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Old 09-13-2010, 01:07 PM   #1
86 951 Driver
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Default Cruise Control Fix

I was curious if anyone had a fix for the cruise control brain. I have heard that sometimes its the cold solder joints in the brain. I was thinking that maybe I could just reheat up the solder on the joints so the cracks would be fixed? Worst case I just have to buy a reman unit I guess. Is there a tutorial for this?
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Old 09-13-2010, 11:02 PM   #2
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Yes I would like to know to.
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Old 09-14-2010, 01:15 AM   #3
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There are bad solder joints but then like mine it has several blown resistors. Original dealer receipt shows replacements ran $675 dollars. I have not been able to source the resistors yet as they do seem like odd *****.

You can get the soldering equipment at any Radio Shack but if you are working with electronic components a de-soldering gun will work best cleaning up bad joints. Suck the old solder out and replace it with new.

http://www.youtube.com/watch?v=I_NU2...eature=related
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Old 09-14-2010, 12:34 PM   #4
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Does the speedo need to be working properly for the cruise control to work? I have no speedo at the moment and the chip board on the back of the speedo is broken in two pieces. The Cruise control doesn't do anything but that might reasonably have something to do with the speedometer not working.
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Old 09-14-2010, 10:52 PM   #5
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Search the forums; I've had some success with repairing cruise brains in the past. I'm still available for the service if there is any interest. I have cores for parts as well (luftpirate).
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Old 09-15-2010, 04:17 AM   #6
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What kind of symptoms do you have? The infamous WOT when you try to set the speed? Mine started doing this about three years ago. I did the resolder thing and it worked for a few months. I then found a used brain on ebay for $20 so I didn't bother trying to fix it anymore. Now my used one is starting to do the same routine. A common theme seems to be that it mostly happens in colder temps. This sounds like a typical electrolytic capacitor failure. 20+ years is a long time for them to last, and the electrolyte dries out. They can become more within specs when they are warmer, and start presenting problems when cold. There are two blue axial caps that could possibly be the problem. I remember a thread where someone was going to swap those out, but that thread seemed to fizzle out without a resolution. As soon as I get the time, I'm going to check those caps and replace them to see what happens..
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Old 09-15-2010, 11:57 AM   #7
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Jeff, talk to Scott, he usually keeps repaired cruise control units on hand. He has a guy that repairs them. Last time I checked it was 75 bucks or something like that.
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Old 09-15-2010, 12:35 PM   #8
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This is a number 4 on my list right now. But if I was able to do the work myself I could maybe it to tonight or tomorrow night, I may just buy a repaired one since that will save me the frustration and what not.

basically if my cruise wants to work it will only acclerate. I'm not sure if I just don't know how to use the cruise or not, but I got it work once and then after that it would never hold the speed. I can acclerate all day long but once I let go of the stick it will turn off.
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Old 09-15-2010, 04:13 PM   #9
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Quote:
Originally Posted by PorscheDoc View Post
Jeff, talk to Scott, he usually keeps repaired cruise control units on hand. He has a guy that repairs them. Last time I checked it was 75 bucks or something like that.
Can you give me Scott's contact info? I need to fix my cruise control as well, and $75 sounds like a pretty good deal. I've been thinking about going the $200 rebuilt unit route or trying to do it myself.
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Old 09-15-2010, 05:35 PM   #10
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On my 87 NA there is a speedometer speed reference signal output that is used by the cruise control, yes a functional speedometer is required by the cruise control.
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Old 09-15-2010, 05:42 PM   #11
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I think the first step is to redo the solder joints. I didn't trust my solder skills so I took it to a TV shop and they did them all for $25. The owner said that on visual inspection, they looked OK, but everytime he touched one with heat, there were bubbles, which evidently means a bad solder joint.

There can be cables and other stuff, but that's an easy first step. Good luck.
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Old 09-15-2010, 06:02 PM   #12
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Thanks Yarf. I figured as much but wasn't certain.
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Old 09-15-2010, 06:02 PM
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