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Cruise control fades then disconnects
This has been an issue since I bought my 1984 96″ coach. I gave it a low priority, but it has been slowly climbing the list as other items are addressed. When I engage the cruise control, it tries to maintain speed, but can’t quite do it. The speed drops very slowly until the cruise control simply disengages after a minute or two. I think it happens more quickly going up an incline, but I haven’t tested it in some time, so I may be wrong. I was looking at something in the steering compartment when I noticed slack in the cable that goes from the cruise control air cylinder to the linkage below the accelerator pedal. I’m now thinking that slack shouldn’t be there and the air cylinder may be running out of travel before the accelerator is fully depressed. Thoughts?
1984 96" with 8V92TA
(remodeled Liberty Coach)
Greenwood, MO -
10 Replies
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Chad,
Is that a KING cruise control system ?
AL
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Good question Al. If it is its probably the acutator which is no longer available. If that turns out to be the case post back as i found an actuator that works the same. I believe it was for an isuzu Rodeo but i would have to verify.
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Al, it looks like it is a Bendix unit. You can see the diagram below doesn’t show slack in the cable, although I don’t know if that’s meant to show normal tension, or lack there of. I’ve never worked with cable controls, so I may be way off track.
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Just wanted to bump this to the top to see if anyone has any ideas on this. I messed with it a bit yesterday and there is no apparent looseness in the way it was mounted. It seems unlikely that the inner cable was somehow stretched. Is there a shop that specializes in this stuff?
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Have you tried calling Prevost PASS? They might be able to point you in the right directions.
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Thanks for the suggestion, Dick. I figured that was more of a “roadside assist” for urgent situations. I may give them a try.
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So, here’s a follow up to my Bendix cruise control issue. Documentation is sparse on these old units, but I found a nice stash over at:
https://www.wanderlodgeownersgroup.com/downloads/
It seems that parts are nearly impossible to find, so people were usually converting to the Cruise King system. Cruise King has since ceased production and servicing on those systems too. http://www.cruisecontrolking.com Fortunately, my system seems to be working okay now, and I’ll do my best to keep it that way.
The picture I posted with slack in the cable definitely indicated a problem. There should be no slack in that cable when the throttle is not depressed. The full travel of the Bendix cruise control pneumatic cylinder is only 1.5″. The bad angle of my original photograph hid from view the bolts that provide an adjustment to the connection between the throttle linkage and the arm that connects the end of the cruise control cable to the linkage. I mistakenly thought the pieces were welded together. Here’s that connection from both angles before I took the slack out of the cable:
1984 96" with 8V92TA
(remodeled Liberty Coach)
Greenwood, MO -
I loosened the bolts and took that slack out. I think what may have happened was the bolts had loosened just enough that the pull of the cruise control cylinder on the cable caused the adapter arm to just pivot on the throttle assembly, rather than applying throttle pressure. When the Bendix cylinder released the cable, it would leave that slack.
A test drive showed the cruise control is now responding normally, although I suspect it still can’t apply full throttle. If I go into a hill, I get a little more power if I mash the pedal that last bit. Before though, it wouldn’t even hold speed on level ground, so I’m happy with my progress. The other issue I discovered is that application of brakes didn’t cause the cruise control to disengage. It would resume speed when I released the brakes. I tracked that down to a faulty stop light switch. Fortunately, the Bendix system uses an inversion valve as a backup to the stop light switch, meaning I wasn’t fighting the cruise control when I braked. The only difference being that the cruise will re-engage upon brake release if relying on the inversion valve. That was a $25 fix. Frankly, the stop light switch was already suspect, as you can see in this photo. Yes, I replaced both of them.
1984 96" with 8V92TA
(remodeled Liberty Coach)
Greenwood, MO -
I had some other work scheduled at a shop this week, so I had them double check my work on the cruise control. They liked what they saw, so I guess my total cost was $25 plus whatever they charged me to look it over. This would have been extremely difficult to diagnose if I didn’t already have both CruiseAir condensing units out of the steering compartment. I also went ahead and replaced some other air fittings that are normally inaccessible, including a double check valve that had a fairly large leak. Both low pressure switches were leaking, too. All in all, I’m very satisfied with this project!
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Impressive research & work on your part. DIY projects can be so educational and rewarding. Hoping the best continues for you…
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