I've got a '99 4 cyl auto with 250k with orginal Japan built tranny. About month ago while in garage I noticed a loud clicking noise/slight clunk when shifting into reverse or drive. Few weeks ago some infrequent late shifts/ slow acceleration/hard shifts. Last week symptoms became worse and tranny started to slip intermittently usually after driving around for 20-30 minutes.

Checked for codes and found none except for 1457 evap. Tranny fluid was changed prior to all this starting. Old oil had no metal in it but the magnet had some slurry. I thought the oil had a strong odor, but not sure about how abnormal the odor is. The color was a darker red.

Yesterday I removed the lock up control solenoid and found the screen was 99.9% blocked - no light passing through, so the solenoid was replaced with a screen like new from junk yard. Before taking the car on road test I jacked up front end. Accelerated and the front end started shaking at 30-40mph. It sounded like noise was coming from right side by tranny but it was a quick test so not really sure. The ball joints, tie rods are relatively new and car was aligned a few months ago at a trusted shop and no front end issues found.

Took the car out last night for about 20 min drive and the tranny is back to shifting normally. Will find out about longer trips today. On the road the car has been running smooth at highway speeds. Today the tranny is shifting like new and I can’t detect any shaking. The only other symptom I’ve noticed over the past 6 months is what feels like a very slight but persistent vibration in gas pedal and possibly louder engine or tranny noise.So my big concern is the shaking while on jack stands.

Is the tranny on it's last legs. Could the shaking be the differential or some other major tranny component?

 

Shaking while on jack stands at higher wheel speeds is pretty normal. The parts have zero load and tend to be quite unsettled

 

Thanks for the info. After driving all day on highway and local it's hard to believe but the tranny seems to be running well.