Possible Causes:
* Governor: The governor controls shift points based on vehicle speed. A malfunctioning governor (clogged, damaged, or out of adjustment) could be preventing the shift into 2nd gear at the proper speed.
* Valve Body: The valve body contains numerous valves and passages that control fluid flow within the transmission. A problem here (worn valve, clogged passage, incorrect fluid pressure) is a common cause of shifting problems.
* Low Transmission Fluid: Low fluid level can cause erratic shifting or inability to shift correctly. Check your fluid level immediately – it should be checked while the engine is running and warm. Important Note: The color and condition of the fluid is also crucial. Dark brown, burnt-smelling fluid indicates serious internal problems.
* Transmission Linkage: While less likely, there's a possibility of a problem with the linkage connecting the shifter to the transmission.
* Shift Solenoid: A malfunctioning shift solenoid can prevent the transmission from shifting properly. This is more common in electronically controlled transmissions, but some components might be present in your 1985 model.
* Internal Transmission Problems: This is the worst-case scenario. Worn clutches, bands, or other internal components can lead to delayed or failed shifts. This often requires a rebuild or replacement.
Troubleshooting Steps (Proceed with Caution):
1. Check the Transmission Fluid: This is the FIRST thing you should do. Check the level and condition of the transmission fluid as described above. If low, add only the correct type of fluid (consult your owner's manual). If the fluid is dark, burnt, or smells bad, that's a major red flag.
2. Inspect the Linkage (If Accessible): If you're mechanically inclined, carefully inspect the linkage connecting the shifter to the transmission for any damage, looseness, or binding.
3. Professional Diagnosis: Given the complexity of automatic transmissions, taking it to a transmission specialist or a reputable mechanic experienced with older vehicles is highly recommended. They have the tools and expertise to properly diagnose the problem. They can perform a pressure test to assess the internal condition of the transmission.
Important Considerations:
* Driving with the problem: Continuing to drive the truck with this issue could cause significant further damage to the transmission, leading to a far more expensive repair.
* Cost of Repair: Repair costs can range widely, from relatively inexpensive fixes (like adding fluid or adjusting linkage) to a costly rebuild or even replacement of the transmission.
Do not attempt to repair the transmission yourself unless you have extensive experience working on automatic transmissions. The risk of causing further damage is high. Get a professional diagnosis and get it fixed as soon as possible.
