ZF8 shift pressures and timing - for Steven@HP

[16AudiS8+]

bumping this just because its a thread with a bunch of information. Appreciate it all.

[ezhik89rus]

I've had a chance to experiment with stuff more. Take this with a grain of salt as this could be completely incorrect and only based on my experience and tuning so far.

Shift Pressures -> Upshift -> Oncoming Ramp
Shift Timing -> Upshift -> Ramp Time
These two seem to correlate to each other. I'm going to call this the Oncoming Clutch apply rate. I've zeroed out these two tables and its actually the "proper" way I'd go about it for tuning the correct pressure since this seems to mask any issues with correct pressures and timing. If everything is zeroed out you can think of the oncoming clutch pressure as "on" and 0 torque (clutch plates just touching) as off, it is instant and as fast as possible. The ramp smooths out how fast this happens. 50ms and a ramp of 0.5 is a good starting point for initial tuning.

I don't completely understand the math behind these two parameters but it seems to be inverted from what you'd normally think. The lower the ramp rate (bar/s) the less it dampens.

EDIT: 1.0 ramp near the upper torque rows is probably better to start on.

Shift Pressures -> Upshift -> Oncoming Clutch
This is the actual pressure that gets applied to the clutches and is what you feel as the final portion of the shift or the RPM differences from what I can tell. If the ramp is too aggressive it makes this stage really hard to tune. 6 bars is about the max you want to use here. I've gone to 9 bars and at the point where it feels like your going to break internals or driveshafts. 0.6-1.0 bar seems like a decent place to be on lower torque areas and 5-6 is a good spot for firm shifts in the higher torque areas. 2.5-4 seems to be the sweet spot for "smooth" shifts.

Shift Pressures -> Upshift -> Offgoing Clutch
This is just how much pressure is used to hold the current clutch while phasing in the next clutch. When going for aggressive tuning, I always zero this out. My theory is if the shift is fast and firm enough you don't need to hold this and its too hard to tell if you are doing premature wear until its too late.

Shift Pressures -> Upshift -> Fill Offset
I don't have as much experience with these tables but this seems to pre 0 torque condition of both plates slipping. Not enough pressure here and you'll see a flare and too much and you'll have an overlap condition. The ZF8HP75 on the 2019 RAM for example I couldn't figure out for the life of me why the 3-4 shift was "binding" until I lowered these. My advice is if you increase oncoming clutch pressure by say 20% you should lower the fill offset by at least 10%.

EDIT: After more tuning, increasing the oncoming pressure, less ramp, and possibly holding the offgoing clutch longer is a lot easier. The values in the fill offset are extremely sensitive. Changing by 0.01 bar was enough to make it flare 100-200RPM during the shift. 3-4 on my vehicle (2019 RAM) the fill offset on the low end were too low by ~10% and the upper I couldn't change from stock without flare so I increased the ramp (pressure not time) to avoid binding.

EDIT2: After more tuning I realized I was getting owned by adapts. It seems the current settings here are only good until a key cycle. The second ignition cycle the adapts adjust everything and will mess up tuning in this section. The stock tune for example on the 3-4 has a lot of values that are way too low on the low end torque and low RPM. (0.10 bar @ 74 lb-ft / 1702RPM). After driving on the first engine start and having flares, the second start would see the majority of the flare go away, third even more. The farther away from "correct" the more key cycles it takes. The same value I mentioned before took almost x3 more pressure to not flare after an adapt reset. I suspect without an adapt reset any added pressure is too much as the adapts have already adjusted for it and its too dumb to know we modified the tables.

Edit3: This seems more like a preliminary stage of the oncoming clutch pressure. If the fill offset is 1.0 bars and the oncoming shift pressure is set to 2.0 bars and there is a ramp the actual pressure applied seems to be 1.0 to 2.0 bars. the fill offset is the "floor" or base of when the pressure gets applied. I don't believe this should be above the oncoming shift pressure. Consider it fine tuning for the ramp and a way to move the shifts closer together.

Shift Pressures -> Upshift -> Flare Adder
I haven't actually played with this one yet but it seems pretty self explanatory. If the Fill offset isn't high enough these tables say how much pressure needs to be added to make up for the slip.

Shift Timing -> Upshift -> Nominal Slip Time
As far as I can tell this doesn't have any say on how fast the shift actually takes place. This held true for my tuning of the 6L80 (GM) also and I'm going to assume it applies here also. This is more or less the time it takes for the Torque Reduction stage to happen, the shorter this time the faster and less time the engine pulls back torque (timing). If you have a flat spot or hang in the middle of the shift, more than likely this is too long.

Torque Management -> Upshift -> Forced Torque Intervention
I didn't play in this area too much but this seems to be the pre-cursor torque management stage. I played around with this by making it so the all the values would equal 0 engine torque (5500 turbine speed @ 350 ft-lb = -350) would actually cause the transmission to never shift even at WOT because it guaranteed the output shaft speed never hit the right speed to shift. It went into a really fun bounce back and forth of the RPMs but never shifted. If I added power to the engine I would account for it here to protect the transmission.

Torque Management -> Upshift -> Main Torque Intervention
This is basically the same as forced torque intervention but is applied DURING the shift instead. Again if I added power to the engine I would account for it here to protect the transmission. From what I can tell on the RAM 200 ft-lb is roughly what OEM spec'd at as reliable; This is a huge increase from the 6L80 as it usually never seen over 40-70 ft-lb on a shift.

EDIT: WOT drops the torque a little bit lower. Roughly around 130 ft-lb which is what I'd expect.



NEW 5/19/22:

Shift Timing -> Oncoming Inertia Mode Delay
I haven't quite figured this one out but reducing this and keeping this LONGER than the offgoing inertia mode delay seems to help the shift timing. I believe this is when the clutch start to engage.

Shift Timing -> Offgoing Inertia Mode Delay
I haven't quite figured this one out but reducing this and keeping this SHORTER than the ongoing inertia mode delay seems to help the shift timing. I believe this is when the clutch start to disengage.

Shift Timing -> Fill Time
I've had really strange delays in WOT shifts and randomly in other spots (very obvious in WOT shifts). Reducing this when increasing the shift pressure seems to have helped here. I suspect too long of a fill time causes the transmission to attempt to reduce or "bleed" the pressure before the shift actually happens causing a really long delay that can be felt. 100ms seems okay here across all temperatures so far. I haven't tested in cold weather yet, this will have to come in the winter months.

Shift Pressures -> Downshift -> Oncoming Clutch
Removed: Update later

Shift Pressures -> Downshift -> Offcoming Clutch
Removed: Update later

NEW 8/6/22:

Downshifts: REMOVED, will update later with better information.

I have found that almost all the pressures in the stock tune are way too low. This is the opposite of the 6L80 tuning GM does where the pressures are set high and the adapts bring it down. The ZF8HP75 has the stock pressures low and the adapts increase pressures.

When to wait for a new article that will help many people navigate the program for tuning. I decided to start all over again in order to achieve the perfect job. But I'm worried that maybe I'm missing something or there is new information ..

[LilSick]

Get the converter locked-up earlier and it can shift quicker. The converter tables from the TRACK transmission settings work really well with a stock converter.

the input shaft accelerates at a rate of X

X varies depending on where you are on the pass

the torque convertor is NOT between the input and output shaft

[LilSick]

can you post of log of one of those passes and the tune that was in it?

[LilSick]

wtf are you doing?

why would anyone put a convertor in a street car on a street tire...

and 3.70's too?

what is wrong with you? lol

last week on the last pass i forgot to put the trans in sport mode (see shift id 5) \/ \/ \/

tune is commanding shift at dss 1250 but as you can see its 100+ rpm over that

tune for normal mode was not opening the E solenoid quick enough, nor was it closing C quick enough, so it nicked the limiter

i since have redone entire trans tune. no more need to put it in sport. test tmrw

[james1595]

wtf are you doing?

why would anyone put a convertor in a street car on a street tire...

and 3.70's too?

what is wrong with you? lol

last week on the last pass i forgot to put the trans in sport mode (see shift id 5) \/ \/ \/

tune is commanding shift at dss 1250 but as you can see its 100+ rpm over that

tune for normal mode was not opening the E solenoid quick enough, nor was it closing C quick enough, so it nicked the limiter

i since have redone entire trans tune. no more need to put it in sport. test tmrw

Can you share what you did? Im having a problem where my car does not want to shift into second at wide open throttle. No matter what i do it wont shift until i hit the limiter. Even had it set to shift at 5000 rpm, still went to 6700rpm

[LilSick]

what do you have selected for 44825 and the two below it 2048,2049?

post the tune

[james1595]

im not sure what tables those are, i couldnt find them, but i can post the tune for you to look
9-23-2023.hpt

[LilSick]

some of the switches mighta got switched in the software updates

the 3 i mentioned ^^^

try this