6l80e kick down tuning

[ccrp]

I have a customer 2009 SIlverado Z71 with a Maggie and when cruising around 45mph, smashing the throttle like trying to pass a slower car on a cross country road it violently shifts from 5th gear to 2nd, stays a few second in second and shifts up to 3rd. It has always done that from the factory and it really annoying.

How can I prohibit that stupid down shifting so that it shifts down just one gear, maybe two but not three for a split second?

this stock behavior can not be good for the transmission, it feels like it is ripping the axles out.

what tables effect that?

[johnh]

Sounds like the MPH tables need adjusting...

[C5pilot]

You need to raise the downshifts. The factory settings are usually VERY poor but they have their reasons, like MPG. Don't make the downshift too close at lower speeds where there tends to be erratic pedal movement. You can make the downshifts closer to the upshift at higher speeds where there is less pedal movement under normal conditions. You also have to readjust the TCC settings afterward. I find that to be the tricky part. The shifts are easy by comparison.

[ccrp]

I lowered the full throttle downshift speeds considerably, same for pattern 1 and 2. It sort of castrated kick down but now it accellerates smooth with no violent downshifting from 6th into 3rd, and back up to 4th.

from 50kph to 90kph it down shifts either from 6th or 5th to 4th and stays there.

nice fine down shifts, no more violent jerking where you believe it rips the tranny apart. Which GM fool designed it like that anyway and for what?

TCC locking/unlocking was no issue at all, they lock/unlock at much higher speeds already.

[C5pilot]

You should raise the part throttle downshifts as well. Make sure 100% matches your WOT table. BE SURE NOT TO EXCEED ANY GEARS MAX SPEED. Your upshift and downshift for each gear should look basically parallel to each other. Stock download parameters make you push the pedal a larger percentage the faster you go. That means, when you finally hit the stock trigger mph, your foot is so close to the floor, the lower gear is going to scream! That's what's happening to you.

The factory's goal is completely backwards from ours because they're concerned with every ounce of economy and they don't know who is behind every wheel. In the real world you get better performance and more control if downshifts occur with less pedal movement, not more. This is especially true at higher speeds. At low speeds you want a little extra room for quick adjustments, bumps etc. (how many bumps do you hit at 65 mph?)

Here's a pic to give you an idea of what the 2D view should look like. Just try it for high gear to see if you agree. If you like the results continue raising the rest. But don't forget, you have to adjust the TCC to correspond to your new shifts.

[ccrp]

did that of course, now it shifts as it should.

But, I do not understand why you want to raise those values, it makes the problem even worse.

you need to lower the mph values as the function is it shifts down at WOT at or below that value. If you raise it is the opposite effect which I tried at the beginning.

F.e. stock was kick down into 3rd gear at 84 kph. If you floored it above that speed let's say at 90 kph it shifted from 6th to 3rd, stayed there for a few seconds and back up to 4th (3-4 WOT upshift was at 92kph) and accellerated.

I changed values to 60kph, now at 90kph it shifts 6th to 4th and stays there until it is time for WOT upshift again. NO harshness, no violent shift just as it should.

Now

[C5pilot]

But, I do not understand why you want to raise those values, it makes the problem even worse.

I'm not doing a very good job of explaining my method. You don't raise the low gears, you raise the higher gears downshift points. If you don't want to ever get into 2nd gear at that speed from any gear, then you've done it. And if your customer insists on flooring it in 5th just to pass, then it was probably necessary.

I'm suggesting going the next step because if I had a Silverado with a SC I wouldn't want to resort to flooring it to downshift. It's too light in the rear and flooring it during a lane change can be unhealthy. But that's what the stock settings do, they make you use so much throttle just to get it to kick down. With a Maggie, that's gonna scream.

My method simply allows you to command a SINGLE downshift without having to floor it and offers much better control of which gear you end up in. With a little practice, you can learn exactly how far you need to press to drop 1,2,3 gears from any speed or any gear. Stock downshift settings can be all over the place.

[SoCal]

Well said, C5pilot. I've always thought it odd that the stock up and down shift curves had such drastically different shapes. This is an interesting explanation.

[ecuboss]

Hi,
I changed all the shift speeds on my G8 in sport mode. The difference is amazing - holds onto the gears if I lift of the throttle and changes down to the right gear quickly when coasting down to a corner.

OEM:
Mine:

It also seems to go into PAS mode more readily now as well.

[HoldenG8GT]

Hi,
I changed all the shift speeds on my G8 in sport mode. The difference is amazing - holds onto the gears if I lift of the throttle and changes down to the right gear quickly when coasting down to a corner.

OEM:
Mine:

It also seems to go into PAS mode more readily now as well.

Is there anyway you can make these pics a little larger so I can see what you did? Or can you post your tune? Thanks!

[C5pilot]

Hi,
I changed all the shift speeds on my G8 in sport mode. The difference is amazing - holds onto the gears if I lift of the throttle and changes down to the right gear quickly when coasting down to a corner.

I can't tell from the small pic but it looks like some major increases. If that's your sport setting I assume you left normal shifts near stock because you're gonna use a lot more fuel just driving around town. Can you upload the pics as thumbnails so we can see the numbers?