Cruise Control

[SDJHAWK]

Good Afternoon Everyone,

I am new to this forum and am hoping that you can help me out. I have a 1993 Mack CH 600 with 780 K. For the last 500 K the cruise control will kick off. I am able to re-engage it by hitting the resume button, sometimes it stays on sometimes it kick off again. Sometimes I can go for 10,000 miles before this happens, sometimes its 3 miles. There does not seem to be any situation that this is associated with, like going up a hill or a particular speed. The shop foreman at out local dealership, who has worked on the truck since it was new, has replaced everything he can think of including the wiring harness. Nothing has worked, I have spent thousands of dollars and we are all baffled. Please let me know if anyone has any question or can help me out.

[theakerstwo]

This is going to be a hard problem to solve if it does not do it any more often than you have stated. But all i can think of is the common probles and that would be a bad connection any were but to the VSS as well as the clutch and brake switch.Loose connetion on the cruze switch but if it dont do it when some one is working on it you will be living with it a long time.

[DavidT]

The most obvious to check is the clutch switch. Check it for adjustment make sure it is right. The next thing to check is a problem that I have seen several times in my shop. On the rear of the truck there should be an external ground wire that bolts on to one of the bolts that holds the bar on that holds the tail lights. I have seen that wire broken or just loose cause this very problem! Simple fix just a pain to track down.

[Mackpro]

We have seen this alot, loose yoke on back of trans, remove MPH sensor and see if you can spin tone wheel with a screwdriver. We see it alot with Mack trans and a couple times with fullers. Did have one with shorted out tail lights sending 12Volts back up brake/turn signal wires and computer thinks your hitting the brake. Goodluck

[motortrans]

I had this problem. In my case, it was the accelerator pedal. Replaced it and problem went away

[RowdyRebel]

The most obvious to check is the clutch switch. Check it for adjustment make sure it is right. The next thing to check is a problem that I have seen several times in my shop. On the rear of the truck there should be an external ground wire that bolts on to one of the bolts that holds the bar on that holds the tail lights. I have seen that wire broken or just loose cause this very problem! Simple fix just a pain to track down.

Now if the cruise in his 1993 Mack is set up like it was in the freightshaker I used to drive, where tapping the clutch would turn off the cruise until I reached up and hit the resume button, then I would say that it may be a possibility....but if his '93 is anything like my 2001 Mack, I'm not sure the clutch switch would be a source of the problem. When my cruise control is set, I can touch the clutch to disengage the cruise control and shift, but as soon as I take my foot off the clutch pedal, the cruise control reengages. The clutch switch does not turn OFF the cruise control, just temporarily disengages it.

If the problem were in the clutch switch, either the cruise would turn on again on its own, or he would be unable to reengage the cruise control with the resume switch.