Strange quirk that's popped up on my manual-controlled 4L80E swap. If I downshift from 3rd to 2nd its almost like I put it in neutral, the rpms don't rise and the car doesn't slow down any faster. But if I give it gas it's like all of a sudden it found 2nd again, no slipping and it takes right off. It also works perfectly from 1st into 2nd. Is this a wiring issue for 3-2 downshift? I admittedly don't know much about the fluid circuits on the 4L80E so I'm hazarding a very rough guess here. Previously if I was going say 40 mph and decelerating I could put the shifter into 2nd and the rpms would jump to about 2800, but all of a sudden there's nothing at all. Anyone ever heard of this before?

 

you do not have engine braking.
Front band issue
the rest is fine
no, not a wiring issue or tune issue...front band

 

Does the front band have a function other than downshifting? E.g. applying gears like the 2/4 band in the 4L60E?

 

The front band is only used for engine braking

unless the intermediate sprag is broken...in which case I guess one could say the front band is being used for the 1-2 shift...but for "normal" operation is a properly functioning trans...the front band is only responsible for engine braking in 2nd gear (note...in a 4l80e, the overrun clutch must also be applied in addition to the front band for engine braking to occur)

 

If you are familiar with a Bicycle, that when the Pedals are rotated backwards... the Rear Wheel is stopped.
Of course the Rear Wheel can rotate Forwards when the Pedals are not rotated backwards.
This is a somewhat similar action to the One Way Roller-Clutches or Sprags used in Automatic Transmissions.

Some Bicycles do not have the Rear Wheel stop when the Pedals are rotated backwards, or not rotated at all.
When the Rear Wheel spins freely with the Pedals not rotating/ being still...
This "free-wheeling" action is similar to the action of the 4L80E when an Overrun Element is not functioning... such as:
-Low-Reverse Band (Overrun Band in Manual First-Gear and Reverse).
-Intermediate Band (Overrun Band in Manual Second-Gear).
-Overrun Clutch (Overrun Clutch in Manual First, Second, and Third-Gear).

 

So essentially, 2nd gear will only be "applied" when engine torque is higher than the negative torque being applied by the spinning wheels?

 

No...

Second-Gear is still applied by the Intermediate Clutch (Forward Clutch is also applied).
However the Unit will "Free-Wheel" without the Intermediate (Overrun) Band applied in Manual Second (Overrun Clutch also applied).

 

yes that's why I said "applied". I understand the clutches are applied the whole time the vehicle is in 2nd, but from the stand point of applying power to the wheels, torque is not being transferred until the engine torque is greater than the inverse torque being induced by the spinning rear wheels. Is that correct?

 

During normal automatic Shifting with the Gear-Selector in the "OD/ D4" position...
The Transmission will start off with only the Forward Clutch applied.

When the 1-2 Shift occurs, the Intermediate Clutch applies (Forward and Intermediate Clutches applied) with no Engine Braking.
When the 2-3 Shift occurs, the Direct Clutch applies (Forward, Intermediate, and Direct Clutches applied) with no Engine Braking.
When the 3-4 Shift occurs, the OverDrive Clutch applies (Forward, Intermediate, Direct and OverDrive Clutches applied) with no Engine Braking.

While all of this was happening, the One-Way Roller-Clutches, and the Sprag are doing their jobs.
If not, you would feel like the Transmission was in Neutral (would not move) on a particular Shift that corresponds with the above components.

Only in the Manual-1ST, Manual-2ND, and Manual-3RD Gear-Selector Positions, are any of the 3 Overrun Elements used
(Low-Reverse Band, Intermediate Band, and Overrun Clutch).
They provide the Engine-Braking feeling.

 

We would be getting into a Torque-Converter discussion here.

 

In my particular case, I have a full manual conversion harness controlling my transmission. The pillow switches that determine gear selector position are tied directly to the A and B solenoids; the pcm is not involved. The only outside wires to the trans are switched 12v power and switched ground for the TCC. So in this case, are the Overrun elements always applied?

 

I feel like I'm not making myself clear here. If the engine is running, it's always applying some amount of torque to the input shaft. My question is: at what RPM does the engine torque overpower this free-wheeling affect to the point that it "feels" like the transmission is in gear? Immediately upon throttle input? Does it depend on wheel speed? Please don't take this as condescending, I'm an Engineering student and I'm genuinely interested in how these systems work.

 

the shifter has to physically be in manual 1, manual 2 or Drive range for engine braking/"overrun elements". In your case since you shift manually, yes they would. however, once in 4th/OD there is no engine braking.