92 240 cruise control

I just installed a factory cruise control setup in my 92 245 (Automatic). Installation couldn't have been simpler. That part was great, however it wont work. I tested the vacuum servo/pump with 12V directly and it works. Somewhat noisy.
I have 12 present at the switch and control unit.
What else can I check?

Is the vacuum pump/servo unit supposed to be running constantly? Mine's not.

Thanks in advance

??? any help out there?

Make sure your vacuum break valve is adjusted correctly. If it is leaking with the pedal all the way back the system won't work. Also, I remember having problems with a system when the brake light switch was bad. The system is designed to not work if there is a bad circuit to the brake lights.

I did the same retrofit into my 93 245. I would concur with making sure the vacuum switch on your brake pedal arm is adjusted/aligned correctly as the first step. One thing to also to test is the continuity of the brake pedal switch when it is opened. The set up for manual transmission cars use a electrical/vacuum switch on the brake pedal and just a vacuum switch on the clutch pedal.

Next quick test is to take the line coming from the pedal assembly and check that to make sure it holds vacuum. If you have a mighty vac for the brake lines or just use your mouth to create the vacuum. If that doesn't hold then you know its an issue with the rubber/plastic lines, brake switch and/or diaphragm unit on the gas pedal.

Next I would check the electrical connections to the vacuum unit on the firewall, to the brake switch, computer unit , turn signal stalk and into the dash wiring harness. Potentially could be a bad computer unit, but don't know of a way to test that. The other aspect is if your speedometer/odometer aren't working from getting a signal from the tone ring, that would also kill the signal the computer uses to set a speed.

Pictures from my retrofit: https://www.flickr.com/photos/68144590@N00/albums/72157650461834275/

Brake pedal switch:


M-47 Interior-related parts except for the CC-specific turn signal stalk

Ill check it out as you've described.
Question:
Is the vacuum pump/servo unit supposed to be running constantly? Mine's not.

Thanks

The cruise control greenbook might be of some use.

https://ozvolvo.org/archive/?download=Vm9sdm8gMjQwIFRQMzA4NjYtMiBDcnVpc2UgQ29udHJvbC5wZGY=

vcolper said:

Ill check it out as you've described.
Question:
Is the vacuum pump/servo unit supposed to be running constantly? Mine's not.

Thanks

Click to expand...

No, the pump kicks in once the button on the stalk is pressed. Once the pedals are depressed or you shut the system down via the stalk on the stalk is shuts down again (or turn the ignition off.)

BTW: Recently picked up a 1990 240 and trying diagnose a in-operative CC system, will be putting up a separate post on my issue.

Put a length of hose on each of the vacuum switches at the brake and clutch and see if you can suck air thru. If you can then adjust it until you can't If you can never adjust it to be fully closed, then you will need a new switch. This is usually the culprit.

I got it working, It was the connection/plug to the vacuum pump. As usual the insulation inside the bray connector had deteriorated and the butt connectors never made full contact.

Thanks you all