Locking Converter Early?

[jamesbond2509]

Well I have done all I could with DFCO and picked up 1 mpg consistently on the highway. Im now thinking of locking up the converter in second third and forth. Can you please provide pros and cons of doing this. Will the converter clutch wear faster - will there be any harm in doing this - Please advise.

Thanks

[Mr. P.]

What converter is in the truck now?

Mr. P. :)

[99TransAmls16spd]

I currently have mine locking in third and obviously fourth. I like the fact that it locks in third now, being that it isn't in OD the truck is still really responsive. The pro is better mileage and lower rpms (stock 6.0 converter with 4.10s is too big imo, and mine is stock). I haven't had the time to figure out why it sometimes stays locked during the upshift while other times it unlocks (which is very annoying - rpms jump to stall speed during the upshift).
It will wear the clutch faster - how much I am not sure. Another con is if you are like me, the stupid PWM valve is worn in the tranny. The easy fix for me was to increase the minimum tables, but when in third gear on very rear occasion, I can feel my truck "buck" a little when going downhill b/c of this.
But overall I like it locking in third as to not. With that said however, with 4.10 gears and the speed limits of where I travel, it hasn't made enough sense to lock second - so I have no feedback for you there.

[spy2520]

I've been thinking about doing this for a while. Wondering how low i can go. 3600 stall with headers and duals is kinda ridiculous sounding when i'm only going 20-30 mph.

[joecar]

I've been thinking about doing this for a while. Wondering how low i can go. 3600 stall with headers and duals is kinda ridiculous sounding when i'm only going 20-30 mph.Depends on your cam... more duration/overlap needs lockup minimum speed to be higher to avoid surging/chugging...

you have to see how low you can go and check engine behaviour.

[swingtan]

Also....

Locking the converter results in reduced slippage loss in the converter, which can help economy. However, it also,


removes the "torque multiplication" that the converter provides.
lowers the engine RPM, reducing manifold vacuum and pushing the ECM closer to PE mode.


So while it can help, it can also hinder economy by loading up the motor too much. Sometimes, running a lower gear but locking the converter is better than running a higher gear without locking the converter.

The 6 speed boxes in Aus. lock up in second and I've tried locking up in 1st which seems to be fine for light throttle. If you are going for every last bit of economy, you could also look at the pressures, but need to ensure you don't introduce any slippage when reducing the pressures.

[spy2520]

cam is 236/238 .601/.605 on 113 lsa. economy would be nice but i just don't want to sound so ferocious when i'm cruising or on my way to work.

[spy2520]

Is it even possible to have the converter lock in 3rd and remain locked as it shifts to 4th? I've been experimenting with having it lock in 3rd around 20-22 mph, then when it shifts to 4th a few mph later it unlocks and then locks up again. I've been playing with D0902, D0903, as well as D1001-1006. Making sure not to overlap apply/release curves. This is on a 99 LS1 pcm with 2002 OS.

[joecar]

For durability of single plate TCC, it's best to allow it to unlock during shifts.

[spy2520]

This is only for extremely light driving, like <12% TPS. You think it affects durability that much? If so, any suggestions on minimizing the time that it is unlocked? I'm thinking maybe lower the apply speeds, but disable locking during upshifts or something like that.

[hog]

For durability of single plate TCC, it's best to allow it to unlock during shifts.
I would agree, hits pretty hard for WOT use on a stock TC.

What is your opiion for an aftermarket TC with a single clutch that has extra surface area? Would you lock a multidisk TC through WOT shifts? Opinion on shock load ing the trans? Thanks man.

peace
Hog

[joecar]

the stock TCC has two weaknesses:
- single surface (i.e. only half of a clutch when you compare it to a manual trans clutch),
- shock-uptake springs in the TCC hub may not be very strong;

aftermarket TC/TCC may address those...

but, each upshift takes only a few tenths of a second... i.e. the TCC is unlocked for a very small percentage of the time, I don't believe you will see any fuel mileage increase from keeping TCC locked during upshifts.

[spy2520]

I have an aftermarket converter with single lockup clutch. I really only intend to lockup a little early at light throttle. Before I started experimenting i was locking up around 30-32 in 4th. Now I'm thinking about locking in 3rd and maybe delaying the upshift til later.

[joecar]

. . .
Now I'm thinking about locking in 3rd and maybe delaying the upshift til later.

Locking in 3rd is fine (especially if you run in manual 3rd (for example when you're not on the freeway)).

Delaying the upshift (to a higher mph) is ok... in 3rd it keeps the TCC locked longer (since the upshift is delayed), and in 4th it allows the TCC to stay locked easier (since mph is now higher due to the later upshift and so you don't need as much throttle to maintain the mph).

[spy2520]

Seems to be the way to go. I'll play with it and hopefully get it right.

[spy2520]

Delaying the shift works pretty well. Is it really bad for the converter clutch to stay locked during an upshift at such low throttle? Right now I have it unlocking and there is a noticeable flare because of the high stall. Again this is only for low throttle applications, to avoid getting pulled over on my way to work etc.

[joecar]

At low throttle the TCC staying locked is probably ok.