Alright, about a year ago I did the TC Lockup Mod. Honestly, I rarely, if ever, use it. I see what it does, and it is cool, but I get overly concerned about placing unneeded stress on the drivetrain. I have read about not using it below 1500rpm, and also below like 35 mph. So which is it? There are times when I'm over 35 mph and still below 1500 rpm (or real close).

Also, I just today picked up a heavy 5th wheel rv. Should I use the TC Lockup switch while towing? Or is it placing more stress somewhere?

Sorry for being overly cautious, but I dont want to kill my truck while I'm towing my 12.5k+ lb new RV. My young family depends on me to get them where we need to go. My wife and I have a good understanding....I handle the towing, she handles the kiddies.

Thanks for the help.

Bob

 

I am also interested in installing one...So I would like to see the responses.

 

I've had my TC lockup switch for about a year also. When towing heavier loads(5000 and up), I won't lock it until 30-35 mph. I've found that anything less and it shifts really hard into the next gear. Not towing or lighter loads I'll throw the switch as soon as I have forward momentum. I always figured it's no worse on the drivetrain than what a manual transmission would be.

 

I've had mine about six years. Its on a toggle switch. I added two small lights, a green when the butterfly valve is closed and a red when the Valve is closed AND the TC is locked. In the process of wiring I ended up with the red light comming on everytime the TC locked whether by the computer or by me. So, what I learned is that it locks almost all the time except when you are slowing down below about 35 MPH. The only time I feel the need to lock it manually is descending a major incline. I drop out of overdrive, lock the TC manually and try to stay off the brakes. Then I try to remember to unlock it prior to stopping. If it's locked below about 5MPH the truck will stall. Just like leaving the clutch engaged in a stick shift. I guess if you really want to save braking you could use it more but I never felt the need and I towed about the same weight you do until recently and now I'm a giood bit heavier. Also, every time I get the interior cleaned somebody trips the switch and I look like a doofus trying to start the truck. Hope this helps.

 

OT, but how do you like the firestone airbags? After picking up my 5th wheel today, I'm thinking I may need some at some point. Truck is sitting nose high for the first time I've ever seen.

 

That's the only time I use mine. Towing is the only reason I have one.

Back in June of '07, while towing my 10k lb 31' TT into Yosemite, a long, curvy, uphill two-lane road, I couldn't keep the speed high enough (too many tight curves, had to slow down all the time, dropping the converter out of lockup) to keep the converter locked, so my EGT's and tranny temps climbed into the red zone.

When my tranny failed in December of that year, and John Wood installed one of his built, monster 4R100's, I also had him install a torque converter lockup switch.

I used that switch when I towed into Yosemite again in August '08 (we camp there every year) and my EGT's and tranny temps stayed well in the safe zone.

Stewart

 

I've had one for about 7 yrs now. Most helpful when coming into town, 5ver in tow, lock O/D out, hit TC lockup and motor on thru town at 30 or 35 whatever speed limit is, without tranny "hunting" for a gear.

Also when going down a grade while towing and using exhaust brake.

 

My switch is like this one...


It eliminates accidental activations.

Stewart

 

Wow, as an apache helicopter pilot in the army, I am very familiar with safety switches. Seems like a bit of overkill for the tc lockup switch (they are typically used for switches that will kill you if used at the wrong time) but whatever floats your boat

 

I like them fine. But, I liked the over load springs better. They were more stable under load (side to side) than the airbags. Problem was when I got the new 5er it was so heavy that to level the truck I had to tighten the heck out of the overload springs and when I took the trailer off it rode like a buck board. So I went to airbags. I didn't notice what your truck was but I thought you said the 5er was 12K lbs. At that weight I would get the springs. I had Hellwigs, cost about $200 and install with a socket set. But that's just MHO.

 

Truck is as in signature...trailer, realistically, will weigh about 13k.

 

As Stanley already stated, my TC switch comes into play when towing and decel-ing down a grade to help save my brakes. I also use it when going up steep grades that I know there is a chance that the truck will downshift tring to maintain speed. Reason being, your TC normally unlocks and locks momentarily when it downshifts out of overdrive. With the TC switch in the locked position the TC stays locked when the truck downshifts, that way there is no slippage while tring to get the the 5ver up the steep grade.

 

Greetings from a former member of the 282nd Assualt Helicopter Co, Black Cats, Marble Mountain Viet Nam, 1968/69.

 

I didn't choose it, it's the switch John used when he installed it for me, but it really does float my boat because it's kinda cool looking, and it does keep someone from activating the lockup toggle accidentally.

Stewart

 

Here's how I towed a 14K 5er for 100K with a bone stock 4R100 without any tranny issues whatsoever. As a matter of habit I pushed the OD inhibit button just after starting the engine. Then I started up from a dead stop by manually selecting 1st gear with the TCC unlocked of course and eased into the throttle to get rolling. Then as I got to 20 MPH I let up on the throttle just enough to unload the drive line and I locked the TCC solid with my special manual switch.

Then I eased back into the throttle until I got to 30 MPH and again let up on the throttle enough to unload the drive line and I manually shifted to 2nd gear while keeping the TCC locked then eased back into the throttle. At 40 MPH I'd again let up on the throttle enough to unload the drive line and I manually shifted to "D" which is 3rd gear if you've remembered to punch the button to inhibit OD. When I got up to 65 MPH in 3rd I'd let up on the throttle enough to unload the drive line and push the OD button to engage 4th gear.

All these upshifts were done just like when driving a manual, and when it's time to downshift you just reverse the process but now you have to first let up on the throttle enough to unload the drive line, then manually shift out of the higher gear, then apply a little throttle to raise the engine RPM enough to match the road speed so you can smoothly catch the next lower gear without putting a strain on the driveline.

Basically I locked the TCC solid at 20 mph in 1st and it remained locked solid until I had to slow below 20 MPH again. I executed all shifts with the TCC locked solid by using throttle adjustments while shifting to unload the driveline. I never let the tranny shift on it's own because shifting like that with the driveline under load is what causes wear and tear on the clutch packs, and towing with the TCC unlocked builds heat.