerocoupe View Post
    This is on my 1993 Coupe but should apply.

    Revision 1
    Stock 94-98 SN95 front calipers / rotors
    Stock 94-04 SN95 rear calipers / rotors
    Stock 95 GT MC
    Stock 95 GT Booster

    Revision 2
    Stock 99-04 SN95 front calipers / rotors
    Stock 94-04 SN95 rear calipers / rotors
    Stock 95 GT MC
    Stock 95 GT Booster

    Revision 3
    Stock 94-98 Cobra front calipers / 94-04 Cobra rotors
    Stock 94-04 SN95 rear calipers / rotors
    Stock 95 GT MC
    Stock 95 GT Booster

    Revision 4
    Stock 94-98 Cobra front calipers / 94-04 Cobra rotors
    Stock 94-04 SN95 rear calipers / 94-04 Cobra rotors
    Stock 95 GT MC
    Stock 95 GT Booster

    In all instances that car has had and has great brakes. I also have the proportioning sided of the stock combination valve gutted and a manual proportioning valve installed on the rear brakes. You need to adjust the proportioning valve such that the rear brakes just lock up before the fronts. You need to adjust the booster rod so there is a 0.015" to 0.020" which allows for complete release and no dead pedal. I cannot stress how important it is to get the air out of these systems but we all know that.

    If it was me I would suspect the booster (or some kind of vacuum loss) or the MC. This could be because under light to moderate braking the booster has enough vacuum assist but under heavy braking there is not enough, the booster has a leak, or the MC is fine under light pedal pressure but under high pedal pressure the pistons are bypassing fluid.
    Great info Aerocoupe. Having that larger booster supposedly makes the difference. Before I go through the headache of installing that larger booster I'm going to play with my master cylinder and verify all of the air is out of my system.
    '79 Z7 w/sunroof, first car, 302, 5-speed, 8.8 Rear Disc
    '68 Cougar 302 4v Auto
    '84 Jeep Grand Wagoneer
    '03 F250 V10
    '04 Volkswagen Golf 2.0
    '07 Hyundai Entourage

  17. #17

    Default

    Yeah, swapping to that MASSIVE booster should be a last resort. I wish I'd known that back in the day. Good luck! Following with interest!
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  18. #18

    Default

    I would suggest getting the 1993 Cobra booster as it has the same firewall bolt pattern as all fox boosters. To get the correct braking out of these systems you need to run it. Will the fox booster work? Yes but not as well and you have to determine if the effort is worth it. It was for me so that’s what I did.

    Make sure you properly bench bleed the MC and a pressure bleeder works really well to bleed the whole system. I have one and although it was not the cheapest tool I wouldn’t do one without it if I could void it. Gravity is your friend as well. Make sure you don’t completely rely on gravity bleeding as the caliper bleeders may not be at the highest point when bleeding the brakes so some manual bleeding will/may be necessary.

    Also, make sure the flexible lines between hard lines and calipers are not swollen. They will do this and shrink the ID of the hose and pinch off flow.
    Last edited by Aerocoupe; 08-29-2022 at 05:38 PM.
    http://vb.foureyedpride.com/attachme...1&d=1418488062
    '83 351W TKO'd T-Bird on the bottle

    http://vb.foureyedpride.com/attachme...2&d=1418488063
    '93 331W Mustang coupe that beat your mom's LTD

  19. #19

    Default

    IMO--The Cobra brakes are fine with the fox booster. The master cylinder size difference is small enough that pedal effort increase is non existent.

    The larger MC used with the GT brakes will likely require an upgraded booster to maintain performance. The small MC is one of the reasons I went with the Cobra setup, and it worked out perfectly.
    Jeremiah

    1986 Mustang GT 5spd, 3.27's
    PimpXS ECU/Android Single DIN Touchscreen
    SN95 Cobra Brakes/SN95 Front LCA's/Axles/S197 Wheels
    1998 Explorer Engine/Stock HO Cam 281rwhp/326rwtq

  20. #20

    Default

    Quote Originally Posted by Two86fiveoh's View Post
    IMO--The Cobra brakes are fine with the fox booster. The master cylinder size difference is small enough that pedal effort increase is non existent.

    The larger MC used with the GT brakes will likely require an upgraded booster to maintain performance. The small MC is one of the reasons I went with the Cobra setup, and it worked out perfectly.
    Yeah, I would love to try a 15/16" bore master cylinder and see the difference. I'm going to try and go out today and re-bleed and see if there is any air trapped in the system I missed last time I bled.
    '79 Z7 w/sunroof, first car, 302, 5-speed, 8.8 Rear Disc
    '68 Cougar 302 4v Auto
    '84 Jeep Grand Wagoneer
    '03 F250 V10
    '04 Volkswagen Golf 2.0
    '07 Hyundai Entourage

  21. #21

    Default

    I'm sorry that the pushrod adjustment didn't help.
    it helped me on my car.
    79 Zephyr, 4.6L 4v/4r70w swap, with team z front and rear suspension, 8.8 and upgraded brakes and coil overs. Running Holley Terminator X Max.

  22. #22

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    Quote Originally Posted by massacre View Post
    I'm sorry that the pushrod adjustment didn't help.
    it helped me on my car.
    No worries, my stock booster pushrod isn't even really adjustable. All I have is a little cap with a couple spacers underneath it that I removed to make it slightly shorter. My pushrod length was like 1/8" too long so I adjusted it to be correct, but I think if I need any more adjustment I'll have to swap boosters to one that I can adjust more.
    '79 Z7 w/sunroof, first car, 302, 5-speed, 8.8 Rear Disc
    '68 Cougar 302 4v Auto
    '84 Jeep Grand Wagoneer
    '03 F250 V10
    '04 Volkswagen Golf 2.0
    '07 Hyundai Entourage

  23. #23

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    My pushrod was too short, mine isn't adjustable either i just welded onto the end and ground it down to size lol
    79 Zephyr, 4.6L 4v/4r70w swap, with team z front and rear suspension, 8.8 and upgraded brakes and coil overs. Running Holley Terminator X Max.

  24. #24
    FEP Senior Member Patrick Olsen's Avatar
    Join Date
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    Where the Navy sends me...
    Posts
    680

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    1/8" too long seems strange to me - that would mean the brakes were being applied all the time, which isn't the problem that you've described.
    '89 GT convertible - not a four-eye
    '82 Zephyr Z7 - future track car

  25. #25

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    Quote Originally Posted by Patrick Olsen View Post
    1/8" too long seems strange to me - that would mean the brakes were being applied all the time, which isn't the problem that you've described.
    It was probably less than 1/8" I just don't remember the exact measurement. They weren't dragging before and it made a pretty minimal change in brake feel, although it does feel different. I don't think that has anything to do with my problem.
    '79 Z7 w/sunroof, first car, 302, 5-speed, 8.8 Rear Disc
    '68 Cougar 302 4v Auto
    '84 Jeep Grand Wagoneer
    '03 F250 V10
    '04 Volkswagen Golf 2.0
    '07 Hyundai Entourage

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