Downshifting pointers needed

[Pocket]

Now that I have my upshift points and torque converter lockup points set how I like them (this thing is shifting like a dream ), I'm looking at some downshifting changes.

Some background... My old tunes had two settings with downshifting (daily driver and tow setting). As my truck slowed, the trans would downshift from 4th into 3rd. This came in handy in the mountains, especially when towing a load. The only issue I had with the downshifting was the torque converter remained locked as it downshifted, often resulting in a very jarring and harsh downshift (also heard it wasn't good for the transmission).

So my question, can I tune a 4-3 downshift that unlocks the torque converter, then locks it back up for a smoother downshift?

[cleatus12r]

Two things to try. I say "try" because I've noticed that there is quite a difference between PCM families and how they react to certain changes.

There are three converter lock/relock delay parameters for the 4-3 downshift. These are listed in seconds. These work well for PMT1 boxes but I know that your tunes are TNAA7 based so the best I can say is to try.

The best solution (but it won't reapply the TC clutch), is to raise the unlock speed in the 3rd gear function to the 4-3 downshift speed. Don't raise it above the apply speed, because it just won't lock then.

[Pocket]

What are those converter lock/unlock parameters called?

[cleatus12r]

Delay Converter Lock after 4-3b
Delay Converter Lock after 4-3
Converter Relock Delay after 4-3

[Pocket]

Ahh, I see! Thanks Cody.

Now of course that brings up an all new question. What's the difference between Delay Converter Lock after 4-3"b" and Delay Converter Lock after 4-3? I noticed it's there on the upshifts too. Now I've changed the delay converter lock on upshifts in the "non-b" set, but not in the set with the "b" tag. Does that make a difference? Do they both need to be the same?

[Pocket]

Well I tried those parameters and increased the time to delay the lockup on the 4-3 shift with no luck. It just refuses to unlock the torque converter when it downshifts. The only change that I saw was that the jarring was slightly less if I was completely off the pedal, and it almost downshifted smoothly (just not quite as smooth as I wanted, still a bit of jarring). The problem that still remains is that if I'm going uphill, and have my foot very lightly on the pedal (light enough that it's registering the pedal is applied, but not enough to maintain speed going up a steep hill), the jarring is still extremely harsh. So for that scenario, it made no difference at all.

Just to note, that second scenario with the pedal lightly applied has always had a much harsher downshift, even with my old tunes. So I'm guessing that it's something to do with the TNAA7 based tuning.

I also tried the other suggestion you gave Cody, by raising the unlock speed in 3rd, but that results in a big RPM drop when shifting into 4th as the torque converter re-locks, and I'm stuck lugging the engine going uphill.

If there's any more suggestions, I'm open to try them. Right now I seem to have hit a brick wall, and can't find a way around it, other than disabling the clutch coast function like it is in stock VDH2 tuning. But I really would like to have a working downshift solution for this. Reason being is that up in the mountains, some of the roads wind around quite a bit, so if I'm at a lower speed and let off the pedal without a working downshift, the engine just coasts until I re-apply the pedal, and I'm stuck with lag as I'm waiting for the RPM's to climb and turbo to spool back up. It really does make a difference, as the turbo seems to light up quicker if the RPM's are kept up at least a little bit more.

Altitude sucks for tuning, makes things much more difficult

[907DAVE]

I am experiencing a similar issue with my 4-3 downshift, I was going to try and tackle this issue when I get the emulator. I feel you pain when trying to fine tune things with no real progress.

Not trying to sound to dumb here........have you tried backing down the 4-3 shift pressure?

[Pocket]

Originally Posted by 907dave

I am experiencing a similar issue with my 4-3 downshift, I was going to try and tackle this issue when I get the emulator. I feel you pain when trying to fine tune things with no real progress.

Not trying to sound to dumb here........have you tried backing down the 4-3 shift pressure?

I could try that. It's set at whatever stock is.

[907DAVE]

Another thing worth trying is the parameter Downshift Slope into 3rd.

I do not know what this will do but might be worth a shot.

[GTS]

What transmission are you running? Could it be the way the hard parts are set up in the transmission? Orifice size for the TC lockup, valve body set up etc?