Caprice V8-307 5.0L (1987)
Technical Service Bulletin # 8755
Date: 870101
A/T Throttle Valve System - Condition Summary/Diagnosis
Number:
87-55
Section:
7A
Date:
JAN., 1987
Subject:
SUMMARY OF THROTTLE VALVE (T.V.) SYSTEM-RELATED CONDITIONS AND DIAGNOSIS
Model and Year:
ALL HYDRAMATIC BUILT THROTTLE VALVE CONTROLLED TRANSMISSIONS/TRANSAXLES (EXCEPT THM 180,
THM 350, THM 400)
TO:
ALL CHEVROLET DEALERS
This bulletin covers background and diagnosis information on the Throttle Valve (T.V.) system and applies to all THM transaxles/transmissions, except
the THM 180, 350, and 400 models. Included are revised procedures using a pressure gage during adjustment/diagnosis, inspection of components and
other items not yet covered in the Service Manual.
Background
Throttle valve (T.V.) pressure controls the shift pattern and the amount of hydraulic line pressure used to apply clutches and bands. (NOTE: The THM
440-T4 T.V. cable controls shift timing, not shift feel, line pressure is not directly affected by T.V. cable setting.). If proper line pressure is not
available, excess slippage may occur during the shift. If the T.V. cable is tailored in an effort to modify shift pattern/feel, this misadjustment can result in
transmission/transaxle failure.
IMPORTANT:
Do not attempt to correct a condition by changing the T.V. cable setting from its proper adjustment. Apparent improvements from
T.V. cable "tailoring" indicate a need for further diagnosis into the real cause of a condition (such as engine performance, the control
valve, governor or servo assemblies, etc.).
Dealer personnel and customers should know that certain types of heavy duty or high performance vehicles have transmissions calibrated to provide
crisp, firm shifts for durability/performance. Once again, the T.V. cable must not be tailored in an effort to modify shift pattern/feel on these applications.
IMPORTANT:
Make sure engine fuel, electrical and mechanical systems are performing properly before attempting transmission/transaxle
diagnosis. For example, a fouled fuel injector, cracked spark plug, damaged spark plug wire or vacuum leak can affect
transmission/transaxle performance.
The T.V. system may cause one or more of the following conditions:
--
Delayed or harsh upshifts
--
Early and slipping upshifts
--
High or low line pressure (except the THM 440-T4)
--
No upshifts
--
Chatters on takeoff
--
1-2 shift at full throttle only
--
No full throttle or part throttle detent downshifts
--
Intermittent second gear starts
The above listed conditions may be caused by a T.V. cable that is:
--
Improperly adjusted
--
Kinked or binding
--
Disconnected
--
Broken
--
Wrong part
CAUTION: To avoid possible personal injury and/or damage to the vehicle, the following diagnosis procedure must be performed with the vehicle
parking brake properly applied.
Diagnosis
Inspect
^
T.V. cable for correct part number, listed in the parts catalog.
^
T.V. cable for kinked, binding, disconnected or broken condition.
Install or Connect
^
Line pressure gage.
