Cruise control?

[rusty ol ranger]

Never had a vehicle this old with functioning (kinda) cruise....

87 ranger 2.9/5sp

The cruise when set is very erratic, its constantly stabbing and letting off the throttle, set it at 55 and it might keep it between 45-65.

I also have the bouncing/erratic speedo.

My question is, could this all be in that little speed sensor on the end of the cable? Or does this system rely totally on vacccum for the cruise? Planning on attempting a 3 hr road trip next month in it, so id like to have it functioning.

 

[Craig0320]

A few more beers and everything will look and function just fine. I know I am not helping but I couldn't resist.

 

[RonD]

No, it wouldn't be a vacuum issue if speedometer is effected

Its the cable from trans to cruise control, it has 1 or 2 broken wires in the twisted wire cable, they catch on the sheath and then release causing the jumping around of speedo and, of course, unreliable cruise speed

Thats IF you have the dual cable setup in 1987, trans to cruise cable(in engine bay) then shorter cable from cruise to speedometer(in Cab).

If your trans speedo hook up has a cable AND a VSS sensor both...
Pictures here of both types: http://www.therangerstation.com/how-to/interior-and-interior-electronics/speedometers-how-they-work/

....you have the VSS, then it will run the cruise speed, and cable is speedometer only.
But.........since both are showing erratic speed then problem could still be the cable catching and releasing, AND it could also be the Driven gear is worn out, need to pull out the unit to inspect it.
Long shot is the Drive Gear, worm gear on the output shaft, it is held in place on the shaft by a ball and it can slip, but this would usually show No Speed at higher speeds, not erratic speeds
Worm gear can also get worn down, causing intermittent contact to Driven gear and erratic speed shown on speedo, you can usually see it thru the hole when unit is removed

With the dual setup, cable/VSS, you could unhook the speedo cable at the transmission end and then go for a drive, set cruise and see if speed stays constant, if so then speedo cable is the problem.
If speed goes up and down, as before, then problem is in the cable/VSS end of things

 

[adsm08]

My 88 used to do that. Speed sensor fixed it. I would start there.

 

[rusty ol ranger]

Ron, mine does not have the 2 cable setup. My 77 F250 has that setup (granted its aftermarket and never worked) but the ranger does not.

It has the VSS/Cable combo. On rusty #1 i had no speedo for years, even after replacing the cable, and gear. I didnt know what that sensor was, or what it did, so i didnt screw with it, it read 0 untill you got to about 80 then it would work till you slowed down.

Rusty #2 (truck in question) has a functioning speedo, but i didnt know exactly how that sensor operated, and if maybe there was something in there binding things up. Either way, ill yank it from the trans and have a look see, will i screw the cable up if i remove it from the VSS, chuck it in a drill, and spin it while someone watches the speedo for bounce? To rule out the cable.

Adsm, im gonna order one this afternoon, i miss having cruise.

 

[adsm08]

If your speedo does not bounce when not using cruise you can pretty much rule out the drive gear, cable, and speedo head.

The sensor, which is what tells the cruise module if it is going fast enough or not, is just a standard VRS style sensor. They can get funky after so many years, and give signals that aren't good enough.

So say you set the cruise at 55 with a weak sensor. It may show the computer 45. Computer thinks you want to go 10 MPH faster, now it runs up to 65, where the signal is correct, and it sees you going too fast. Now it slows down by what should be 10 MPH, and whoops, back to 45. This is what creates your surge.

I also had noticeable throttle surging. This should be easy to find, even without a tach. Just leave your foot laying lightly against the pedal, just enough that your foot won't move if the pedal does, when you set the cruise. If the sensor is really the problem you will notice the pedal bouncing back and forth with the speed surges.

 

[rusty ol ranger]

If your speedo does not bounce when not using cruise you can pretty much rule out the drive gear, cable, and speedo head.

So say you set the cruise at 55 with a weak sensor. It may show the computer 45. Computer thinks you want to go 10 MPH faster, now it runs up to 65, where the signal is correct, and it sees you going too fast. Now it slows down by what should be 10 MPH, and whoops, back to 45. This is what creates your surge.
.

It bounces even with cruise off, but seems some what steady in the 25-35mph range, below that it bounces a bit and above that it can read +/-10mph.

That second paragraph i quoted just described, to a tee, what its doing

 

[adsm08]

Well a binding in the cable will cause the a corresponding surge in the signal from the sensor. You need to find and fix the issue with the speedometer in general before going too nuts. I may have misunderstood the initial problem. I had a kid screaming as I read the original post.


Pull the sensor out and inspect the gear for damaged teeth. You should also be able to feel any bind in the cable by turning that gear by hand. Remove the cable and turn just the sensor/gear to verify binding in the cable.

 

[bobbywalter]

pop the cable off.....cruise down the road at a good clip and set the cruise. if it quits surging then the cable is definitely causing bind and may have wiped the gear on the drive. if it dont change then a new vss is likely or that gear is really pooched..

you may need a fresh cable gear and vss...

 

[rusty ol ranger]

Kinda thinkin about just replacing the whole damn thing. I even found a NOS speedo head for 40 bucks on ebay.

Im hoping to have some time this weekend to tear into it, ill post results.

 

[85_Ranger4x4]

Mine is kind of like that too, nowhere as refined as my pretty much anything else I have driven with cruise.

I have only been around one first gen cruise system and the powertrain I fused it to is radically different than the one it was intended for.

It isn't smooth with the throttle, I don't know if it is because it is figuring on putting the spurs to a 2.9 and there is a 5.0 on the other end of the cable or if it figures it needs to move the cable this much for a throttle body and it is doing that much to a carb and the geometry isn't quite right or what. My speedo bounces some too so that may be playing with the slop in the gears. My speedo drive on the t-case was new last year and the driven gear was new when I did the engine swap in 2011.

BUT while it feels erratic with the throttle it actually holds speed pretty well. I ran it with the GPS on my phone this morning and it varied from 57 to 60. Speedo varies from 50 to 60.

Without an overdrive trans it has hit the secondaries once on a steep hill, that was... enlightening. I think it even scared itself.