I don't think you are over reacting........just follow up you concerns with some sensible deduction. Yes....D52 was the other super popular pad for 20 some years on GM.
Remove the wheel and spin the rotor.......is it rubbing badly on the pad? If not.....put it together and drive it.....just verify the hangup first.

Jebby

 

rotor is difficult to spin with the caliper on and the wheel off.

took the caliper off and rotor spins nicely—no hang ups.

 

These lead me to believe you either have hydraulic pressure or mechanical pressure on the pads.

Crack the line as Jebby suggested above to see if there is hydraulic pressure in system. Opening a bleeder should work.

Second when you push the pistons all the way back into the caliper to install the new pads does there seem to be some leftover clearance? IE feel gauge size? Just not jammed tight.

Third if clearance is it the same front and rear of pad, or are they not parallel enough to the rotor.?
Fourth did you check rotor run-out with a dial indicator?

 

Opened up the driver front bleeder, fluid immediately began to flow, without anyone touching the brake pedal.

ONce I got the pads off, I cracked th ebleeder again to make pushing the piston back in easier....I could barely budge the piston (by hand), even h the bleeder open. My only experienc with this was ehwn I changed the pads on my C3 rear, and cracing th ebleeder made those VERY easy to push back into the bore...not so much here.

Not sure if that's because the 4 piston vs this single psiton, buttwo very different experiences.

 

Sounds like you had pressure in there for some reason.

Were the pads a loose fit? or tight?

 

very tight...

 

Any chance the pistons did not go all the way down into the caliper? till they were flush? or binding near the bottom?

I'm grasping at straws here but tight does not sound correct. Feeler gauge snug maybe, but not tight.

 

I'm confused. If they are getting abnormally hot, they are hung up. but if you can spin the tire by hand, they are generally not hung up. With single piston calipers, it is not unusual to need some force to push them back. If you pushed them back by hand they are probably OK. Generally after applying and releasing the brakes, I can shake the caliper when it is in-place and see movement on the slides and pins. Can you do that?

You indicate that the problem is both front wheels. That seems to imply hydraulics. If it is one wheel, One area of hang up is the slides. I usually lightly sand the rusted slides so that the caliper moves smoothly. But slides hanging up only wears the pad on one wheel and one pad; the pad opposite the piston. Again one side hanging up can be caused by a bad rubber hose. It is possible but unlikely that you have two bad rubber hoses at the same time.

I think you have to take the "open bleeder" suggestion a bit farther. After pressing and releasing the brake peddle spin the wheel and open the bleeder while spinning the wheel. Does it get easier when the fluid leaks out? If it does, then you have something wrong upstream. There are several fittings upstream. Each fitting isolates another portion of the system. You can pinpoint your problem by releasing the pressure at the appropriate fitting.

Finally, if none of these suggestions found your problem, I would start the car and repeat the "open bleeder test" with vacuum on the booster and then I would run the car get it hot and repeat the "open bleeder" test.

 

a little more research (as I wait for a tool to compress the piston back int he bore at the moment).

The master cylinder I installed that came with the kit was a 1" bore. In looking at replacments (in case that's the issue), almost all of the stock replacment stuff is 1.125" bore...could that be the issue?

 

One size is manual brakes. The other is PB.
But it doesn't seem like that is your issue.

 

The 1.125" bore is for PB on a C3. The 1" bore is for manual. That part reduces pedal effort needed under high pressure with the manual brakes. Should not have any effect when released.

I would chase the hydraulic pressure build up and see if cracking the bleeder helps. Did the release of some fluid make the wheel spin more freely?

If not that it must be mechanical binding.

 

got a new PV2 valve...see if that changes anything this weekend...while I am replacing that, I will re-placing that, I will re-measure the clearance fromt he booster to master clearance (although I really don't think that's the issue, due to appropriate pedal free play, and nothing changed when I unbolted the master last weekend)...

 

Your pads had an allergic reaction to cast iron and swelled up. (or not)

 

LOL. Yeah that's it. They are mad because they really wanted some trick aluminum Wilwood calipers......

 

Had same issue once. I bought a front disk kit for my 57 chev pickup, and after I went round and round with the place that I purchased it from, I gave up on them. They kept insisting it was air in the lines, improper install, etc, etc. I insisted it was the vacuum booster. Well, after the third booster they sent me failed to fix the issue, I got a usa made booster from MGM brakes. Problem solved. Totally different, very good pedal feel.The way it should be. Anyway, food for thought. I do have the tool for setting booster push rod, and all three they sent me were set good. This was a master/booster kit.

 

Cracked the bleeder and used a caliper tool to compress the piston back into the bore.

when compressed, should the piston be flush with the caliper, or still slightly protruding?

Using a feeler gauge, it measures to still protrude about .090

photo below is fully compressed, with bleeder valve cracked

 

narrowing it down...
1. R&I'd the calipers, and was was able to get the calipers adjusted so the rotors could spin fairly freely...

2. Pumped the brakes, and it locked the rotors...after some time, they released "somewhat" to where I could actually turn them with a lot of effort by hand but could not get them to "spin" or get even one revolution without continued pressure applied--still way too much drag.

3. Removed the master and measured clearance against the plunger using the special tool...(if anything) there is just a touch too much space ( a tad more that .060) between the plunger on the master and the pushrod on the booster, so it is not the booster or the master that is retaining pressure.

4. Removed the proportioning valve (I have not yet installed the replacement); however, there is still the same amount of drag on the rotors, even with the prop valve completely off the car, and the lines not attached to anything.

Given all of the above, it has to be either two bad hoses (as the issue is the same on each side, or two bad calipers, correct?
What are the odds that I'd get two bad hoses, or two bad calipers?

Tried checking both advance and pep boys, to see if there was a thinner pad available, and all measure (with a caliper tool) slightly THICKER than the current pads I have, so I doubt it's pad thickness...and like I said, I was able to get the calipers to allow the rotors to spin comfortably after and R&I and backing the caliper manually as far into its bore as it would go...

 

Wow. Number four has me scratching my head.

Sure sounds like rubber hoses. But if its not . . . . . . . . . . ?

You don't have a old Line-Lock parts hidden somewhere do you?

 

ha! No line lock parts....
I think I’m just gonna order new calipers and hoses and see if that clears it up....it’s got to, right?!? Lol

 

The calipers is supposed to have a shape to the recess for the seal that twists the seal a bit and then when the pressure is released the twist in the seal relaxing is supposed to pull the piston back ever so slightly. Those disk brakes will always drag a little, but the wheels or rotors shouldn't be overly difficult to rotate. There may be a build problem from the manufacture of the calipers if the pistons are not retracting the slight amount like they should. possibly the shape of the seal groove is wrong on the pistons are dragging in the bore enough they won't retract.