Well I have an sn95 master in there now. 68 stock brakes up front, SN95's in the rear. The pedal effort is high (Power brakes, bendix cylinder), and the rears won't lock on gravel, even with the adjustable proportioning valve set to full rear bias.
So I'm thinking I might try another master, even though I'd like to find out what's going on with the rear brakes. So I've read through searches, and some people are saying SVO (Which is $150+ around here) and 84 crown vic. Now, crown vics only seem to come with drums, so what is everyone doing about that? That doesn't seem correct? Wondering if I should use a 1" bore, or go even smaller?
I have 4 wheel manual disc(gm calipers front and 7.5" lincoln rear) I used an '85 T-bird master(some of these ae aluminum, some are cast iron...I found an aluminum one remanned at autozone) they have a 7/8" bore....pedal effort is fine...I would suggest that your master cylinder isnt the issue, since you have power brakes...maybe its the booster? low vacuum?
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66 mustang coupe,Heidts Mustang II front end 4.6L DOHC mod motor, T45 transmission, 8.8" disc rear end, twin turbo system in progress, and a ton of other crap
Pump the brakes a few times with the car off, leave your foot on the brake pedal and start the car. If the pedal sinks a bit, you can wager your booster is working OK.
Booster definitely has more travel when the car is on. As well, if i shut the car off and come back to it after a few hours and pump the pedal, I get a good 2 pumps before it's hard as a rock again, so I think the booster is ok.
MC is plumbed correctly.
I doubt i'm getting the correct PSI at the corners, but it might just be a matter of mechanical advantage due to bore size.
Hi Johny,
most likely what you will find is that your front and rear calipers are incompatible. If the piston size and chamber volume difference is too great, the only way to over come this would be to run separate master cylinders of differing bore sizes with a balance bar.
Maybe check with some others to see if anyone else is successfully running your caliper combination, and see what they did.
Good luck man.
I believe, from memory before i bought these rear brakes, that the SN95 fronts had a similar bore size to these 68's I had (As opposed to 67, which my car is), so I'm not sure anymore. I don't want to start replacing stuff if something else is amiss. I suppose the only thing I can do now is see where the pressure stops? (Why the rears won't lock, I mean). Even with the prop valve dialed all the way to the rear.
Hey guys, still deliberating about this. Read all I could find on the internet, and a lot of guys talk about Town cars and such, but they never came with rear discs, so they are kind of out of the question (I wonder how safe those cars are with people running 4 wheel discs with them). So IS there an affordable < 1" M/C for 4 wheel discs that will fit? I'm running SN95 right now as I said (1.125? Or is it 1/16), so I'm wondering if 1" will make any difference, and if 15/16 will be too small..
Johnny
Lots of Crown Vics came with 4 wheel discs. Unless they didn't make it into the Great White North. Don't know what the MC dia is, though. I'm using an '06 (or so) V6 Mustang MC (1" IIRC), and I had the opposite problem; they'd grab with a feather touch. Car broke before I could expermint, though, so I can't help much.
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Dennis Harrelson
65 2+2, owned since '72
Lots of mods, now just another sad project hoping for resurrection.
1985 Lincoln Town car, 1" bore, aluminum, no residual pressure valve.
They did have rear discs available. (the actual rear end is in my '66 GT,
shortened and with leaf spring pads added because Lincolns had coil springs)
I've got the big 65/66 Galaxie/Tbird front calipers too.... stops like you threw
out a boat anchor, even without power assist or special pads.
on my 65 i use a dual master cyl from a granada with a 15/16 bore (same as the 65-66 disc brake cyl) manual brakes ,wilwood proportioning valve. i have wilwood diferential bore 4 piston calipers in the front 1.88" & 1.75" bore and symetrical bore 4 piston in the back 1.375" with 1.25"x12" rotors front .810"x12" rotors rear. can lock up the fronts with light pedal pressure with 17x11 rims on all 4 corners. i tried a 7/8 bore master cyl but pedal travel was a little much for my heel and toe action so i put it on my 4 wheel disc brake station wagon. something aint quite right. what size brake lines did you use. i use 3/16" for minimal pedal travel and higher pressure delivery to the calipers. i dont recomend any other size. did you use street type pads, race pads need to get hot before they bite , i use porterfield brand R-4S and they also work good on the roadrace track. also you never ever want the rear brakes to lock unless you like doing 180 deg. spins !! the rears should still be rotating a little after you have pushed the pedal to the floor with both feet and then some having the rears lock up is dangerous and will cause the back end to come around ! i always love doing 180's especially in the rain
Last edited by supershifter2; 11-19-2009 at 01:28 AM.
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Back to the brake M/C dilemma!
!! the rears should still be rotating a little after you have pushed the pedal to the floor with both feet and then some 
