So many helpful folks here. Thanks for posts that got me this far.

Problem: 1999 Blazer with p1870 transmission torque converter slip. Poor mpg. Bluetooth scanner with Torque app shows 150+ TCC slip on level ground and steady mph. Also a slight amount of fluid leaks from small tranny vent tube while driving. Fluid temp at 205 degrees after 30 minutes of driving. Tranny Fluid pressures 80 psi at idle, and about 120 psi on highway.

Dropped tranny pan. Fluid red. No debris. Discovered previous owner had already tried Transgo shift kit with TCC regulator/isolator fix. I thought it might be severe bore wear, so I installed a new valve body with reamed bore and Sonnax regulator/isolator sleeve and valves. Cleared code, but still no joy, P1870 and slip continues.

To avoid tranny drop I tried one last ditch effort. Checked TCC apply valve for 1/2" of travel. Checked fine. I removed TCC apply solenoid, removed its screen, and put a check ball in its snout. Should have made engine stall in drive while stationary (brakes applied) as converter would be locked. No stall or stumble.

So I dropped tranny. Converter looks brand new. No burn marks, perfect paint. Clutch packs not burnt. Drum where band rides still has scotch brite marks where someone removed any glazing. This tranny appears to have been recently rebuilt.

However, rear stator bushing is worn badly on one side. 180 degrees from the wear, it doesn't even look like it's touched the shaft (see photos)





Also, there is no plastic orifice capsule in the hole at the pump back. I thought there was supposed to be one installed.



I plan to replace bushing and possibly install an orifice capsule.

3 questions (see photos too):

1. Is the bushing wear enough to cause TCC slip? Maybe the tranny pressures say "yes"?

2. Any good reason the bushing would side load and cause that wear? Pump bolts tightened evenly and pump halves are aligned. Pump rotor "dogs" that torque converter engages don't really look centered around stator. Not sure if they are supposed to be that way.

3. Is there supposed to be a TCC orifice capsule installed?

Thanks for help.

 

A few clarifications to my narrative above:

1. I discovered from an exploded parts diagram that the TCC orifice capsule goes in a hole inside the pump halves. I opened the pump and it is intact. The hole facing the pump back is apparently supposed to be open. So no worries here.

2. The plastic pump "dogs" that the torque converter slots drive have some side-to-side play. This appears to be by design. So I don't think there is a problem there.

3. The rear stator bushing is wore on one side to the point where one of the four bushing grooves is completely gone.

4. I remembered that when swapping the engine and few months ago (previous owner ran engine dry of oil), one of the torque converter bolts was missing. Could this have caused side-loading and uneven wear on the rear stator bushing?

 

I noticed today that the journal of the input/turbine shaft (that inserts into torque converter) is worn. Burn marks and a pronounced dish/wear. Guessing 0.020 wear. O-ring seemed ok. I plan on replacing the turbine shaft and o-ring.



Maybe between the input shaft journal wear and rear stator bushing wear, I lost enough pressure to cause slip and P1870.

Parts on their way. Will keep you posted.

 

SOLVED!

I installed a new bushing and new turbine shaft/input drum. The P1870 code is gone and TCC slip is back to acceptable levels at lockup.

It was a long journey and I learned a lot. It would have been simpler to just pop a new tranny in and drive on. But I'm glad I stuck with it and learned.

Thanks. Hope this helps someone else down the road. Remember that if the Transgo or Sonnax band aids don't fix your P1870 code, the problem is deeper. In fact, if you have the code, you probably are on borrowed time if the bandaid valves make your code disappear.

 

Nice job! Quite possible the missing torque converter bolt started the whole mess. Thanks for sticking with it, and for the detailed thought and repair process. Always nice to see a problem correctly diagnosed, and the results posted.