Gear change affecting VSS/MPH in 7747 ECM

[PlayingWithTBI]

This is good stuff!!! That's what I was hoping for was moving the ECM wire from the OEM circuit to the DD speed output, as long as it is calibrated to the same speed as the DD display and not just a pass-through from the OEM circuit.

I'll get my son to come over for a steak on the barbie and rope him into helping me play with it. After all, he's the one that installed the DD in the 1st place.

[1project2many]

Hmm... The DD speed output option is not gauranteed to work. Changing the programming clip might turn out to be less work and is the best solution. It's just a plug-in device in the back of the OE circuit board.

[PlayingWithTBI]

Changing the programming clip might turn out to be less work and is the best solution. It's just a plug-in device in the back of the OE circuit board.

What will that involve, changing jumpers or a different device? What does this device look like?

[CDeeZ]

Yeah, as 1project mentioned the Drac for a 747 was in the instrument cluster itself. I moved some jumpers around in mine way back when, when I put 4.88 gears in mine in one of the previous iterations of this truck. But since you are Dakota digital gauges I guess that won't be an option!!!

I wonder if it would be possible to wire in a seperate drac module like the PCMs used and calibrate it that way???? THere may be an easier way I don't know, but I'd think it WOULD be possible to address this issue this way.... If not, maybe time to consider upgrading from a ECM to PCM so you can easily use the DRAC, along with the many other advantages it offers.

[1project2many]

What will that involve, changing jumpers or a different device? What does this device look like?

Here is a link to a forum thread that has plenty of pictures and even talks about how to make the changes without the programming clip. The information here is similar to what's in the DRAC paper. Many links are dead now but there's still plenty of good information.
http://67-72chevytrucks.com/vboard/s...d.php?t=313815

I wonder if it would be possible to wire in a seperate drac module like the PCMs used and calibrate it that way????

Possibly. If you Tee the DRAC into the VSS signal it would probably work. But you'd still have to gain access the 2K ECM speed signal wire in the dash to cut it and connect it to your new DRAC.

[ony]

that's the way my 91 is works good with a gps to calibrate the switch.