1967 Disc Brake Conversion: Question on Master Cylinder

[colnago]

All,

This has probably been discussed before, but I can't find anything, so here goes ...

I have a '67 F250. I want to convert to front discs, and have most of the components (discs, calipers, proportioning valve, etc). The one thing I don't know about is the master cylinder. I'm not too worried about the valve that holds pressure in the line for drums (as I understand, they don't tend to use those anymore, and if they did, I should be able to remove it). I'm more concerned with the bore and stroke of the piston in the MC itself being the right size for a disc/drum combo.

I know '67 is a "special" year for the brake pedal and MC. Would a regular '67 MC for drum/drum work, or should I go with a newer MC for disc/drum? If I go newer, what will I have to do to make it work in my '67? I've heard that some master cylinders come with an adjustable rod; do I need one of these? Where do I get one?

Thanks for any pointers,

Joseph

[ultraranger]

You can get away with running a disc/drum MC on a drum/drum brake system but it's never a good idea to run a drum/drum MC, with equal sized reservoirs, on a disc/drum system.

A disc/drum MC is designed with a larger primary bowl to provide the extra fluid reserve the calipers will need when the pads and the surfaces of the rotors wear down. Extra fluid volume has to be pulled from the MC to put more brake fluid in the calipers, as the caliper pistons move outward to compensate for the pad/rotor wear. Typical drum/drum MCs don't have this added fluid reserve capacity to support disc brake calipers, after the pads/rotors wear down.

To get the full potential out of the added disc brakes, it would be best to run a brake booster. Drums are self-energizing, discs are not. To get around the odd-ball nature of the '67 brake MC/brake pedal/pedal hanger situation, you would probably be better off to pull the pedal/pedal hanger from a '68-'72 F100-F350 donor truck.

This would allow you to run any '68-'72 Bumpside booster as well as many of the Dentside brake boosters --like the '75 F350 dual diaphragm booster I have in my '69 F100.

[colnago]

Sounds like I need to spend some "quality time" in the local junk yards this weekend.

My local pickings are slim. Do I need to stick with the 68 - 72 years for the brake pedal setup, or can I go with something from a dent side? If I can't find a brake setup from a newer truck, can I put a disc/drum MC onto my '67 booster? Or will the output rod from my booster be the wrong length for a later-style MC?

Joseph

[ultraranger]

Sounds like I need to spend some "quality time" in the local junk yards this weekend.

My local pickings are slim. Do I need to stick with the 68 - 72 years for the brake pedal setup, or can I go with something from a dent side? If I can't find a brake setup from a newer truck, can I put a disc/drum MC onto my '67 booster? Or will the output rod from my booster be the wrong length for a later-style MC?

Joseph

Dentside pedal hangers won't easily swap over into a Bumpside. Bumpsides had one type of brake pedal (from '68-'72) and one type of clutch pedal. The Dentsides had something like 22 different brake pedal engineering numbers on them. If you get the pedal(s) and the pedal hanger from a '68-'72, you will be in good shape to run most any brake booster from '68-'77. Some major changes were made in '78/'79 that could make their boosters potentially less compatible.

I have a dual diaphragm booster in my '69 F100 but I would definitely run a dual diaphragm booster if I had an F250/F350.

....I'm guessing your disc brake parts are from a Bumpside or Dentside F250?

http://www.fordification.com/tech/clutc ... ackets.htm

[colnago]

....I'm guessing your disc brake parts are from a Bumpside or Dentside F250?

At this point, I don't remember where I got everything. As I recall, disc/brackets were from a Bump F350 (junk yard), proportioning valve from something post-Dent (different junk yard), pedal/booster/MC from a '67 (stock or rebuilt from AutoZone). It looks like my stock spindles will take the discs. I plan to run new lines to everything, and rebuild my rear drums.

I think the only unknown is the MC. It looks like the drum/drum uses a 1" piston, and the disc/drum uses a 1-1/4"piston. So, I now know that I need a new MC. But I don't know why I can't use the '67 pedal with a post-67 MC. Can I use a '67 booster? Do I need a '68+ booster? Will it not work with a '67 pedal? If not, why not? Is the post too long? Can I use the post from my current booster? Can I use a '68 booster with an adjustable post?

Questions, questions, too many questions! I probably need to make an educated guess, and go for it! Learn on the fly!

Joseph

[ultraranger]

Does your '67 booster have a bellcrank (cantilever) bracket assembly on the firewall or, does the booster input rod connect straight from the brake pedal and directly to the back of the booster?

Do you have any photos of your booster assembly you could post here?

[colnago]

Well, I couldn't post a photo, because my phone resolution is too high. But basically, my booster bolts up to a set of those parallelogram-shaped brackets that holds it about 3" from the firewall, and drops it about 1" or so. The booster is connected to the brake pedal lever by a straight pushrod. The brake light switch is mounted at the point where the brake lever and the pushrod connect.

The stock booster has a single diaphragm, by the way. Not sure what I would have to do to integrate a dual-diaphragm booster.

I decided to try a '67 booster with a '68 MC that's designed for a disc/drum configuration. If I don’t get it right, I can try swapping in something else. But I think I can adjust the booster pushrod to conform to the MC, even if the years don't match. It will take a few days for parts to come in, so I'm hoping that I can rebuild the rear brakes this weekend, then tackle the disc conversion next week. Since I have time, keep the advice coming.

Joseph

[ultraranger]

I haven't seen a '67 Bumpside power brake setup, first hand so, I don't know if the bellcrank firewall brackets are the same as a Dentside bellcrank bracket assembly.

By your description, it sounds like your brackets drops the booster down some, but without actually being able to see the '67 bracket/booster setup, it's hard to say for sure. The Dentside bellcrank brackets raises the booster (raises the booster approximately 3" higher than other boosters not mounted on a bellcrank assembly).

I know the '67 booster has a short input rod. I also know there was a short input rod dual diaphragm bellcrank booster used on the '77-'79 F350 trucks with a 460 engine --up to serial number DJ0,001.

If you wanted to experiment with seeing if this dual diaphragm booster would bolt up to your brackets, you could order the booster from O'Reilly Auto Parts to see if the (4) mounting studs on the back of the booster will line up with the holes in your existing brackets and you could see if the dual diaphragm booster short input rod is the same length as the rod on your single diaphragm booster.

If the dual diaphragm booster mounting stud pattern is the same and if the dual diaphragm booster input rod is the correct length, it would work with your brackets. --however, if it didn't work, you can simply return the booster for a refund and not be out of any money on it.

The '77-'79 F350 (w/460 engine) dual diaphragm bellcrank booster is O'Reilly part number 54-73311.

http://m.oreillyauto.com/mt/www.oreilly ... &ppt=C0066