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Surging Cruise Control

December 21, 2011, 05:39:24 pm

Yesterday, on our way down to the Rio Grande Valley in South Texas, I could feel the coach surging, then backing off.  It wasn't enough to show up on the tach or on the speedometer, yet both my wife and I could feel it.  When I shut off the cruise for a few minutes and turned it back on, it would remain normal (no surging) for about 10 minutes, then return to surging.  When the cruise was shut off, the engine purred normally with no surging, so I am convinced it is in the cruise control.

This is a Bendix system.  With Barry Brideau's help, I replaced the Mini-gen I (signal sensor) on the cruise the summer before last.  Does anyone have suggestions as to what I might do?  I know that eventually I will have to replace the whole system with a King Cruise system,  but would like to use this until it crashes.

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Re: Surging Cruise Control

Reply #1 – December 21, 2011, 06:23:46 pm

Don,
Is the Bendix cruise mostly electronic or partially electronic with air operation?  I always look for the primary "driver" as the culprit and go from there.  I would check all the electric connection points first only because mother nature has a tendency to build corrosion on anything & everything thus reducing effective contact surface area for these connections.  (I'd give a touch of CorrosionX or dielectric grease after cleaning the contacts to prolong a good connection).  Then again, you've probably thought of this already.

Someone more knowledgeable and an electric diagram of the unit will be much more help.  Don't know that a fluctuating or surging air pressure would cause such a change in RPM's.

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Re: Surging Cruise Control

Reply #2 – December 21, 2011, 07:03:52 pm

Don, Is possible the fuel filer could be causing this, if it has some trash/dirt, the symptom could be the instability issue.  Just a guess, with a little sperience.

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Reply #3 – December 21, 2011, 07:07:15 pm

My 87 w/ Cat did the same thing. I turned it off then right back on and it would work just fine for who knows how long. Learned to live with it since it was fine after the on/off. Ten years of that was no big deal.

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Reply #4 – December 21, 2011, 07:24:53 pm

May not be relevant to the bendix system, but on surging car cruise control systems, my first suspect was always the vacuum canister and a possibly leaky diaphragm. Just had that experience a few times...
Don

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Reply #5 – December 21, 2011, 08:53:31 pm

Don, A Web search for Bendix Cruise makes ref to slack in the cable, could not find much except many references to the Bendix being obsolete.
Even on Barry Beams Site not much on Bendix.
Good Luck, I'll keep looking t'morrow, looks like best bet is cable adjustment or wear or electrical connections.
Gary B

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Re: Surging Cruise Control

Reply #6 – December 22, 2011, 03:28:56 pm

Also remove the fine screen that serves as the exhaust for the Bendix Cruise and make sure it is clean and open.  If partially clogged, it can delay the release of throttle, causing surging.

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