Agreed, and the early Toyota ABS systems were very primitive and limited in ability. But....
I tend to look at things from liability perspective.

 

Well I think I may have isolated the problem to the abs valve body or block or whatever you call the part on the top of the abs pump. It seems like the port that feeds the front driver’s caliper is not allowing the same volume through as the passenger front caliper port. I blew some isopropyl alcohol through both ports from the inlet multiple times and definitely do not get the same volume of air through that port which would explain the caliper holding pressure. Going to try a couple times to blow through it but figure I can probably get that from the salvage yard as long as one of the 4Runners is 4wheel abs…guess we’ll see. The rest of the brake system has been flushed and ready for fresco clean brake fluid as soon as I figure out the abs oddity.

 

Are you saying that when the brake was locked up you cracked the fitting loose at the ABS unit and the caliper released?
If not you are chasing the wrong rabbit down the wrong hole.

 

Correct. I know this thing sat a lot over the last few years from the previous owner. My fear is that humidity got in there causing corrosion and has internally restricted the passage.

 

Well I have 100% confirmed the abs valve block on top of the pump is the problem. After putting everything back together I drove around the neighborhood and stopped after about 2 miles to take temps on the rotors and the drivers was already running about 20 degrees higher. As soon as I got back to the driveway I jacked it up and that when had severe drag and the passenger side was fine. I cracked the compression nut and let a very tiny amount of fluid bleed out and the drivers wheel instantly freed up. Headed to the salvage yard in the morning to see what I can find. Thanks for all the help folks!

 

Just for some closure on this issue, turns out when the previous owner put the new brake booster in, it wasn’t adjusted properly and the pushrod that compresses the master cylinder was a little too far out, slightly compressing the master cylinder. Not sure why it didn’t seem to really show itself until after I replaced the brake pads and the drivers side caliper…but the brakes are working wonderful now.

 

Nice sleuthing! And thanks for the follow up.