C 20 3/4 Ton Pickup 2WD V8-379 6.2L DSL VIN J FI (1982)
Shift Modulator: All Technical Service Bulletins
A/T - High or Late Upshift
Number:
82-I-150
Section:
VIIc
Date:
July, 1983
Subject:
HIGH OR LATE UPSHIFT - 1982 "C-K-P" WITH 6.2L DIESEL ENGINE AND 400 AUTOMATIC TRANSMISSION
TO:
ALL CHEVROLET DEALERS
Comments regarding high or late upshifts in the model described above, may be caused by a poor vacuum signal to the transmission.
During the early 1982 production, the engine end of the transmission modulator vacuum pipe was changed. The reduction in the pipe
diameter resulted in eliminating resonance in the vacuum regulator valve, increasing the lift of the valve.
When diagnosing a vehicle complaint, the following procedure is recommended:
1.
Remove the vacuum hose from the modulator pipe (hose from pipe to valve).
FIGURE 1 - MODULATOR PIPE
2.
Check for the correct modulator pipe. The pipe, P/N 14054204, should be 5/32 I.D. and approximately five
(5)
inches long. Refer to Figure 1 View B.
3.
Replace with correct modulator pipe if required.
4.
Check for proper vacuum pump output. When hooked up to a vacuum gage, the pump should produce approximately 70 KPA (21
in. Hg.) of vacuum. If sufficient vacuum is not being produced, determine cause and correct.
5.
Check for the correct regulator valve, P/N 14057219. Set the valve to the correct setting of 27KPA (8 in. Hg.) as per shop manual
procedure. If the setting of 27KPA is not obtainable, the valve should be replaced.
