Mystery Cruise Control & bad speedo cable
 

Thanks in advance for any assistance, here's the deal: my speedometer doesn't work and I know it is because the cable is ruined from touching the exhaust. But I can't figure out which cable to buy to replace it.

According to my SPID, my 1980 K10 Suburban should have had the YE9 Silverado package plus the K30 Automatic Speed control (see attached pic). The YE9 part checks out, but the cruise control clearly is not factory. I can only imagine that the buyer specified cruise, but on delivery it was clear somebody goofed and the cruise was missing so the dealer installed whatever they could to make the customer happy. But definitely not a factory cruise package.

Fortunately, the previous owners had kept the info package complete so I do have the operating manual for the Cal Custom Hawk cruise control package that was installed (attached pic). What I don't know and what I wish I had was the installation instructions, because I cannot figure out how the heck the system works. It appears that the speedo cable from the transfer case (which is the one that is ruined and needs to be replaced) goes through the firewall and to the cluster, and then a separate cable comes back out to the cruise unit on the drivers fender well (see pics). I know the GM system has the cable enter the cruise unit and THEN go to the cluster. I even have an extra cable for just such a system, but it doesn't appear that it will help now.

I really, really, really don't want to have to completely dismantle my cluster to address this issue. The speedometer hasn't worked since I bought this truck, but I didn't mind because I use a GPS. But I would like to get the cruise to work again.

Does anyone have any experience or knowledge of these Cal Custom Hawk cruise control units? How does the unit on the inner fender know what the speed is? Is there some sort of goofy "Y" split in the back of the cluster? That sure seems like the hard way to do things.

And how in the heck did a Silverado get built in 1980 without cruise anyway? I thought that was integral to the YE9 package? This isn't the only SPID oddity - this Suburban also does not have the HE4 3:42 gears nor does it have the NE2 40 gal. fuel tank. Everything else seems correct, and after discovering the oddities I even double-checked the VIN vs. the title and vehicle, but it sure seems weird.

Re: Mystery Cruise Control & bad speedo cable
 

You're in luck. I have an 83 factory manual with cruise control info. I have wiring diagrams and section scanned into PDF files. Send me a PM with your email address. I'll send you the files. It's 14 pages long. It gives instructions on how to check the servo with a voltmeter. Testing the entire system requires a special tool. With inputs and signal info and good electrical troubleshooting skills, you can find the problem. The speed sensor is an optical sensor. It plugs into the back of the speedo. So you will have to fix the speedo to make it work. The switch connections are paper gum wrapper thick. Fortunately, you can still buy switches if you need to replace it. I keep a spare in a tool box. I bought a servo several years ago but never used it. I ended up remove the entire system. I installed cruise from www.rostra.com. I have vacuum unit. Now they have an electrical unit to pull the throttle. I may switch to that type later.

Re: Mystery Cruise Control & bad speedo cable
 

Pages 6-14 of your manual may have as much info as you are likely to find.

If you aren't going for a complete resto you can get a Rostra cruise control system.

The 1983 Cruise III system Gerardo the mad chemist is referencing is very different from what your truck was born with... Cruise III is a nightmare when it breaks and parts are hard to find. Your SPID shows RPO "K30 Automatic Speed Control". In 1980 this is the 68-82 Cruisemaster mechanical transducer cruise control system. If you look at the brake pedal there's probably still a vacuum release valve installed...

The fairly complex 83 -87 Cruise III electronic vacuum servo system has an optical pickup on the speedo. Not yours...

The Cruisemaster speedo cable was interrupted on the LH inner fender by an aluminum transducer box. A short speedo cable ran from the transducer to the speed head and a long one ran to the transmission or transfer case. The reason your speedo doesn't work is likely because the transducer got gummed up and the transmission to transducer speedo cable broke from the added stress. If you don't re-install Cruisemaster you can likely make the speedo work again with a one-piece cable.

Cruisemaster is an extremely simple to use and troubleshoot cruise control system but if you're missing the vacuum lines, servo, wires, and transducer and don't have a good donor it'd be less time consuming to install an aftermarket unit. Usually the stalk switch or brake pedal switches fail. Then the transducer gets gummy and vacuum lines get crunchy.

Look in the manual posts in my sig for the GM Cruise control training manuals I scanned to PDF.

Re: Mystery Cruise Control & bad speedo cable
 

gchemist, hatzie - thank you for your responses. My primary challenge is the fact that what is currently installed is not in fact the Cruisemaster system that GM claimed to have installed on the SPID, but rather an aftermarket system by Cal Custom. I have considerable info from the previous owner (who was also the original buyer and person who place the order at the dealer), and they insist they did not install the cruise themselves. It had to have been done by the dealer, and it is my theory that it was done to cover up the fact that the factory screwed up and failed to install any cruise system at all.

I was hoping for convenience and cost reasons that I could simply repair what is already there, but I don't have any sentimental reason to keep the old aftermarket system running. It would be neat to be period correct, but not that neat. I think I will just yank it out and go with either a Rostra or Audiovox system.

Re: Mystery Cruise Control & bad speedo cable
 

If Cal Hawk used fragile column and brake pedal switches that may be the problem. This is the most frequent failure point on the OEM systems. Rostra and others sell OEM-look column switches.

Odd that the dealer didn't just ding GM for the Cruisemaster parts and the install. There's a lot less to it than the period aftermarket systems.