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Discussion Starter #1
I've been reading a lot about the TCC manual lock up mods and I think it's worth doing in some situations, but for smaller hilly areas it'd be nice to have a TCC lock out as well for smaller, longer hills that 4th does fine in, but maybe not 4th+TCC.

Does anyone have any info on that? It sounds like the TCC lock up mod is applying GND to the TCC lock wire, would applying +12v to that wire do the reverse and act as a lock out? Just throwing ideas out here more than anything.
 

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Applying 12V+ to a ground switch circuit can fry a lot of components.

Simple method would be to install a toggle switch in the dash that mimics your brake switch, but that will also kill Cruise and leave your brake lights on.

Also, I fail to see the benefit in allowing TCC slip on extended up hill climbs, that would increase transmission temperature and lead to premature failure, especially if you have the ability to lock TCC in 3rd.
 

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Discussion Starter #3
I was under the impression the transmission didn't move as much fluid with TCC applied, meaning 3rd+TCC would move less fluid than 4th+no TCC? Am I thinking about that wrong?

I have a transmission cooler out front with -8AN lines, I'm not terribly worried about trans temps. I was thinking more for EGT increasing when TCC is applied. The truck dumps more fuel in but doesn't allow it to rev and spool the turbo to match, causing EGT's to go up. Going up a hill in 3rd at 55mph is kind of annoying when 4th without TCC will do just fine.
 

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Do you have a trans temp and EGT gauge?

Do you have black smoke while TCC locked and trying to drive up hill?

If you have something that's not working right, lets fix that first....but allowing the trans to slip and generate heat shouldn't be a fix for a separate issue.

Sounds like a situation where if it ain't broke don't fix it.
 

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Discussion Starter #5
Do you have a trans temp and EGT gauge?
Purchased, need to install.

Do you have black smoke while TCC locked and trying to drive up hill?
A slight amount, but not "rolling coal". It's noticeable in the right light and depends on how hard I'm really pressing the pedal down.
 

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I just realized, you can install 2 toggle switches. 1 that opens the TCC circuit to the TCC, so when the switch is open, it can't get a lock up signal. and 1 that grounds the system to force lock.

I'd install the switches, and the gauges....and run a couple test runs to see what your Trans and EGT temps are, and what gains you make. I think you'll find that your better off using the TCC Locked on straight runs regardless of flat or uphill. Unlocked when freewheeling down hill, Locked when power braking downhill.

Who was the 4L80E expert again....I can't remember his name....
 

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respect the DB4 5722....
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gen.bilstein
 

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ahhh yes.

If anyone will know the answer to should you....it will be he.

I've sent him a PM but I wouldn't expect an expedient reply, he hasn't been online in a couple months.
 

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Discussion Starter #9
I just realized, you can install 2 toggle switches. 1 that opens the TCC circuit to the TCC, so when the switch is open, it can't get a lock up signal. and 1 that grounds the system to force lock.
That's a clever solution. I could also wire it up to a triple throw switch so I can have one that will do all the functions you mentioned. I may do that and play around with the temperatures. I'll at least have all my options at my disposal then.
 

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Blueburby asked me to drop in a comment so I will.
Imagine yourself running a full marathon on a cold day. You are dressed in layers of clothing with the plan of stripping off those layers as you heat up.

Now imagine yourself running said full marathon with sixteen individual layers on and you are into your 12th mile.

Now imagine yourself running said full marathon with sixteen individual layers on and you are into your 12th mile and you die of heat exhaustion.

This is what happens to your transmission when you mod it to command TCC lockup. The 4L80-E cannot exhaust transmission fluid to the transmission oil cooler as fast it would like.

The transmission fluid temp sensor sends a signal to the PCM saying the fluid is too hot/too thin. The PCM will then take the transmission out of TCC Lockup.
If you remove the PCMs ability to protect your transmission then you run the possibility of killing it. Heat kills a transmission quicker than anything else.

Another reason: If there is any transmission component slippage the PCM will take the transmission out of TCC Lockup. You cannot tell when your clutches might slip. The PCM uses three speed sensors, a throttle sensor and possible two temp sensor to take the transmission out of TCC Lock up.

You still want to run the risk and mod your electronics to command manual TCC Lockup?
Simply rewire a functioning ground commanded by you with a switch. This will command your TCC Solenoid. However: You run the risk of screwing up your Torque Converter Clutch. Why? Because your TCC is engaged in increments until it fully engages.
If you choose to interrupt this Pulse Width that goes from ten percent, twenty percent ectetera… At a minimum you could overheat your TCC Piston.
 

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Blueburby asked me to drop in a comment so I will.
Imagine yourself running a full marathon on a cold day. You are dressed in layers of clothing with the plan of stripping off those layers as you heat up.

Now imagine yourself running said full marathon with sixteen individual layers on and you are into your 12th mile.

Now imagine yourself running said full marathon with sixteen individual layers on and you are into your 12th mile and you die of heat exhaustion.

This is what happens to your transmission when you mod it to command TCC lockup. The 4L80-E cannot exhaust transmission fluid to the transmission oil cooler as fast it would like.

The transmission fluid temp sensor sends a signal to the PCM saying the fluid is too hot/too thin. The PCM will then take the transmission out of TCC Lockup.
If you remove the PCMs ability to protect your transmission then you run the possibility of killing it. Heat kills a transmission quicker than anything else.

Another reason: If there is any transmission component slippage the PCM will take the transmission out of TCC Lockup. You cannot tell when your clutches might slip. The PCM uses three speed sensors, a throttle sensor and possible two temp sensor to take the transmission out of TCC Lock up.

You still want to run the risk and mod your electronics to command manual TCC Lockup?
Simply rewire a functioning ground commanded by you with a switch. This will command your TCC Solenoid. However: You run the risk of screwing up your Torque Converter Clutch. Why? Because your TCC is engaged in increments until it fully engages.
If you choose to interrupt this Pulse Width that goes from ten percent, twenty percent ectetera… At a minimum you could overheat your TCC Piston.
Added to the FAQs. Thanks GenBilstein :thumb:
 

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Thanks Gen.Bilstein! Always good to hear from you, and I thank you for your prompt reply!
 

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Discussion Starter #13 (Edited)
Thanks GenBiltstein, that supports what I originally thought with keeping TCC unlocked will help keep temps down.

I'm going to go ahead with a TCC keep out switch (not manual lockup) for towing. I'll report at a later time (probably much later) with temps and such.
 

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TCC lockup.

I've had an OTC Genesys scanner for a long time, and have hooked it up to my '93 6.5 with the 4L80E trans. Once when I had a TCC that would lock out after driving a while, the TCM was generating a code for TCC slippage. I don't remember the code number. You could set the scanner up for an analog dial display and see just exactly what was happening. Clear the code, drive it until the TCC locked up, give it some fuel or go up and hill and watch the slippage occur. Code popped up at just exactly the slippage that was specified as unacceptable to the TCM and the TCC was locked out. I replaced the trans. with a GM Goodwrench unit for the 3 yr./100,000 warranty as I was going to pull a load from NC to NM and if the trans. died I could take it to any GM dealer for service on warranty. That is a very good post from Bilstein, in my opinion, and the trans. operates just exactly as he specified. Just my .02, but I think a TCC manual lockup switch is a bad idea.
I didn't realize there was a fluid flow/cooling issue when the TCC was engaged.:bow:
 

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Discussion Starter #15
So everyone keeps saying TCC LOCKUP in this thread, and what I'm after is a TCC LOCKOUT. I want to prevent the TCC from engaging for the soul purpose that has been said, reduce transmission temperatures and exhaust gas temperatures.

I'm just clarifying this for anyone else coming into this thread.
 

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Sorry to de-rail the tread, but ...

I'm a little confused. As I always understood it, the lock-up feature of a torque converter was to reduce slippage and therefore reduce heat. The torque converter has to slip and inherently does slip. Doesn't this slipping generate heat? Lock-up converters came along to address slippage and get greater efficiency from energy lost through slippage and heat.

The final rpm drop experienced, after shifting to 4th, is not from another gear change but from a reduction in the slippage of the torque converter. With reduced slippage wouldn't there be reduced heat?

I'm sure forcing the converter to stay locked as rpm's drop would create a problem beyond just the engines ability to create enough power. If the pump is moving less fluid at slow rpm then heat would build up. The above post made it sound that lock-up makes more heat than being unlocked in general and not just in certain circumstances. I would imagine if you ran down the highway with two identical vehicles at 70 mph and one was forced to stay unlock and the other locked, the converter that was unlocked would generate much more heat and probably end up cooking. I think this would be compounded if the vehicles were pulling a load.

My only experience similar to this was in my CUCV with a 700r4 that had a manual switch to lock the converter. When driving long stretches through soft deep sand, the transmission would never get out of 2nd gear. Prolonged driving like this would send the transmission temp gauge soaring. Once I started to use the switch to lock the converter, temps would be held at a reasonable level and the truck, engine and transmission would just keep working, plowing along.

Maybe I just misunderstood the previous posts or I'm wrong. Am I missing something?


Sent from AutoGuide.com Free App
 

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Discussion Starter #17
The final rpm drop experienced, after shifting to 4th, is not from another gear change but from a reduction in the slippage of the torque converter. With reduced slippage wouldn't there be reduced heat?
The whole point GenBiltsein was getting at is with TCC engaged the trans pump is not able to move an adequate amount of fluid volume through the cooler lines. If you are pulling a load, this may result in the trans cooking itself because it cannot expel the heat fast enough (fluid is moving too slow).

I would imagine if you ran down the highway with two identical vehicles at 70 mph and one was forced to stay unlock and the other locked, the converter that was unlocked would generate much more heat and probably end up cooking. I think this would be compounded if the vehicles were pulling a load.
With TCC engaged there is very little fluid movement through the torque converter. The torque converter also happens to be the biggest generator of heat. Given your example, the unlocked TCC vehicle may be running slightly hotter without a load, but it will also better handle cooling down since it can move the necessary amount of fluid volume to the cooler.

I've read plenty of stories of people who were towing in 4th going 65+mph on the highway only to have the trans puke fluid out the dipstick tube or worse. Towing in D (3rd gear) will generate heat, like said, but the pump will be able to take care of that heat fast enough that you won't explode your transmission.

The whole point I'm getting at is, I would like to tow in 4th without TCC engaged. Not necessarily at 65+mph, but at 55mph would be nice. My trans pump can keep up with the required fluid volume to the cooler, and I can benefit from a slightly more economical gear without fear of cooking my trans.

The biggest reason I see people putting manual TCC switches in is for downhill engine braking, since our trucks do not have exhaust brakes or really anything besides good old fashion discs/drums.
 

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I think running in 4th unlocked would generate far too much heat. The high gear ratio in 4th with the slippage in the tcc would be a trans cooker for sure.
 

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TCC lockup

So everyone keeps saying TCC LOCKUP in this thread, and what I'm after is a TCC LOCKOUT. I want to prevent the TCC from engaging for the soul purpose that has been said, reduce transmission temperatures and exhaust gas temperatures.

I'm just clarifying this for anyone else coming into this thread.
You're right. Had to reread it from the top and I misunderstood what you were after.
 

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The whole point I'm getting at is, I would like to tow in 4th without TCC engaged. Not necessarily at 65+mph, but at 55mph would be nice. My trans pump can keep up with the required fluid volume to the cooler, and I can benefit from a slightly more economical gear without fear of cooking my trans.
I'm trying to understand, because this idea of TCC engaged generating more heat than when it's unlocked goes against everything I've previously read.

Assuming 4.10 gears and 31" tires, 55 mph in 3rd gear (1:1 ratio) with TCC locked up, rpm's would be around 2400. 4th gear (.75:1 ?) with TCC locked up, rpm's would be around 1800. If the TCC is unlocked, rpm's come up a couple hundred, maybe 2200? Everything I've ever read says in this scenario you are better in 3rd locked up. As far as economy, the couple hundred rpm is negligible as to engine impact, so it would seem its just a question of whats best for the trans. Again, everything I've read tells me that towing at 55 mph in 4th gear unlocked, 2200 rpm, the transmission is going to cook.
 
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