Disc brake conversion

[mrtexas]

Originally Posted by basel

I just ordered the basic kit from ECI for my 1939 ford pickup. They told I can't use my original wheels any more with this conversion. Can any one please tell me what wheels I should be using. I have 5 1/2 lug pattern. Is it a newer ford model wheel?
thanks.

40 wheels work

[mrtexas]

Originally Posted by luvmyclassics

I want to convert to front and rear disc brakes on my 51 f1. I am thinking of using the Speedway kit for the fronts and I am searching for a kit for the rears. Any help or suggestions is greatly appreciated.

For rear discs you need a modern rear end, say Ford 8 or 9 inch.

[Old Ford Addict]

Rears are not necessary but a setup for the rear is easily fabricated if you have even basic skills.

Speedway doesn’t offer a kit for 5 on 5 ½ bolt pattern as far as I know.

[basel]

Thanks . 51 merc

[36tbird]

It has been a long time since I did the press fit of the bearing adapter but I remember I used a different technique, spindles in the freezer for a day, adapter slightly warm, pipe and BFH used as required.

Be aware that discs kits on the front usually move the wheel out about 1" per side. Could cause some interference on lowered front ends.

Rear discs are a waste of time and the associated emergency brake adjustment is a major PIA.

I get into a lot of arguments with my friends over this, so some should stand by to get pissed off. You want your front brakes to do 75% of the work. Therefore a proportioning valve is necessary no matter if you have discs or drums in the rear. If you look at new cars, the front discs are larger diameter (bigger moment lever) than the rears and that is how the 75% ratio is engineered in. But, aftermarket kits are usually all the same size so a proportioning or ratio valve is needed.

Drum brakes require less pressure than disc brakes because they are "self energizing", the shoes expand and get twisted into the anchor bolts or each other, depending on design, and a mechanical advantage results. Therefore in a disc/drum combo if you put the same pressure into the front or back, the rear brakes will lock up sooner. You need a proportioning valve to reduce the pressure to the rear drums.

Now having typed out the diatribe let me say that I am not an engineer but a guy who did a technical paper on disc brakes back in college when dinosaurs roamed the earth. FWIW.

I'll leave it to someone else to point out why residual pressure valves are different but also a good idea to incorporate into your old Ford brake system.

[Pete]

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"Therefore a proportioning valve is necessary no matter if you have discs or drums in the rear. If you look at new cars, the front discs are larger diameter (bigger moment lever) than the rears and that is how the 75% ratio is engineered in. But, aftermarket kits are usually all the same size so a proportioning or ratio valve is needed."

Not necessarily. The Wilwood pedal assembly has a mechanical proportioning system built in. You can change the front rear bias in less than a minute.

[bobH]

Why do we want disc brakes? Not trying to be a smart a**, just wondering what a good reason is.
And, if we do want them, why on the rear? Seems like a waste, except if you have something like a 9-inch. Then they become a 'safety feature', because they hold the wheel, tire, axle 'IN', when (not if) the axle bearing fails, and the axle and wheel assembly wants to take off down the bank. (Been there, done that)
I haven't seen mention of a power booster. When adding disc's to an early Ford, is it generally accepted that a power booster be added, or not necessary?
(Reason for asking, I have one factory produced vehicle that has front disc's, drum rears, and NO factory power booster. It takes a LOT of pedal force.)
Thanks for a good thread.

[41PICUP]

ECI, talk to Ralph, he has the answer to your questions.
Have their disc brakes on my 41 pickup, no power booster.
Lincoln brakes on original rear end. eleven in F-150 rotors
no proportioning valve. Works great, stops on a dime.

[36tbird]

Yo 41, it never rains in So. Cal, right? And if it does or you run down the road and come upon a fire hydrant flooding the street with kids running out to play in the water and you do a panic stop, are you gonna swap ends? The way you test or adjust prop. valves is to find some place dusty or slippery (loose traction) to see how the rig stops then.

And Pete, the Wilwood has a "mechanical proportioning system built in" but it's still a prop. valve, right?

Don't take my questions as being ornery or confrontational. Just asking.

Size of the master cylinder piston determines power assist needed or not. I have 4 wheel discs on my '36 pickup with 15/16" m/c piston. It does the job fine. My regrets have been the e'brake adjustment and in hindsight to other old cars I have upgraded, the rear discs are not worth the effort.

[gmc1941]

Another problem with the rear disc is what are going to use for a emergency brake. Calipers can be a pain in the ass. With rear shoes theirs no problem installing and bleeding

[Pete]

"And Pete, the Wilwood has a "mechanical proportioning system built in" but it's still a prop. valve, right?"

Roger on that and it really works keen. Does the same job as a valve but without the extra plumbing. Saves a couple of pounds which is important in race cars.

[Pete]

Originally Posted by gmc1941

Another problem with the rear disc is what are going to use for a emergency brake. Calipers can be a pain in the ass. With rear shoes theirs no problem installing and bleeding

If you use Wilwood's they have a mechanical single puck calipers that bolt right on and use the stock cables.

By the way, I don't work for Wilwood but I use their stuff on most brake conversions because it bolts on with NO machine work or mods required.