Adding Cruise Control question

[hatzie]

Originally Posted by 75C10

Hatzie,
Thank you for all of the great info.
Very very helpful.
Darwin

I've done a bit more reading and deleted my incomplete post on the DRAC and VSSB...

I would pass on the 4K VSSB or the DRAC and use either a cable mounted 2K VSS or an Optical VSSB for the speed signal. You should do your own research on VSS signals.

My Cruise module is from a late 80's early 90's T400 chassis truck. I used a two pulse square wave VSS mounted between the NP208 transfer case and the speedometer cable. There's no rule that says you can't have two. **EDIT** You may be able to use the 25071437 4K sine wave VSSB to amplify and split a two pulse square wave VSS but I have not bench tested this approach to see what the output signal would look like. If you have the skill set... you could roll your own signal buffer amplifier circuit that doesn't slice and dice the signal.

For you folks with the 1981 and later speed heads... The Optical VSSB that GM used for cruise control on cars and trucks in the 80's provides a 2,000 pulse per mile squarewave signal on the cruise control terminal. This will work fine and it's protected inside the cab.

If you're using a 4K sine wave VSS for 90's TPI or LT1 Fuel injection. You're probably already using the 25071437 VSSB from a late 80's F-Body to get your conditioned ECM VSS. Plug into the cruise output pin for your square wave cruise control speed signal.

The later trucks that used a DRAC had a 40 tooth reluctor in the transmission or transfer case that generates vehicle speed information in the form of a variable amplitude high frequency sine wave. The voltage output ranges from one-fourth (1/4) volt AC peak (.2 volts AC RMS) at 2 MPH to 100 volts (70 volts AC RMS) AC peak at maximum speed. This AC signal is sent to the DRAC which conditions and converts it to a squarewave of 1.112 Hertz/MPH for the cruise control module. The output frequency from the DRAC is proportional to vehicle speed. If you have one of the engines that needs this signal you already have a DRAC to condition the signal to the ECM/TCM/PCM. You can grab the cruise signal from the appropriate terminal on the DRAC... but A DRAC is not going to be useful for conditioning and splitting a two pulse squarewave signal.