I am now in a phase of life where I have precious little time to work on cars or transmissions. So it doesn't all drain out of my head before I put fingers to keyboard....
A few things I have learned when working on my own 4L60Es and helping others with theirs:
Rule #1 when you think your trans is hurt: don't do WOT anymore, and ESPECIALLY don't do it through the shifts. You'll just slip away whatever clutch material is left. Transmissions aren't like piston rings - running them harder only makes the problem worse, not better. If it does something screwy at WOT, don't do it again and again and again just to be sure... this is dumb
. I've babied hurt 4L60E's over a year before finally pulling and repairing them, but that was NO WOT, waiting for it to complete shifts before applying throttle, etc.
Rule #1b. The only time the clutches wear is when they are applying and releasing. So avoid a lot of throttle during shifts, and only change directions when the car is completely stopped, and your clutches will last longer.
Rule #2. Yes, flush the fluid, but only after you understand this thread
and have the time and budget for it. Sorry, but nobody to date has been able to come up with a better, more coherent explanation in the 3+ years that thread's been up. Use this method
to do it.
Rule #2b. Do not wait to flush the fluid until the trans acts up. It's just like checking the engine oil when you break down on the side of the road.
Rule #3. If you have a funny drivability problem and you think it's the trans, but it could be the engine, it's the engine. Period. Always.
Rule #4. The FIRST step in diagnosis before figuring out most transmission problems is to see if the transmission is simply doing what the PCM told it to do. As these cars get older, this becomes increasingly important, especially with late shifting or TCC problems. If you don't have the ability to monitor PCM inputs/outputs, you need to get this capability before pointing fingers at anything.
Rule #4b. The '94-95 cars will throw a number of transmission codes without illuminating the MIL. If you have a drivability problem, scan the car with a scanner FIRST, then go read the factory service manual and follow the diagnostic charts BEFORE blindly replacing parts or going on the forum and making a post that looks something like "hey guys my car shifts funny I stuck a paperclip in the diag port but nothing happened I replaced these four parts but it's still doing it i don't know what to do pleez hlp thnkx". This is dumb.
Rule #5. If your car drives like 1-2-N and does it repeatedly, this is the 3-4 clutchpack gone out. Yes, it happened to you too. Sorry.
Rule #6. Print this
out and stick it in your glovebox. If you have a problem on the road, pull this out and read it.
Rule #7. The factory service manual is the best diagnostic tool you will ever buy, for any car, period. UPDATE 2015 October 28 - GM removed the detailed overhaul procedures from the '96 FSMs. The '94 and '95 FSMs have the material and the '95 transmission diagrams are essentially identical to the '96 transmission internals.
Rule #8. A line pressure gauge is the second best $50 for a transmission diagnostic tool you will ever spend if you are trying to assess your line pressure. Ebay seller cmbclalb sells them.
Rule #9. All electronics in the 4L60E can be repaired/replaced without removing the transmission. Don't be afraid to diagnost and repair these problems yourself.
Rule #10. The Sonnax 4L60E-HP-01 is the best shift kit you can buy for the 4L60E, hands down. TransGo was good, but the Sonnax kit is newer and much better.
Rule #11. The Throttle Position Sensor and throttle body are critical to proper operation. If your TPS is faulty, or you replaced your throttle body with a larger one and didn't get the PCM reprogrammed to compensate, then you will have transmission problems.
Rule #12. Don't bother with Dexron VI unless you are racing. Dex/Merc3 is just fine. Your trans will benefit from regular flushes (minimum once a year, ideal is every other oil change). Because you'll be changing out the fluid so often, you will never realize the benefit of the longer life additives in Dex6, and that stuff isn't cheap.
Rule #13. More obscure but you need to know: If your car is a '94 or '95, Reverse very likely WILL eventually fail, due to a design defect. But if you act now, you can stop it. The way to prevent this failure is to install a '96-up manual valve (this is the valve connected to the shift linkage - get one out of a junkyard from any 4L60E) and then drill two small holes in the bottom of the valvebody. PM me and I can send you a picture. I let this slide too long on my '94 and finally paid the price for it at 154k. The rest of the trans is still fine and won't hurt it to drive, just know you can't back up. Once that clutchpack is worn out, you have to pull the trans to replace the clutchpack.
Rule #14. The 4L60E is a "mature" transmission. Its faults are well-understood and the big rebuilders now know how to properly rebuild it so it lasts. The proof is by the warranty they provide. Do not accept anything less from a local shop. Be sure to get a warranty in writing and read it completely so you understand what it covered and who pays what.