Confused Cruise Control

[Roger Shultz]

When I assumed the care of my 1987 Carrera Targa, the cruise control did not work. The first obvious problem was the cable end was broken or cut a couple inches from the throttle. I fabricated a temporary extension which solved the connection problem but still no response. Next I used the Bentley guide and though most readings were as they specified, I couldn't validate the clutch switch readings though I didn't quite believe what they showed based on the wiring schematic. Nevertheless, I followed the instructions to find the switch and while I could see the switch with a light and mirror, there was no way to get to the switch the way Bentley described it. Haynes showed access through the tunnel which probably meant removing the console. At this point, I didn't think it was the problem so I moved on.

Next, I sent off the controller module to ATE for rebuilding. Though they never reported what if anything was wrong, I figured it was $90 well spent to eliminate it as the problem. Unfortunately there was no change in operation until...

So as I'm driving I keep flicking the cruise control lever and suddenly it accelerates! Wow, something came alive! So, I keep setting it and after several tries it more or less regulates speed though at times the speed just sags off. At least I was able to test out the stalk controls, brake disconnect as well as clutch switch operation. As I continued to "exercise it", the operation became more and more consistent and I thought it was
fixed".

At this point, sometimes it will come on but it always sags slowly downward. I strongly suspect the vacuum servo is the problem with a bad diaphragm. At last my question is how hard is it to change the entire servo? Can it be serviced without replacing the entire unit? Am I missing something? Based on it's location I suspect I will say bad words! Thanks for any and all advice.

[kodioneill]

The servo is somewhat easy to access and very easy to test for holding vacuum. The servo is to the left rear of the engine compartment there are two hoses connected to it one large, one small, the small hose is the supply. Pull it off, and use a vacuum pump, and gauge to test the diaphragm. The larger hose is a dump for the vacuum. Use the search function for many posts on this subject.

[Roger Shultz]

Thanks and like many newbies I missed the search function. Sure looks like the majority of problems are clutch switch which I now know where to find it, control module though mine was "rebuilt" could still be a problem of intermittent solder joints and like all intermittents may or may not be discovered in test, and leaking vacuum lines. The searched threads certainly have provided the necessary info to run this down so I'm good!

[kodioneill]

I have had two cruise units rebuilt by this business absolutely satisfied , lifetime guarantee, reasonable price, cant go wrong.

http://www.autoecu.com/R&RFormOL.pdf

[Por_sha911]

Roger: Welcome to Pelican. Have you posted a picture of your car yet? If not, let me be the first one to harass you about it. :0)
I had the problem that the cruise would set but then slowly drop off in speed that you described. I had the brain rebuilt and it fixed it. I wonder if the rebuild you have is iffy? Find someone with a similar year car and swap out the box to see if that fixes it. It could also be a vacuum leak. Don't forget you have some 23 year old vac hoses going to the servo back there.
Lastly, I am curious about how you fixed the cable end. Did it have to be an exact length? Post a pic if you can.

[Roger Shultz]

There is a pix under my name but I have some new ones to post.

I will take a picture of the cable end I made which was a 1/2" aluminum post tapped for 6-32 screws found in those grey boxes at places like ACE and Sears Hardware. I drilled a small hole through the middle then inserted 6-32 hex Allen set screws in each end, tightened until it pinched the cable and so far no slippage.

After reading many posts on cruise control and looking at pictures, I took another close look at the servo to see if there were any "loose clamps". There were no loose clamps because there were NO CLAMPS! The T fitting had none nor did either hose on the servo. Certainly that is the place to start once I can find some suitable clamps.

I suspect they were removed at one time when the engine was removed and never replaced. This maybe the problem since the control unit was already rebuilt. Fingers crossed, report to follow.

[Roger Shultz]

Well, my hopes of it just being a vacuum leak due to lack of clamps were dashed yesterday. After stretching my arms to the limit to get some stainless worm gear clamps on the lines, there was no change. I again measured the resistance of the servo and it came out at 15 ohms which was nominal. Previously I had bypassed the clutch disconnect switch at the relay so I knew that was cleared. I can hear relays click in when the stalk is acutated. I again pulled the controller and something is rattling around inside, like a small blob of solder. This was rebuilt by ATE in April with a lifetime warranty and they gladly encouraged me to send it to them again as the problem seems to be of an intermittent nature.

As they say, "film at 11". If the controller does nothing I hope to find out exactly what signal is being sent to the servo and I will observe that before changing it out. This is not rocket science! I'm going to fix it!

[Roger Shultz]

As promised, I took some pictures of my initial temporary fix of the servo cable and then that prompted me to go to the next step which was to fabricate a cable.

When I got the car the cruise control cable was disconnected and the PO said he never used it and had no idea if it worked. The cable was cut about 2 inches short, not sure why but my guess is during a previous engine removal it occurred.

When I checked on the price of a replacement I got sticker shock like other Pelicans have reported. To find out if the cruise control would do anything I fabricated a splice to hold the orignal cable and a new piece to the throttle. I used a 1/2 aluminum spacer that I drilled and tapped with 6-32 hex nuts as the spice and another 1/2 aluminum spacer as a keeper on the throttle. In this case I drilled a small hole through the center and then just inserted a hex nut in each end to pinch the extended wire. This worked very well mechanically but the long term fix was to replace the cable with new wire.

I measured the existing wire diameter and it measured .039" and #18 piano wire is .040 in diameter, close enough. After wondering where to get a short piece, about 42 inches, I found no good online source however I just went to a local piano repair shop and the kind owner gave me more than enough for a new cable.

Last night I pulled the original out of the servo and made the new one. I used half of the original splice spacer for the keeper inside the servo and the orignal throttle keeper with the new cable. Getting to the plastic clip in the servo was difficult but I got it out without breaking it, yea me!

Installation was straight forward. After fussing a bit to get the throttle keeper straight without losing the Allen wrench in places never to be found, I got ti right then I adjusted the tension using the fitting on the bracket. It is important to not have any tension on the keeper or idle speed will be affected. Tighten the tension adjustment just enough to where the throttle keeper can still slide back and forth easily and go from there.

Attached are pictures of my original kluge experiment as well as the repalcement servo cable that in my case cost less than $1! Hope this save us all some money and I'm pretty confident it will be a lasting repair.

Best regards,

Roger

[dshepp806]

NICE,..........thanks!

Doyle

[Por_sha911]

Most excellent.
Edit: Roger: PM sent to you with a question.