therock

iTrader: (2)

Unfortunately this will be a bit difficult for two reasons, (1) is determining the exact nature of the harshness and (2)Tuning it out.
First; The truck (from the factory) are notorious for a 1-2 slide-bump. This requires some understanding of the accumulator. The goal is to have the
(2nd) band apply before the accumulator piston fully strokes and bottoms out. When the acc piston bottoms out there will be a spike in band apply pressure. This can be seen when apply pressure is graphed. As the piston strokes, the apply pressure proportionally rises, when the piston bottoms, apply pressure spikes up to match line pressure. The goal is for the band to apply before the spike. If it does not, you get the soft initial apply and then a harsh "end-bump". This is know as a slide with end-bump. Technically the shift is too soft, but it feels harsh. At the opposite end is a shift that is just too harsh. The problems is for the slide bump, you want to raise accumulator pressure, for a plain harsh shift you want to lower accumulator pressure. As I was saying, many of these GM trucks have a bad slide bump problem from the factory. Usually a low speed light throttle maneuver with a surprising sliiiddde bang shift that is difficult to reproduce but always seems to happen under the same conditions. Sometimes the sliiidde is almost imperceptible and all that seems apparent is the "bump"

So your issue depends on the exact nature of the harsh shift, then also what the accumulator regulator valve spring you have (this is inside the valve
body) and usually requires VB removal, though some Trans-go kits had a pin that would let you remove the valve without pulling the VB. So any tuning would most likely involve removing the accumulator regulator valve and switching springs. There are a lot of springs. I know of at least 8 factory, Trans-go has 4 or more and we (Sonnax) have 3. You would need a selection of springs, then based on you exact symptoms, try either a firmer or lighter spring. Programming. . .you could try raising light throttle line psi about 5-10 psi and see what type of difference that makes.

BigKID

iTrader: (5)

Good info. I have always had this issue with my 4L6xE trannies. This slide bump can sometimes be described as a hesitant upshift. My Tahoe still does it under light acceleration but it still has stock valve body with a corvette servo only. Feels like manual gear change where first disengauges before second engauges harshly. I am going to try an add a little more line pressure via the tune at low torque values and see if it helps any.

AKlowriderZ71

iTrader: (22)

I've never seen this condition corrected by tuning. It has always been a mechanical problem.(internal trans).

therock

iTrader: (2)

That is what it looks like but you never know. I just wanted to post a clarification on the condition.

FLT trans builders seem to avoid it as I have not seen complaints on this with transmissions coming from them.
We tried Transgo stuff on my 05 truck and it never worked correctly, and after several tries and valve bodies we went back to OE and went with all Sonnax stuff and it's great. but for the ity-bity bump and I'll not be tearing it down to go after it.

And you successful Transgo guys need not say anything. I know it was just my luck as there are lots of happy transgo users.

Jeteys5.3

iTrader: (4)

does sonnax offer a "shift kit" that compares to the transgo?

02 WS6 TA

iTrader: (7)

Kenny, I removed roughly 10% LP below 50 percent throttle after the converter swap and billet servo install, and have no issues... I have a few spare Transgo Accumulator springs laying around as well if you want to try 'em.

therock

iTrader: (2)

They are different animals or strategies.

I did the performance pack and both super hold servos and after market frictions along with a conversion to the 65e.


Sonnax Performance Pack List

Performance Pack

therock

iTrader: (2)

I'm attaching HPT log & config files replacing the LTFT's in the bottom chart with, Current Gear, Force Motor Current, Trans Torque, Time of last 1-2 shift.
Change file extension of the TRANS Imperial.txt to a .cfg to use it.

I did several stop and go runs to try and duplicate. It's tough to do it but easy when not trying. Heh! Several in a row at the back end.

What I see in the log at low speed 1-2 shifting is:
The less pedal position the more harsh the 1-2.
The less pedal position % the more force motor current.
The more pedal position % the more torque.

My harshness is minimal at the worst and occurs only at 22% or so and below. Not enough to tear down the trans and experiment with springs, enough to where passengers wonder. But if I can tune it out it would be great. It is less @ full operating temps but not by much.
I'm not experienced enough to know where to make attempts. Mr. Nader @ Sonnax says it's a low pressure thing that one tends to think is too much pressure and the chart reflects this as he says, as I read it.

Where would you attempt to tune it out and how?

SC6PT0

My truck has a very harsh 1-2 shift after a 4L60 rebuilt. It only happens after the transmission reaches operating temperature. At partial throttle like when driving down the street. It feels like someone rear ended me at times. (its that harsh) It's still under warranty, is this something to be really concerned about? Will this ruin the life of the transmission?

therock

iTrader: (2)

I would address it for sure.
Mine was like that with our first attempts at this build that just would not be fixed. We even called FLT and got some pointers from them but to no resolve. FLT was great at offering help even knowing it was not to do with their work.

If you have a tune with other than stock calibrations in the transmission tables put them all back to stock before doing anything. All these aftermarket kits are based on a stock trans tune.