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4l80e hard, hard shifting "neck snapping"

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Pat_Opsahl

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Location
Tracy, CA
I have a problem with my 4l80e transmission. It shifts very hard through all the gears and especially hard on the 1-2 shift.
It is a 1991 Suburban, 3/4 ton, 4X4 with 244k miles. Original engine, 350ci runs great. The original owner replaced the trans at 100k and I took ownership at 190k. I put in a rebuilt trans at 233k purchased from the dealer. It rarely got driven over the next 5 years. Last year the trans failed, stopped shifting out of 1st. I installed a used 4l80e from a 1996 hummer. It shifted hard from the get go. I put on several hundred miles, no change. The 1-2 shift is almost violent. I can kind of feather the throttle to help smooth the shifts. The engine revs high then the trans just goes fast and hard to the next gear.
I tried the Lucas trans additive. I drained 24oz out of the trans and put in the additive. OMG, it worked! It shifted perfectly normal. What is this miracle juice? Hold the celebrating, it went back to hard shifting after 150 miles of driving. Drove another 100 miles, still bad. I tried the additive again. Yeah, its shifting correctly again. This time I use the Suburban to tow a project car on my trailer, about 170 miles to its new location. Some good hard towing, worked perfectly. Then after disconnecting the trailer, back to hard shifting. What is going on? Any and all ideas are very welcome.
Thanks, Patrick in Northern Calif
 
I'm guessing hummers have higher line pressures and firmer shifts due to their weight and intended use.

"Thefermanator" or "Will L" will likely chime in with actual knowledge on this.
 
Wish I could help. I know with the hummer when I disconnect the batteries for an hour or so if shifts just like he is describing. I asked about it "learning" but everyone said no. When I drive it long enough it starts playing nice. Sometimes 250 miles, sometimes 50 miles.

There is one thing that happened though: one time it never "learned" and constantly shifted hard, and when coming to a stop after having been in 2nd gear or higher it would take off in 2nd gear limp mode. End up finding out I'm a moron, uh I mean I found I pinched a wire inside the trans pan when changing the trans filter one time. Idk what circuit I pinched/ grounded, but if you ground (short out) whatever circuit I did, that could maybe be an issue.

The hard shift / learning is still there, has been since day one in talking to the original owner, and another 95 hummer owner.

ps. I hate transmissions, always have and always will.
 
Sounds like limp mode. Any codes in the ECM? "Service Engine Soon" not equal to "Service Transmission Soon" so transmission codes do not turn the light on.

Did you make any changes for the TCC solenoid? Those are different for some years. TCC is PWM control for 1994+ and simple on/off for 1993 and older. Off the cuff I think the pressure control is also different for different years. So dropping a OBDII 1996 4L80E into a OBDI 1991 may be your problem.
 
Ahh! That is a great price. Patrick, save that link...but wait for Theferminator to get his 2 cents in, or billyg? I know there's more of you trans experts out there...

I'm not sure about the limp mode thing, when mine was in limp mode it started and stayed in 2nd. never 1st,3rd or 4th.
 
When the TPS is off like below .5v (code set) at idle mine does the neck snapping shift, or when the TPS wires are shorted, or any other time it's pissed off at me.
 
"I hate transmissions" - Yes I agree with this statement. I am researching converting to a manual transmission...
No I did not make any modifications to the TCC. I will look for codes tomorrow. To read OBDl codes is shorting pins 1 to 12? I'll have to look that up.
I kind of agree with the line pressure theory, but why does the miracle lucas additive make it work perfectly - for only several hundred miles? Should I try a higher quality trans fluid, synthetic, dex Vl, ....
 
I put new filter and fluid in when I installed it last year. I have only 600-700 miles on it. When I purchased the trans I was told it had 50-60k miles. The filter I removed looked fine.
 
Generally the transmission is 100% electronic. Mods to the valve body aside and different years are controlled differentially.

So start with grounds (after reading codes.) including the ones for the ECM by the dipstick - remove and clean.

If you didn't change the ECM for the 1996 trans and made no mods to the transmission this be your issue. Get a stand alone 4L80E controller and you may need a MT 350 ECM (maybe just PROM chip) to run just the engine. Better yet, rip the tired 350 out of there and drop in a mechanically injected 6.2/6.5T and eliminate another computer. MT with that and No ECM's required....
 
Sounds like you got one of them fancy shift kits. Could be the shift solenoids are clogged up or they are just bad also could be a speed sensor causing it because it tells the transmission what speed it is then it shifts at that speed point.
 
WarWagon said:
Sounds like limp mode. Any codes in the ECM? "Service Engine Soon" not equal to "Service Transmission Soon" so transmission codes do not turn the light on.

Did you make any changes for the TCC solenoid? Those are different for some years. TCC is PWM control for 1994+ and simple on/off for 1993 and older. Off the cuff I think the pressure control is also different for different years. So dropping a OBDII 1996 4L80E into a OBDI 1991 may be your problem.
Click to expand...
This was for 4L60E trans, not the 4L80E. For the 4L80E the pressure control solenoid changed from 91-93 to the 94+ style. And putting a 96 trans into a 91-93 truck without making any changes WILL cause issues due to the different control logic used for controlling line pressure. 91-93 is one style trans, 94 another, 95-96 is another, 97-early 99 is another style, then late 99+ is another. They don't all just swap in without mods. I know to put the 96 trans in you had to either swap out the shift shaft in the trans, or rig up a cable to make it shift. Chances are you had to change your trans plug, or it had already been changed before you got it. What is happening is you either have a bad PCS that is holding max trans pressure, a limp mode condition where it is shifting at full line pressure to protect the trans, or your just lucky enough to have it shift everytime the ECM commands a cleaning cycle of the pressure control solenoid. We need ALOT more info to help you with this problem. We MUST know which valve body is in the trans, and if it still has the factory PROM in the ECM.
 
Alright, some heavy duty questions! I put on some engine mods over 15 years ago. Shorty headers, Airaid air filter and a Jet performance chip upgrade.
When I installed the trans it was plug and play. Did not change shift shaft or trans plug. What is PCS? Did I get a 1996 Hummer engine/trans? It was ebay so anything is possible.
We are in the middle of moving, so I have not pulled any codes yet. I drove it over the weekend and had it working correctly without adding any more additive. It was random when it would shift correctly. I did notice that when it shifts hard it will not go back to correctly shifting unless I stop and turn the truck off. Likewise, if shifting correctly it will not go to hard shifting during that run.
So I need to look up the trans code to see what year trans I have. I have the engine too, if that helps? The engine looks just like mine but has a lot of heat shield plates on the exhaust manifolds. I also have the ecm but its connectors are different than my suburban. Once we get through our moving I'll post the info and maybe some pics will help in solving this.
The one thing that is consistant is that it shifts correctly after adding the lucas additive.
 
PCS = pressure control solenoid.
Additive may or may not be helping a random limp mode issue. The simple act of pulling the trans dipstick to put the additive in could be helping the ground wires attached to it's hold down bolt.

Good luck on the move.

Key off then on resets the limp mode / protection mode - aka high pressure shifts to try and save the trans during unusual conditions.
 
Thanks!
It does kind of feel like a shift kit, hard to believe since it random.
At some point it sounds like the pan is going to be coming off...
 
It is not a shift kit. The fact that key off resets it, and each time it will shift hard from the beginning until you cycle the key. Definitely a limp mode shifting at full pressure.
 
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