2000 Transmission Problem

ImConfused666 · January 17, 2007

I have a friend... great way to start the description of the problem. He drives a 2000 3500 Gas Burning 350. He thinks he has a 700R4 but from reading this site, he must be wrong. Anyway, he says it just started downshifting out of OD on him when he's driving down the highway. Once it downshifts, it will not go back up until he pulls over and shuts it off and restarts. He says it will also sometimes do this to him from 3rd down into 2nd. He had a dealer install a GM rebuild about 11,000 miles ago. Still under warranty (but for parts only). As expected, they wish to screw him big time on the labor as they say they have to do a complete rebuild in order to diagnose the problem. They believe it to be an electrical problem (which I think means solenoids) but cannot know until they open it back up. What do you think he should do? Where should we look to figure out the problem ourselves? Right now, he's in New England, the truck is in Alabama and I'm in Louisiana. I'm willing to fetch his truck over here and work on it myself to save him $1500-2000 in labor but I'd need some idea as to where to start. I just did a rebuild on my tranny. It turned out that it really didn't need it. The TCC had come apart and pieces had plugged some ports. I still needed to tear it down to clean it out but I really didn't need the new parts that I installed. Not sure what I'd find in his tranny but I know his pain.

95Sierra2500 · January 17, 2007

You're correct that he does not have a 700R4 as that designation went out back in the early 90's. GM now calls that transmission the 4L60E. However, I doubt he has that either in a 1-ton truck. He probably has a 4L80E, the electronic version of my 4L80 in my '95. These are actually pretty good transmissions, I've got 200K miles on mine and it's running strong still. However, what I would recommend would be to first check the fluid level. If that's fine, then drop the pan and see what you can see. If there's nothing in the pan, I'd suggest pulling the trans yourself and if you know alot about rebuilding them, then go ahead and do it for him. Remember that while you're in there you might as well change all the clutches as there are NO bands in a 4L80. If you don't feel secure doing it yourself, find a reputable tranny shop in your area and have it rebuilt.

Edit: since it's an OBDII truck, if you have access to a Tech II, take it for a drive and monitor the transmission. If you don't, I'd say have a dealer take it for a ride and monitor the transmission. With this technology they don't need to do a complete rebuild to attempt to troubleshoot the transmission...they can collect ALOT of data from a Tech II.

ImConfused666 · January 18, 2007

Thanks very much for the info. I think that is useful infomration and advice that I can pass along to him. While I've only done one tranny rebuild in my life, my youngest brother has done 4 and they all worked fine. I've come to the conclusion that if you have a really clean and organized work area and a good book, you can fix dang near anything with the right tools and plenty of time.