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4l80e hard, hard shifting "neck snapping"

Alright, you guys are giving me valuable information. I will get codes and check trans info tag for date code next. I need to know what year trans I put in the Suburban. I will also verify the grounding wire to the block/head.
I still have the old/removed trans, maybe I can use parts (solenoids) from it? Eventually how will I change the line pressure?
The move is going well, next stage - unpacking.
 
Ideally thru the pcm. The force solenoid has an adjusting screw in it as well but I don't know how much you can really there.
 
The problem with using a 94+ trans in a 91-93 truck is the valve bodies are physically different in how they control line pressure. You would need to swap valve bodies, drill a couple of holes in the seperator plate, and I believe swap the accumulator housing as the 91-93 has an extra accumualtor in it than the 94+ did.
 
OK, so I am not afraid of making some modifications, and I have always been interested in learning more about automatic transmissions.
But I now see I made the mistake of not doing my homework before buying this transmission. Unless the trans tag shows it is older than I was told, I'm screwed.
So do I tackle the mods, or try rebuilding my old one, or try converting to manual, or keep resetting the limp mode, or...
Did I say I love transmissions, not!
 
If you have your original, I would lean toward rebuilding it, then you can sell the current one as a runner to recoup some of the cash. Although the cash for it sucks, a good rebuild is a lot of trouble free miles.
 
Rebuilt trans from Phoenix, shipping should not be to bad to San Francisco area?

I tested the key off resetting today. Drove a few miles from work to lunch - hard shifted. From lunch to work (started, waited 5 seconds and turned it off, restarted) -normal shifting. From work to home, about 20 miles (started, waited 5 seconds and turned it off, restarted) - again normal shifting. Let me tell you when this big suburban is shifting correctly it is a nice drive.

The tag on the installed trans has typed in numbers in the source ID section: 95____5291. The letters above the numbers are BK P.

The codes are 85=undefined gear ratio and 87=high gear ratio error.

If the start, idle, key off, restart, then drive, works everytime I could live with that. Any harm in this?

Now I am remembering that when I put in the previous transmission (remanufactured from the chevy dealer) I changed some of the wiring from harness to plug via instructions with the transmission. I know I saved the instructions just have to find them after this move we are going through.
Maybe I can wire in a "every start" reset?
 
I think I now know what your problem is, and you won't want to hear it. Does your trans use 2 speed sensors that hook up to the transmission as well as one to the transfer case(3 total)? The 2 codes you have deal with an error between the input and output speed sensor readings. 91-93 4X4 trannies used an input AND output speed sensor in the trans itself whereas in 94 GM did away with the putput, and used a signal from the VSSB based off of the output speed sensor reading from the transfer case. I know this has been an issue with diesels, but not sure about gassers. If so, the ONLY fix is to get one of the rare 91-93 trannies back in it that has the output speed sensor in the trans. If yours does not have 2 speed sensor hookups for the trans, but instead just 1, then the general consensus for these 2 codes is a bad input speed sensor giving false readings and replacing the input speed sensor seems to fix it.

EDIT: changed putput to output.
 
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Can't he get a chip or manual trans ECM from a 1991 and drop the Optishift trans computer on it? Leroy diesel sells them...

Either find a local cheaper trans rebuild shop, vacation drive old 1991 trans it out here for rebuild as cargo, or about $200 each way truck fright on a pallet. U-Ship website maybe?
 
Hmmm, it has 2 speed sensors. I compared it with the removed transmission, exactly the same. On the drivers side one located above the big plug and the second above the shift shaft. Also verified one on the transfer case, passenger side.
Am I right in reading the trans tag that it is a 1995?
 
Pat_Opsahl said:
Hmmm, it has 2 speed sensors. I compared it with the removed transmission, exactly the same. On the drivers side one located above the big plug and the second above the shift shaft. Also verified one on the transfer case, passenger side.
Am I right in reading the trans tag that it is a 1995?
Click to expand...
Starting in 94 the 2nd one became a dummy plug. It looks like a speed sensor, but there is no reluctor wheel inside the trans for it to get a speed sensor reading from(unless the HUMMER is different than pickups, vans, and motorhomes). I'm not sure how to read the tag date codes, and my manual is out in the shop. It's starting to sound like you found your issue, and I'm sure it's not the one you wanted to hear. I know I have ridden in 4L80E trucks without the output speed sensor hooked up, and they will shift, but shift like you describe at full line pressure since they are only shifting based on input speed sensor readings. Hence it cannot verify which gear it is in, or how fast it is shifting since it needs both speed sensor readings to do this. He could run an optishift, but then the problem is how does it shift in 4X4 low range. The optishift doesn't have the ability to offset for low range last time I read the setup manual for it, so unless this has changed he will have problems if he ever puts it in 4 low.
 
Yeah, I am sad that this trans is not going to work. But, it does feel good that you guys and thefermanator figured it out. Thanks!
The suburban is our back up vehicle. And we got everything moved, so I can do the swap at a easy pace. I am considering trying the rebuild. I purchased and watched the video, looks doable?
 
I like it when things work the 1st time. Always time to learn, but, automatic transmissions are something I decided to skip because everything has to be perfect including rebuilding the TC clutch in the converter (or replace with new), repairing the TCC valve body due to wear, replacing the 4th gear (OD) planetary due to wear and there are other changes that can be done. Like improving the oiling on the early 4L80E's that the shop listed does. Then there is some special tools you may need.

Last if you nick a seal and it can't generate enough pressure to fully stop slipping it quickly burns the clutches/band up. Then you get to rebuild the whole thing over including the TC from the debris.

The 4L80E is like a McDonald's cheeseburger with only your 350 being more common. Finding a shop that can cost effectively rebuild these in their sleep isn't that hard.
 
How about using different transmissions in a 95, 96, 97 ,98 or 99

I have a 99 I am planning to install in my 98.

I am also looking for a transmission for our 1996 K1500 6.5 diesel Suburban. What years would be drop in? I was told they made 2 different styles in 1996.

Would there be any differences other than the spacing and size of the lines?

Any advice would be appreciated.
 
With an adapter set and line, you can put any 4L80E from 95+ into a 95+ truck. 95-96 trucks used 5/16" lines, and had both cooler lines hooked up at the bellhousing, 97+ used 3/8" lines and had 1 line at the bellhousing and one at the rear. The 97 style trans made it into some 96's as well. To run the 97+ style in a 95-96, you run adapters to hookup to the larger ports, and a short adapter line to extend back to the rear hookup. And with adapter fittings and some cutting, you can run a 95-96 trans in a 97+.
 
THEFERMANATOR said:
With an adapter set and line, you can put any 4L80E from 95+ into a 95+ truck. 95-96 trucks used 5/16" lines, and had both cooler lines hooked up at the bellhousing, 97+ used 3/8" lines and had 1 line at the bellhousing and one at the rear. The 97 style trans made it into some 96's as well. To run the 97+ style in a 95-96, you run adapters to hookup to the larger ports, and a short adapter line to extend back to the rear hookup. And with adapter fittings and some cutting, you can run a 95-96 trans in a 97+.
Click to expand...
I just installed a 98 4L80 into my 95 Burb and found that the rear adapter (return) must be the extended nipple type to reach deeper into case.
 
FellowTraveler said:
I just installed a 98 4L80 into my 95 Burb and found that the rear adapter (return) must be the extended nipple type to reach deeper into case.
Click to expand...
Hence the adapter's. The adapters for installing the late trans into an early truck is already the correct depth. I know more than a few reatailers carry the adapter fittings and line set for not much money.
 
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