Torque Converter Lockup Mods for 99 4L80e

[DA BIG ONE]

Any mods that work on a 1999 4L80e?

I recalibrated my VSSB for the 33.1" tires & 3.42 gears= 3.09:1 +-, I don't like the way it shifts now.

Any thoughts?

[jspringator]

GMC hauler has a homemade mod for his, but I don't know if the wiring colors or placement are the same as his, so I have been too chicken to try it. I would like mine to stay locked up at lower speed and in second.

[rjwest]

96 and latter ( obd2 ) uses trans speed
sensor to set lock up speed,(i believe older models are the same )
Increasing MPH for a given Trans speed( lower rear end ratio or bigger tires) the higher the lock up speed for the tcc.

IE: increasing tire size, or lowering rear end ratio will increase tcc lock up speed.

going from a 4.10 to a 3.73 ratio will change
lock up speed from 45 to 50 mph.

The " torque loc" (BD) will work to lock the tcc at lower mph, but will not work on 96 and newer without setting a code.

There is a way to make tcc lock up in and 2nd and at a lower MPH in 3rd by making the transmission
think it is operating at a higher temperatutes,

a 50 ohms resister in parrallel to the temperature circuit will do this, but it will cause HIGH pressure shifts, therefore a switch is required , along with some practise, to make this a usefull method of TCC lock up. Do a search...
for details.

Hope this helps.

[DA BIG ONE]

Thanks for the replies.

I have 3 speed sensors (on t-case) because of the AutoTrac.
I remember when I first changed out the diff gears then tried to calibrate speedo w/aftermarket fixes (none of them worked)which only made things worse, banging when shifting, t-case would not work, just a nightmare.
After I learned how to hack VSSB things went back to ok.
Having, only stock sized tires up until now I liked the change from 4.10 to 3.42 great for all around driving. But this taller tire while riding better has put lockup too high IMHO.
Just holding off buying stand alone tranny controller because I have been unsuccessful getting information for my application. Kind of like when I wanted to buy Gear Vendors od/ud only to find they had none for my t-case/tranny combo.

Performance has not suffered and highway manners after lockup is great.

[ 09-10-2005, 01:39 AM: Message edited by: DA BIG ONE ]

[rjwest]

The resister mod to force TCC lock up will not effect the MPH of lock up in 4th gear.

If will allow 3rd gear to lock up at a slower speed.

Also allow lockup in 2nd.

For a 3.73 ratio with 235/85/16 tires
the lock up speeds with the resister is:

2nd - 28MPH
3rd - 40 mph
4th - 50 mph ( no cahnge )

The only effect on 4th gear is it will not
unlock the TCC as throttle is depressed,
it will shift to 3rd though with sufficent throttle.

I try to not allow shifts with the TCC forced to
Lock (above) I anticipate shifts and manuelly
shift transmission with the shift lever.

1 of the down sides to taller gears is when loaded
you spend more time in TCC unlocked, which I believe worsens fuel milage, 4.10 seemed better
on fuel milage(loaded) than the switch to the 3.73 ratio. For me ( Truck camper ) 4.10 gears ( no mods)were better. was getting 13-13.5 mpg with 4.10 rear
just getting back close to that with mods,
12.5mpg approximate, But I have seen occasional
14-15 mpg qith good fuel, steady interstat,
and VERY judicial use of the thottle ( 1800rpm)

The most significant improvement with the forced TCC is lower Tran temps, especially climbing
back country roads in 2nd ( TCC locked ).

[Diesel Dan]

GM is too lazy on their TCC engagement, IMO. When I replaced my TC in went a trans-go 4L80E HD-2 kit. It really helped firm up the shifts and TCC engagement but the lockup points are still the same, too late. It will lock under full load(11K) and full power without slipping now.

Also wish when running manual 3rd the TCC would come on sooner. For comparision when running in manual 3rd on my Dodge/cummins the TCC will come in at <30mph running 3.54 gears.