I was hunting around for a way to determine when my T/C goes from locked to unlocked when towing (other than watching for the slight tach increase), and knew there had to be a signal to the T/C lockup solenoid. Well, I found THIS POST at TheDieselStop.com detailing (I mean really detailing) the addition of an LED. I found the wire in question at connector C172 on the passenger side of the firewall. (Its' a grey connector under under a snap-off plastic cover/metal bracket assy.)
The discussion also gets into adding a T/C lock-up switch, which I think could come in handy as well, but I'm hesitant to install this. I assume Ford knew what they were doing when they programmed the PCM to lock/unlock it under certain conditions (and I don't see any long-term reports on the effects of the manual override switch in the linked post). It would be nice, though, if the trans would downshift directly from OD to 3rd without the "3.5th-gear" slip mode. It might also be nice to get a little dynamic braking?
I'll be adding the LED, but would like to know others' thoughts on the switch.
Andy
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Last edited by OhioLariat; 06-25-2009 at 02:07 PM.
The reason the 4R7x transmissions take a moment to downshift from 4th is because the transmission needs to fully release the overdrive band before the forward clutch comes back on. If that doesn't happen then the transmission becomes mechanically locked. Kind of like park and is bad.
I have 0 opinion on a light or switch though, I only wanted to address that one concern that you voiced to try and explain why it has to be that way.
While I can appreciate the function of this mod, and in a diesel, it probably makes sense, since the rpm range on one is very small compared to a gas engine.
In my case, I've become so accustomed to the shift patterns of my truck, that I can tell what's going on pretty much by feel now... Then, it only takes a second to blip the gas to check the tach since I'm already looking there anyway!
My vote is to leave the wiring harness alone and I don't even like the idea of a tuner, so that'll tell you where my 'conservative' mind is!!
But more power to those that have the gumption to do this kind of stuff!
The reason the 4R7x transmissions take a moment to downshift from 4th is because the transmission needs to fully release the overdrive band before the forward clutch comes back on. If that doesn't happen then the transmission becomes mechanically locked. Kind of like park and is bad.
I have 0 opinion on a light or switch though, I only wanted to address that one concern that you voiced to try and explain why it has to be that way.
Darrin
Well, it sounds like having an override switch activated would be a bad (possibly very bad) thing if the trans wanted to downshift out of OD, then. Trouble is, though, it's not just an OD --> unlocked --> 3rd shift. It seems like it likes to stay in the unlocked condition too long (or at least longer than I'd like it to). As soon as I see the tach jump, I hit the OD button, and knock it into third. Maybe I'm exhibiting some "conservative-ism," too.
Regardless, that pretty much seals the deal against the switch for me. The light OTOH, couldn't hurt anything.
Thanks.
Andy
Last edited by OhioLariat; 06-25-2009 at 03:51 PM.
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