Cruise control coming back to life - sort of - need help

schoward · 07-29-2006, 10:36 AM

On an 81 SC -- previously dead cruise control now perking up after replacing the brain with a used one.

Problem: Cannot set any cruise control speed. Tap the switch up and get nothing, HOWEVER hold it up and car accelerates using the 'accel' feature as it should.

Servo unit , speedo and column switch check out on the ohms/voltage mutimeter test procedure. clutch switch is new.

Since the brain seems to be responsive to me using the 'accel' feature, my thoughts now turn to the vacuuum hoses on the servo unit. My mechanic recently manipulated my decel valve which now strangely has no hose on it.

Anyone know where the large and small vacuum hoses that are on the servo unit go to? Can't seem to find the other ends. I have heard that vacuum leaks on these can cause speed to bleed off (or perhaps in my case never let it get set at all(?)).

Any ideas welcome - thanks in advance.

MXMARK · 07-29-2006, 10:45 AM

Big hose is a vent on my Carrera. Thanks Mark

MXMARK · 07-29-2006, 10:52 AM

Try This for vacuum line routing
Vacuum line mysteries w/pictures.

schoward · 07-29-2006, 11:26 AM

thanks, mark.

A quick check of my car reveals big/vent line goes to canister on far right (vent i assume).

Small vacuum line Ts into line off intake area just as it should and other side of T for decel valve is securely plugged.

Based on this, my theory is kind of shot.

Could my 'new' used Brain be bad??? Servo canister bad??

Since my cruise occasionally worked fine with old brain (when it decided to respond), I am wondering if the used brain is to blame again.