Got an 89 iroc with a 350 and 700r4. When I drive it(hot or cold) it will slip briefly going from 2nd to 3rd. Its done this for 12 years or since I've owned it and its never gotten worse and the rest of the gears shift just fine. It doesnt do it all the time but most of the time. I did a trans flush to it about a year ago when I worked at a repair facility and no change. No worse, no better, but I didnt expect it to get better. Any thoughts on it? Also, when I'm driving and I am slowing to a stop(foot off the gas and using the brake), the trans downshifts into 1st, I hear a light clunk in the rearend. Only when it downshifts into 1st gear coming to a stop. No other clunks or noises are made while driving. Its done this for the 12 years I've owned it without getting worse. Any thoughts on this? Let me know if you need more info.

 

first thing that comes to mind is bad u joints. but then a clunk would be heard when going from park to drive or reverse to drive

 

I'm thinking you have a timing problem of the band releasing and the 3-4 clutch not coming on fast enough. A simple shift correction/improver kit should solve it

 

Thanks guys. I dont know if it has a shift kit in it. I've havent done much to the trans since I bought it. I did a filter kit a long time ago and did that trans flush about a year ago. It hits great shifting into 2nd when I floor it and it will chirp the rear tires, and it will briefly slip going into 3rd(very noticable when you hear the engine) and the rest is fine. If I drive it normal, it shifts like it should into 2nd and briefly slips going into 3rd and the rest is fine. It has hit good shifting into 3rd sometimes but not very often. Thought it could be a valve or something else since it has never gotten worse over the years. The rearend, I think it could be a little play in the ring and pinion but not forsure. Thought there could be a common problem that others have had with a light clunk when the trans downshifts into 1st. Like I said, it doesnt do it everytime. The u-joints are fine. Its done it before and after I have replaced them. Still open to probable causes.

 

glad i read through the posts that were already up before starting a new thread. mine does the exact same thing from 2 to 3 only. i am curious to know if anyone else has any ideas about the problem though.

 

X2.

The 3-4 clutchpack is a problem area anyways and also the 4-3 release was an issue. Superiors 700R4-HP kit will correct that among other issues. Also it gives you a shift kit thats progressive and not harsh during low-throttle input shifting.
The clunk I agree with also being bad u-joints. Sometimes you also notivce them clunking during a shift into reverse from park or into drive from neutral. But the later 87-later trannys use an auxillary valvebody which was added to the 700R4/4L60's to soften the shift engagement from park/neutral into a gear. So you may not notice the clunk there with a 89 tranny.
The reason IMO for the clunk from 2nd downshift to 1st is because the seperation of the ratios on a 700R4/4L60 from 1st to 2nd are fairly wide. They have a deep 3.06:1 ratio 1st gear. So theres usually a big jump in RPM and power transferred through the tranny when downshifing to 1st from 2nd.