'89 Suburban Transmission Problems

[Chantz]

So here's the problem. I've got a 1989 Suburban 4x4 with a 4-speed overdrive transmission that shifts from first to second and back again just fine, but will not shift from second to third or third to fourth, whether in drive or overdrive. Now, the dilemma is that I've got a friend with a 400 Turbo transmission (or it could be a 350 Turbo, he's not 100% sure), and I need to know if I could adapt this to my application. I've been told that it's more than likely a 700 Turbo that's in there right now. Any suggestions? Anything would help

[idmetro]

You can tell what trans you have by the shape of the pan; check the LMC truck site here http://www.lmctruck.com/icatalog/csb/t12.html for an explanation. The 700R4 (which you most likely have) has an overdrive; going to a different model will cost you fuel mileage but I have heard it can be done. Have you checked your "kick down" cable; I understand it is VERY important to the proper operation on the 700R4. Make sure it is properly adjusted and not broken or disconnected.

[Willyswagn]

I had a similar problem and may have just gotten lucky. I had changed my fluid and that may have realeased some gunk. There is a cable that gets sticky and pulling on the cable solved the problem for a while. Don't know what the cable was as buddy did it. Finally out of desperation put in seafoam trans additive and so far have solved the problem.

Mechanic wanted me to spend $1,800 on trans replacement.

Do a web search for ARX as it is a more gentle additive for trans before problems.

[2000CAYukon]

When you say it will not shift from 2nd to 3rd, does stay in 2nd or does it feel like it shifts to neutral?

//2000CAYukon

[Chantz]

It would shift to nuetral. However, it is no longer an issue since I found someone selling a 700R4 (the exact model we had, just three years newer) for $500 cdn. We just finished swapping them out tonight, and it shifts like a dream. There's only two things:
1. Can you use Dextron III trans fluid in a chevy?
2. We blasted the transmission lines with air, is that sufficient?

Originally Posted by idmetro

You can tell what trans you have by the shape of the pan; check the LMC truck site here http://www.lmctruck.com/icatalog/csb/t12.html for an explanation. The 700R4 (which you most likely have) has an overdrive; going to a different model will cost you fuel mileage but I have heard it can be done. Have you checked your "kick down" cable; I understand it is VERY important to the proper operation on the 700R4. Make sure it is properly adjusted and not broken or disconnected.

I'm taking it in to get it professionally adjusted tomorrow, actually. The guy who sold me the tranny was very adamant that I should get it adjusted, and it will void my guarantee, so yeah.

[2000CAYukon]

Yes you can (and should) use Dextron III.
I would have flushed the tranny cooler and lines.
The TV Cable should be adjusted or you may be back where you started (worn 3/4 clutch pack).

//2000CAYukon

[idmetro]

I'd also suggest runnning the trans for a couple hundred miles and then changing the fluid and filter again as a safety measure. At that point I would switch over to synthetic fluid (I use Mobil 1 since it is relatively cheap and available most places) in my case it made a very noticeable difference. If you don't already have one install a transmission cooler as heat is the main enemy here. If you tow anything do it in Drive NOT Overdrive!

[Chantz]

Okay, since it seems that this thing is never happy, today I had to take transmission fluid out because it was too full. I got it back to where it should be, and then took it for a drive and it shifts really hard. I added more fluid back in, and it hasn't helped. However, under medium high throttle it shifts just fine. What's the deal? I'm taking it to a tranny shop tomorrow

[2000CAYukon]

Did you adjust the TV Cable? Firm shifts indicate a rise in line pressure which the TV Cable controls.

See http://www.tciauto.com/Products/Inst...ble_adjust.htm for instructions on how to adjust it. Otherwise, make sure that is the first thing the tranny shop does.

//2000CAYukon

[Chantz]

I had it done just a little while ago. Monday, I'm pretty sure. But the problem seemed to cure itself. This morning it was shifting like it should be, and when I drained off the excess oil off today, it shifted fine, EXCEPT for when I tried to go into fourth. It wouldn't go. I had it up to 130km/h (about 80mph) and it wouldn't go. It didn't even try to shift. I've go the first three gears, however, and I'm taking it to the tranny shop on tuesday to get diagnostics run on it. The fun just never ends...