68 F-100 4x4 disc swap master cylinder?

[JoshT]

I believe that I've got all the parts to put disc brakes on the front of my 68 with the stock D44 axle. I'm doing the conversion that uses Chevy Calipers and Ford F-150 rotors. Also replacing all the hoses front & rear while I'm at it.

I know that some people have sucessfully used a the stock Drum/Drum master by removing some valve or restrictor in in the rear brake port. I considered this, but the truck has been sitting for a long time and I'm not even sure what I currently have for a master cylinder and brake booster. I understand they are not original to the truck and were swapped in at some point, but I don't have any idea what components were used.

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I just realized that a leaf was blocking part of that last shot, but hopefully it still shows enough.

Since I'm opening the system and will need to bleed brakes anyway, and because the truck has been sitting for so long, I want to go ahead and replace the master cylinder and add a proportioning/combination valve.

What parts do I need to order, or what do I need to order them for?

[DuckRyder]

That looks like the booster and MC on my 1972.

[cep62]

When I put discs on my '71 I believe I used a '78 master cylinder .
Mine aren't power .

[sargentrs]

Bronco Graveyard has the prop valve.
https://shop.broncograveyard.com/mobile ... nfo/12564/
They also have a complete kit including M/C, booster, prop valve, etc for $409. Not a bad price when you start adding up the individual parts.

[Ranchero50]

I used one from a '94 F350 with the 1 1/8" bore on my '70 F350 to escape from the leaking iron one. Just needed to make up new lines and recycled the fittings from a salvaged MC. Best part is I should be able to get parts for another 20+ years unlike the 50 year old originals...



If you use the 1" bore I think you can get the Ranger / Explorer version with the lines coming out on the fender side for more clearance on a V8. Not an issue on the I6. Someday I'll even wire the low level connection to the brake warning lamp.

[JoshT]

Just a little update. Was going to try to use the existing master cylinder to get the truck back on the road and see how the brake upgrade responded to the 1" (I think) bore master.

Well after getting the brakes put back together I can't get them to bleed. Getting clear clean fluid on the passenger side no bubbles, driver side keeps getting bubbles. Getting absolutely no pedal. No leaks in the system. Probably just lots of air trapped in the system, but getting no where with the standard 2 person bleed method. I'm wandering if the master cylinder could also be part of the bleeding problem, and also not entirely sure if I trust after sitting for the last 10+ years (no idea how old it was before then).

With this in mind, I'm going ahead with replacing the master before continuing with attempting to bleed the system. I'll also be adding in a proportioning valve while the system is open. Will be using the GM/Universal style proportioning valve mounted on a bracket directly under the master cylinder. Could probably get by without, but I figure its better for peace of mind and a properly working brake system. It'll also make it easier to connect my current hard lines, set up for a left side port M/C, to the right side port M/C I'm considering.

I used one from a '94 F350 with the 1 1/8" bore on my '70 F350 to escape from the leaking iron one. Just needed to make up new lines and recycled the fittings from a salvaged MC. Best part is I should be able to get parts for another 20+ years unlike the 50 year old originals...



If you use the 1" bore I think you can get the Ranger / Explorer version with the lines coming out on the fender side for more clearance on a V8. Not an issue on the I6. Someday I'll even wire the low level connection to the brake warning lamp.

The calipers I'm using came from a 74 Blazer 4x4. Based on the info I can find (RockAuto) they were paired with a 1 1/8" bore master cylinder in the stock application. As such I think I'm going to get a F-350 master like you did. Now I've got to decide on which one.

85 F-350 Master Cylinder that is all cast and looks same as what one would expect to find in a 68 F-100.

-or-

94 F-350 Master Cylinder with plastic reservoir.

[JoshT]

I decided on the 85 F-350 master, probably for the wrong reasons.

A) I think cast iron master looks better in that engine bay.
B) My research lead me to believe cast iron master might be simple bolt on.

well...

A) It will look good in there, but it's a really stupid reason to select brake components.
B) My research was wrong, mount bolt spacing is wider on the 85 Master Cylinder than what the booster has. Aluminum might have fit better.


Mount holes weren't far off, but enough that it won't bolt on. Have to find a smaller bit for my die grinder tomorrow and I'll slot the holes in the master. Struck out checking Lowes and HD tonight. Will hit up Tractor Supply and Harbor freight tomorrow, or I'll go at it with a Dremel.

Should have more tomorrow!

[Ranchero50]

My cast iron one siphoned fluid out between the casting and the rubber seal on the lid. Took the paint off the inner fender, frame rails and was a PITA to keep topped off. That's the major reason I went aluminum with a plastic reservoir. Plus I wanted to be 20 year newer for parts replacement when this one fails. Sooner than later '70's parts will be obsoleted.

[JoshT]

Well the 10+ year old master that was on there still sealed up well enough. No external leaks, but I think internal seals had broken down.

Way I see it, if the master is going to leak, it's going to leak. Doesn't much matter if it is aluminum with a plastic reservoir, or cast iron. I'll be using the same style master you did on my 86 Ranger V8 swap that's getting 13" cobra brakes up front and explorer discs in the rear. I decided I liked the style of the cast iron master better for this truck.

The master I went with was used up to 86 on F-350. I think I've got a decade or two left before that one goes obsolete. If not I'll swap to a cast aluminum style when the need arises. Way I have things set up I'll just have to remake the short tubes between the master and proportioning valve.

Got the brake system wrapped up today. Felt like it took forever to get the master cylinder and proportioning valve bled, but once that was done, the rest went quick. It's possible I'll need to upgrade the booster to match the larger master cylinder bore, but won't know until I can test drive it.

[JoshT]

Figured I should update this for anyone reading in the future. After getting the truck back on the road the brakes seemed to work better than they did prior to parking the truck, but they still didn't work right. They'd slow the truck down and eventually stop it, but better hope no one decided to cut you off. Seemed that after the first bit of pedal travel it the pedal would get rock hard, it would probably stop harder if I had enough ass to push the pedal harder, but I'm @200 lbs and could nearly stand on the pedal with no effect. Can't say I was surprised, kinda figured something like that might happen after going to the larger bore master.

After a bit of reading I confirmed what I already knew. I needed a smaller bore master and/or a bigger brake booster. Sounded like a smaller bore master might work better, but that I'd probably still need a bigger booster to get full braking effect from it. Already have a new master cylinder so started with dual brake booster from a dentside F-350. That's exactly what it needed.

With the new booster backing the F-350 master cylinder I promptly blew out one of the 20+ year old rear wheel cylinders. After getting everything fixed, bled, and adjusted the truck stops better than it ever has. It'll lock up the brakes for the first time ever, or at least since dad put over size tires on the truck 30 years ago. If the brakes are capable of locking up you can't ask for much better, so I'm more than satisfied with the truck's brakes for now.