Torque Converter lockup switch

[Ozymandias]

So run from a keyed 12-volt source to the LED, then to the wire going from the transmission to my switch, correct?

Yes that's how mine works.

 

[Tuesdak]

It's cheaper to replace brakes than it is to replace the transmission. The differential and transmission are not really designed for the reverse torque of engine braking.

I would look at the parts list on the "built" transmission and be asking if it has a billet or other major upgrade on the input shaft as well as a triple disc torque converter clutch.

I put one of these switches on my 1993 GM 4L80E and learned a few things... Yes, I did the wire mod in the dash by the ECM not by the transmission.

Expanding on the snapping the input shaft off: just going on off on the throttle can be enough to do it. This is why the TC clutch will unlock if you lift off the throttle.

(GM) There is a weak overrun clutch that only comes on in manual select 3rd. It surges with engine braking with the TCC locked some before burning out. Doesn't affect the forward gears however. Too small of an area to do anything aftermarket about it in the 4L80E.

The TC clutch itself is weak. I burned several of the OEM ones out before getting a billet triple disc. Pulling grades with the wick turned up didn't help life either.

Originally my goal was to keep it locked at 35 MPH, GM stays unlocked till 45 MPH. MPG was barley double digits in 35MPH town driving. This goal failed when the TC Clutch would slip lugging a minor grade in town. I tuned the trans computer to lock at 30 MPH and when it slipped it was all mad trying to lock and unlock several times in a row with wild RPM changes. The triple disc TC cured this.

When coming to a stop it bangs the shifts when, you will, forget to turn it off.

 

[BigPapa]

Yes that's how mine works.

Good deal. I’ll definitely give that a try. Thanks.

 

[cerberusiam]

I believe I'm correct in stating that lockup in 1st or 2nd requires VB mods. I have locked mine in 1st once and a few times in 2nd while towing heavy up a slow winding hill.

A 47RE requires mods to the VB to get 1 and 2 lockup, 48RE does not or should not. The problem is the 03-04 48RE's are a hybrid 47\48 and may not react like the 05 and newer units.

Activating the TCC lockup in automatic mode just stack shifts the trans into OD UNLESS you are WOT. Then it will shift as shift points are set locked to locked. It is real kick over a stock converter and one can really see how sloppy they are. Not so much with a good tight TC but with a turned up engine it is still very noticeable. The 1-2 and 2-3 shifts are pretty safe but the shift to OD has a missive TQ rise that will shred a stock trans quickly. Billet input at minimum and output if must though the output shaft is frequently used as fuse if one does not do a billet intermediate shaft.

 

[BigPapa]

the output shaft is frequently used as fuse if one does not do a billet intermediate shaft.

That's why I didn't go with the billet output, using it for the "fuse".

 

[Ozymandias]

Use it wisely is my way.

 

[CoastyAV8R]

It's cheaper to replace brakes than it is to replace the transmission. The differential and transmission are not really designed for the reverse torque of engine braking.

I would look at the parts list on the "built" transmission and be asking if it has a billet or other major upgrade on the input shaft as well as a triple disc torque converter clutch.

I put one of these switches on my 1993 GM 4L80E and learned a few things... Yes, I did the wire mod in the dash by the ECM not by the transmission.

Expanding on the snapping the input shaft off: just going on off on the throttle can be enough to do it. This is why the TC clutch will unlock if you lift off the throttle.

(GM) There is a weak overrun clutch that only comes on in manual select 3rd. It surges with engine braking with the TCC locked some before burning out. Doesn't affect the forward gears however. Too small of an area to do anything aftermarket about it in the 4L80E.

The TC clutch itself is weak. I burned several of the OEM ones out before getting a billet triple disc. Pulling grades with the wick turned up didn't help life either.

Originally my goal was to keep it locked at 35 MPH, GM stays unlocked till 45 MPH. MPG was barley double digits in 35MPH town driving. This goal failed when the TC Clutch would slip lugging a minor grade in town. I tuned the trans computer to lock at 30 MPH and when it slipped it was all mad trying to lock and unlock several times in a row with wild RPM changes. The triple disc TC cured this.

When coming to a stop it bangs the shifts when, you will, forget to turn it off.

I'd say the differential in these trucks is fine with engine braking but as you stated, the transmission may not be up for long term engine braking in stock form. My transmission has been built but even still I only plan on using it when I'm towing and need to use my exhaust brake on a long grade or when I"m slow n steady towing our trailer on slower roads when I see the transmission temp climbing because the TC is unlocked.

 

[sag2]

I used this in the Dakota. Works great as you just tap the brake to unlock. When the PCM hits the lockup point, it takes over from the relays and acts just like the truck normally does. You need a momentary contact switch, and LED (not shown on the diagram) if you want to see when the manual lockup is active, four ISO relays, and four ISO relay wiring connectors with pigtails.

 

[Mhennessy]

I am running the "mystery" switch and it works great for low speed tows up the dirt roads. I installed a small LED in my POD gauges ands it kicks on every time the TC locks up. I ran a 12v power to the LED and the negative to the TC lockup wire. It was simple and works great. I recommend finding a very dim light or it will blind you in the dark hours.
I wired my mystery switch to the pin on the trans but would defiantly move it to the ECU if somebody would care to share that wire location. 04.5.

 

[BigPapa]

See, you guys are so smart. Once Ozy explained needed the 12v supply for the LED it was like I got hit in the head with a brick. I could hear Fred Sanford saying “you big dummy....”

From what I see on Alldata the transmission is controlled through the ECM. Looks like it’s the Light Green/Yellow wire from the PCM to the transmission. I’d leave it alone if it’s working.

 

[petersonj]

@CoastyAV8R , I just read through this thread. I thought you may be interested in how I operated my '99 truck with a stock automatic and a mystery switch and an exhaust brake. I know I am not comparing apples to apples, but the concept of operating the transmission is very similar.

My installation was simple - one relay and one momentary floor switch operated by my left foot. The floor switch was a durable, low profile switch that required very little pressure to operate, just the weight of my foot. I think this low profile momentary floor switch setup is key for smooth seamless operation.

I owned the '99 truck for 70,000 trouble fee miles before I traded it in for my '02 that I am currently driving. I towed my tractor many times (gross combined weight 15,500 lls). I also had a slide-in camper (gross combined weight 11,500 lbs).

Below is an article that I had written a few years ago regarding the operation of just the mystery switch (not the exhaust brake) for my '99 truck. Here you go:

A couple of helpful things to know:

1. A stock automatic transmission will only lock the converter in 3rd and 4th gear (overdrive).

2. A stock automatic transmission unlocks the converter during a shift and then relocks the converter after the shift.

3. The mystery switch does not lock up the converter. The mystery switch allows you to keep the converter locked up after the converter locks up on its own. This is important to know, otherwise, you won't be able to maximize the benefits of the mystery switch.


Behavior of the of torque converter lockup with mystery switch operation:


1. Fourth gear (overdrive), converter lockup, foot on mystery switch - converter will remain locked and transmission will stay in fourth gear (will not downshift) regardless of throttle position or use of the foot brake. When mystery switch is released, the transmission will resume to normal operation.

2. Third gear (overdrive locked out), converter lockup, foot on mystery switch - converter will remain locked and transmission will stay in third gear (will not downshift or upshift) regardless of throttle position or use of the foot brake. When mystery switch is released, the transmission will resume to normal operation.



Driving the truck using the mystery switch:


Getting up to speed quickly from a stop - lock out overdrive (4th gear). Accelerate moderately until transmission shifts into third gear. Back off the throttle and let the converter lock up. As soon as the converter locks up, depress and hold the mystery switch and step into the throttle and continue to accelerate moderately. Pre select overdrive (the transmission will not shift). Continue accelerating to about 50 mph (this will be your shift point). Back off the throttle, release the mystery switch. You will feel the converter unlock, the transmission shift into fourth gear, and the converter relock. As soon as the converter relocks, depress and hold the mystery switch and accelerate moderately until you get to your desired speed. You can now release the mystery switch since the converter will stay locked on its own. With a little practice you will find the truck will accelerate quickly and shift smoothly.

Slowing for 45 mph curve – Depress and hold mystery switch and back off the throttle. The transmission will remain in overdrive (fourth gear) and the converter will remain locked (even if the brake is applied). Upon exiting the curve you can accelerate as hard as you wish. Once getting back up to speed, you can release the mystery switch.

Approaching a steep uphill grade (downshifting to third gear) – Depress and hold the mystery switch. Stay in the throttle as you approach the grade and preselect 3rd gear (lockout overdrive). The transmission will not shift. When you are ready to make the downshift, let the truck slow to about 50 mph. Ease off the throttle and release the mystery switch. The converter will unlock and the transmission will downshift into 3rd gear. As soon as the converter relocks, depress and hold the mystery switch and use the throttle to maintain your speed. Again, a little practice and the shift will be smooth.

Downgrades – 3rd or 4th gear – Select whichever gear for the downgrade. After the converter has locked, depress and hold the mystery switch for the duration of the downgrade. Brakes can be applied to help maintain speed.

Once these techniques have been practiced for a while, the mystery switch operation will become second nature and you will be using the switch without thinking about it.


I hope this helps.

- John

 

[BigPapa]

3. The mystery switch does not lock up the converter. The mystery switch allows you to keep the converter locked up after the converter locks up on its own.

Maybe yours is wired differently, but mine locks the TCC when you hit the switch and it will not unlock until you hit it again.

 

[petersonj]

Maybe yours is wired differently, but mine locks the TCC when you hit the switch and it will not unlock until you hit it again.

It may more about how the PCM controls the transmission in different year models rather than how the switch is wired (98.5 vs. 02). I would have preferred mine to have worked the way yours does, but it didn't matter that much because converter lockup was very predictable.

- John

 

[cerberusiam]

1. A stock automatic transmission will only lock the converter in 3rd and 4th gear (overdrive).

Not totally true. A 47RE is that way but not a 48RE and the 47\48 Hybrid in the 03's I have tried. They all locked in any gear.

The mystery switch does not lock up the converter. The mystery switch allows you to keep the converter locked up after the converter locks up on its own.

Both the 47 and 48 circuits are the same, power is supplied to the TCC solenoid and the TCM locks the TC by grounding the TCC sense wire. If you tag into the sense wire AFTER the TCC solenoid then whenever you hit the switch it will lock the TC, in drive on a 47RE, any forward gear on a 48RE.

What you do NOT want to do is leave out the resistor on the mystery switch circuit, that is asking for PCM\ECM\FCM issues.

 

[AEdelheit]

1. A stock automatic transmission will only lock the converter in 3rd and 4th gear (overdrive).

Not totally true. A 47RE is that way but not a 48RE and the 47\48 Hybrid in the 03's I have tried. They all locked in any gear.

The 48RE's I have wont lock in 1st that I have ever felt but will lock 2nd only if the shifter is manually in 2nd, I dont believe they will lock 2nd if the shifter is in "D" will it?

 

[cerberusiam]

48RE will lock in every gear except reverse, in D or manual select.

 

[2Farr]

I had ATS build me a Stage 3 trans a few years ago. I tolled them that I wanted to install a torque converter lock switch. They did a mod on the valve body so I can use the exhaust brake all the way down to first gear, 20mph. So far no problems, works great.

 

[CoastyAV8R]

I had ATS build me a Stage 3 trans a few years ago. I tolled them that I wanted to install a torque converter lock switch. They did a mod on the valve body so I can use the exhaust brake all the way down to first gear, 20mph. So far no problems, works great.

Do you have a separate switch for it or is it just a mod they did to the valve body?

 

[DavidC]

My DTT will lock and unlock to 18mph if 2nd gear is selected.

 

[cerberusiam]

It has to be a switch to hold lockup. The factory programming is set way to the safe side of activation, even more so on a 47RE because you could snap an input shaft just rolling off and rolling back into the throttle hard enough. Stock input shaft will not take the TQ rise on a shift point or hard throttle operation. Bille tinput i shihgly recommended or you really cannot use the lockup ability to its fullest.

The other thing that is needed is making sure the TV pressures stay high enough to hold the clutches when off the throttle. A 0 throttle input clutch apply pressures can go from 140-180 psi to 50-90 psi depending on the shift installed. 50 psi is barely enough to hold things together, 120 psi would be optimal but you won't get that unless there is controller on the the TV lever. BD used to have that item but it has since been discontinued so the only real option is idle pressures as high as possible.

Transmission has to be out of OD to have much if any benefit from EB also.