'02 Excursion. Mine will stay locked down to about 41MPH in OD and 30-ish in D (don't recall the exact speed in D). With most vehicles they unlock as soon as you let off the throttle and I've read that the diesel 4R100 does also so I'm wondering if mine has a hidden mod or if it's normal. If I turn the OD off while decelerating it'll unlock, shift, then re-lock. I think it does it in 2nd too but it's been a long time since I tried.

 

Never fails when i leave the neighborhood, that i get nailed by the red light a block down. Thingbis, im on it making the left onto the blvd. Already at street speed(40mph), i cost to the light. I can feel the tc locked. When i get to around 25mph, it unlocks and the truck moves faster, causing me to apply brakes even more...weird

 

Mine unlocks no matter what as soon as any pressure is put on the brake pedal. There is a 6% grade that we drive almost daily and it really sucks that it unlocks at the slightest tap of the brakes, you have to push the brakes more to slow down because the second the converter unlocks you pick up speed.

 

This all depends on tuning and transmission temperature. If you just start driving first thing in the morning, it takes a while before the TC will lock up at all - even at freeway speeds. The colder the environment, the longer it takes. The slipping is a method to warm the transmission up quicker.

I have tuning that makes the TCLU behave in a very logical manner. DD for better economy, towing for better engine braking and town driving. I call the latter "TNT" or "Tow-N-Town"

 

This is an excellent question. Until about a week ago, I was running a TS 6 chip with BTS tunes. I never noticed Brian's tunes unlocking the TC below about 45 mph or so and as somebody pointed out, that's pretty nice when descending a grade.

I just took my first trip towing our 5er with a Hydra chip and I noticed the Diesel 1023 tow tune unlocking the TC and allowing the engine to essentially go to idle when coasting in traffic. It locks up smoothly and immediately when I get back into the throttle (I monitor slip with Torque Pro), but I haven't made up my mind if I like that behavior......

 

Over the 5 model years that Ford produced the 7.3L + 4R100 drivetrain combination, Ford changed the enabling parameters in the PCM calibration which would cause the torque converter to unlock or remain locked when applying the service brakes, and at what speeds. Of course, since so many FTE members run tunes, the original calibration may be a moot point, but my point is that there was a definite behavioral difference in TCC engagement between stock trucks, depending on model year and calibration, and this is important to understand when comparing how one truck behaves vs another. Two entirely different reported experiences can both be valid, without operator error or misunderstanding, because Ford really did change how the TCC behaved during the 5 years that this drivetrain was produced.

 

02' cclb 2wd 4.10s here, all stock w/285-75r16

 

Very true, and often misunderstood. Thanks for explaining that.

 

Different programming makes sense. I like how mine's set up quite a bit. I'd like it to shift at lower RPM when cruising, but other than that the trans strategy is about the best I've driven. I mostly love the TCC programing on mine, but I plan to add a switch to manipulate it.

It's interesting that the different factory programmings apparently respond differently to a tuner. My friend's '00 F-250 shifts similarly to my Ex when stock. His super chips 1705 makes mine shift early and quickly, almost perfect to my taste, but on his truck the tuner doesn't seem to change it much. My accelerator pedal also becomes a bit touchy/jumpy off idle and his doesn't seem to.

 

I got a chance to check mine out today after installing my new shift tube and OD switch and it behaves just like yours (02 F-350). I didn't try second but it would be nice if it would stay locked in second at lower speeds, will check that out next time. Braking did not seem to have any effect, it stayed locked during braking as long as I was over 30 MPH.

 

So maybe it's an '02 programming thing, and mine doesn't change with brake activation either. Pretty lame that it unlocks when braking, guess Ford finally figured that out. Unlocking with brake dates back to the 80's, some of the guys I drag raced with would hold the brake pedal going down the track to keep the converter unlocked 'till they wanted the lock, mostly Mustangs and a few T-Birds. They'd lock pretty early even at WOT and drag the RPM & power down.

Someone said that it'll stay unlocked when cold; mine doesn't unless cold means arctic cold, I only have SoCal cold.

I played with second a couple days ago, once it locks it stays locked down to an unknown speed, wasn't looking. In an empty vehicle it slows down fast in 2nd gear locked. I was driving in 2nd, not a downshift to 2nd.

Tho I haven't played with this enough to absolutely confirm, it seems that if it hasn't locked during acceleration it won't lock for the deceleration. When cruising locked in OD and start to decelerate, turning off OD makes it unlock, shift, then lock again. I assume that's to make the shift smoother. I haven't tried downshifting to 2nd to see what it'll do, I'll probably need a steep hill or heavy load to push it long enough to find out.

 

My '03 originally did the unlock thing when coasting. Even when I first got it tuned it still did it. Then when I got the BTS valve body and had new tunes burned for it, Jody tuned it to stay locked and at first, I didn't like it, but after about a month I got used to it, and now I wouldn't want it the other way.