Banging rev limiter on first couple of shifts.

[Harlech]

Hey gang,

Haven't been around in awhile as I've been working on other aspects, like the 4-link suspension, the last few months. But I've had a chronic problem of banging the rev limiter on WOT shifts for the first two gears, originally when I was running 4.56 in the rear I chocked it up to the fact with the short gears it was hitting it faster than things could react. Now that I'm back running 3.42si still have the issue and I've tried shortening the shift time, setting it to shift earlier, even bumping the rev limiter 200 rpm, to be honest, I'm about to jack it all the way to to 6800 or something as nothing seems to help keeping it from bumping when going 1>2 and 2>3, so I thought I would check here.

Signature should be fairly to date on mods, this is the 6l80 with stock convertor. I know I can't be the only person with this issue so any feedback or solutions would be greatly appreciated.

Kyle

[ahmedabri97]

Return Full throttle shift speed to stock if you adjusted it, only adjust WOT shift RPMs.

[Harlech]

Return Full throttle shift speed to stock if you adjusted it, only adjust WOT shift RPMs.

I'll give that a shot. Thanks. Doesn't make sense as to why that would be the issue but seems a lot of the time these things don't have much rhyme or reason.

[Harlech]

Return Full throttle shift speed to stock if you adjusted it, only adjust WOT shift RPMs.

Not finding what your talking about. There is only the option for full throttle shift speed, nothing relating to WoT shifting. Guess I'll keep throwing numbers at the shift speeds/rpms in the hope of finding a solution.

Must not be very many people with the issue of short gears and high horsepower on here.

[castorjames]

Not finding what your talking about. There is only the option for full throttle shift speed, nothing relating to WoT shifting. Guess I'll keep throwing numbers at the shift speeds/rpms in the hope of finding a solution.

Must not be very many people with the issue of short gears and high horsepower on here.

Can you post a log and the trans tune file

[ahmedabri97]

I meant return full throttle shift speeds to stock and adjust only the full throttle shift RPM.
And keep a distance from shift point and cutoff. I saw some tunes with shift point RPM = cutoff RPM which caused same problem.

[jpierro79]

heres all the info i can provide. There is a trans timing tables along with bluecat tool that can help and it can help i am not well diversed in this area other than you have to change a lot of settings in the trans if you have a larged increased in power as you outrun the trans shift tables and bounce the rev limitier especially in first few gears. I would research the bluecat trans tool tutorial as it may help.

[IARLLC]

I have seen a similar thing several times on Gen3 and Gen4. ahmedabri97 is right. I don't know that all GM platforms run this way but on many the speed signal takes longer to get reported so in the gears that add RPM very quickly (1, 2, and 3) we get this type of issue if the shift speed is raised. Of course it happens more if the speedo is off because of gears/tire height or related mis-calculation. Some suggest that you drop the whole table to 0 as a test. As I have run into this several times I just prefer to leave the full throttle shift speed stock and raise full throttle shift RPM to the desired level....or just a little lower than the desired level if the trans does not execute the shift immediately on command. I have seen many experts on here recommend the same thing and it almost always resolves the issue.

[jpierro79]

heres a link this go goes way fast so expect to pause alot he uses key pad not mouse controls hes extremely fast but this is the be tutorial with blue cat auto tool i know of https://www.youtube.com/watch?v=X8vi7A7RGEs

[SultanHassanMasTuning]

if you tire/wheel size was changes you may need to calibrate it

[jpierro79]

the transmission does not shift off tire size this has no effect there are drums and clutch packs inside the trans that have rotational speed sensors that have only to do with trans, abs sensors off the wheel do not change shift times. These are two completely different systems. I can put 18's or 20's and larger and different tires its giong to shift off of the trans internal speed sensors. The only thing that changes is the reading on the dash board and your overall gear ratio not the internal transmission ratio. I said i dont tune these transmissions for higher hp but working as a shop foreman for AAMCO I do know how they work. You can put a darn 14' rim its still going to shift the same. you can calibrate your speedo all you want but i can promise you this your still doing damage to your trans as we speak.

[castorjames]

and why it would not correctly shift in 4Low? on a custom swap build? it should shift perfectly fine for what you say?

[kingtal0n]

When I did my first 4l80e recently I had it hitting the limiter before a shift initially.
It took me some time to realize the rate of change of the engine rpm plays a role.

In other words, how fast the engine is accelerating is a fundamental property of when the shift occurs.
For example with 4:1 gears the engine RPM climbs very fast at WOT, compared to a 3:1 rear gear. This should seem common sense.

The trans being commanded to shift is only the beginning. Once the command is made, the hydraulics of the trans need some time to do their thing.
This hydraulics work time adds a delay to the shift. So if you command a shift at 6000rpm with a 4:1 gear, it will happen finally at say 6500rpm or whatever. Whereas the same shift commanded at 6k with a 3:1 gear would happen sooner, maybe 6200rpm instead, because dRPM was lower (rate of change of rpm is slower)

SO here was how I got the shift I wanted finally.
I set WOT mph shift very low so it was met wayyy before the shift I wanted.
Then I reduced the shift RPM commanded kind of low also. say 5200rpm at first.

Then just gradually raise the shift rpm commanded until it mates with your engine's rate of change to give the desired shift point.
If you add power, change tires/gear, anything that affects the rate of engine rpm, it will need a re-adjustment.
So, second gear for example the engine rate of change is lower, so the rpm to shift at was higher even for the same shift.

For ex.
5700 1st
5900 2nd

both might give 6300rpm shift with XXX pressure.
sorry if this isn't what was being asked I may have misunderstood.

[ddtech]

Trans is shfiting based upon MPH.

Set target RPM for shift, and base mph to achieve. Up or down.