1988 Toy pickup, SR5, 22RE, 2WD, 465K

My brake pedal has been soft/low for several months after I replaced the brake booster last summer. If I had to depress the pedal hard to stop quickly, my big foot would touch the gas pedal, too. Not a good situation.
So, I am trying to adjust my brake booster rod.
Twice this week, I thought I had it right, as demonstrated by a short local drive. When I took to the highway, the brakes would start to drag after several miles to such an extent that the pickup would nearly stop while shifting gears. The front wheels were warm, and the pedal was very hard/high.
Each time, when I returned home and removed the master cylinder, the rod was "longer" than it was before my recent adjustment. After the first event, I had to remove the lock nut (0.200") to shorten the rod enough to match the MC measurement.
After the second event, the rod was about .040 longer.
When I rotate the rod 6-10 turns, the rod shortens about .020".

Do any of you have any idea what is happening here?
Should the rod be able to rotate freely?
Is the master cylinder misbehaving?

Thanks.
____________
I made a snap of the rear end of my brake booster rod . I might get a sharper snap soon.
What is happening here? It appears to me that a threaded brass segment has become loose and backed out.
Second attempt to upload snap of rod.



Is something coming loose here?. Thanks for looking.

 

link to pic isn't working.

there is a toyota sst measurement device for getting that brake booster rod set to the correct height, see the pdf in this thread, there are probably aftermarket substitutes: https://forum.ih8mud.com/threads/bra...sh-rod.809938/

 

Thanks.
Is it normal that the pin withdraws into the booster when the engine has been off for several hours, when the vacuum has depleted??
I have been fiddling with the pin adjustment for several days, on and off. I have the H tool and have viewed and read many instructions.
I think the problem that caused my brakes to lock is this: My pin shortens (retreat into the booster about 5mm) when the vacuum decrease. I probably set the pin when the booster vacuum was depleted, when the pin had retreated into the booster.
Now, I am running the engine briefly to increase the vacuum before I set the pin.
However, it seems I have to lengthen the pin about 1.0-1.5 mm to reduce the soft pedal, to shorten the pedal movement.
.I am wondering about vacuum leaks. I have replaced two vacuum hoses. The check valve is OK.

 

Is you brake pedal linkage adjusted properly? Make sure return spring is on. The pedal brackets are known to crack, seize up and the little nylon bushings wear out. The pin holes also get wallered out. More so the clutch, but might be worth looking at. Just to make sure it's not keeping pressure on your booster and master.

 

Blurry snap added above. The pedal linkage seems OK.
Checking for vacuum leaks today.
When I set the rod with the H tool, the pedal was soft and low, which I am trying to harden/raise.
When I extended the rod 1 mm, (one turn of the 6mm-1.0 screw) the pedal was still soft.

 

what i'm referring to is the pin height between the booster and the master, which is inaccessible after installation... are you talking about the brake pedal height adjustment?

 

I dont want to get wrapped up in semantics.
I have the H tool for pin adjustment. When I adjust the pin for a firm "high pedal." then the brakes start to drag after several miles.
When.I shorten the pin height, then the pedal becomes soft and engages braking after an inch of pedal push.
The booster rod moves when I push the brake pedal.