1990 Cherokee cruise control

[heavyequipment]

I'm having trouble with my cruise control - it quits intermittently. I suspect the speed sensor. I found it in the speedometer cable, but it looks different from the one on my '89. The '89 has a pancake shaped metal case and threaded connections to the cable on both ends. The one I see in my '90 is black plastic and I can't figure out how it connects to the cable. I don't want to break it - has anyone had to change one of these? How does it come apart?

Thanks for any suggestions!

 

[MoFo]

Why do you suspect the speed sensor? Do you have any data on which you base this suspicion? The usual failed part when the cruise control just stops holding the speed, is a broken (intermittant) wire to the cruise control switch on the turn signal post at the steering column. To test this, get out on the open road and set the cruise control, then wiggle the black wire where it comes out the front (blind side) of the black switch on the turn signal post. If the cruise control drops out, you need to replace the switch, since the wire that is broken internally is moulded to this switch. You can buy an aftermarked one on ebay for about 1/3 of an OEM switch. The steering column (and switch) are designed by Saginaw Steering (GM) and are the same as a 1980 to 1990 Chevy or GMC vehicle. Look at the pictures on ebay to match it with yours. I have been running one from ebay for over 8 years.

 

[Demonoid369]

How's your vacuum lines? If I recall, a vacuum leak can cause this

 

[tjmotter]

How's your vacuum lines? If I recall, a vacuum leak can cause this

Yup, the brake sensor for the cruise control is vacuum activated. In fact, I would recommend you check to see if it is adjusted all the way forward (touching the brake pedal). This device is actually pretty sensitive and if it worked its way back even a little, the slightest bump or vibration can cause movement in the brake pedal that would de-activate the cruise. Easy fix, it is held in place with friction so a quick reach up under the dash near the top of the brake pedal and you can push it forward.

Send me a PM if you need pictures. I have mine apart right know as I get ready to paint it and it would be easy to grab some shots.

Todd

 

[heavyequipment]

The switch stalk is new. After I installed it and a light to let me know that the brake light switch is working the cruise control worked for a while and then quit. I know the servo unit is O.K. because when I push the slide switch to accel/resume it accelerates. When I press the "set" button, nothing happens. When I pull the vacuum supply hose off the servo unit I hear it sucking air, even if the Jeep's been sitting a few days (I built a big vacuum reservoir in order to have the A/C controls work when I'm pulling a travel trailer uphill).

I want to get the speed switch off to bench test it, but I can't figure out how to disconnect it from the speedo cable.

I'll check the brake switch/valve, but I've tried holding the pedal up with my foot on bumpy roads, and it didn't help.

 

[MoFo]

The switch stalk is new. After I installed it and a light to let me know that the brake light switch is working the cruise control worked for a while and then quit.

If the cruise control was working when you installed the switch, why did you put the monitor light on the brake switch? Did you originally start with a Torque Converter lockup problem?

I know the servo unit is O.K. because when I push the slide switch to accel/resume it accelerates. When I press the "set" button, nothing happens.

Not being able to set the cruise speed is another symptom of the brake switch signal in the wrong state.

When I pull the vacuum supply hose off the servo unit I hear it sucking air, even if the Jeep's been sitting a few days (I built a big vacuum reservoir in order to have the A/C controls work when I'm pulling a travel trailer uphill).

I want to get the speed switch off to bench test it, but I can't figure out how to disconnect it from the speedo cable.

I'll check the brake switch/valve, but I've tried holding the pedal up with my foot on bumpy roads, and it didn't help.

 

[heavyequipment]

I had replaced the tail/brake light bulbs with LEDs. I hoped installing a light in the circuit would provide a ground path for the cruise control. It would also let me know that the brake light switch turns on and off at the appropriate times. It did - the cruise control worked, and I could see that the brake light switch works. Then, another problem came to light, and that's what I'm working on now. I think it's either the speed sensor, the control box, or a bad wire or connection. Finding a bad wire or connection is the hardest thing to troubleshoot, so I'm trying the easiest things first.

The converter lockup clutch has never given trouble. I pay attention to it when I'm pulling the trailer up a long grade because the converter produces less heat in lockup, and it saves fuel.

 

[heavyequipment]

Well, I just found out that the gadget I thought was the speed sensor - isn't. It's a black plastic cylinder-shaped device that's spliced into a cable. I think it may be the safety interlock that won't allow the key to turn if the trans isn't in Park. I disabled that nuisance long ago. I found the speed sensor and it seems to test OK. I guess I'll try replacing the control box and see what happens.

I pulled out the vacuum dump/switch and it tests OK. It's adjusted right, too...

 

[heavyequipment]

Resolved - I found a connection unplugged at the brake switch, and the plug connection for the new switch assembly didn't plug in far enough until I slid the plastic insulator back a little.