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1990 Suburban Cruise Control not working, Need Help!

Discussion in 'GM Electrical Tech' started by purtdamngood, Apr 16, 2014.

  1. purtdamngood

    purtdamngood New Member

    Hello all,
    I recently purchased a 1990 Suburban and the cruise control wires were cut in two, looked intentional. I watched a how to video on youtube and purchased a replacement turn signal lever and I've successfully installed the new lever. Everything works with the exception of the cruise, just like before. I see a few post on here that resemble my problems but don't really help me out. I did see where someone had an issue with a "sagging" brake pedal and had to adjust/replace the brake switch. That's gonna be my next path forward. Until then I'm open to any suggestions. I'm not a professional mechanic so please be easy on me.
  2. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    On that model vehicle the brake pedal switch is normally the culprit when dealing with a malfunctioning cruise system.
    Some of them can be adjusted by turning out the mount nuts, Ive found a few that tweaking the bracket does the job.
  3. purtdamngood

    purtdamngood New Member

    Yeah I think I'm gonna try the brake switch this afternoon when I get off work. Thanks for the advice. I'll let you know what I find.
  4. ph71ss

    ph71ss New Member

    Can you be more specific about the brake light switch in correlation to the cruise control malfunction. I have a 93 silverado. The cruise control started working intermittently for a short time(a few weeks) then stopped working completely. I have never dealt with troubleshooting a cruise control system before. Any help would be appreciated. Thanks, Pat
  5. purtdamngood

    purtdamngood New Member

    Update: I've checked the brake switch and everything appears to be working correctly. I carried the truck to my neighbor who worked a Chevy dealership in the late 70's to late 80's. Within 5 minutes he'd identified my problem. The linkage from to throttle body to the "cruise servo" was disconnected. I told y'all I'm no pro mechanic! The bracket on the servo was broken but I was able to "securely wire" the linkage back to the servo. After doing so I took a test drive, still no cruise! I've found replacement servos for around $76 on Amazon and eBay. Before spending the money can anyone tell of their experiences with cruise servos?
  6. Crawdaddy

    Crawdaddy Thread Killer Extraordinaire Staff Member 5+ Years 1000 Posts Platinum Contributor

    Ah, the little bracket on the diaphragm was broken. That seems to be quite common. I had to replace mine for that exact reason. In addition to the linkage being physically connected, it also needs to be adjusted to the throttle arm.

    If you noticed, the arm has a slot and then the hook which is screwed into the arm. The total length of the linkage needs to be slightly longer than the distance from the cruise control actuator to the throttle arm. If it's too long, there's not enough travel and the cruise can't engage or adapt to inclines and such. If it's too short, the throttle doesn't close all the way and the engine tries to run away; ask me how I know! The slotted part of the arm is held to the throttle with a simple clip and is adjusted from that side.

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