Some small 4L80-E stuff to help you along.

[GenBiltstein]

Its all to common to see another 4L80-E transmission die off when they can last longer. They.were at the time were one of the strongest transmissions built for light truck duty. Other than the low/reverse band there were no bands to wear out or adjust and it's computer controlled. If you have a dependable 4L80-E on your hands there are things that you can do to help it last. Change out the transmission fluid and filter. I am old school so I will recommend a manual flush. That means dropping the pan and refilling the transmission case just more than several times over. This prevents a build up clutch crud in the torque converter, the valve body parts like clogged solenoid screens. In this case an ounce of prevention is worth a pound of cure. Contaminants in the fluid that are down to the microns can wear out pump seals, the valves and bores and similar components like the actuator feed limit valve that is susceptible to leaking because of side loading.
Give a once over on occasion like inspecting the passthrough connector for oil contamination because with these it will happen and its not if but when. The contaminated pass through connector can cause electrical shorting to take place right there at the connector. There are internal components that you can check with a multimeter set on resistance, and with the transmission fluid temperature sensor an infrared temp gun and a temp chart is all that you need.
Give yourself the chance to understand the 4L80-E transmission before it hits the ignore list and forgotten about until its too late.

 

[GM Guy]

Do you have any recommendations on what to replace for preventive maintenance on a higher mileage unit? like harness and solenoids, and how difficult that is?

I have a 94 suburban that I just bought, seller acted like the transmission worked great, it was parked 10 years due to a bad LP letting the PMD cook itself, after a new OPS and PMD, engine is running, but transmission is not acting quite right, was definitely going to do a pan drop and filter change, but was curious if I needed to go deeper.

 

[ak diesel driver]

There's a pretty good article online about fixing reverse. Basically you adjust it for band wear. My reverse went totally out and I did the adjustment. Been working good so far. Got around 20k more miles on the tranny so far

 

[MrMarty51]

There's a pretty good article online about fixing reverse. Basically you adjust it for band wear. My reverse went totally out and I did the adjustment. Been working good so far. Got around 20k more miles on the tranny so far

Not knowing the history on the transmission in my truck, this might be something I should check out.
The PO claims the transmission is a reman out of Browns in Billings Mt. but He didnt get documentation on that, and, I might could give it an inspection to see if there is a reman date wrote, or stamped, someplace on the transmixer.

 

[MrMarty51]

Easy TH400, 4L80-E reverse servo setup: Craft your own tool - Transmission Digest

While not as sensitive as some shifting bands, the Reverse band adjustment on a TH400 or 4L80-E transmission is critical, and failure to get it right has tripped up even the best builders. There is nothing worse than getting the transmission installed, putting it in Reverse and then not going...

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