Well I have finished my brake job on the M51, had a learning curve with it, thought would tell my side of it.
To start with I was losing brake fluid, having to watch the level all the time . This is a old system with a single master cylinder. So as soon as the fluid drops out of the master you have NO BRAKES! I am working with the truck on my farm but am hauling up a hill. So super sketchy if they fail.
To start with replaced the two front cylinders, both were leaking, was still losing fluid so replaced the remaining 4. All were bad.
First had to brake the lug nuts free.
I know everyone else knows but I didn’t, the lug nuts on the right side have right hand threads , “righty tightly, lefty loosely “. The truck left side has left hand threads “ lefty tightly...... “
So if your slow like me standing on the pipe that is slid on the biggest breaker bar I have was not helping matters.
At least I didn’t brake a stud.
Once they were loose I jacked the axle and was careful not to let the tire fall over, and moved it out of the way.
Next unbolt the axle
That was pretty easy, once the bolts are out you can hit the top of the axle shaft to brake it free from the hub .
The axle should slide right out.
Now you have a couple of huge nuts to deal with, I had a pipe wrench just big enough, as you disassembled be careful of the order and orientation of nuts, lock washers seals and bearings.
I used a couple of tie down straps to support the hub because I didn’t need to take it all the way off. Then used a couple more straps to spread the shoes
Now your finally ready to remove the old cylinder.
when you reassemble be careful of the load on the bearing, not sure what it is supposed to be, I tightened the nut until it was tight to the bearing, then backed it off a quarter turn, it should not bind the bearing.
After you get the lock washer on the second nut you should get after, as that is what makes sure the wheel stays on the truck.
After l got all the cylinders replaced, I bled the brakes,
Was not happy with the level of the brake pedal, Tried bleed again, no help
Phoned a friend, he told me on old style drum brakes there is a cam nut to adjust the brakes,
Figured out not just one cam nut but TWO nuts per drum. They are at the 10 and 2 o’clock position on either side of the cylinder.
So had to jack to get the tire off the ground, then tighten the cam nut until it grabs the wheel, then back it off til it turns free.
Didn’t seem like I was doing much but when I was thru the brake pedal was spot on!
If you think about the physics of it makes since, one master with about 6 inches of travel, has to displace 6 cylinders with 2 pucks each that’s moving 12 pucks
anyway, that’s what I learned on this project.
