After several weeks of research and building, I am happy to report that my Barth now has an electronic cruise control instead of the vacuum system.

I found that a GM unit from a 1999 K2500 Suburban with a small interface box works very well, I had to convert the electronic signal from the Allison electronics box to be compatible with the GM unit. GM want to see 0-5 volt signals and the Allison puts out 0-12 volt signals, the frequency of the speed signal of the Allison is also 10 time higher then the GM unit will accept, was easy to make a a simple buffer and a divider. Mechanical attachment of the control cable to the throttle system in the Barth wasn't bad but did require some small metal parts to be fabricated.

GM cruise control unit and the buffer/divider box:



Buffer/divider box:


As installed in the Barth:




For a write up you can download or open up the PDF file here, it is a big fill!
Cruise control write-up

Took it out for a 50 mile run and it works very well, I was worried that the response or gain of the system might not work well with the heavy coach but it seems to do very well, it maintained speed to with in 1 MPH over fairly flat freeways with some grades, It will go to full throttle and downshift if needed to keep the speed but doesn't jump back and forth as many systems do, I am VERY happy with the results.

Total cost for the system as installed was less then $100.

Got a 2K mile trip at the end of the month and will be anxious to see how it works on a long haul.

Very nice... Is that a rheostat on the outside of the buffer box?

Would you please send me the buffer box schematics as I'm interested in what you did. I don't need to do it, but I would like to see the schematics.

Bill N.Y.

Ed,
Just wanted to comment what a great job you did on this write up. I am continuously amazed at the talent on this website.
Regards,
Ray

quote:

Would you please send me the buffer box schematics as I'm interested in what you did. I don't need to do it, but I would like to see the schematics.
Bill N.Y.

Finally got around to cleaning up the input buffer schematic



Still have to draw the schematic for the switch control interface, the control switches on the Barth are not compatible with the GM cruise unit, the GM unit wants to see a contact closure to +12V for the Set/coast and Resume/accel function, on the Barth the set is normally closed and has +12V all the time, when pushing set it goes to "0" and resume goes to +12V, so I had to flip the set button function and eliminate the resume function during set operation. Sounds complicated but is really not, just used a small relay.

I now have 4K miles using this cruise control and find it to work VERY well, I was a bit concerned that the loop gain would not be enough to control the speed of a heavy vehicle with a slow responding diesel engine. Going down a hill where it will pick up speed followed by entering an uphill rise, the speed will drop off 2-3 MPH before recovering, on most freeways even with some small undulations, I never see the speed change.

One feature that I really like about the GM cruise control is by tapping the set/coast button the speed will drop by exactly 1 MPH for each tap, conversely, by tapping the resume/accelerate button it will increase the speed by 1 MPH for each tap.

I know this post is old, but would you be interested in improving your cruise control for hills and speed traps and traffic? See Wikispeedia.org, specifically "ACC".

-jim

Ed, great job! I recommend you file a copyright immediately with the web site disclosure and your OUTLINE of what you describe, ie "converting gm cruise control for diesel applications" and then submit it to Rostra and King Cruise and ask fo r a royalty from their sale or exploitation of the ideas. You earned it!

I have a Winnebago 'Vectra" motorhome with the same engine,transmission , Sparton chassis and vacuum assist cruise control that I want to replace.I have a question on the Input Buffer Schematic : On the left side of the diagram there is a capacitor that does not have a value on it. Could you please advise. I appreciate your presentation and the unselfish sharing of your information
KAS

Yes I forgot to put the cap value on the schematic. Unfortunately, I don't remember the value either. In the next few days I will open the box and get the value and update the schematic.

Stay tuned!

Hi ED,
Where can I find the supply for the input side of the conditioner module.(41k pps) Is it on the transmission or elsewhere ?
thanks very much for your help.

Hi Ed,
Just thought of another question about the cruise control conversion. I am assuming that the cruise control switches shown on your diagram are as follows: on/off - maintained contact , set/coast - momentary contact , resume/accel - momentary contact. Are these the switches that are intended to replace the existing controls on the steering column ?