I'm almost done coverting my '68 M100 2wd manual drum brakes, to power disk brakes from a '79 F150 2wd. Everything went relatively smooth. My problem is that the '68 brake pedal assembly does not match up to the '79 master cylinder push rod under the dash. The rod is about 2" too short to meet up with my pedal. I have a '78 that I pulled the pedal mounting bracket out of, but it won't fit under the dash of my '68. I read the article in this forum about doing the disk brake conversion, but it doesn't mention about converting to POWER disk brakes. I was going to cut/lengthen the '79 master cylinder push rod to match up with my pedal, but I thought I'd better check here first. I'm hoping there is a simple solution, but could somebody please point me in the right direction. Once this is done, the MERC will finally be mobile. Thanks in advance from way up North.

 

I dont think you needed to use the pedal assembly from the donar truck, when I converted mine over i just found a brake booster from anther 72 truck and bolted it in. But now that you have every thing done I would weld a pice of round stock to the rod to make it the right lenth.

 

In the disk brake conversion article in this forum, I read something about adjusting the length of the master cylinder push rod. Is this possible? How?

 

Have seen the article, but does it say anything about changeing the portioning valve? Just curious

 

I Put 1977 Power Set Up On Mine.booster Bracket Has The Rod And Bolts Right To Pedal. I Had It Bolted To My 1968 Pedal . But Changed The Pedal To The 1977 Pedal I Would Say No Diffrents In Pedals.

 

Just Reread Your Question Do You Have A Bracket Between Booster And Firewall. Because Your Booster Bolts To A Arm On The Bracket And The Arm Bolts To Brake Pedal. Also The Rod Between Master Cylinder And Power Booster Some Are Not Adjustable.the Adjustible Ones Have A Screwed On Tip That Can Be Turded To Make Them Longer Or Shorter. Hope This Helps.

 

This is interesting, I am about to undergo the same thing on my '68. I did the same thing on my '69, but the booster I used put the pedal farther out than it was original. It doesn't really apply to me though, I have power drums and am putting on discs off of a manual disc F150. I am going to keep the power, I will remove the check ball from the maser cylinder to allow the calipers to function properly. I am not sure what else will be an issue. Hopefully it doesn't need much else.

 

I just went back and read the brake conversion articles.

68murc, you need a brake pedal from a doner truck with power brakes.Pedal is different.

Wyndell1970, yes the proportioning valve is different between drum and disc.

scottfreeman, I'd take a look at the master cylinder before you remove the check valve.The reservoirs on a drum brake master are about the same size, on a disc master the reservoir for the front brakes is much larger than the one for the rears.Disc brakes have much larger pistons than drums and require a larger volume of fluid.

Hope this helps.

 

I cut the push rod off of my old manual drum brake master cylinder, and welded it to the end of the push rod on the new power disk brake master cylinder. I got it the right length. I bled the brakes and went for a ride. The pedal travels too far before the brakes work. It moved 5-6", kind of softly, then all the brakes you could ever want. I almost kissed the windshield! I adjusted the rear brakes until I could just hear the drums touching the shoes as the drums turn. Now the pedal moves 4-5" before the brakes grab. The brakes do work, but the pedal moves too far. I'm used to about 2" of pedal travel. I do have the '79 proportioning valve installed. Is there sometning I missed? Why so much travel? Are you supposed to have the engine running to bleed power brakes? Thanks in advance from way up North.

 

I'd check the rod at the master cylinder side of the booster.As bmuhlbach said some of these are adjustable in length.If you extend the rod it would shorten the pedal travel.Be careful doing this though.If the rod is too long and the cylinder can't return the whole way the brakes will drag.On brake bleeding, I've bled them both running and shut off.Other than more pedal effort it never seemed to make any difference.Hope this helps.

 

I was just glad to have the booster, I can swap a power disc master cylinder onto it if need be. My father probably has a few lying around.