Ok so I've had this problem for a while. I swapped to disks in the rear of my '79 F-250. Originally had a soft pedal. Added an adj. Prop. valve and it helped a bit but it is still soft. I have definetly properly bled the system. I am still running the stock M/C. What do you guys suggest I do to get a better pedal? Different M/C? Which one? The truck came stock with a Dana 60 front also. thanks

Have you replaced your 25 year old vacuum booster? Maybe it's worn out.
A common swap when upgrading your braking system is to use a 1 ton M/C
and vacuum booster; i.e., F-350 stuff, or so I've read.

edit: some search info for ya
here (http://www.pirate4x4.com/forum/search.php?searchid=805905)

I would think the booster would be fine because it was fine before the swap, also I think with a factory dana 60 up front I am already running a one ton master?

No, the F-250 master cylinder is different. My F-250 is virtually identical to what you have....came with front/rear 60's.

The F-250 uses a fairly large single diaphram booster. The F-350's use a smaller (9" maybe?) dual diaphram booster. I have also heard that this booster provides a significant improvement.....but I've never used one. I believe that you have to change master cylinders if you go to the other booster, which is not a big deal. They're all about $20. If I ever have to replace my booster, I plan on trying the F-350 unit.

I'm interested in this topic in regards to the F-350 booster.

Anyone have any real world experience with one? Is it a significant inprovement?

How are your lines ran?
You may need to add a 2lbs residul pressure valve.

i just looked on the autozone site and it says that the M/C for a 79 F-350 is the same a a 79 F-250 with dual piston calipers? I dont know what to do I have been living with it for a while. I was thinking of just changing the M/C because of its age alone maybe that could be it? Also When I get some time, I think I'm going to bypass the stock proportioning valve and run the bigger resevoir of the M/C directly to the fronts, and the smaller to the rear incorporating the adj. prop. valve.? what do you all think about that? Also, what about using a M/C off of a late 70's lincoln with all disc brakes? or would that piston diameter be too small? help please!

i know that the mc's off the lincoln's (as well as the rear c-brackets, and calipers are the same as the early 80 front disc brake parts) are the same as the mc's on the 80-86 ford 1/2 tons in terms of bolting it up to the brake booster (i've done this to my 82 flareside). Here's a picture of what the lincoln mc looks like along with the p-valve as well (front resvior is for the rear brakes and the back is for the front brakes, i'm running an adjustable wilwood p-valve after the lincoln one)

http://www.ford-trucks.com/user_gallery/tmp/586/58630.520.390

Question for ya, did you remove the check vavle in the MC when you did the disk swap? It's located inside the rear line port on the MC. It's suposed to be a 10# check valve to ballance out the drum spring tension, I'm wondering if that may be adding to the problems.............anyways, here's a cool link to help with brake problems maybe it'll help you.

http://www.mpbrakes.com/troubleshooting.htm

i went to the mpbrakes site and read what they had to say. I am thinking that I am just going to bypass the stock Prop. valve totally. run straight from the master to the front and then from the master to the adj. prop. valve then to the back. so then I know I am gettin full pressure front and rear. Then I will work from there. What do u all think?

Discs will give you a slightly lower pedal feel vs. Drums. You already have the F-250 MC with the 1 1/16" bore so I would guess that would be enough for any rear caliper. Oh yeah are you running Caddy calipers? Those are notorious for having slop in them and never working right. Do a search on them if you do because they never work right.

You could upgrade to an early 70's F-250 camper special to get the larger MC and that might fix it. That would be a 1 1/4 MC. Here's the link for it:

http://www.wsu.edu:8080/~i6735189/discbrakeconversion.htm

I am using '75 k20 front calipers (no ebrake). So if I upgrade to an early 70's camper special i would get more fluid flow correst? Is it a direct bolt in?

Should be. I would make sure the ports are on the same side as your existing M/C.

Discs will give you a slightly lower pedal feel vs. Drums. You already have the F-250 MC with the 1 1/16" bore so I would guess that would be enough for any rear caliper. Oh yeah are you running Caddy calipers? Those are notorious for having slop in them and never working right. Do a search on them if you do because they never work right.

You could upgrade to an early 70's F-250 camper special to get the larger MC and that might fix it. That would be a 1 1/4 MC. Here's the link for it:

http://www.wsu.edu:8080/~i6735189/discbrakeconversion.htm

Can't get that link to work, but 1-1/4 is a huge MC. I've used an 86 SVO MC (1-1/8 bore), it also bolts up directly in place of F150-F350 4X4 MC's (fittings are exactly the same as 1/2 ton, but different than 3/4-1 ton). The upgraded F250/350 MC came on 2WD's only. That is the one that has the dual diaphr, small dia booster. It requires a matching MC, as the bolt pattern is different than the 4X4's. I'm not sure of the bore on the 2WD MC, assume it is also 1-1/16 bore. Also, 78 and 79 had different linkages on the back side of booster, so get it year specific if you are going with 2WD F250/350 stuff. One more option which requires a bit of work is using a 93 F350 booster with SVO MC. Requires 79 brake linkage and custom firewall brackets. It is a hell of an upgrade over anything made in the 70's short of hydraboost.

i just looked on the autozone site and it says that the M/C for a 79 F-350 is the same a a 79 F-250 with dual piston calipers? I dont know what to do I have been living with it for a while. I was thinking of just changing the M/C because of its age alone maybe that could be it? Also When I get some time, I think I'm going to bypass the stock proportioning valve and run the bigger resevoir of the M/C directly to the fronts, and the smaller to the rear incorporating the adj. prop. valve.? what do you all think about that? Also, what about using a M/C off of a late 70's lincoln with all disc brakes? or would that piston diameter be too small? help please!
I think the stock proportioning valve is the problem. I used a 78 F350 booster/MC in my 78 Bronco when I did the rear disc brakes and plumbed it like you're thinking to do here direct to the fronts and adjustable prop. valve to the rears and it has worked great for a couple years now. It should be an easy fix. Good luck.