TCC Unlock during shifts

[dennisL]

I was looking at the TCC Unlock during shift code, and found something odd. I'll ask my question, then explain. The question is directed to those who understand the transmission and torque converter. I sure don't.

Question: Should the TCC be unlocked whenever the tranny is shifting?

Expalnation: The factory code has provision to detect shifts and unlock the TCC for a brief time. The code I'm referring to starts at $3885 and uses a table ($33DF) for the unlock time based on which shift just occured.

Assumptions: The transmission has 2 (normally closed) switches, one for third gear and one for fourth. The third gear switch opens in third and stays open in fourth gear. The fourth gear switch is only open in fourth. This produces these bit combos:
00 = 4th gear
01 = can't happen
10 = 3rd gear
11 = 1st or 2nd gear

These two switches control two bits in register $03 (b5 & b6). These bits are shifted left to represent the previous gear. The $33DF table has an unlock time for 3 of the 4 possible shifts. There is a 4th entry in the table but I don't believe its used. The 4 possible shifts (that the ecm can detect) are: 2-3, 3-4, 4-3, 3-2. The table addresses 4-3 (0010), 3-2 (1011), and 2-3 (1110). There is no unlock time in the table for 3-4 (1000), but there is an entry for (0110).

Is this another "anomaly" with the factory code? Can a torque converter expert please jump in here. Thanks.

 

[TurboJim]

My guess is to take the high power "shock" from beating the crap out of the TCC clutch. It is not designed for high power and despite many using it at the track, will fail with repeated abuse.

Since the ECM cant detect 1-2 and 2-3, yes, it can see 3rd come on, but what good is unlocking AFTER its in 3rd gear... I dont see the logic there. And if youre in it for the 3-4 shift at 100+ then I cant see there being that high of a shock at the shift, the car really isnt accelerating that hard anymore.

What I wonder is if this code is in the 148 cal for the FWD cars mainly, which could lock the TCC in 1st, and MORE damage would occur with that POS 440 (I think they used the 440 trans, if not, maybe a 125 which was worse than a 440, and the code was there to save those transes from self destructing. I personally dont know ofr certain how much of the chip section is different from a FWD to TR, so maybe my theory is totally wrong.

Maybe since it didnt HURT anything, the engineers never removed it?

 

[BJM]

I hope some more experts chime in. This board needs way more posts like this one.

Very few car brands have such easy access to the inner workings of their cars. GM enthusiasts are really lucky, we should take advantage of it.

 

[bruce]

Originally posted by dennisL
Question: Should the TCC be unlocked whenever the tranny is shifting?

The better strategy is killing HP while the gear change is taking place.

If you were to make a table with %TPS vs VSS you could pretty well match up the shift points, and then enable a spark retard to do the above. Taking 8d timing out for the .1 sec of gear change would really lenghten tranny life, I'd imagine.

 

[BJM]

I have noticed many of the rental cars I have had (mostly the big 3) now implement some very noticeable power reduction during shifts. One taurus I rented drove like a manual car. Every shift the engine would cut right out for a large fraction of a second and come back on. I would never own a car like that.

 

[dennisL]

Taking 8d timing out for the .1 sec of gear change would really lenghten tranny life, I'd imagine.

Bruce, this is where I was headed with this. I was thinking of using the Unlock table to indicate retard (y/n) along with unlock time. I just wanted to get the unlock portion of the table straightened out first.

To control the same amount of retard for each upshift, I was going to use 1 bit as a y/n. If the retard differs, like 2-3 gets .2 sec and 3-4 gets .1 sec, then I'll have to use more bits.

I agree that a tps vs mph table will provide shift point processing. I'm hoping the 3rd and 4th tranny switches open early enough in the shift to use them to trigger the retard. If the switch doesn't open until "well" into the gear, then its too late and I'll have to go to plan B. These switches are activated by pressure, right?

 

[Eric Stage I]

If they're working right, the switch will open before the shift takes place. If you look at some DS runs, you'll see that the 3rd gear indicator comes on, then the shift happens. So you should be good.

On some other cars that use the same ECM, the TCC is unlocked only on the downshifts for 1 second (abyr4326 for example). I suspect they did it to soften things up, and maybe reduced it to .2 on our cars to make it feel firmer...I dunno. I think the 2-3 delay is so you don't get the double whammy of 3rd gear and tcc all at once. There, I used "whammy" in a sentence today.

Eric

 

[bruce]

Originally posted by dennisL
If the switch doesn't open until "well" into the gear, then its too late and I'll have to go to plan B. These switches are activated by pressure, right?

That's pretty much the case from what I've seen. The pressure changes as the valves are opening. You want to unload the clutches, and band as the shift begins, and until the next gear is fully applied for it to be really meaningful. That's why I mentioned a table. Say starting at 50%, and then just worring about heavy throttle shifts rather then all of them.

 

[dennisL]

OK, now there are 2 issues here. The first is, should I add a 200 msec unlock to the 3-4 shift? [table $33DF entry 1000] Keep in mind this table is intended for "street/cruise" use. During PE, the TCC is unlocked.

The other issue is timing retard during shifts, which could or could not be in PE, but is more critical during PE. How much retard for 2-3, how much for 3-4? Bruce, you're saying about 8d for .1 sec, right? I know it will need tweaking (sorry, Eric) but is this a good starting point for both 2-3 and 3-4?

Whadda youse guys tink? (spent too much time in Newark, NJ)

 

[TurboJim]

Originally posted by Eric Stage I
If they're working right, the switch will open before the shift takes place. If you look at some DS runs, you'll see that the 3rd gear indicator comes on, then the shift happens. So you should be good.

Eric

While I am not gonna argue the fact as I am not a 100% trans guy, and dont know what psi it takes to open the switches, but you cannot have pressure applying a band and a clutch at the same time. The result is a transbrake. So, I must disagree here.

But, I have no other explanation so I digress.

 

[Eric Stage I]

Jim,
I'm definitely not a trans guy! I'm just going off what I observe in DS. Look at some runs and see. The 3rd gear light will come on before the rpms drop. I have no idea how it works inside the trans.

Eric

 

[Drac0nic]

dumb question and everything, but I'm going from a 200R4 to a 700R4, the 700R4 only seems to indicate a "4th gear" pin, any thoughts on what I need to do to use the 700 with the '7148 box?

 

[RabidHamsterFab]

Originally posted by TurboJim

What I wonder is if this code is in the 148 cal for the FWD cars mainly, which could lock the TCC in 1st, and MORE damage would occur with that POS 440 (I think they used the 440 trans, if not, maybe a 125 which was worse than a 440, and the code was there to save those transes from self destructing. I personally dont know ofr certain how much of the chip section is different from a FWD to TR, so maybe my theory is totally wrong.

Maybe since it didnt HURT anything, the engineers never removed it?

I know in my FWD it's a 4t440/4t60 hydrolic (same thing) .. and my car won't go anywhere near lock up till 3rd and 4th gear over 35mph .... from what I can tell the chips aren't that different from an N/A 3.8 regal.. but very different from a TR (although pretty much all the harness and sensor stuff is the same... minus the lack of MAP sensor.. .but the ECM itself is identical)

as for unlocking the TC between shifts ... I would think it's a pretty good idea... put it would depend on how the trans/TC takes to being relocked after that shift has occured?