1. Simple Checks (Do these FIRST):
* Fluid Level: Check the automatic transmission fluid (ATF) level. Is it low? Is the fluid burnt (smells burnt, dark brown/black instead of reddish-pink)? Low fluid is a major cause of shifting problems. If low, adding fluid is a TEMPORARY fix only; you still need to find and fix the leak.
* Fluid Condition: The condition of the ATF is crucial. Burnt fluid indicates severe internal problems.
* Selector Lever: Make sure the gear selector is firmly engaged in the desired gear (Park, Reverse, Drive, etc.). A loose or malfunctioning selector lever can prevent proper shifting.
* Battery Voltage: A weak battery or faulty alternator can cause erratic shifting behavior. Check the battery voltage with a multimeter.
2. More Advanced Troubleshooting (Requires Mechanical Knowledge or Professional Help):
If the simple checks don't reveal the problem, the following are possibilities, requiring more expertise:
* Transmission Linkage: The linkage connecting the gear selector to the transmission could be bent, broken, or adjusted incorrectly.
* Torque Converter: The torque converter could be faulty, failing to transmit power efficiently. This is often accompanied by slippage or inability to move.
* Valve Body: The valve body within the transmission controls shifting. Problems here can manifest as incorrect shifting or complete inability to shift. This often requires professional diagnosis and repair.
* Solenoids: Internal solenoids control hydraulic pressure within the transmission. Faulty solenoids can prevent shifting.
* Governor: The governor controls shift points based on engine speed. A faulty governor can cause incorrect shifting.
* Low/Reverse Clutch Pack: Failure in the clutch pack responsible for low gears and reverse is very common in these transmissions. This usually results in the inability to engage those gears.
* Internal Transmission Damage: Worn gears, bearings, or other internal components could cause shifting problems. This usually requires a rebuild or replacement of the transmission.
3. Diagnosis:
To accurately diagnose the problem, you'll likely need to:
* Use a scan tool: A scan tool capable of reading OBD codes (though 1989 may not have a fully OBD system, a more general scan tool might be useful) can help identify electrical problems related to the transmission.
* Check Transmission Fluid Pressure: Measuring the ATF pressure under various conditions can help pinpoint the source of the problem. This requires specialized tools.
Important Considerations:
* Driving the Vehicle: Avoid driving the vehicle extensively with transmission issues, as further damage can occur. Driving with low fluid can severely damage the transmission.
* Professional Help: If you're not comfortable performing these checks and repairs yourself, it's best to take the vehicle to a qualified mechanic specializing in automatic transmissions. Repairing an automatic transmission can be complex and expensive.
Without further information, it's impossible to pinpoint the exact cause. Start with the simple checks above and work your way down the list if necessary. Remember, safety is paramount; don't attempt repairs beyond your skill level.
