A/T - 180C Erratic Shift,, Late Shifts, Burnt Clutch
TSB 85-28SUBJECT: 180C
COMPLAINT:
Erratic shift points1 late shifts, burnt second clutch.
CAUSE:
The cause may be carbon, or dirt build-up in the steel vacuum line to the modulator. The dirt will act as a check valve, either preventing vacuum from getting to the modulator, or trapping vacuum at the modulator. If no vacuum gets to the modulator, the results will be late up-shifts and high line pressure readings. If vacuum is trapped in the line, the result is slipping under medium-to-heavy throttle, and burnt clutches.
CORRECTION:
To correct the problem, cut the end of the vacuum line off where it fits into the engine. This removes the restriction in the steel line.
Secondly, blow out the vacuum line to get all dirt and carbon out.
Last of all, be sure to clean the vacuum fitting in the engine manifold of all carbon. This procedure should be followed on all Chevettes/T-1000 vehicles with the THM 180.