Friday I purchased a 1993 GMC 2500 vandura with transmission problems. I checked it out and found that it shifted from 1st to 2nd around 20 mph with no problem and was strong but had difficulty going into 3rd, if it ever did go into 3rd. It definitely never got to 4th or lock-up. I found a junk yard with a 4L60E at a very reasonable price. It was pulled from a 1993 Chevy 1500 pick up with only 64,000 miles. The junk yard man said it was VERY GOOD and had driven the truck around till he sold the motor out of it. I swapped the transmissions with little difficulty. The wiring harness plugs were different so I swapped the internal wiring harness (had to swap the lock-up thingy too, it was hard wired in with no connectors). I noticed that the original transmission had been worked on before by the condition of the terminals on the wiring harness. When I removed the harness from the plug the pins came out and I had to work them back into position in the plug. I got the transmission installed and first noticed that when I shifted from park to reverse that he wheels spun forward until I accelerated then they appropriately turned backwards. When I got on the road it wanted to take off in 2nd unless I pulled down on the shifter to manually shift into 1st. It shifted to 3rd fine at about 35 mph or so. It never shifted to 4th or if it did it was so soft that I didn't notice it. In every gear it is shifting very soft.
At this point I don't know which is the best course of action and desperately would like some opinion or advice or helpful diagnosis. I know little about automatic transmissions but am considering pulling this one out, returning it to the junk yard for a refund and doing my very first automatic transmission rebuild or just pulling off the valve body, flushing it, putting in a new wiring harness and solenoids and hope for the best.... PLEASE help... need some very good helpful information. I desperately need this vehicle for my home repair busienss and am going broke just trying to stay running and get a decent vehicle to work out of.
BTW.... I did put in a new filter and new front and rear seals before installing the "new" used tranny.

 

Start off by replacing the in pan harness with a new gm one for the appropriate year model of the van. New from gm they are about 43.00 shop cost to us. It sounds like a few pins could possibly be mixed up. If the 12v power pin is in the incorrect spot the shift solenoids will not function and reverse and second are all you will have. The tcc also has to function or the pcm will deny OD to prevent burning up the 3-4 clutch pack from slipping.

 

Thanks guy. I'm almost positive that this is an electronics issue and too, that the harness is the best place to start. I'll try to pick one up today and see about installing it tonight. My other concern is about it not down shifting into 1st for take off unless I manually shift to first.
Thanks,
RJ

 

hey guys little side question for you 4l60e guys, my car is getting sluggish these days, and just of recent when the car goes into shifting to 3-4 the tranny feels like it is shuddering almost like it doesnt want to go...also, if i were to give it a WOT, it kinda sputters, and shudders even harder, and the check guages light kinda flashes, im thinking it might be either the band, or clutches or maybe even the torque converter, i had the tranny rebuilt last year, and didnt have any problems with it..i wish i could explain with more detail to what exactly the tranny is doing, but like i said, it feels like a jerking motion, and only does right after 50mph when the lockup range for the converter kicks in, and at wot, any opinion or tips would be appriciated

 

The torque converter is causing the shudder. It's fixing to explode internally and then you are screwed once it starts coming apart and circulating debris through the rest of the trans. Park it now and you can avoid a more expensive problem if the damage is not done yet. Pull the pan and look for debris when you change the converter.