GM'S Auto 4speed w/od.

[Galaxi-99]

It would be nice to here some input from some tranny doctors out in the forum(aamco) that have repaired or rebuilt or have some know how as to why GM trannys shift so hard the hole truck shakes or will clunk so bad you stop to see if your drive shaft fell off.

[RexNfx400]

The GM rear wheel drives trannys shift hard when they are in limp mode.

When the PCM detects a problem, whether its electrical or mechanical it will store a history code and set high line pressure. Usually you will feel this when the tranny shifts from 1st to 2nd gear on the 4L60E or from 2nd to 3rd gear on the 4L80E. If its a transaxle the PCM will inhibit 4th and TCC when there is a problem.

If its an Allison. Well, Thats a whole different story for another day.

It sounds(I'm really guessing here) That your truck(judging by this forum) with a 4L60E is making a harsh 1-2 shift. Most likely (I said "most likely") the computer system has detected a slip within the TCC system(very common)(code 1870). This is usually due to the valve body wears out the TCC regulator bore, so the TCC cannot apply fully. When the PCM sees more than 150 RPMs slip once PWM TCC is on for 2 seconds...You got limp mode. It does go way beyond this but this is the basics

[Mike K.]

? for RexNFx400...I have a 96 K1500 Sub. with 350 vortec and auto tranny and 3.73 gears. What tranny do I have - the above mentioned 4L60E? If I do, could be similar problem I'm having. Will having bands adjusted correct this?

Thanks in advance, sounds like you're turned a wrench or 2 on these whiz-bangs!

[RexNfx400]

You do have the same tranny. There is no adjustments The computer system "adapts" for worn parts. Very little I might add

It has to be determined, with a scanner, if your harsh shifts are because of limp mode or broken accumulator springs.

Maybe some more info on how the symptoms come about?

[Galaxi-99]

Holly shit man you r computer has a cold ,,,,,do not send me e-mails anymore,,,(automated) need to click this off, .... But your puter needs a doctor dude .......... oh,,,,,,,,,,,,,yea!
You sent me 8 post of the same quote!!!!!!!!!!!!!!!

[dilligaff82]

I had the same problem with my 97 1500 4x4. It started at about 50,000 miles, and kept getting worse and worse until one day I took it out and beat the hell out of it and buried it in a couple feet of water and mud. 15,000 miles later and a lot of long road trips later I haven't had the problem come back. I guess I just needed to show it who was the boss!

[GMMerlin]

Originally Posted by Galaxi-99

It would be nice to here some input from some tranny doctors out in the forum(aamco) that have repaired or rebuilt or have some know how as to why GM trannys shift so hard the hole truck shakes or will clunk so bad you stop to see if your drive shaft fell off.

From your post, I gather you have 2 problems...First is a harsh shift concern and the second is the clunk felt when you come to a stop.
On the harsh shift, could be caused by a broken accumulator spring or if you have a DTC (relating to the trans)stored in your PCM, the PCM puts the trans into a fail safe mode applying full line pressure at all times..makes for a pretty harsh shift...there are a couple bulletins regarding these concerns.
On the cluck, there is a bulletin for an updated slip yoke, although it doesn't apply to every GM vehicle
GM is aware of the clunk concern and the engineers have been trying to come up with a final fix for the problem