Need help with proper master cylinder bore diameter for brake system

[drdano]

Please excuse my double post from the other FE forum.  Need some help from the brake gurus here.  I've got a '62 Galaxie wagon I'm doing my rear conversion to discs, the front already has a disc conversion.  Current MS is non-boosted and want to stay manual.  Fronts have single 60mm pistons, rears will be single 52mm units.  Pedal ratio with the manual pedal I'm using is 6.625.  Car is 95% street, but driven pretty hard.  What would an appropriate master cylinder bore diameter be for my application?  Thanks all!

[GJCAT427]

Check with MP brakes. they gave me some very good info when I put 4 wheel disc on my 56 F100. My system concists of mustang frts and linclon rear discs. My master is a corvette 4 wheel manual unit. The bore as I remember is 15/16" asper there advice. I put in an aftermarket nonadjustable proportioning valve and I have 2# recidual valves frt&rear. The recidual valves are there because the master is under the floor same height as the disc to prevent siphoning when parked on a hill or uneven ground. My brakes work excellent. I have panic stoped the truck several times and they do work!

[drdano]

Do you remember the calilper piston sizes of the front and rear calipers?  I've got a 1" bore disc/drum MS now with the current disc/drum setup and its damn hard to lock up the front tires and the pedal is a bit heavier than I'd like.

[jayb]

I don't have direct experience with a setup like yours, but for what it's worth I've had 1", 15/16", and 7/8" bore master cylinders on manual disc/disc or disc/drum setups, and the 7/8" bore always worked the best.  I currently have 7/8" bore master cylinders on all three of my street/strip cars, all with Wilwood four wheel discs.  Pedal effort is pretty reasonable, and no trouble locking the brakes.

[ScotiaFE]

And here's a blurb from SSBC.
Most vehicles, power or non power brake, develop 1,200 P.S.I. When you panic stop or jump on the brakes hard, a surge of 1,400 P.S.I. can be achieved. If a factory proportioning valve installed on the vehicle, the rear brakes are only developing 600 – 700 P.S.I. Drum brakes require lower pressure because they grab more quickly. When rear disc brakes are installed, the rear brake pressure may be increased to 800 – 1,000 P.S.I. or more. A good way to check the pressures and to see if the system is working correctly, use a pressure gauge screwed into the bleeder port (SSBC part # A1704). A vehicle with less than 600 P.S.I will not stop!

I like the 7/8" bore also.
Works great on my junk and I've done this test, but get a kit for the front and back.
This way you can read the pressure at the front and back at the same time.

[drdano]

I called wilwood and talked to one of their tech guys.  He recommended I upgrade all of my brake hard line to 3/16", eliminate all rubber flex lines with braided flex lines and run a 1" bore MS.  Sounds like a lot more work than I'm wanting to do right now.  Can I not use the OEM lines that I think are 1/8'' and the new rubber flex lines?  I was a bit surprised at the 1" bore as well, that is what I have now and I can't lock the front wheels into a skid even if I want to.

[machoneman]

Yes, you can use your new rubber lines and the OEM-sized steel lines. The upgrade is a nice thing to have but not 100% necessary. The bore size of 1" is too big IMHO as well; I'd stick to the 7/8th's size as recommended by Jay and GJCAT.

I have btw the SSBC 9" rear disc kit on my '70 Stang but Baer Racing's 12.75 discs and PBR calipers on the front. I've also followed SSBC's tech recommendations in many ways, but not all, with good results. The key as already mentioned is that disc/disc system, aftermarket or not, requires much higher line pressure to the rears than most large diameter master cylinder bores can supply (this with manual brakes, not power assisted). The smaller 7/8ths master and an adjustable proportioning valve will get you in the ballpark.

I'll mention something else here too. Many 'hard' race pads are not the best for street use as they are designed to get hot and stay hot in road racing or roundy-round action. A 'cold" stop the first few times will make one a believer in not using some brands of race brakes on the street! A medium or street oriented pad both in the front and rear will heat up quickly and grab much better in all-around use. And once one sets the adjustable prop valve for the front to lock up just before the backs do, leave the adjustment alone, regardless of the pad used.  JMO.   

http://www.essexparts.com/learning-center/cat/brake-pads/post/choose-brake-pads

   

[BruceS]

Guys,
Great brake info but I've noticed no one talks about power assist... Is it because of the lack of vacuum at idle from the cams you're using? 
Thanks,
Bruce

[drdano]

In my case, yes.  My hyd roller cam makes at best 8-10" at idle. 

Thanks for the additional info guys.  The consensus seems to be 7/8" master.  I do have already an adjustable proportioning valve for the rear, so that will get reused. 

[drdano]

Would there happen to be an off the shelf Ford 7/8" MS for disc/disc that would have the appropriately deep hole for the pushrod to the pedal?  The Wilwood unit is nice...but it's also $200.  I'm always trying to use OEM parts when possible because I have this chronic fear of having a problem out on the road and a specialty MS may require specialty parts if it goes bad on the road.

[machoneman]

I actually do use a Ford power booster on my '70 Stang (see brake details in other post) with a Crane vaccum accumulator tank under the hood. Yes, it's solely due to a 10" to 10.5" vacuum at idle (it's not a FE but a hot 351W) with a hydro roller cam. Can't really make power boosted brakes work with such little vacuum unless one uses a.) an electric vac pump b.) hydroboost c.) a reserve cannister.

http://www.autoanything.com/brakes/69A3151A0A0.aspx

And yes, I did envision a hydro-boost set-up like some late model Fords but found it too expensive and I had already dumped my OEM P/S setup for manual steering....a great way to get true road feel in older Stang's. 

I like the 'tip-in' btw of my power-assisted 4-wheel disc setup as it allows rapid deceleration with a light-to-medium foot on the brake.  With no power booster at all, I felt the car would not decelerate from speed quite as quickly unless I hit the brakes harder....at least harder than I wanted to. 

Guys,
Great brake info but I've noticed no one talks about power assist... Is it because of the lack of vacuum at idle from the cams you're using? 
Thanks,
Bruce

[machoneman]

The only link I have is from Raybesto's catalog as follows:

Re: 7/8" Bore Master Cylinder - OEM Applications?

--------------------------------------------------------------------------------

Raybestos # MC39037 (RH) cast iron 7/8 bore 78-81 Ford Fairmont,Granada,Futura,Zephyer(Merc)

Raybestos #MC39531 (RH) alum 21mm 81-86 Tbird, 82-86 Mustang, 83-86 Marquis (Merc)

Raybestos #MC 39310 (RH) cast iron 7/8 bore 81-83 Escort, Explorer, lynx, Mark VII (Linc)

Would there happen to be an off the shelf Ford 7/8" MS for disc/disc that would have the appropriately deep hole for the pushrod to the pedal?  The Wilwood unit is nice...but it's also $200.  I'm always trying to use OEM parts when possible because I have this chronic fear of having a problem out on the road and a specialty MS may require specialty parts if it goes bad on the road.

[GJCAT427]

The frts on mine are stock mustang 10" I think? And the rears are 11" markV linclons. I don`t run a booster because of the 427 -"B" cam. Not enough vacum. The system I built  does stop and at times feels like power. Thats the nature of discs. Last 3 family cars all had power 4 wheel discs and I really like them. I do run SST braided lines and no problems.

[fe66comet]

Napa # M2036 made for four wheel disk, bolts on direct,no linkage mods and costs less than the rod kit for the SSBC.

[drdano]

That looks like a winner Jon, is it 7/8" bore?

[GJCAT427]

That looks exactly like the vette master I used. I didn`t use that rod but used the stock rod in my applacation.

[afret]

That one looks like a Ford drum/drum MC.  A Vette manual MC that is used often for disc brake conversions looks like the one in the link:

http://www.ebay.com/itm/1-Bore-GM-Corvette-type-Manual-Master-Cylinder-Hot-rat-rod-T-Bucket-1932-ford-/160974451393?pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr&hash=item257ad332c1

[fe66comet]

Yes it is for a 68 wagon with four wheel disk and a  428. Should be plenty...Jon

[drdano]

Napa # M2036 made for four wheel disk, bolts on direct,no linkage mods and costs less than the rod kit for the SSBC.

I called my local NAPA and they told me that is a 1" bore, so I'll probably skip that one.  Thanks for the heads up.