sig_a

While working on a high idle problem with my 1987 Carrera, I accidently broke the cruise control cable plastic adjuster located at the throttle end. I temporarily cable-tied it into place. Time, heat and 20 years finally took it's toll. It was so brittle a simple adjustment did it in. So I thought a replacement plastic adjustment fitting would be cheap and simple to fix. I ended up replacing the complete cable at $184.00. There is no replacement plastic adjustment fitting available. It now works most of the time, although intermittently. Except for the fact that I like cruise on expressway driving, I would remove the complete system. On a few occasions it didn't really cancel when I thought it did. Touching the accelerator reactivates it as the car speeds up to its former setting. Not good when exiting onto an off ramp.

Peter Zimmermann

Good post. Yes, the plastic anchor parts of the cable do get brittle with age and break. Causing sticking is new to me, and is probably something that's beginning to happen more often. The "theory" behind the cable design is that you can create a stuck throttle by opening the throttle as pictured, but that is not supposed to happen when you depress the throttle pedal as is done while actually driving. This is good stuff, and I hope that we get additional feedback, because the routing of the cable isn't nearly as easy to get wrong on a Carrera as it is on an SC.

equality72521

Glad I don't have cruise.

AJ88CAB

I 've had the same thing happen in my 88 Carrera. There are two things to check.

The clutch switch (located in the tunnel by the pedals) could be sticking due to age or a bent lever, or it could just need adjustment.

The cruise control uses the brake light switch circuit to dis-engage the cruise control when the brake is depressed. With age these switches get a little "slow" to react. So if you just brush the brake pedal it doesn't dis-engage the cruise. The switches are on the master cylinder, so replace the switches or the master cylinder. I track my car and just decided it was time to replace the 120k mile master cylinder. This weekends project!

scarceller

I see this is a 83 CIS car.

I have a 86 Euro Motor and it has cruise but in my car the cable attaches to the throttle linkage diffrently. In my car the cruise cable does NOT move when you step on the gas pedal. The point that the cable attaches to the linkage is designed so that the cable simply stays put when the linkage moves. The cable has a ball on the end and the linkage simply slides over the cable leaving the ball behind. Only when the cruise is applied does the cable retract and then the ball on the end of the cable comes in contact with linkage and pulls the throttle open.

Attached is a picture, look at the cable that attaches to the top of the linkage. See how the linkage bracket is slotted, this simply allows the bracket to slide over the cable without moving it. (ignore all the red notes, I'm re-using the picture)

Very good info, just thought I'd mention that in my car the cruise system seems to be diffrent and re-designed by Porsche.

Peter Zimmermann

The anchor bracket for the CC cable (not its Bowden Tube) on the SC is also slotted, and when the CC is not being used the CC cable is not active in any way.

scarceller

Peter,

Right, in my car if the CC is not in use I don't see how it could bind? Cause the throttle linkage bracket is slotted and simply slides over the cable.

As in the picture I posted above.

So do some cars have a diffrent system for the CC cable atach point to the bracket? It seems other posts here imply the CC cable always moves in and out even if CC is not activated, or did I read the posts wrong?

Peter Zimmermann

That's what has me confused, the slot-design is the fail-safe of the system, and when a new cable is purchased the bracket is installed at the factory and is part of the cable. As per my pictures in Post #8 of this thread, installation/routing is very important on an SC, but in a Carrera the cable just sits there. When CC is activated the Bowden Tube is supposed to remain stationary, and the actual cable moves inside of it, much like a clutch cable or heater box cable. I guess, if, during a service or safety inspection, someone doesn't see that the anchor end of the Bowden Tube is broken and is (1) removed, or (2) replaced, then all bets are off.

Amber Gramps

So the end of the CC cable that is designed to slide in the slot in the throtle linkage when not in use is getting stuck in the slot and bushing the cable and bowden tube to a point that the tube then gets stuck and holds the throtle open? I think they call that dominos.

Peter Zimmermann

Exactly (getting stuck in the slot would be virtually impossible), and the "cable" is quite stiff, which drastically reduces the chance of it grabbing and pushing the Bowden Tube out of position, even when the tube's plastic anchor is broken...if the cable was built with strands the possibility of sticking would increase by a good deal.

scarceller

Peter,

You sound real certain that we are not missing something here, I only know how my car looks and functions. You seem to imply ALL the CC systems use this slotted bracket design and can't bind, I agree that with this design I don't see how they could bind.

I'm just wondering if maybe Porsche had some other design for the CC in the earlier cars (pre-84 Carrera)?

Would be nice for the fella who started this thread to post some pictures of how his cable attaches to the Throttle Plate on his CIS system. He posted pics of the failed part but not the arm and end of the cable at the Throttle Body. But, he clearly stated that the CC cable moves ALL the time with the linkage, but not in my Carrera.

Here is what he said in post #1:
I'm just plain confused.

AJ88CAB

My theory, at least for the Carrera setup....

The Bowden tube is pretty stiff. When the anchor breaks as shown on the first post & #14, the CC cable assembly is free to move. When you depress the throttle the cable would normally stay put. But, since there is nothing holding it now (broken fitting) the stiffness of the Bowden tube can pull it back as much as an inch (post #14). when you release the throttle the CC cable in now 1 inch "shorter" and the end of the tube can catch on the broken anchor and hold the throttle open. It hasn't happened to me but I could see it happening based on the pictures posted.

That's my story and I'm sticking to it! Now I got to get back to work.

Peter Zimmermann

In post #1 the pictures do show the slotted bracket, which allows the CC cable to float with no outside influence. My '82 is the same, and every other CIS car, from memory, also uses the same design. The CC cable is never supposed to move unless the CC is activated.

Amber Gramps

Here is a picture of a 3.2 with back dated heat and no cruise cable. If it gets cruise, the cable will have no mid-cable mounting point and is going to potentially have the same problem. (sorry to the owner of the picture. I jacked it about a year ago) If it had normal heat it would have the anchor hole in the plasic fan tube/shroud thingy.

And in the original pictures the slot is clearly showing and not damaged, blocked, kinked, or shoing any reason to hold the cable.

Amber Gramps

here is one with the anchor clearly showing. so on the 3.0 it's a zip tie and on the 3.2 it's that funny little grey plug thing. (picture also jacked from a fellow Rennlister)