BlownFuse

Picked up a 2012 Silverado 1500 WT 4x4 4.8L 4L60E (120k miles) recently and it’s in really good shape. Drive it home, about an hour trip, no issues. Drove around all weekend, including some light off-roading on dirt and gravel roads in 4LO.

A couple days later, after driving on the freeway for 20 minutes, the engine starts surging and the transmission is heating up fast to around 230°F. Pull off the freeway and let it cool down, using the AC to run the fans. Then i drove it home on backroads between 30 and 60mph, no issues. No more slipping.

So I service the transmission, do my planned fluid flush, filter change, new pan, filter and gasket, and it’s driving around town feeling good.

But then one day, I drive about 20 minutes, park for a while, then head back home and it starts slipping and heating up rapidly once more. Sit and let it cool back down to about 175°F and it drives home.

I’m not sure what’s wrong. The fluid level is just right when tested at ~180°F, it drives around town and on the freeway smoothly and strongly—but then on that return trip it starts acting up.

I would think if the clutches were slipping, it would always slip, but it drives around great initially. It’s like after it warms up then sits hot for a while, something inside acts up.

Any suggestions?

jfmorris

The way it is heating up makes me wonder if the torque converter lockup solenoid has failed.

While I know it's not a Chevrolet, our Subaru had that solenoid in the valve body fail this spring, while 100 miles from home, and it caused the transmission fluid temp warning light to come on. I ended up parking the car after limping along driving 2 mile stretches, pausing to cooldown, for about 10-12 miles until I got to a spot I could park on a 2 lane highway, and waited for a tow home. Once home, the car acted fine for a few short drives around the neighborhood, but I didn't trust it beyond that.

The Subaru dealer wanted $5000 to replace the valve body and torque converter, and I could not get a 3rd party transmission shop in town to touch a Subaru. I was fortunate that the ODB2 reader was able to pull codes from the Transmission Control Computer (TCC) on the Subaru, pinpointing the issue to the failed solenoid. I opted to pull the valve body, replace the $50 solenoid myself, put it back together, along with a fluid change, and we've put 3800 miles on the car since then. That said.... the Subaru is getting traded sooner rather than later...

To my understanding, Chevrolet doesn't report internal transmission failures via ODB2. I sure had no check engine light when my 2003 Yukon 4L60E transmission bit the dust at 130k miles, and had to be rebuilt.

BlownFuse

Thanks. I have a manual forester and a CVT legacy. Got the manual because I didn't like the old 4 speed auto they offered. Surprisingly, the CVT is going strong at 150k. Engine drinks oil like an alcoholic, but the CVT has been rock solid.

Yesterday it happened again. Same scenario. Except this time, cooling it down didn’t eliminate the slipping. If I put it in 1st or 2nd, it works great. If I put it in 3rd, it’s like being in neutral. In D it crawls until it tries to shift (to 3rd I guess) and revs up like neutral. Clutch material gone or bad solenoid??

Would be awesome if it was just a solenoid. In fact, when I changed the pan, one of the solenoids was a bit looser than the other. I also read that the 3-4 clutch packs go out on these transmissions pretty routinely, caused by a number of internal pressure issues.

i have no idea if the trans has ever been serviced before, but it was a fleet vehicle before I bought it and it’s been very well maintained otherwise. Not a leak anywhere. Super clean and engine so smooth. Could have been the original fluid and filter for the whole 120k miles, but idk. Was dark brown but not black or burnt smelling. Only fine, graphite-like metal content on the magnets.

I could try changing out all the solenoids and maybe even the servo—but at 120k, should I just assume the clutch packs are worn out? can I know for sure if we dont drop the tranny out and tear her down?

jfmorris

I can swap a valve body or solenoid, but beyond that, I've only pulled and worked on a manual transmission back in the late 70's, with my dad, that we took apart on his workbench. I know when the 4L60E on my GMC Yukon went out, around 130k miles, it was missing gears and they had to replace solenoids and bands and such. But I knew less then than I do now on how these things work.

FYI, if you have that Subaru CVT, I recommend changing the CVT fluid every 60k miles. Unfortunately, most of the dealers won't do it, claiming its "lifetime" fluid. I had drained the pan and refilled mine back at 60k miles, then again after this mess. It didn't prevent the bad solenoid, but my understanding is the lockup solenoid is common on Subaru CVT's.

Back to the Chevrolet - I think you may end up like me, paying a shop to rebuild it, unless that is something you are up to. Knowing I paid $2100 (cash) to get mine rebuilt maybe 14 years ago, I think if I had to do it today I would find a good rebuilt one online, and just try to swap the transmission myself... maybe!