I recently performed a disc brake conversion on my 1970 F-250 2x4. I got the information for the job off of this Web Site. The Conversion went rather well. Replaced all parts with new or rebuilt parts. Installed all new brake lines, and used the porportioning valve, and all front brake parts are from a "76 F-250 junker. On her maiden voyage I found that the truck stops very well, in fact a little too well. My rear brakes are lock-up happy. Only problem I can think of is my rear wheel cylinders are smaller than the '76's. I can't think of what the problem would be, any suggestions would be very appreciated.

 

J. the problem must be the rears. I have the same problem except I don't experence lockup. I have had to learn to feather the brake pedal, to keep my nose off the glass. The difference has to be in the rear brake size. I have spoken to others and was told that the braking would either be weak or strong. I only have to drive my other 66 (not coverted) to get the full respect of the power brakes. Those FE's run like a big cat, but stopping, even with all new parts is awful. I have another project started that I will use the rear axle from the 76 as well, but testing is a long ways away.

Did you replace the rear shoes or inspect them? You may have to drive the truck a little to get things to settle in.

John

 

Check the rear brakes for size of the shoe and drum, also check the size of the wheel cyl and type me back

Did the 76 donor truck have dual or single piston brakes in the front?

Type me back at deleontow and I will tell you what size drums and cyls you should have in the rear, I beleive the problem lies in the size of the wheel cyl, causing too much presure on the rear brakes, one other thought would be over adjusted rear brakes, though I don't think this is your problem. Let me know

Deleontow(No Email Addresses In Posts!)

Dave

 

The '76 F-250 had single piston calipers and was rated under 6200 Ibs. GVW. I checked at work today and the '76 had 2 or 2.5 inch width brake shoes. I don't know what size the'76 rear brakes were, the parts came out of a junk yard. The big Ford Truck dealer in town all agreed that the problem is probably my porportioning valve. The problem isn't so much that the rear brakes lock up early. The problem is that all my brakes grab to soon. Lets say I have 6 - 8 inches of brake peadal travel. We'll I could get all 4 wheels to lock up within 2 inches of travel. SO I'm not sure what the problem is. ANy help would be appreciated.

 

Just a thought as I have seen this before, are the lines to the master cylinder hooked up correctly? The rear brake line should go to the smaller resevoir on the master cylinder which is actually the resevoir on the front end of the master cylinder.
Like I said I saw this before and with the lines hooked up wrong the rear wheels locked everytime, it was really noticeable on wet roads.
Hope you figure it out.
Sparky

 

Hey JN...

you could try plumbing in the rear line, what's called a restriction valve, which merely cuts the line pressure going to the rear. These little inexpensive devices ($10) are abundantly available from aftermarket brake parts manufacturers (Tilton, Jamar, CNC, etc) through race car parts mail order firms. The reason they sell them is because they have no idea what kind of results a buyer is going to get from his/her project car--and this is a shortcut and inexpensive/painless way to fix just that.

Also, some manufacturers, like Tilton, make adjustable proportioning valves which are meant to
be installed in line to either the front or rear brakes. (the ones meant for only front or only rear brakes--you wouldn't need one for both) They're easy to plumb-in--(an adjustable restriction valve), but like anything that is made adjustable, they're more expensive (like 80-100 buckaroos) and even though they are meant for race cars (changing track conditions), they allow you ALOT more flexibility in what braking adjustments you want to make. There is a locking handle on top of the valve you adjust manually, in like six possible positions. It could be handy for someone who either makes alot of suspension modifications (or planning to do so in the near future) or say, someone who carries heavy loads from time to time.

CW

 

 

bringing back an ancient thread to ask a related question regarding brakes. Is there anyway to set up say the 67-72 F100 with 4 Wheel Disk Brakes???? and if not If I do the front conversion would it be pertinent to also swap the rear brake assembly from the donor vehicle aswell??? if it matters my 68 has Pwr Brakes from the factory

 

Yes there is,........but not with the same donor upgrade that we talk about here.

We are in debatable territory when we start talking 4 wheel discs. 4 wheel disc is available on the new trucks now, but it hasn't been long. I believe it has been said that 60% of the braking is done by the front and 4 wheel discs were not necessary.

For the guys that have to have them, I have seen mix and match kits offered on Ebay for years. I don't read the mags so there could be simpler kits offered now. Garbz prolly would know.

It was 68 when the rear drums were increased in size, and those coupled with front disc provided excellent stopping ability.

So yes there is but not a simple answer.

How can we help from here?


John

 

Thats a big part of what I wanted to know. it sounds like for the most part that converting the back to disks on the 68 would be both complicated and overkill. so the answer is obviously convert the front to disks and leave the back drums. But if I do that should I also ****** the donor trucks rear brake drums wheel cylinder and put them on the 68 to balance out the system????

 

court1100f in a word yes get the whole system if you can. the brakes were designed as a system so keeping the system together would provide the best increase in stoping power and as was posted earlier the rear brakes are larger on the later models.

as for me mine is gonna be cobbled together i have a 9" from a 79 LTD that has disks i am going to try and swap those onto my truck when i install my new front axle with disc brakes. the fun part is going to be remembering where all the pieces cam from when i go to get new parts.

 

The 68 has the larger rear drums that were used to 86 when the 9" was dropped, so there is no advantage to get more parts. IMHO

I don't advocate doing it, but I learned to tow when trailers had no brakes, and pull my big trailer with just the trucks brakes. There is a photo in my album with a 4X4 on the trailer that the total combined weight was about 10.5 and the truck stopped it ok.


John

 

lincoln mark V had a ford 9" with disc on the rear. its fairly popular swap for cars. Also the 9" is so popular that you can find disc kits out there for drag cars and buggys a like. The buggy guys that run 9" rears sometimes use 4wheel independent braking to help do digs.

I would love to put disc on the rear of all my trucks. Does it need it for stopping power, no. but disc brake systems are very simple, and a lot easier to work on.

The biggest thing you run into if you start monkeying with kits for rear disc is parking brake issues. A lot of those kits will use calipers that dont have a parking brake. You can purchase a separate caliper that is cable operated for a parking brake or you can use a hyd. line lock(not recommended).

 

Wow, this is the absolute oldest thread I have ever seen brought back.
The best way to go would be to do the front conversion except for the proportioning valve, keep your old distribution switch. Use an adjustable proportioning valve, and either an off the shelf kit from someone like SSBC, or custom brackets to mount Cadillac ElDorado rear calipers on the manufacturer's recommended rotors. When I get to this point on my 72 F100 4x4 project, I'll do another article on it.