Vacuum diagram

[drharper1]

I am putting the finding touched on a rebuild. One minor issue is with the cruise control. Does anyone have the diagram of the cruise control system and the vacuum diagrams? Finally got almost everything working - power windows, power locks, radio, CB, lights, etc. I am not getting anything when trying to engage the cruise control.

I have a 1985 Current K20 Silverado with the 6.2l diesel.

Any assistance in troubleshooting and any diagrams would be greatly appreciated. Thank you.

 

[75gmck25]

With a diesel, don’t you need to have a vacuum pump? Or am I getting confused (again)?

 

[fast 99]

Need the pu

With a diesel, don’t you need to have a vacuum pump? Or am I getting confused (again)?

Depending on application may need the pump for AC doors or cruise. Unsure if a GM diesel was made with vacuum power brakes but that's another one.

 

[drharper1]

Need the pu

Depending on application may need the pump for AC doors or cruise. Unsure if a GM diesel was made with vacuum power brakes but that's another one.

The problem that I am having is that everything else seems to work without issue, so I am seeing if it was disconnected, misrouted, pinched off, etc. There is nothing in the owners manual or the Chilton's manual to show me what to look at sir how it is routed. Even YouTube seems muted on the subject.

 

[75gmck25]

Cruise control uses a vacuum servo to pull the throttle, and it's usually mounted on the driver's side fender well. There is a cable that runs from there to the carburetor and it connects in parallel with the cable from the accelerator. On my '75 the back of the cruise control servo points at the firewall and the cable is connected there. Both the vacuum line and the cable run to the firewall, loop back behind the brake booster, and then over to the engine. Basically, that servo just pulls on the cable to the carburetor linkage whenever the cruise module calls for acceleration.

The cruise control servo is connected to full engine vacuum, and when the cruise is on it will switch (electrically) and apply vacuum to the cruise control servo, and the cable will move the carburetor linkage.
There is a 2nd vacuum line on the cruise control and it runs through the firewall to a combination switch on the brake pedal linkage. When you hit the brakes this switch cuts off the cruise electrically, and at the same time vents all the vacuum so it cannot pull on the accelerator.