* Low Transmission Fluid: This is the most common and easiest to check first. Low fluid means insufficient lubrication, leading to friction and grinding. Check the fluid level with the engine running and warmed up (following the procedure in your owner's manual). If low, adding fluid might temporarily alleviate the problem, but it doesn't address the underlying cause of the fluid loss.
* Worn or Damaged Transmission Bands/Clutches: Automatic transmissions rely on bands and clutches to engage gears. Wear and tear, especially in a 30+ year-old car, can cause slippage and grinding. These parts are often worn beyond repair and require replacement.
* Failing Transmission Solenoids/Valve Body: The valve body controls fluid flow to the clutches and bands. Faulty solenoids or internal valve body wear can prevent proper engagement, resulting in grinding and difficulty shifting.
* Low Fluid Pressure: This can stem from several issues: a failing pump, a clogged filter, or a leak somewhere in the system. Low pressure means insufficient force to engage the gears properly.
* Worn or Damaged Planetary Gears: These are internal gears within the transmission. Severe wear or damage can cause grinding noises and shifting difficulties. This is a more serious and expensive issue.
* Torque Converter Problems: While less likely to directly cause grinding *when shifting from park*, a failing torque converter could contribute to overall transmission problems and make shifting harder.
* Shift Linkage/Cable Issues (Less likely with a fully automatic): Though less common in fully automatic transmissions, issues with the linkage or cable could prevent the transmission from selecting the correct gear, leading to grinding.
What to do:
1. Check the transmission fluid: This is the crucial first step. Inspect its color and smell. Dark, burnt-smelling fluid indicates significant wear and likely needs a complete transmission service or rebuild.
2. Seek professional help: Given the age of the vehicle and the severity of the problem (grinding), it's strongly recommended to take the car to a qualified mechanic specializing in automatic transmissions. Attempting to diagnose and repair this yourself is risky and could lead to further damage.
The grinding noise is a serious warning sign indicating significant internal transmission damage. Ignoring it will likely result in complete transmission failure. Repair costs can be substantial, so it's important to assess the cost of repair versus the value of the vehicle before investing heavily in repairs.
