Having never been around a 4L80E much let alone one with a shift kit it was a big change for me going from a slipping 4L60E to a peppy 4L80E. With my 4L60E each shift was like a huge drop in power. I guess the clutches just ate up the momentum. With the 4L80E each shift launches the truck forward. I've gotten the shift line pressure down to where its firm but not hammering the gears but I guess its just because I've never been around a good transmission before. Like I said its not hammering the gears at all, just when it shifts its like you feel the clutches actually biting and the truck is thrown forward and actually gains speed through the shift. I guess this is perfectly normal? FWIW my truck weighs around 5300-5400 pounds as it sit. I also have the 6.5 turbo diesel converter in there that came with the transmission which stalls at a low tight 1500 rpms. I'm sure thats part of it but I was just curious.

 

I just rebuilt my 4l80e. While I was in the trans I installed a HD2 transgo kit (old version) as well as some Sonnex upgrades to the tcc circuit. I replace the valve body plate and drill all the holes .090... 1>2 shift is a bit on the harsh side at light throttle, but at WOT it is very firm, and feel like you are describing as a increase in speed during the shift. My 2>3 shift feels O.K but I have had little time to see if I could inprove the shift with tuning..
All of this is with a factor gas engine torque converter, and my new engine @ 130 kpa of boost.

 

That low stall diesel converter will make your shifts more firm than even a stock gas 4l80e TC. That converter makes for a pretty snappy driving feel I bet, esp. with the BIG off ifle torque of that TBI engine.
Some guys when they go to high stall converters have to install shift kits to get rid of the sloppy shifts.

peace
Hog

 

Before we played with the computer you could hold mine wide open and drink coffie. We sped up the shift by .05 i think and bumped the pressure just a little bit. Its not firm but it doesent sound like a slippping trans anymore. Now for some reason in tow hall if you lock in first and let the comuter shift it out at 5K rpms it about rips your head off and you almost get some tire spinnage. kinda hard to on a sububran with a 33's though.

 

I know the diesel converter leaves a lot to be desired espeically when I open it up and its basically like accelerating through the gears with a locked converter but when it shifts it kind of makes up for it good or bad. Personally I can not stand a soft shift but I wanted to make sure what I'm feeling is kind of the norm for a shift kitted 4L80E. Apparently with this converter it is.

 

What you are feeling is the ability of the 4L80-E to overcome the inertial energy of the crank and torque converter as it pulls down engine RPM to match the driveline at the next gear ratio. 4L80-E shifts feel precise and robust compared to a 4L60-E because 80's shift with clutch packs only, not a band. If feel like it "doesn't lose as much power" because the gear ratios are closer together - some consider the narrower overall ratio range an unacceptable compromise, but I think the closer ratios yield superior performance.) Also, each upshift in a 4L80-E is handled by the single engagement of a completly different clutch pack for each upshift, none are shared, each upshift is only one engagement of one clutch pack. There are no synchronous engagements or disengagements for any upshift in the 4L80-E. This is possible because the 4L80-E has three distinct planetary gearsets.
Back to the shift feel...
Bands used to shift a transmission have similar characteristics to drum brakes. As more pressure applies the friction material to the drum, the more forces become imparted by the rotating drum to the engagement of the material with a self-energizing effect. Material on the inside of a drum (like a brake shoe) wedges itself against the drum as it imbeds. Material against the outside of a drum wrapped around it will tend to tighten itself as tension on it increases. As applied force rises linearly, imparted forces from the rotating drum rise exponentially, which is why drum brakes lock up so easily. Clutch discs in a transmission do not have this problem. They do not receive any apply forces from the interaction of the two surfaces being engaged. Their engagement remains linear no matter how much torque is being overcome in the process. From a standpoint of precision and control, clutch discs packs function more predictably than a band aound a drum. This is one of the main reasons that disc brakes work better than drum brakes do and why they have less tendancy to lock up.

In comparing the 4L80-E to 4L60-E in design you'll find they have nothing mechanically in common - and that's a compliment to the designers of the TH400 back in the early 60's.

 

The 2-3 shift on my 60e is the most pathetic thing I've ever experienced in my life.

 

I installed a Transgo HD-2 shift kit in my 80E before i put it in the truck.
I drilled the holes .094 1-2, 2-3 and .090 3-4..
My 1-2 shift is a tad to hard at WOT, it spins my Drag Radials at the track. Id like to redo that to .080 or so?

2-3 is absolutly perfect all around.

3-4 is to harsh for me while in boost. I need to redo the seperator plate.

All that with a stock Converter..

Guess i could start lookin for a seperator plate, eh?

 

The 4L60E has the 3-2 downshift solenoid to make it have a better feel I believe is the reasoning behind it but I totally agree 2-3 and 3-2 are so sloppy it amazed me the thing even worked.


Now I understand what was causing the shift firmness inconsistancy vs speed and load with my 4L60E. Sometimes it would grab and kind or jerk to the next gear, the next time it would slide into the next gear. That much be the bands not grabbing hard enough or grabbing too hard. I knew that the 4L80E uses bands as thats how you hold the drum? for the planet gears to get the reduction but I didn't realize it had 3 seperate planetary sets.

Predictable is a good way of describing the shifts. Predictable and consistant.

 

Someone here told me that the 80e still uses a band for upshifts. This isnt true?

How is OD applied?


I have always liked James B's band/drum engagement analogy using the drum brake setup. MAkes it very easy to visualize.


I agree with the above opinions, but still insist that the tighter diesel TC is at least partially responsible for a snappier shift, for the same reason a high stall TC will make shifting more sloppy, not sloppy, but MORE sloppy. Am I at least partially correct?


peace
Hog