RE: Cruise Control

["Buchholz, Steven" <Steven.Buchholz@kla-tencor.com>]

By any chance did you mean the vacuum pump rather than the servo?  The
cruise control's pump has a vent valve to open the system when the CC is
off.  IME with the car off you can squeeze the vacuum servo all that you
like, air will enter and exit the system from the vent.  OTOH, if you pull
the vacuum hose from the _pump_ and then squeeze the air out of the servo
and then seal the line the servo should remain in place.  This will allow
you to confirm that there are no leaks in the other components and that the
vacuum switches on the brake and clutch are closed, but it does not
exhonerate the pump itself.  

On the electrical side the obvious suspects are the electrical switches on
the pedals and the control switch on the steering column, but as we found
out here on the list some time back you also need to confirm that the brake
light switch is working properly and the brake lights are working.  As a
fail safe the cruise control system gets its ground through the brake light
filaments!

HTH!
Steve Buchholz
San Jose, CA (USA)

> -----Original Message-----
> 
> I've had many a vacuum problem in my 86 5ks. Never an electrical one.
> 
> From my experience, testing the vacuum system is simple. I've always 
> disconnected the vacuum line at the servo, squeezed the servo 
> to let all the 
> air out and create a vacuum, then reattatched the line. The 
> system should 
> hold that pressure, and the servo should stay squeezed. If it 
> does: you've 
> got an electrical problem. If it doesn't: you've got a vacuum 
> problem. Once, 
> I even squeezed and let go of the servo to create the 
> air-leakage noise 
> which led me right to the leak. Of course, I was lucky and it 
> was within 
> earshot.