Say, are you by chance an engineer of some kind? You are way, way overthinking this simple matter.

D is for drive, put it in D and Drive, no thinking required. How many people are driving auto transmissions? How many are having the debate in your thread? Just the other day two people at the grocery store were debating whether to use "3" or "D" on the way home after buying a cart of groceries.... because of added weight.

The auto makers know how their stuff works and if it were important, it would be in the owners manual. Like avoid too many auto transmission shifts/lockups and do this or that. Maintenance is far more important than selecting anything other than D. You sense shifting because load and speed changes, just like the factory program to you PCM was designed to do. Under an extrapolation of your concern, perhaps we should all be downshifting our ATs when slowing down to avoid wear on the brakes? Or drag one foot out the door?

When was the last time you changed the Trans fluid and filter?

Ah well, carry on.

 

ONLY 3 IS NEEDED!
The need for a fuel-saving overdrive high gear put the squeeze on three-speeds!

 

I’m not trying to start a debate, I was just simply asking for opinions out there on this matter. Also, the number one thing that kills these 4L60’s is shift cycle counts, not maintenance. They simply shift themselves to death. The habit of shifting out of “D” and into “3” around town has faded into the history books. Go on and keep on having the transmission fail every 100-150,000 miles or so by driving around town in “D”. It’s totally up to you, but I like getting 300-400,000 miles on the original trans before it fails.

 

Remember the good ol'days?

Oldsmobile 4-4-2:

2-speed Jet-Away automatic
3-speed Turbo Hydramatic automatic

 

In an automatic transmission, the wearing parts include clutch plates, bands, bushings, bearings, sealing rings, thrust washers and other metal parts.....all wearing as a direct result of friction. The most crucial of those parts are the clutch plates. An automatic transmission does not use gears to propel the vehicle, it uses clutch plates. Each gear in an automatic transmission is comprised of three to six friction plates sandwiched between smooth steel reaction plates. When you move the gear selector to drive or reverse, a valve opens and extreme hydraulic pressure moves a piston, compressing clutch plates together, resulting in vehicle movement. Each time the transmission shifts, the computer opens another valve selecting the next gear and so on. Each time the clutch plates are squeezed together (applied) they wear against the adjoining reaction plates. The more they are applied, the faster they wear.

 

I'd like to see the data supporting the claim that "shift cycle counts" is what kills 4L60 transmissions. I'd also like to see the data that using only 3rd in town rather than Drive will double or triple the average expected lifespan.

 

Likewise.

 

No worries, I was just messin with ya.

IMHO the reason ATs go is because many people drive 100K+ miles without ever changing fluid & filter and some come on here and ask why their truck won't shift or move. Not rocket science.

 

The 4L60 was designed in times when people were taught to drive around town in “3” to avoid the unnecessary shifts to 4th Gear, the 3-4 and 4-3 are extremely harsh on an overdrive transmission. So any shift involving 3rd or 4th requires the TCC to be disengaged, then the shift sequence of events to happen, then the TCC to be reapplied. The TCC is one of the more failure prone components in the transmission. GM did us a huge disservice by switching the transmission gear labels from “D” to “3” and “OD” to “D”. Stop them from shifting 3-4-3-4-3-4 and the 4L60 will outlast the whole Hummer.

 

All is good