Could a guy make a fixture with an o-ring (exactly like the tip of the input shaft) to slide into the TC to air check the clutch. Not to see if it slips, but rather to check the condition of the apply piston to see if it holds air.
Are there bleed orifices in them? Should they hold pressure for a while? (4L60-E)
Are there bleed orifices in them? Should they hold pressure for a while? (4L60-E)