i have a 90 Bronco automatic with overdrive and recently the transmission has been makeing a large knock when it shifts in and out of overdrive, and now its starting to make a smaller but similar knock going into and out of 3rd gear. Also when shifting in and out of OD above 60 mph it doesn't knock but vibrate. Am i looking at major transmission problems or it is something somewhat minor. thanks

 

Sounds more like maybe a broken tranny mount. I burnt my e4od out and have a friend who just toasted his too, and we both were experiencing slipping as the primary symptom.

Good luck,
Chris