Automatically a bad idea?

My youngest son recently bought a 2012 Chevrolet 1500 with 108k miles on it. It has a 4 speed automatic (4L60E). It now has 110k miles and it drives fine in first and second but third gear seems to be gone. A little internet research indicates likely a worn out third gear clutch pack or the piston that actuates third gear has seals that have failed. It happened suddenly and the fluid doesn’t smell burnt so I lean towards the seal failure on the piston as the likely cause. Anyone familiar with this trans and failure modes? Any easy ways to further diagnose and isolate the likely root cause?

I have not torn into an auto transmission before but I have watched a few videos now for this model transmission and found decent step by step rebuild guides making me think I might give it a shot. Anyone strongly discourage such a foolish endeavor? It looks like being very detail oriented and methodical is key and I can do that once in awhile.

It would surprise me if you can't find a local shop to go through that transmission for under $800. It's hardly worth buying the tools and parts. 

Id say go for it, good chance to learn something and gain a new skill, 4l60E are cake to work on.

Step 1) Buy spare. Swap transmissions. 2) Attempt rebuild on old transmission. Successful? Put old trans back in. Sell new one. Break even. Failure? See step 1 above. 

Is this an Express van? The trucks went to the 6L80E in 2010.

In reply to MINIzguy :

It's a 2012 LS 1500 Extended cab short bed 4x4 with a 4.8l and 4 speed transmission (4L60E). There are 2012 models that use the 6L80E but the cheaper and smaller engine trucks still used the 4 speed.

In reply to fusion66 :

Huh. I thought it was an across the board replacement in 2007-2008. Guess I was wrong. The 2013 5.3 truck I put some miles on had the 6L80 and that was definitely an improvement over the 4L60 stuff I've driven.

4l60s are not that hard to work on aside from the usual auto trans stuff like working with snap rings, getting directional lip seals into the clutch drums without damaging them, not screwing up the sealing rings on the input shaft, not accidentally gouging bushings during teardown and reassembly, lining up pump halves, pushing servos in while you install snaprings, etc.  If you really can stand to go slow enough you will probably be fine. Attention to detail is critical as anything you screw up while installing will henceforth be buried in the middle of a giant assembly and require another trans removal and teardown in order to do over. 

So I decided to dive into this as the quote my son received was $2500 and timing is not critical as he still has his prior vehicle.

Removal of the transmission was pretty straightforward and aside from needing the heat wrench on the exhaust flange nuts everything came out as it should. No broken fasteners or plastic clips so that went as well as can be expected.

Teardown of the transmission also went well thanks to some excellent highly detailed YouTube videos for this transmission. As expected, the issue is a 3-4 clutch pack failure which appears to be the result of a 3-4 clutch piston seal that is no longer sealing.

Currently waiting on a rebuild kit and pro-actively replacing a few other known weak points as well since I don't want to do this again if I can avoid it.

Total investment to date is $350 including fluids.

Hoping parts arrive tomorrow and cleaning and rebuild can start this weekend.

In reply to fusion66 :

Incredible, good job! I hope the reassembly goes as well.

I figured I would post a quick follow up.

I should have read the post from Vigo a few more times, as this part bit me in the ass, "getting directional lip seals into the clutch drums without damaging them".

When fully re-assembled and installed it was slipping in 4th after a couple of miles and the 2-4 band was toast. I pulled it and tried again, replacing the 2-4 band and the  seals in the 2-4 servo again thinking I must have messed one up. Same result.

Took it to a shop and they tore it down  and found I had boogered up a seal on a piston which was allowing enough oil to flow where it shouldn't to prevent it from flowing where it should with enough pressure to apply the 2-4 band properly.

Shop charged $350 for bench time plus $70 in parts (most of what I had just replaced was useable) which seemed very fair now that I know what a tear-down and rebuild takes. Total cost to my son was $550 and I ate $200 for my screw-up, basically charging him for the repair shop cost plus the parts and fluid that I purchased.

I will say that I learned a lot but ultimately was pretty disappointed that I failed at a successful repair. I am quite glad that I can close that chapter and move on to basic maintenance of the rest of the fleet.

"Every experience is a learning experience."

This sounds like a happy ending, since you did still save money. I've used the same technique, try something, not get it right, then have it fixed properly. It usually cost me a lot more! 

In this case, I'd call it a win.

Yeah, that's not all that bad a result considering the circumstances. You learned a lot and got 95% of the way there, and when you gave up it only cost you $500 which you now know and can appreciate is a good price when they could have just charged you the normal 1600-2000. You might have earned that price from a sympathetic gearhead by impressing them that you were willing to try. I cant put a value on your time but that's not a lot of money for the amount that you learned from it, and i still give you major props for bravery!!