1997 Pontiac Bonneville Repair Question
Could over fillin the transmission cause it not to shift when it gets warm
Those symptoms could be related to overfilling the transmission, but the first question is why did you have to add transmission fluid in the first place? If there's a leak, low fluid level will allow the pump to draw up air instead of fluid. If the level is excessively high, rotating members will whip up the fluid and introduce air into it. Since air compresses, the aerated fluid won't be able to put pressure on the clutch packs to apply them. That air in itself will not hurt anything. It's the clutch pack slippage from continuing to try to drive it that way that will do the damage.
Address the fluid level issue, then allow it to sit a little while for the air bubbles to work their way out of the fluid.
Also be sure you're following proper procedures when checking the fluid level. The engine must be warmed up and idling in neutral or park after briefly running the shift lever through all the ranges. If you try to check the level with the engine off, the fluid level will appear to be too high.
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