Hard Transmission Shift

[fire24resque]

I know of EVERY other transmission, drive shaft, steering column, fuel guage etc.. problem that these damn things hold in their devlish little frames, but now I have a new one.

I am experiencing a hard/rough shift from 1st to 2nd when pulling out. The driveshaft doesn't clunk, it's more of just a hard forceful shift. Doesn't do it everytime, probably 1 out of 3 accelerations. Its mostly at a lower RPM, if I tear out of an intersection and let it shift at around 4500 it's the smoothest shift you'll ever feel, but if I'm moving slow through a parking lot it tends to almost give you a boost when it drops. Same with a gentle acceleration. I had the tranny flushed and fluid changed about 15,000 miles ago. Is anyone else experiencing this? Or can someone tell me what may be causing it? I've heard about getting your PCM ... flashed/changed something, what exactly is this and what does it entail...could it be that or something else?

Thanks.

[2000CAYukon]

the 1-2 "bang" shift can be caused by a worn accumulator valve and is pretty common on the 4l60e (and 4l60). See http://www.transmissionspecialty.com...arts/77777.htm

A transgo reprogramming kit will fix this along with some other weak points of the 4l60e. Not to mention that it will probably make the tranny last longer.

A transgo reprogramming kit would be my recommendation.

//2000CAYukon

[maxwedge]

Another possibility is the precursor symptoms of the dreaded p1870 code issue due to a worn tcc apply valve in the valve body. This causes the pcm to command full line pressure to overcome the pressure loss, usually though yopu would get harsh reverse as well.

[fire24resque]

Originally Posted by maxwedge

Another possibility is the precursor symptoms of the dreaded p1870 code issue due to a worn tcc apply valve in the valve body. This causes the pcm to command full line pressure to overcome the pressure loss, usually though yopu would get harsh reverse as well.

Explain harsh reverse....

[2000CAYukon]

Originally Posted by maxwedge

Another possibility is the precursor symptoms of the dreaded p1870 code issue due to a worn tcc apply valve in the valve body. This causes the pcm to command full line pressure to overcome the pressure loss, usually though yopu would get harsh reverse as well.

Good point, but he did not mention that the check engine light is on or not. He also said that it does not happen all time (1 out of 3). Once the code is set, the tranny would be shifting hard until the check engine light went out.

So magic question is "Is the check engine light on?"

Also transgo reprogramming kit will help with p1870 code.

//2000CAYukon

[fire24resque]

Never had a SES/Check Engine code or any other problem. I had my transmission fluid changed a while back and I was starting to wonder if they just didn't put in a generic fluid that wasn't totally compatible with the transmission. A friend of mine had a Chevy Express (?) work van, same year and transmission, and they put a generic fluid in it and he said it shifted very hard until it was changed out. I looked in the book and it recommended using Dexron III ATF, no substitutes. I wonder if they didn't use a generic fluid for that type and that's the problem. I just want to make sure it's not something serious I'm letting go.

Can anyone explain this PCM thing to me.. I've read how you can "flash" it... ?

[2000CAYukon]

Originally Posted by fire24resque

Can anyone explain this PCM thing to me.. I've read how you can "flash" it... ?

The PCM (Power Control Module) controls the engine and tranny. The program for the PCM is stored in flash memory. The program contains parameters such as shift points, tire size, gear ratio, etc, etc as well as the program to control the engine and tranny.

A programmer can create a new program with new parameters and reflash (or rewrite) the new program to flash memory. One of the parameters is the line pressure for various times of the tranny; however, the PCM can only increase the line pressure so much. The transgo kit fixes a lot of issues with the 4l60e including correcting line pressures for given situations.

If you are going to update the PCM, make changes for shift points to meet your needs but don't mess with line pressure. Let the transgo kit do it's job.

//2000CAYukon

[fire24resque]

Where would I go about getting one of these Transgo kits and whats it entail to use it? I have the 2001 with the 4.8...would that automatically make me have the 4l60e or would I have to look into that further? Last time I got new tires I got the 265s up from the stock 245s, would that small change have any effect on shifting, since you said the PCM works with the tire sizes? I know its an option with the truck so I wouldnt think so but the thought crossed my mind.

Thanks

[Legasus233]

I have a 2000 Sierra, 5.3L, don't know which tranny yet, but have same symptoms as original poster. Doesn't happen at all when in tow/haul mode, just in normal use, under slow acceleration. Also seems to happen during downshift as well. Just had tranny fluid changed out too, nothing really changed though. Never have had a check engine light. How should I diagnose this problem??

[horse482]

Originally Posted by fire24resque

Where would I go about getting one of these Transgo kits and whats it entail to use it? I have the 2001 with the 4.8...would that automatically make me have the 4l60e or would I have to look into that further? Last time I got new tires I got the 265s up from the stock 245s, would that small change have any effect on shifting, since you said the PCM works with the tire sizes? I know its an option with the truck so I wouldnt think so but the thought crossed my mind.

Thanks

Any parts store or tranny shop should be able to get you a transgo tranny kit. To use, you have to drop the tranny pan and the valve body to replace some of the valves.

[rcm01]

I have a 2006 silverado z71- with 3.73 gear ratio,only 1200 miles, I am experiencing hard shifts also at slow starts and sometimes when i am on an incline, only when going from 1st to 2nd gear, does not happen all of the time. Is this something to worry about and if so, what repairs should i request?

[ColoradoSilverado]

I had the same problem with my 2000 Silverado (118,000 miles) and just installed the Transgo Shiftkit myself. It's not too hard to install and it will make a big difference, no more clunking or 1-2 bang.

Bert

[fire24resque]

I have absoloutely NO clue what I'm doing when it comes to transmissions. I can drop the pan and change the filter but beyond that I'm lost. Would anyone even recommend me attempting to install one without any prior knowledge?

[06CREWCAB]

The dealership installed some new software for my transmission today and so far, it is shifting great. The updated software is for the harsh 1-2 shift and for the clunk when putting it into reverse in the mornings. My truck had both problems . I'll post tommorrow after I drive in traffic. Cliff

[masamunexc]

My 2004 4x4 silverado has/had the exact same problem as the original poster. Under hard acceleration it shifted nicely from 1st-2nd but when under normal acceleration it really banged into gear and was audible and felt from within the cab. The dealer flashed the PCM and now it shifts fine from 1st to 2nd, but now 2nd-3rd is shitty.....I especially notice this after I turn a corner and step on the gas to speed up. It will downshift hard into 2nd as I'm going into the corner, then hard into 3rd as I come out. It really pisses me off and I'm forced to live with the constant banging. Any solutions to this?? Is this Trango thing a fix for this problem?

I've test driven another Silverado off the lot (2wd) and man was it ever smooth as butter in every gear, upshifting and downshifting. Couldnt even tell when it was changing gears.....this leads me to believe that the 4x4s are the ones with the problems. Any reason this could be?