Learn Me: Improving a 4L60E

If you've seen my recent thread, I just picked up a 1998 K1500 Silverado with the ubiquitous Vortec 5.7/4L60E combo. 172k miles. The truck runs very well and the transmission is incredibly well behaved considering the mileage. It has a little lag going into reverse, but otherwise shifts smoothly around town and firmly enough when accelerating harder. No slipping that I can tell. However, after quite a bit of driving on some twisty back roads with a lot of shifting between third, fourth, and lockup, I got on the highway and got the notorious torque converter clutch shudder. It was a very specific condition - 55mph cruise behind a slow prius, WOT downshift to second up to the 75 mph speed limit, then lift off and when I reapplied throttle to maintain speed, it shuddered. 5 seconds or so later, there was a slight lurch and it was back to normal operation. After that, I also realized the truck doesn't seem to completely lock up - at 75 mph, I can get the tach to move ~100 rpm without a change in speed or unlocking the converter. This may have already been happening, but I didn't notice it before.

Because the trans otherwise seems to be in good shape, I want to do some preventative updates if needed.

My must do list is:

• Transmission fluid (not flush)
• Filter
• TCC PWM valve or PWM eliminator

What else should I do while I'm in there to make this trans last as long as possible? Since this is the truck, I want to do everything I can to not have to touch or worry about it again, at least for quite awhile.

Unless you are on the highway and just cruising along I'd operate the truck as a 3 speed auto and leave the shifter in D most of the time instead of OD. It saves a lot on unnecessary 3-4,4-3 shifting which prevents wear and reduces heat.

My Suburban has the same combination and is a much happier truck when I leave it in D.

Dad recommends a specific transmission fluid additive for those to fix the shudder. It works. He refers to it by part number because it has a ridiculous name.

https://www.amazon.com/Lubegard-19610-Tranny-Instant-Shudder/dp/B0002JMLQU

The Corvette servo was a popular addition back in my 9C1 days.

+1 for the Corvette servo and the anti-shudder additive. I also added a cooler to mine, but I tow with it in the summer. Same combo in a 2001 GMC Savanna.

Personally, it's a "bazillion" mile 4l60. It's either rebuild time or leave it alone until its broken. Once broken, fix it right. the Lubegard shudder fix is almost snake oil. Certain vehicles it works great, others it doesn't fix E36 M3 or it shortens trans life by getting rid of the varnish and deposits that keep it going.

The corvette servo is outdated now, you can get a bigger servo now.

Well, the transmission part of it isn't broken. It's almost definitely the TCC PWM solenoid, which is known for wearing the piston resulting in low apply pressure. this is also for a completely stock engine that will never see power adders, though I do occasionally tow with it. It will be getting an external cooler.

I have little intention of putting additives in the trans. It's not that far gone; I just want to prolong its life if possible.

Things I've seen mentioned that can be done without pulling the trans that seem to have a good reputation:

• pinless aluminum forward, 1-2, and 3-4 accumulator pistons
• Transgo SK4L60E shift kit, minus drilling the holes and minus the too-firm 1-2 accumulator mod
• Corvette servo (I don't think I need a bigger one for stock power levels?)
• PWM valve eliminator (on-off valve with pressure limiter)

Since I think I need to open it up anyway (pending more verification to see if I can repeat the problem) to replace the TCC solenoid, it's pretty simple to do other stuff while I'm already in there, if it's worthwhile from a durability standpoint.

gearheadE30 wrote: Well, the transmission part of it isn't broken. It's almost definitely the TCC PWM solenoid, which is known for wearing the piston resulting in low apply pressure. this is also for a completely stock engine that will never see power adders, though I do occasionally tow with it. It will be getting an external cooler. I have little intention of putting additives in the trans. It's not that far gone; I just want to prolong its life if possible. Things I've seen mentioned that can be done without pulling the trans that seem to have a good reputation: - pinless aluminum forward, 1-2, and 3-4 accumulator pistons - Transgo SK4L60E shift kit, minus drilling the holes and minus the too-firm 1-2 accumulator mod - Corvette servo (I don't think I need a bigger one for stock power levels?) - PWM valve eliminator (on-off valve with pressure limiter) Since I think I need to open it up anyway (pending more verification to see if I can repeat the problem) to replace the TCC solenoid, it's pretty simple to do other stuff while I'm already in there, if it's worthwhile from a durability standpoint.

What's the cost to do this? I'm interested in doing some relatively cheap mods to keep my trans alive as long as possible. Parts list somewhere?

In reply to KyAllroad:

Everything I listed will cost you about $170 plus fluid. It's very cheap to do if it adds any meaningful life to the trans, in my opinion, and would address all of the 4L60E weak spots that I know of (or stock power level weak spots, at least).

I did learn another thing about this TCC deal. Mid-1997, GM transitioned to what they called EC3, or electronically controlled converter clutch. This was a further development of the PWM drive used since 1993 or 1994. Before that, TCC was an on-off solenoid. Then it switched to PWM control that ramped duty cycle from 0% to 100% to smooth engagement, only in 4th gear, or in 3rd if the selector was in D instead of OD. EC3 (or ECCC, or EC^3; it's all the same thing) is one step further, and it constantly slips the TCC, starting in second gear, with more lockup in third and close to full lock in 4th. My understanding is that it only fully locks under very high torque conditions, and otherwise targets a ~50rpm slip. In 1998, the algorithm was further tightened for less slip. This was all an effort for better fuel economy. In the event that the trans can't maintain the target slip ratio, it will ramp line pressure to compensate. This usually results in an overly harsh 1-2 shift, and if the line pressure goes too far out of bounds and the PCM sees a failure to maintain ratio, you'll get code P1870.

Due to different control patterns and slip requirements, the three types of torque converter clutches use different materials, and are not compatible. There is some concern from the major transmission parts houses surrounding getting rid of PWM entirely, because the shock load of slamming into lock can actually delaminate the clutch. There are improved PWM valves that allow less line pressure blowby and can accommodate for a worn bore, and these are worthwhile. Apparently most failing valves are diagnosed as a failing torque converter clutch.

The TL;DR of all this is that my truck is a 1998, so there might actually not be anything wrong with the slight slip I'm seeing.

One thing to add, both times that I though my transmission had a problem it was the engine. This sounds silly but check the cap and rotor, verify that your plugs are working well. My perceived slipping first gear and shuddering in fourth were due to ignition and fuel pressure issues. If you can't make smooth torque the transmission will act funny.

akylekoz wrote: One thing to add, both times that I though my transmission had a problem it was the engine. This sounds silly but check the cap and rotor, verify that your plugs are working well. My perceived slipping first gear and shuddering in fourth were due to ignition and fuel pressure issues. If you can't make smooth torque the transmission will act funny.

QFT! Last year I was about to throw in the towel on my trans and it turned out to be a combination of a bad TPS and E36 M3ty spark plug wires (accel and they were arcing to the exhaust manifold after a whopping 15K miles).