Here's my question.

If I unplug both of the vacuum lines on the bottom of the cruise servo, then press in the servo diaphragm in by hand, then plug both vacuum ports before releasing it, shouldn't the servo stay sucked in until I unplug the ports again if it's working properly?

I see no tears in my servo, and it fails to stay sucked in like that. Possible internal valve or leakage?

The servo itself ohms out fine per the Shop Manual. But I'm thinking the ohm test on it will tell me nothing about an internal leakage or valve failure inside the servo.

If I turn the key "ON" with engine not running, and slide the cruise lever to "On", I can hear the servo click. Yet it won't do jack on the freeway.

My cruise has never worked since I bought the car 4 years ago. The only problem I have not been able to fix on this car.

Every voltage and ohm reading checks out fine per the GM Shop Manual.

Every single vacuum lines is unobstructed, leak free, and routed properly. Check valve is new. No servo bolts missing.

Brake pedal electrical and vacuum release is adjusted properly and functioning as they should.

My cluster appears to be a replacement. It has no ID numbers anywhere on it for me to determine if it's a cruise or non-cruise unit. But it's getting all the right cruise voltages. So that's my only other unknown.

Can someone with a functional cruise verify this simple servo test for me?

 

Have you tried starting the engine & using your finger to feel for source vacuum at the servo? Just a guess?

 

Yes, I did that. The vaccum supply line to the servo indeed has plenty of engine vaccum.

 

Just blocked the lines on my working 85 cruise. made no difference to servo. moved in and out with lines blocked or open.Sorry. Corvette Fever did a article a few months ago on cruise. Check their online archive .you can probably get new info??

 

Found it, thanks.

http://www.corvettefever.com/howto/82001/

Let me take a look at this. Hopefully there's some new info not covered in the Shop Manual.

 

Success!

I fixed the cruise. That Corvette Fever article had a few excellent diagnostic steps that are not in the GM Shop Manual and which did not occur to me to check.

I can say that everything works on my car now.