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.

[burban nate]

A little off topic but, I'll be doing the EFI Connection 24x EFI conversion on the BBC that I use in my '90 V3500. I believe the LS1 ECM takes the raw VSS signal and conditions it, then sends it out 2 or 3 different outputs. There is no need for DRAC's or VSSB's, correct? I'll need one for cruise and one for speedometer.

Nate

[hatzie]

Originally Posted by burban nate

A little off topic but, I'll be doing the EFI Connection 24x EFI conversion on the BBC that I use in my '90 V3500. I believe the LS1 ECM takes the raw VSS signal and conditions it, then sends it out 2 or 3 different outputs. There is no need for DRAC's or VSSB's, correct? I'll need one for cruise and one for speedometer.

Nate

I think you answered your own question. The PCM has the VSSB built in and outputs conditioned VSS signals for a speedometer and external cruise module among other things. You just need to find where the cruise VSS is.
This is a thread on LS1 tech for installing cruise on the cable TB LS PCM. Those guys know a lot more about the LS engine controls than I do.
http://ls1tech.com/forums/conversion...driven-tb.html

[75C10]

I have the early cruise master in my 75 and would like to convert this to the 88 and newer with the electromotor. Can I still use the single button activation from my old system to set the cruise on the electromotor. Of course the old switch cannot turn on and off manually or set the resume feature. But if I have the VSSB and I already have the brake switches I would think it wouldn't / shouldn't be too hard to make this work just will be missing a couple of features. Should I add an extra switch to control the over all power on that is absent from the early systems? Comments appreciated.
Thanks
Darwin

[Katrina/10]

That should work, if you have the schematics for the electro motor system you should be able to just activate the set function with your original button. But what will you use for a VSS?

[75C10]

I have an 80's speedo so it should be easy to add the factory VSSB (optical sensor). The speedo should accept it and I have an extra VSSB kicking around.

[Katrina/10]

I did some research on this cruise control the last time it came up. I found that the Electromotor cruise requires a 4k square wave input, I think your in dash VSS puts out a 2k signal for the cruise control used at that time.

[75C10]

Katrina, thanks for feedback.
Hatzie mentioned in post 26 that the 2k vss on the back of the speedo would work.
I should be testing mine this week and will post the results. I am still in need of fb regarding the linkage connection and adjustment.
Darwin

[Katrina/10]

I read the post you mention again, and I'm not sure exactly what he did. Interested to see how yours works.

[hatzie]

The electromotor cruise module is expecting roughly a 4K signal.
You can use the 2K signal from the 81-91 cluster mounted VSSB.
If you're worried it should be fairly painless to build a frequency doubler.

[Katrina/10]

Originally Posted by hatzie

The electromotor cruise module is expecting roughly a 4K signal.
You can use the 2K signal from the 81-91 cluster mounted VSSB.
If you're worried it should be fairly painless to build a frequency doubler.

That's good news, so the cruise unit doesn't care that it's getting a 2k signal instead of 4k? I'm sure I don't fully understand how the thing works, but I assume it doesn't really know the actual speed you are traveling, it just looks at the pulses it is receiving at the time you press the set button, and tries to maintain that.

[hatzie]

Originally Posted by Katrina/10

That's good news, so the cruise unit doesn't care that it's getting a 2k signal instead of 4k?

I'm sure I don't fully understand how the thing works, but I assume it doesn't really know the actual speed you are traveling, it just looks at the pulses it is receiving at the time you press the set button, and tries to maintain that.

The only part that cares what the actual ground speed number is... is the driver.
The Cruise Module is receiving pulses per second. When you "Set" a speed it will try to keep the pulses within the preset window over and under that setpoint.

[Katrina/10]

That makes sense. Does it affect minimum cruise engagement speed?

[hatzie]

It engages at 50MPH on the highway. Not really useful much below that anyway. Never tried to find how low it will go.

[Katrina/10]

Sounds like that should work fine, then. Thanks!

[burban nate]

I thought I read somewhere once that 25mph is the threshold. Below that it won't engage.

Nate