Speedometer suddenly inaccurate

1994 Explorer XL auto trans, Suddenly the speedometer is reading about
10-15 MPH faster than actual speed. Less of a difference at slower
speeds. What could cause this? thanks.

Bob wrote:
> 1994 Explorer XL auto trans, Suddenly the speedometer is reading about
> 10-15 MPH faster than actual speed. Less of a difference at slower
> speeds. What could cause this? thanks.

I had the same problem with my '94 Explorer. It turned out to be a bad
speedometer, and I replaced it with one from a junk yard. (I wasted a
lot of time lubing the speedo cable etc before deciding it had to be
the speedo itself. The key is the HIGHER than normal speedo reading.)

I took the bad one apart and figured out what caused it. The '94 and
earlier speedos are driven mechanically by a cable. The cable spins a
magnet in the speedo. The needle is attached to a metal cup that fits
over the magnet. To keep the cup centered over the magnet there is a
bushing in the center of the magnet assy, and a mating pin on the
speedo needle assy.

When the bushing wears, the metal cup attached to the speedo needle can
flop around. If the magnet rubs against the cup, it causes the speedo
to indicate a HIGHER speed than actual. In my case, the needle tended
to swing wildly too as it randomly touched the magnet more or less.
Like yours, it only happened at higher speeds, 55 mph and up in my
case.

If you get a replacement from a junk yard as I did ($17 at pick and
pull) check the side play on the needle and compare it with yours. The
new one should have very little side play compared with the bad one.
This is a common problem, so you might see it on other vehicles with
high mileage.

I got a speedo from an old Bronco, a 94 or earlier Ranger should also
work if you can't find a donor Explorer.

If you have a 95 or later Explorer, none of this applies. Those have
electronic speedos that work like tachometers- they use the pulses from
the VSS (vehicle speed sensor) to calculate the speed instead of a
mechanical cable.
-Paul

wrote:
> Bob wrote:
>
>>1994 Explorer XL auto trans, Suddenly the speedometer is reading about
>>10-15 MPH faster than actual speed. Less of a difference at slower
>>speeds. What could cause this? thanks.
>
>
> I had the same problem with my '94 Explorer. It turned out to be a bad
> speedometer, and I replaced it with one from a junk yard. (I wasted a
> lot of time lubing the speedo cable etc before deciding it had to be
> the speedo itself. The key is the HIGHER than normal speedo reading.)
>
> I took the bad one apart and figured out what caused it. The '94 and
> earlier speedos are driven mechanically by a cable. The cable spins a
> magnet in the speedo. The needle is attached to a metal cup that fits
> over the magnet. To keep the cup centered over the magnet there is a
> bushing in the center of the magnet assy, and a mating pin on the
> speedo needle assy.
>
> When the bushing wears, the metal cup attached to the speedo needle can
> flop around. If the magnet rubs against the cup, it causes the speedo
> to indicate a HIGHER speed than actual. In my case, the needle tended
> to swing wildly too as it randomly touched the magnet more or less.
> Like yours, it only happened at higher speeds, 55 mph and up in my
> case.
>
> If you get a replacement from a junk yard as I did ($17 at pick and
> pull) check the side play on the needle and compare it with yours. The
> new one should have very little side play compared with the bad one.
> This is a common problem, so you might see it on other vehicles with
> high mileage.
>
> I got a speedo from an old Bronco, a 94 or earlier Ranger should also
> work if you can't find a donor Explorer.
>
> If you have a 95 or later Explorer, none of this applies. Those have
> electronic speedos that work like tachometers- they use the pulses from
> the VSS (vehicle speed sensor) to calculate the speed instead of a
> mechanical cable.
> -Paul
>
Thanks for the great info. I'll look into a replacement speedometer.

On Tue, 02 Jan 2007 09:13:43 -0800, Bob > wrote:

>1994 Explorer XL auto trans, Suddenly the speedometer is reading about
>10-15 MPH faster than actual speed. Less of a difference at slower
>speeds. What could cause this? thanks.

It's also possible it is just the cable needing grease. You might
want to try that first before you take the whole dash apart to replace
the head.

wrote:
> Bob wrote:
>
>>1994 Explorer XL auto trans, Suddenly the speedometer is reading about
>>10-15 MPH faster than actual speed. Less of a difference at slower
>>speeds. What could cause this? thanks.
>
>
> I had the same problem with my '94 Explorer. It turned out to be a bad
> speedometer, and I replaced it with one from a junk yard. (I wasted a
> lot of time lubing the speedo cable etc before deciding it had to be
> the speedo itself. The key is the HIGHER than normal speedo reading.)
>
> I took the bad one apart and figured out what caused it. The '94 and
> earlier speedos are driven mechanically by a cable. The cable spins a
> magnet in the speedo. The needle is attached to a metal cup that fits
> over the magnet. To keep the cup centered over the magnet there is a
> bushing in the center of the magnet assy, and a mating pin on the
> speedo needle assy.
>
> When the bushing wears, the metal cup attached to the speedo needle can
> flop around. If the magnet rubs against the cup, it causes the speedo
> to indicate a HIGHER speed than actual. In my case, the needle tended
> to swing wildly too as it randomly touched the magnet more or less.
> Like yours, it only happened at higher speeds, 55 mph and up in my
> case.
>
> If you get a replacement from a junk yard as I did ($17 at pick and
> pull) check the side play on the needle and compare it with yours. The
> new one should have very little side play compared with the bad one.
> This is a common problem, so you might see it on other vehicles with
> high mileage.
>
> I got a speedo from an old Bronco, a 94 or earlier Ranger should also
> work if you can't find a donor Explorer.
>
> If you have a 95 or later Explorer, none of this applies. Those have
> electronic speedos that work like tachometers- they use the pulses from
> the VSS (vehicle speed sensor) to calculate the speed instead of a
> mechanical cable.
> -Paul
>

Thanks a lot Paul, what you describe is exactly how my speedo is acting.
I'm shopping for a replacement on the internet, best price I've gotten
so far is $50. It looks like a real job to get to the speedometer, any
tips or tricks in removing and replacing it? Thanks again, I'll post
results after I replace it.

Ashton Crusher wrote:
> On Tue, 02 Jan 2007 09:13:43 -0800, Bob > wrote:
>
>
>>1994 Explorer XL auto trans, Suddenly the speedometer is reading about
>>10-15 MPH faster than actual speed. Less of a difference at slower
>>speeds. What could cause this? thanks.
>
>
> It's also possible it is just the cable needing grease. You might
> want to try that first before you take the whole dash apart to replace
> the head.
You're right, I'll try lubing the cable first. Disconnect it at the
transmission and shoot some grease into it?

On Wed, 03 Jan 2007 11:32:51 -0800, Bob > wrote:

>Ashton Crusher wrote:
>> On Tue, 02 Jan 2007 09:13:43 -0800, Bob > wrote:
>>
>>
>>>1994 Explorer XL auto trans, Suddenly the speedometer is reading about
>>>10-15 MPH faster than actual speed. Less of a difference at slower
>>>speeds. What could cause this? thanks.
>>
>>
>> It's also possible it is just the cable needing grease. You might
>> want to try that first before you take the whole dash apart to replace
>> the head.
>You're right, I'll try lubing the cable first. Disconnect it at the
>transmission and shoot some grease into it?

I don't think you can do it that way. If you are really lucky and
nimble you might be able to get your hand back up there and unclip the
housing from behind the cluster and pull it down so you can pull the
cable out to clean and relube it. It's been a long time since I had
to play with mine but it seems like I had to pop the front off the
dash (take out the two screws at the ashtray) and unbolt the cluster
but not completely remove it in order to see and get to the speedo
cable. It's been a long time.....