What did Selby do for the 2 1/2" brake upgrade?

[Pcunder]

Years ago, I did this on my 66 GT fastback (drums/shoes & Fairlane wagon backing plates) & it worked out well. I did nothing with rear wheel cylinders, master cyl or K-H disc prop valve and track time at Hallett seemed AOK. Is the OEM 65/66 K-H prop valve adjustable?

Now, 20 yrs later, I want to do it on my 70 Boss but am I leaving anything out?
In '65, did Mr Shelby do anything other than what I did 1st time around?
Was the R-model solution any different than the street cars?

I'm about to spring for a set of 2 1/2" backing plates and need to know what else is needed to be accurate or what's recommended as an improvement. (Already have 2.5" drums/shoes)
I.e. Cobra Automotive puts bigger wheel cylinders in their kits...seems like that would change the bias rearward a bit. Maybe THAT is a good thing.

Thanks guys...!

Phil

[papa scoops]

why not just put disc on it? ford offered a rear disc kit for the boss. phred

[Bob Gaines]

Years ago, I did this on my 66 GT fastback (drums/shoes & Fairlane wagon backing plates) & it worked out well. I did nothing with rear wheel cylinders, master cyl or K-H disc prop valve and track time at Hallett seemed AOK. Is the OEM 65/66 K-H prop valve adjustable?

Now, 20 yrs later, I want to do it on my 70 Boss but am I leaving anything out?
In '65, did Mr Shelby do anything other than what I did 1st time around?
Was the R-model solution any different than the street cars?

I'm about to spring for a set of 2 1/2" backing plates and need to know what else is needed to be accurate or what's recommended as an improvement. (Already have 2.5" drums/shoes)
I.e. Cobra Automotive puts bigger wheel cylinders in their kits...seems like that would change the bias rearward a bit. Maybe THAT is a good thing.

Thanks guys...!

Phil

Yes the 65/66 proportioning valve is adjustable.It was adjusted different for the GT350 rear brakes compared to the stock Mustang. Initially they were not but later into 65 production Shelby found it was needed started to have Ford install a pre adjusted proportioning valve . Evidence suggest that this special adjusted valve was identified by it being painted black .The slightly bigger wheel cylinders for the 2 1/2 brakes changes the bias which is why it was adjusted differently. Unfortunately the 67-up system is not adjustable. You will have to install a adjustable valve in place of the cylinder shaped valve used for 67-70. You could use a 65/66 valve but it makes more sense to install a after market version with a easy to adjust knob.

[Bob Gaines]

why not just put disc on it? ford offered a rear disc kit for the boss. phred

Don't let Phred intimidate you  . He's right Discs are ultimately better  (used in Trans AM 68-70 Mustang ,Shelby and Boss)but the big drums are more then enough for the street and even used on many vintage race applications (ask Cobra Automotive) . PLUS less expensive and easier to install.

[shelbydoug]

The ultimate value of rear discs is if you are constantly coming down from 150 or so. On the street, they are a major pain in the butt and 50/50 whether they are worth the agrivation.

Ask me. I have them. They look cool though.


I had the big drums on the car before. The parking brake is much easier to get to work right with them.

[Pcunder]

Phred/Doug, I doubt my '70 will ever see competitive track time, but I do love those parade laps. I bought it from the original owner and want to keep it close to period correct. I also want my parking brakes to work.
Now my 69 Boss will be more of a resto-mod so discs all around will likely be one of the primary upgrades. I DO want it to look cool and I WILL test it enough to know how the bias operates in extreme conditions.... I just want it to be close to 'as-designed' after the Shelby upgrade.

Bob, Good info on the details. The 69 with discs uses that cylindrical prop valve but the 70s eliminated that, somehow... So the rear wheel cylinders WERE upgraded to boost rear brake bias...to what size?
The '75 MPC say originals were 29/32...same as the 70 B2. 

The MPC also lists a different prop valve for 65/66 Mustang w/disks vs 65/66 Shelbys. C5ZZ vs C5ZX. Very cool. I did not know that. So they are both adjustable and Mustangs had a factory setting preset/pre-adjusted...but Shelby had his crew do their own adjustments initially then Ford made a special part (and C5ZX part #) that was pre-adjusted (painted black) to accommodate the bigger drums (and quality control)...?

[shelbydoug]

I have the '65 adjustable proportion valve on my '68. My opinion is that you really don't need it. I think it was added just because the '65 was initially going to be the "race car" and it MIGHT be needed IF you were going to use race slicks?

If anything, what it does is REDUCE the amount of pressure to the rear to reduce rear lockup.

That is kind of the reason the 715 Holley was also. They wanted the largest possible carb homologated for racing purposes. In reality it is way to big for a street 289 and actually hurts 0-60 times. The original source for that carb is a Ford 427. There it is just about right.

Considering the Holley 2x4 was raced on the Trans Am cars, why that set up wasn't included as standard like on the '67 GT500 TO ME raises questions simply because with the vacuum secondaries, it runs so well even on a 289, with better 0-60 times.  Maybe just cost?

I don't see where cost was much of a factor to homologate anything then?

[Bob Gaines]

Phred/Doug, I doubt my '70 will ever see competitive track time, but I do love those parade laps. I bought it from the original owner and want to keep it close to period correct. I also want my parking brakes to work.
Now my 69 Boss will be more of a resto-mod so discs all around will likely be one of the primary upgrades. I DO want it to look cool and I WILL test it enough to know how the bias operates in extreme conditions.... I just want it to be close to 'as-designed' after the Shelby upgrade.

Bob, Good info on the details. The 69 with discs uses that cylindrical prop valve but the 70s eliminated that, somehow... So the rear wheel cylinders WERE upgraded to boost rear brake bias...to what size?
The '75 MPC say originals were 29/32...same as the 70 B2. 

The MPC also lists a different prop valve for 65/66 Mustang w/disks vs 65/66 Shelbys. C5ZZ vs C5ZX. Very cool. I did not know that. So they are both adjustable and Mustangs had a factory setting preset/pre-adjusted...but Shelby had his crew do their own adjustments initially then Ford made a special part (and C5ZX part #) that was pre-adjusted (painted black) to accommodate the bigger drums (and quality control)...?

The only difference between the C5ZZ vs the C5ZX proportioning valve is the initial adjustment(done at KH before being sent to Ford). All internals and externals are identical. That only leaves the adjustment as different. FYI the same KH proportioning valve was used on early Corvettes as well.

[J_Speegle]

The only difference between the C5ZZ vs the C5ZX proportioning valve is the initial adjustment(done at KH before being sent to Ford). All internals and externals are identical. That only leaves the adjustment as different. FYI the same KH proportioning valve was used on early Corvettes as well.

Also other Ford products like the T-Birds

[Cobrask8]

I did the larger drum brakes on my 69 428, but used the F-150 parts, almost the same. But, also added larger front discs from an early 60's Ford, so had to use 15" wheels.

My point is that with larger wheel cylinders and calipers, the fluid pressures and surface areas change, so if there is a big enough change on the wheel end, then there needs to be an matching change in the master cylinder. There is a calculation out there to derive the proper needed M/C to match the changed parts. In my 69, I actually found the Master cylinder from a F600 dump truck provided the perfect needed M/C piston size to match the larger components replaced. I also took out the frozen prop valve, and put in a newer one from a Maverick. That combo worked fantastic, and car car stopped very hard and true.

[shelbydoug]

I did the larger drum brakes on my 69 428, but used the F-150 parts, almost the same. But, also added larger front discs from an early 60's Ford, so had to use 15" wheels.

My point is that with larger wheel cylinders and calipers, the fluid pressures and surface areas change, so if there is a big enough change on the wheel end, then there needs to be an matching change in the master cylinder. There is a calculation out there to derive the proper needed M/C to match the changed parts. In my 69, I actually found the Master cylinder from a F600 dump truck provided the perfect needed M/C piston size to match the larger components replaced. I also took out the frozen prop valve, and put in a newer one from a Maverick. That combo worked fantastic, and car car stopped very hard and true.

I used the 15" station wagon drums with the big cooling fins. It fit right on.

The proportioning valve I got across the counter and it was not painted black.

At first I ran manual brakes that used a 1-3/16" id diameter master. It worked fine. At a later time after I went back to the 302 I put the power brakes back in. The car didn't like it and I could hardly move the brake pedal.

It currently has a 1-1/16" generic with power brakes, the 67 T/A version of the front discs and a 78 Versalles rear with discs.

In the typical "auto cross" tech inspection test, you can't lock up the rear at all even if you stand on it. It does stop straight and true BUT that there is a little tricky because there are things needed on the springs to prevent diving.

The bottom line, is all the parts are there but even changing tires will change the proportioning set up. The original setup really is for the original tires.

If you mess with those, you need to play with the balancing again so worrying about "the factory" set up is not a waste of time, it's just a start. You give this all to the "pit crew" to work out and you just jump in and drive it.

[Bob Gaines]

Aftermarket proportioning valves with adjustable knobs can be located under the (unseen) or in the passenger compartment (vintage race car)for easy adjustment of brake bias on the fly. There are any number of different brands and kinds. https://www.summitracing.com/parts/wil-260-8419   .

[Pcunder]

Lots of good feedback from guys that have been there, done that...just what I was looking for.

I think I'll save this upgrade for my 69 as its got the separate Prop valve. I can slave in an adjustable unit or a pricey '65/66 K-H unit..!!!

Attached is a snip-it from the '75 Ford MPC showing the 5 different "Pressure Control Valves" that Ford cataloged...

65/66; Mustang, Shelby, T-bird, Galaxie (66)
67/69; Mustang, Fairlane/Torino, Falcon, Galaxie, T-bird

Thanks guys!!!

Phil

[shelbydoug]

If you are not a stickler for a "period correct" car, I'd recommend what Bob Gaines suggested.

Ford Motorsports/Racing was selling one with their decal on it. It looks like a repackaged Tilton unit.

They are simple and more practical then the originals.

[98SVT - was 06GT]

Also other Ford products like the T-Birds

Tbird also had the larger 4 piston calipers. They will mount easily if you also get the adapters (which someone is remaking in aluminum).