A4LD-how to get TC to lockup sooner (lower rpm)

[Az_NavajoRob]

Okay everone, especially the A4LD guys (Glacier and Brian), I'm trying to figure out how to get the torque converter to lock up sooner, at lower engine rpms. Anybody know of any mods to accomplish this?

 

[Glacier991]

The TC lockup is processor controlled. Short of reprogramming the processor, I can't say I can think of a way to do what you want to do. I don't know if a low stall convertor has the added effect of a lower RPM at lockup or not, I'd doubt it, but am not sure. Brian might know, or others.

 

[MrShorty]

You would have to reprogram the computer if you want to leave the TCC lockup under "automatic" computer control. If you want, it isn't difficult to wire it up to take control of the TCC away from the computer and control it manually. The computer essentially acts as a ground side switch. Replace the computer in that circuit with a switch of your own, and you can control the TCC manually. Recognize that TCC lockup is hydraulically inhibited in 1st and 2nd, so you can't get lockup when the transmission is in 1st or 2nd, but anytime it's in 3rd or 4th you can.

 

[Glacier991]

As usual Mr. Shorty is right, but fer gawdsakes man why would you want to have to manually lock and unlock your TC ? (and for those reading this and not knowing who Mr. Shorty is, he is probably the best tech on here.... esp on ODB issues!)

 

[Brain]

Hold on a second...the TCC soleniod is an electonically inhibiting device, meaning it prevents lockup from occuring under certain conditions (full throttle, engine temp, etc.). So it doesn't engage the TCC, it just keeps it from engaging.

For the TCC to lockup:
1) the TCC shift valve must slide into the right position
2) the shuttle ball must fall into the right position
3) the TCC shuttle valve must slide into position
4) the solenoid must not be preventing the lockup

I'm going to have to think about this a bit more, but it might be possible to change out the TCC shuttle valve and shift valve springs (to springs with a weaker/lower/lighter spring constant) to allow a lockup at lower RPMs.

 

[Glacier991]

So, if you delayed the signal to the TCC solenoid you would extend the shift point? If that's true, you could devise a simple IC device that delayed the signal to the TCC solenoid... a basic timer circuit...WOuldn't shift based on RPMS or speed, but on a set delay from the time the signal was sent from the computer.

 

[MrShorty]

Not going to outright contradict you, Brain, because you've got a better understanding of how the valve body works on this. However, I have bypassed the computer before (for diagnostic purposes, didn't make it permanent) in the TCC solenoid circuit. Anytime that switch is closed (and the transmission is in 3rd or 4th gear), the TCC locks up. When the switch is open, the TCC unlocks. If you put a voltmeter on the TCC solenoid circuit and watch the computer open and close the switch, the TCC locks and unlocks at the computer's command. I'm not saying that those 4 things don't have to happen, but I would suspect that they all occur at the computer's signal, because that's how it works in practice.

 

[Az_NavajoRob]

Okay, if the computer controlls the TC lockup, is there a way to fool it into locking up sooner? Anybody know what input (sensors) it uses? What about throttle position? It seems that while cruising in 3rd or 4th, if I let up off the gas a little the converter will lock.

Also, what about the cable that goes from the gas pedal to the tranny. Isn't that a throttle position indicator for the tranny? If that were "cheated" to make the tranny think that the throttle was less open than it is, wouldn't that accomplish the desired effect? I know there is a "reset" procedure for that cable and I haven't done it yet but I'm pretty sure I could get the cable adjusted to a length that would simulate a lesser throttle position. It just seems that if the TC was locked up sooner, the engine would rev lower, fuel consuption would decrease, the tranny (TC) would experience less slippage and therefore make less heat. I feal the 4.0 is torquey enough to pull the Ex along nicely with the TC locked up rather than tool along in steady-state driving with the TC unlocking at the drop of a hat. That's what I like about my 5.0 Mustang with the AOD-it feels like the engine is actually connected to the wheels. You push on the accelerator and the speedo climbs along with the tach needle, not tach first and watch the speedo catch up.

 

[Glacier991]

At this point I'm in over my head. I surmise that the TCC lockup command is a processed condition based on multiple inputs... speed sensor, TPS, MAF and/or lord knows what else. Might want to talk to the folks at Apten for example.

 

[Rhett]

One way to get your TC to lock up lower or higher is to get an aftermarket chip programmed to that effect. My Apten chip has TC lockup adjustments done to it.

 

[MrShorty]

Primary inputs that govern TCC lockup are throttle position and vehicle speed. The trouble with interfering with these inputs is that they will also effect 3-4 shift point and, especially throttle position, will cause other undesirable changes in engine management which will cause driveability problems.

The cable from the throttle to the transmission is called a kickdown cable. I guess it's a throttle position sensor of sorts, but all it does is force the transmission to downshift at WOT. It doesn't exert any other control over shift points.

I don't remember the specifics, but I believe the AOD has a completely different 4th gear and TCC lockup algorithm. I remember glancing at some of the other tranny sections while researching some stuff for the A4LD. If I remember right, the AOD automatically (not even sure the computer is involved) locks up the TCC whenever it's in 4th gear.

 

[Brain]

Not going to outright contradict you, Brain
You aren't, you are actually agreeing with me for the most part (but maybe don't realize it).

Anytime that switch is closed (and the transmission is in 3rd or 4th gear), the TCC locks up.

When the tranny is in 3rd or 4th gear the things I listed with the valves and shuttle ball has happened in normal operation. I was just saying that if you open the switch for the TCC solenoid (0 volts), it gaurantees that you can't have the TCC locked up - BUT, the converse is not true...having the TCC solenoid energized (closed switch and 12 volts) doesn't guarantee the TCC locks up. You can try to lock up the TCC in first gear by applying 12V, but it won't happen because the rest of the fluid pressure conditions aren't met.

That's why I was trying to make the point of it being "inhibiting", because it can cause the TCC not to lock up, but, by itself (without the other valves being in the right positions), can't cause the TCC to lock up.

I think you missed the assumption that you made of the transmission being in third or fourth gear, which would clearly have the govenor in the "spinning fast enough" position, which in turn lets the pressure slide the two valves into place. Then it is just a matter of the computer not keeping the TCC from locking up because of WOT, brake application, engine temp being out of range, etc.. (there are seven reason listed in the ATSG manual for why the computer would choose not to allow TCC lock up). All seven conditions have a reason behind them, and for the most part make sense. I can only see a couple of reasons you would want to override those settings (towing up a long hill in second gear would be one of them for example).

 

[MrShorty]

Brain, now I understand how they went about hydraulically inhibiting lockup in 1st and 2nd gear. I always knew it couldn't lockup in 1st and 2nd, but never understood how that was accomplished.

 

[Brain]

I guess you could insert a switch for 12V and tap it into the TCC solenoid, but it would be gambling with the tranny. All it would take it one time of where you had the switch on (keeping the TCC locked up) and stepping on the gas hard enough to cause a kickdown in gears for the tranny to be hurting. The computer makes sure that the TCC is unlocked for all downshifts (passing gears).

Hmmm, how to safely cause the TCC to engage sooner/longer....?

 

[agzaretzka]

Hmmm, how to safely cause the TCC to engage sooner/longer....?

Wondering, has anyone has 'solved' this 'problem' yet?