Northeastconfederate

Truck is a 2011 RCSB Silverado with 4.8, 4L60E, 2WD. It has a Whipple, cam and headers, but none of that is relevant to this post.

I have lost second gear completely. It started out with extremely hard 1-2 shift under light throttle (it was better under hard acceleration). I thought this was the result of the tune it got after engine upgrades until recently. I've realized it maybe could be 2nd gear servo failing. Over time, the 1-2 shift softened. It suddenly completely gave up 2nd. It won't engage 2nd either upshifting or downshifting. All other gears seem normal, including 4th. This is noteworthy, since 2nd and 4th both use the forward clutch pack and the reverse drum band, according to an application chart I found online. This being the case, it seems to me like the band is OK and so is the forward clutch pack. I'd expect it to slip worse in 4th if the either of those were burnt. Also, the fluid doesn't smell burnt. The truck has 120k on it and the fluids never been changed. I haven't dropped the pan yet, but it looks fairly clean on the stick and the little bit that leaked out when I removed the servo didn't look or smell horrible.

There are no transmission codes at all, none stored, current or pending. I scrolled through the list of codes and see various codes for the 1-2 and 2-3 shift solenoids. I would think if a solenoid was faulty one of these codes would be stored. Also of note, the description for PO752 reads, "1-2 Shift Solenoid Valve Performance No Second or Third Gear." All the shift solenoid valve codes describe two gears affected. So I don't think the failure is a shift solenoid valve.

I removed the 2nd and 4th servo this afternoon and didn't find anything visibly amiss. All the Teflon seals were in place, though the seal for the 2nd gear servo came out of its groove when I removed it. I doubt very much it was in this condition installed, though. There's no way it could escape its groove in the servo piston while in its bore.

Anybody have any thoughts on a diagnosis for this loss of second gear? I'm thinking possibly the 2nd gear servo seals leaking despite looking OK, allowing the band to slip in second. If this is the case, the 4th gear servo seal is good, and the band grips in 4th, since 4th doesn't slip. Or maybe a worn shift valve bore in the valve body? Maybe a leaking plug in the valve body? Any input would be appreciated. Obviously, I'm hoping I can fix this without removing and overhauling the transmission, though I'll do that if needed. I've seen Sonnax has a bunch of upgrade parts and fixes for known issues, including an improved 1-2 shift valve for the valve body as well as "super hold" 2 and 4 servos. I'll install whatever upgrade parts I can without removing the trans if I'm able to fix it in the truck. If I have to remove it, I'll build it up with all the Sonnax upgrade parts.

Please let's have your thoughts if you know about auto transmission. Don't bother with, "just swap it for a rebuilt unit" or "swap it for a 4L80E." Both of those options are out of the question.

RB04Av

Sun shell

Esp if you can put it in manual 1st, run it out, then shift to 3rd or D, and it goes to 3rd

Northeastconfederate

Yup, I can do that. It goes right to third.
I see that Sonnex's Smart Shell lists no 2nd gear as a symptom of a failed reaction shell. I guess this ain't getting fixed without removing the trans.

shakenfake

Brother you must remove the trans for a rebuild LOL
The 6Ls do not seem that bad to rebuild by yourself though. There was a book I had seen that was quite good as well as some VERY thorough youtube videos.

Northeastconfederate

Yeah, I was a Benz tech for many years. I've overhauled and done repairs on a number of automatics. Never a 4L60E, but Benz's 722.3 was similar in design. With all the resources out there, I'll get it done and make upgrades to increase its durability.

MaroonMonsterLS1

He says it has 4th and reverse...thus there is no way it could be the sunshell

OP ignore the sunshell

Your issue is band clearance. 2nd and 4th do both use the band, but they use different apply pistons in the servo assembly. The 4th gear portion has more available stroke in some setups...that's why you have 4th but not 2nd.

If you want a bandaid fix, you can either weld onto the tip of the servo pin to get clearance back in spec...but if the band is already worn enough...it might not last long before you're in the same boat
Alternatively you can buy the sonnax extended length servo pin 77787-02K if you don't want to weld the tip.

Either of these aren't a true fix...they're a bandaid. But sometimes a bandaid will last a long while.

Northeastconfederate

Thanks very much, I was hoping you'd weigh in. That makes sense. It seems the band must be pretty worn, and my experience going from super hard shift to softer, to soft and slow to no second reinforces that. I've fixed shift complaints in Benz transmissions by adjusting band clearance using variable sized servo pins. I'm going to dig in and fix it right.

The truck makes 500hp. Please tell me if I'm on the right track:

Sonnax "extra wide" Red band (Kevlar not available).
That will require a new reverse drum to avoid the new band trying to grip uneven wear on the drum. Are aftermarket drums OK? Or should I get one from Chevrolet?

Sonnax 2nd and 4th "Super Hold" servos

Sonnax Performance Pack

Sonnax Smart Shell with heavy duty shaft

I'm not going to replace the factory input or output shafts with the Sonnax HD parts. This truck might see the strip one day, but not regularly. It's my daily driver and we use it for travel. I'm also not going to change the 1st and 2nd gear ratio. This truck has 3.23 gears and a 4.8 motor. Even with the blower, I need the taller gearing and since we drive this truck long distance, I don't want to change the 3.23 gears even for 3.55's.

I have a quite from Jeg's with all the Sonnax parts. I could probably post that, in case I left something out.

I'm planning to install a stall convertor to match the cam while I have the trans out. Cam is a BTR Stage 1 PD torque cam that wants ~3,000 stall. That's not really relevant to the repairs, but thought I'd include it in the plan description...

I need a source for heavy duty clutches.

Northeastconfederate

Tell you what: I'd like to meet the bonehead or team of boneheads who decided it was a good idea not to include a drain plug in the transmission pan. I know Chevrolet has been doing this for decades, but how much are you really saving??? Benz puts a drain plug in the pan AND in the convertor! Imagine that: you service your transmission, you can actually replace the lion's share of the fluid!

Northeastconfederate

Duplicate post

strutaeng

Ehh, I've had some trucks with the drain plug and some without. I haven't figured out the rhyme or reason.

On my 99 Silverado someone over time stripped the drain plug. After all failed I had to go down there with my stick welder stinger and weld a 3/4" nut on it. It must have been tightened with an air impact.

Anyways, what I now do if the pan doesn't have a drain plug is: use a short 1/2-13 bolt and nut, and nylon washer as a sealing ring from the hardware store. Just tack the nut on the inside of the pan. Works surprisingly well and only costs like $8 and a bit of time.

Or you could just find a matching drain pan that did have the factory drain plug and swap it.