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1991 Ranger speedometer needle "floating" "bouncing" "erratic"?


Fairlaniac

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1991 Ranger speedometer needle "floating" "bouncing" "erratic"?

My 1991 Ranger’s speedometer needle is bouncing all around. It started the other week and I can’t figure out the issue? The odometer is keeping proper mileage but the needle seems to float. I’ll be going at a calculated speed of 60 mph and the needle will be bouncing between 85 mph and the 6 o’clock position on the speedo gauge. It never floats below the speed I’m travelling. Is the needle controlled by the cable on these models? I’m not sure when the electronic speedos came onboard.

BTW - it did this last year for a day or two and resumed working well until now, again.

Thanks,
 
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RonD

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'91 will still have a speedo cable.

Speedometer cables are made up of smaller wires twisted to make a larger cable.
It is a common occurrence for one of the smaller wires to break, this causes the cable to slow and then jerk back, hangup then release, this causes the jumping speedo needle, but won't effect odo because turn count never changes, it just hesitates briefly.

I think Ford added a VSS(vehicle speed sensor) in early '90's, this was for ABS brakes and Cruise Control, it was located with the speedometer cable on the transmission.
Have a read here: http://www.therangerstation.com/tech_library/speedometer.shtml

Reason I mention this is because prior to the VSS being added there were 2 speedometer cables if you had cruise control.
One from trans to cruise module in engine bay
One from cruise module to speedometer

You will need to replace the cable with the broken wire, and yes it can come and go as the wire is bent, but will come more than go as time passes :)
 

Fairlaniac

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Update

Thanks for all of the previous responses. I did nothing about the speedo cable as it was too cold and snowy. So now that it's above freezing and for multiple days the speedo is again working. Checked it against my gps and it's within 1 mph at 60mph. So what is the cold affecting?

When it wasn't working the needle was very lightly floating. It would easily bounce around, fly to well past 85mph and come back effortlessly.

It's my beater so I'm not too concerned with fixing it right now, just trying diagnose it for when I do decide to fix it.

Thanks,
 

adsm08

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I think Ford added a VSS(vehicle speed sensor) in early '90's, this was for ABS brakes and Cruise Control, it was located with the speedometer cable on the transmission.
In 1986 the VSS sensor on the end of the cable was present on all vehicles with ABS, Cruise, or auto trans.

By 1987 it was there on all of them. Yes, I am sure of that part because my truck came with nothing that would require an electronic VSS signal (manual trans, no ABS, no cruise) but still had the sensor.
 

frankgeno

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1991 Ranger speedometer needle "floating" "bouncing" "erratic"?

My 1991 Ranger’s speedometer needle is bouncing all around. It started the other week and I can’t figure out the issue? The odometer is keeping proper mileage but the needle seems to float. I’ll be going at a calculated speed of 60 mph and the needle will be bouncing between 85 mph and the 6 o’clock position on the speedo gauge. It never floats below the speed I’m travelling. Is the needle controlled by the cable on these models? I’m not sure when the electronic speedos came onboard.

BTW - it did this last year for a day or two and resumed working well until now, again.

Thanks,
I know this is a very old thread but this is how a mechanical speedometer works. The speedometer cable is gear driven at the tail end of the transmission. The cable is housed in a housing and the top of the housing connects to the speedometer. The cable spins the speedometer and gears inside the speedometer run the odometer. The shaft of the speedometer is what spins a set of 2 magnets that spin around very closely to an aluminum dish, it is shaped like a bottle cap on a pickle jar or pill bottle. The sides of this dish are in close proximity to the magnets and even though aluminum is not magnetic the magnets affect it. The dish is suspended on a tiny spindle that has a sharp point on the end that then rides on a jewel so there is very little friction. a microdot of oil is put on the jewel to lube it. connected to this dish are the speedometer pointer and a hairspring tiny like in an old wrist watch this spring returns the pointer to zero speed when the car stops. To calibrate the speedometer there are adjustments to be made to the spring position and the strength of the magnets. The shaft that the speedo cable connects to has a brass bushing that holds it in place. After years of use, this bushing gets moved forward a bit thus causing the magnets to get very close to the aluminum dish and even hitting it. Cold weather enhances this. The cure is to reseat the bushing to its proper position, put a micro drop of oil on the jewel, and recalibrate the speedometer. Back in the 80s I owned and operated Ross Speedometer and Electronics in Greenville Texas and this was a very common thing we saw and corrected. To calibrate a speedometer you need some specialized tools but it was a job we did often back then.
 

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