INTERMITTENT DELAYED UPSHIFTS HOT OR COLD/PARTS AVAILABLE
MODELS AFFECTED: ALL 1984-90 VEHICLES EQUIPPED WITH HYDRA-MATIC 4T60 (THM 440T4) TRANSAXLES
BULLETIN COVERS:
Background and diagnosis information on the throttle valve (T.V.) and governor system that control shift timing and not shift feel. The T.V. plunger/bushing assemblies will now be available for service. Before the T.V. plunger/bushing assembly is replaced, the entire T.V. system must be checked. The T.V. SYSTEM may cause one or more of the following conditions:
- Delayed upshifts (may also be caused by sediment between the governor seat and check balls).
- Early upshifts (may also be caused by the governor weight(s) binding on the governor rotor). The rotor is not indexed correctly.
- No upshifts (may also be caused by sediment between the governor seat and check balls).
- 1-2 shift at full throttle only.
- No full throttle or part throttle detent downshifts.
- Intermittent second gear starts.
- Harsh 3-2 downshifts.
IMPORTANT:
Some of the conditions listed above could be intermittent or all the time. The T.V. valve and bushing (Figure 1, Items 308 and 309) may be worn, allowing sediment to cause the plunger to stick in the bore intermittently. Another concern could be the throttle valve (Figure 1, Item 311) stuck down in the bore. Sediment could be the cause of both of these concerns. Either of these conditions could cause delayed upshifts when the transaxle is cold or hot.
The listed conditions may be caused by a T.V. cable that is:
- Improperly adjusted - Kinked or binding - Disconnected - Broken - Wrong part
DIAGNOSIS:
Check T.V. cable for correct part number, listed in the parts catalog.
Check T.V. cable for kinked, binding, disconnected or broken condition.
Check for proper T.V. cable adjustment.
Is there tension on the T.V. cable when being pulled and being released with engine off?
- If the T.V. system fails this test, it could be caused by a disconnected throttle lever to cable link, a stuck T.V. plunger in the T.V. bushing or a broken T.V. cable.
If the T.V. cable has tension when the engine is off, but goes slack when the engine is started, the T.V. plunger is being pulled into the bushing because the T.V. plunger that reduces accelerator pedal effort is receiving too much pressure.
- The throttle valve (Figure 1, Item 311) may be sticking or stuck in the bore. This could be caused by sediment. The valve must move freely in the bore. Clean the valve and bore so the valve moves freely in the bore.
NOTICE:
Excessive lapping of the valves for a Hydra-Matic 4T60 (THM 440T4) may cause the valves to stick. Too much lapping can take the sharp cleaning edge off the valve land. Sediment can now wedge between the valve land and bore, causing the valve to stick. Also, the lapping material can impregnate into the valve lands, causing the valve bore to excessively wear. This will cause the valves to stick unless the valves are lightly lapped, then cleaned in an ultrasonic parts cleaner to prevent bore wear.
- If the throttle valve moves freely in the bore, then the pump cover is missing the machining of the throttle valve (Figure 1, Item 311) exhaust.
Check the governor system for a rise in pressure of approximately 1 PSI (6.895 kPa) for every MPH (1.6093 km/h) when a pressure gauge is connected to the governor pressure tap.
IMPORTANT:
Some "rules of thumb" for governor pressure: - At 0 MPH (0 km/h) the pressure will be about 0 - 4 PSI (0 - 27.58 kPa), depending on the model. - Below 30 MPH (48 km/h) the pressure in PSI will be at or below the MPH reading by as much as 6 PSI (41.37 kPa); above 30 MPH (48 km/h) the pressure in PSI (kPa) will be at or somewhere above the MPH reading by as much as 20 PSI (137.9 kPa). - The reading for a cold transaxle and hot transaxle should be about the same; if not, then orifice #5 - a slot in the accumulator cover gasket - may be clogged or the governor assembly could be leaking. Orifice #5 temperature compensates the flow needs in the governor circuit. Also, the accumulator cover to case bolts could be loose, causing the cold governor pressure reading to be much higher than the hot governor pressure reading. This would allow 4th gear when cold and no 4th gear when hot. A clogged governor screen that is in the case will cause early upshifts and not delayed upshifts.
The rule of thumb is that governor pressure will increase with MPH (km/h).
SERVICE PROCEDURE:
If during the diagnosis of the T.V. and governor system it is found that the T.V. plunger/bushing assembly is worn/sticking/binding, replace the assembly with the parts listed below in SERVICE PARTS INFORMATION.
SERVICE MANUAL REFERENCE:
See the 1984-90 Service Manual for repair procedures.
SERVICE PARTS INFORMATION:
T.V. Plunger/ Bushing Pkg. No. Transaxle Model Identification
8649641 OAAH, OABH, OAFH, OAJH, OANH, OATH 9AAH, 9ABH, 9ACH, 9ADH, 9AFH, 9AHH, 9AJH, 9ANH, 9ATH 8AAH, 8ABH, 8AFH, 8AJH, 8ANH, 8ATH 7ACH, 7ADH, 7AHH, 7ALH, 7ARH 7HAH, 7HCH 6AAH, 6ACH, 6ADH, 6AFH, 6AMH, 6ANH, 6APH, 6ARH, 6ASH, 6ATH, 6AWH, 6AYH 5ACH, 5AFH, 5AMH, 5AYH
8646435 OCHH, OCJH OLAH, OLMH, OLNH OYKH, OYLH 9CDH, 9CLH, 9CPH, 9CYH, 9CZH 9YAH, 9YBH, 9YCH, 9YFH, 9YJH 8CFH, 8CMH, 8CRH, 8CTH, 8CWH, 8CXH 7CAH, 7CBH 6CFH, 6CMH 5CMH, 5CPH
8658704 OBAH, OBDH, OBFH, OBHH, OBJH, OBMH, OBPH, OBWH OPAH 9BAH, 9BDH, 9BFH, 9BHH, 9BJH, 9BMH, 9BPH, 9BWH 9PAH, 9PBH 9WBH, 9WCH, 9WKH, 9WLH, 9WRH, 9WTH, 9WUH, 9WZH 9VXH, 9VYH 8BJH, 8BKH, 8BRH, 8BTH, 8BYH 8FBH, 8FCH, 8FJH, 8FSH 8VXH 7FBH, 7FCH, 7FJH, 7FKH, 7FLH, 7FNH, 7FRH, 7FSH, 7FTH, 7FUH, 7FZH 6BAH, 6BBH, 6BCH, 6BDH, 6BLH, 6BMH, 6BSH, 6BTH, 6BYH
8649730 6BHH, 6BZH 5BAH, 5BCH, 5BRH, 5BWH, 5BXH 4BCH
8649317 5ACH, 5AYH
Parts are currently available from GMSPO.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.
