Cruise Control not working

zbph10 · 07-10-2004, 08:26 PM

Any quick checks to repair the cruise control in my 87 Targa.

I've never used or even thought about using the cruise control but I'm taking a long trip in a week and it might be nice if it worked.

Por_sha911 · Por_sha911's Garage

The search button is your friend. There are a ton of listings on this.
There are basically a few things that can go wrong: Vacuum leak, bad brain (in silver box under the radio), problem with actuator or cable. 99% of the time its the brain.

Thomas Owen · 07-11-2004, 03:43 AM

Verify that everything to the brain is correct. There are 2 switches, one on the brake master cylinder and one in the tunnel actuated by the clutch. These are designed to disengage the control when either pedal is pressed. Once you verify the wiring and switches, then look at the cable from the control unit in the engine compartment that goes to the throttle housing. Make sure the cable is not broken or disconnected. If all these points are covered, then I would say replace the brain with a known good one.
Good luck -

fireant911 · 07-11-2004, 04:11 AM

Where does the clutch switch actually reside? Can it be seen / be cleaned / be adjusted? I have the same problem since my cruise control also does not operate. I tried following the electrical testing procedures for the brain as outlined by the Bentley manual but was unable to obtain any signal from the clutch switch nor could I find any physical reference to the location in either the Haynes or Bentley manuals.

Thomas Owen · 07-11-2004, 01:06 PM

There is a small opening on the top of the tunnel, adjacent to the pedal cluster. The clutch switch is held in by two screws from above. Sometimes the tab gets bent that actuates the switch, but using a mirror from the cluster opening in the tunnel you can see how it works.

fireant911 · 07-11-2004, 03:43 PM

Not to steal zbph10's thread... but thanks Thomas, with your help I was able to finally locate the elusive clutch switch. My tab is not bent, it isn't even present - this could be the cause of my non-functioning cruise control.

zbph10 · 07-11-2004, 07:57 PM

Found my cable broken and tucked in a corner not even hooked up.

Aparrently it broke and the PO broke left it disconnected.
I'm going to try and fix the cable and reattach.

Half of the clip that holds the cable in the bracket is gone, I should be able to attach it somehow, also the cable looks to be missing the nub on the end that would attach to the throttle, I'll try and rig something up to at least try it.

If that doesn't work I'll go without cruise, I guess we'll see.

Thanks for all the advice
Brian

Democreature · 07-16-2004, 01:23 PM

Did you find the problem with the cruise control. I'm having the same issue.

Porsche80 · Porsche80's Garage

I am having same problem. Checked out with Bentley manual and clutch pedal switch is mounted right behind the clutch itself. You have to take the borad off to access the pedal cluster. It appears that the clutch pedal switch should attach to a small metal clip. However, in my case the switch and wiring is missing. I can see where the hot wire is coming from the relay and the ground from the control unit, but unable to trace them. I have tried toning the wiring to locate them with no luck. Does anyone have any other ideas how to trace the wires, without tearing everything up. BTW yu also need to make sure the relay is good

Cashmere 1980 911SC in the stable-

C

Porsche80 · Porsche80's Garage

Well after some time I found my clutch switch in the tunnel. It seems to have a little play in it (1/8 to 1/4 inch). It is not all the way against the post when closed. I had my brain checked out and it was good. Should the clutch switch when opened and closed making a clicking sound when opened and closed? Mine doesn't. I removed the cc relay and tried ohming pin 85 from relay back to terminal 12 on the wiring harness where the brain plugs into and get infinity. All other tests check out ok. Does this mean the clutch switch is bad? If so how in the world do you remove it. Or how do you test it in the car other thanwhat I tried. Thanks in advance as the Bentley manual indicates that the clutch switch is on the cluster and not in the tunnel as we all have found .

Thomas Owen · 04-25-2005, 02:52 AM

Use your meter between pin 85 and ground, then work the pedal. The clutch switch is normally open, and closes when you press the pedal (putting ground on pin 85). Not sure if you will hear a 'click' with the switch, so just use the ohm meter test.

For removal, I am 'pretty sure' I pulled mine out through the top of the tunnel with the wires still attached, so if you see the wires, follow them in to the tunnel.

Lastly, be glad your brain tested good. My wife told me over the weekend that mine was definately bad.

Good luck -

zzwhm · 04-25-2005, 05:07 AM

If they are still around Beckmann Technologies 919-381-2700 will test and rebuild your cruise control brain if you determine that's the problem. It cost $166, including shipping, a few years ago.
Bill

Porsche80 · Porsche80's Garage

BTW ZZwhm-I used Beckman to checkout my brain. Thanks for the info though. Owen you say the clutch switch should just pull out I can't seem to easily see how to remove it without removing the tunnel which I don't think I want to do. I mentioned in my earlier post that the switch had some play in it and maybe that is the issue. I will see what the ohm tests come out when I get some more time to check it out. I am hoping that the amount of play in the switch is the problem. Will advise after your recommended testing and another idea I have-thanks for the advice. I was thinking that pin 12 on the terminal was the same as ground since there are 2 circuits on that pin one to the clutch switch and the other to ground via a connection on the speedo.