Brake pedal randomly travels 2x as much

Yeah after the pre mature bendix shoe wear......
I went back in with a vengeance...

new shoes from mcgeorge...

and whole new adjustment system I ordered from napa...
spring set from advance....
new asin cylinder on one side.....and oem rebuild kit on the other cylinder....

think I replaced the brake lever in there too for shits and giggles....

Cleaned and chassis painted the dust cover inside and out when I had it all apart......VHT epoxy....

Fluid filmed the outer drum....



Yeah on a pickup....you should have best tires, brakes, LBJ's you can get....
deck is already stacked against us.....

 

First change brake fluid and include the 5th bleeder in the rear called the brake proportioning valve.
many people never even know this exists. It may be malfunctioning as well.

Make sure all the old fluid is flushed out. Start by turkey basting the master and then refilling.
That should raise pedal and end issue. Make sure when your down there to inspect
all calipers, brakes lines and check if rear wheels rotate nicely when jacked one at a time.
If you can safely raise both rears together, then while they are up and fronts are well chocked,
try using emer. brake to stop rear brakes when both rear wheels are raised and engine going slowly
at around 15 mph. Beware- this is useful test but must be done carefully. Once tested- re-check rears and make sure
rear wheels rotate. You can also, if you suspect rear wheel catching, touch the outer rims after a drive.

Once this is done, if your brakes are still acting up, raise and remove each rear tire and start digging.
Minimally brake cleener off and inspect brakes carefully.
This is a closed system and is not rocket science. Many useful videos on brake maintenance out there on youtube.
Do not rebuild brakes until these simpler cheaper tests are done. I would also consider not driving this until issue is resolved.