Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
sounds like the fan clutch is staying locked up causing the strain
It wouldn't have never crossed my mind about the fan clutch being locked up. However, I am still concern that the noise is coming from the tranny because when you give it full throttle and it downshifts, the truck really has no power to move. The noise just gets really bad.
File In Section: 07 Transmission/Transaxle
Bulletin No.: 99-07-30-016B
Date: October, 2002
This bulletin is being revised to change the Model information and text. Please discard Corporate Bulletin Number 99-07-30-016A (Section 07 - Transmission/Transaxle)
Some customers may comment that at times the transmission seems to slip, or that there is a loud roar from the engine with slow acceleration. This condition is most noticeable after the vehicle has sat idle for 12 or more hours, or on hot days when the A/C is on and the vehicle moves slowly with traffic.
Typical comments from customers may include the following conditions:
The type of concern described above requires further definition. The customer should be asked the following questions:
If the customer indicates that these conditions apply, and your observation confirms that the vehicle is operating properly, provide the customer with the vehicle operating description included at the end of this bulletin. Further action may not be necessary. A service procedure follows if further definition is required.
Cooling fan operation or the resulting sound varies. The cooling fan clutch may be described as a continuously variable clutch. If the vehicle engine is running, the fan blade is always turning unless the fan clutch is non-functional. The speed of the fan in relation to engine speed is temperature dependent. Maximum fan speed (air flow and related fan noise) through the engine compartment is experienced under two conditions.
When diagnosing an intermittent transmission downshift, slip, or busy/cycling TCC, follow these steps:
If the engine RPM display on the tachometer or the Tech 2 increases, verify the scan tool RPM and coolant temperature readings. If the noise increase is due to the engagement of the fan, the engine RPM will not increase and the engine coolant temperature will begin to decrease after the fan engages. As the fan runs, the engine coolant temperature will drop and the fan will disengage, reducing noise levels. The engine RPM will not decrease. This cycle will repeat as the engine coolant temperature rises again.
If the above procedure shows the condition to be cooling fan-related, no further action is necessary. The vehicle should be returned to the customer and the condition explained.
If the above procedure shows the condition to be other than cooling fan-related, refer to the Automatic Transmission sub-section of the appropriate Service Manual for transmission diagnosis information.
The following information regarding the operation of the engine cooling fan should be photocopied and given to the customer.
Intermittent Transmission Downshift
All light duty trucks are equipped with a thermostatic engine cooling fan. This fan is designed to provide greater fuel efficiency and quieter operation than a standard fan. These benefits are possible through the addition of a thermostatic clutch to the fan drive. When the engine is cool (it the engine has been run in the last few hours), the clutch allows the fan to "slip" or turn at a speed slower than the engine. By turning at a slower speed, the fan uses less horsepower, which saves fuel, and is quieter. When the engine temperature reaches a preset temperature or if the engine has not been run for several hours, the fan "engages" and turns at the same speed as the engine.
"Engagement" of the fan provides increased airflow through the radiator to cool the engine. As the airflow increases, fan operation becomes clearly audible.
This increase in noise can easily be mistaken for an increase in engine RPM and may be incorrectly blamed on the automatic transmission. When operating an unloaded vehicle in cooler ambient temperatures, the thermostatic clutch usually won't fully engage. However, if the vehicle is pulling a trailer, is heavily loaded or is operated at high ambient temperatures, the thermostatic fan clutch may cycle on and off as the engine coolant temperature rises and falls.
The sound of fan operation under the conditions described above is a sign that the cooling system on your vehicle is working correctly. Replacement or modification of the cooling system or the transmission parts will not change or reduce the noise level. Attempts to reduce this noise may cause you, the customer, to believe that your vehicle is not reliable and will inconvenience you by causing your vehicle to be out of service.
NOTE: Timing specifications are listed on the Vehicle Emissions Control Information label under the hood. Always follow the Vehicle Emissions Control Information label procedures first before using the following procedure.PROCEDURE: Set timing under the following conditions:
Refer to specifications: See: Specifications