speedo reads +15 or 20mph when cold?

[iangoround]

Hey guys,

I've got a 91 ranger 5spd 4x4. Not sure which trans, my guess would be the M5OD-R1. It got cold here last night, down in to the low 20s, and this morning on my way to work the speedo said I was doing 75 to 80 in 5th gear turning 2,000 RPM.

This thing has a cable driven speedo, right? Normally it reads about +5MPH. I'm quite confused. I would understand if the gear oil was so cold that it was slowing the speedo down but up???

 

[2manyfords]

Common problem on a '91.
It's an electrical problem in the dashboard that corrects it self once the truck warms up.

 

[iangoround]

What exactly is the problem and how can I fix it?

If the issue is in the cluster, can I swap in a cluster from a newer truck and fix it easy? I'm not concerned with accurate mileage as the truck is over 10 years old and already has a NAM title anyway.

 

[AllanD]

Uhhh... how can an ELECTRICAL problem cause a MECHANICAL speedo to read "off"

Oh and BTW, on a 4x4 the transmission is irrelevant when discussing the speedometer, because the speedo cable is connected to the transfer case.

AD

 

[CheapThrillB2]

its in the speedo head, i just read the TSB on it in AllData, my 91 does the exact same thing. I beleive it was something to do with the grease/lube they used in the head. The TSB said to instal a different speedo head.

 

[CheapThrillB2]

"SPEEDOMETER-MECHANICAL (ANALOG)-INDICATES HIGH SPEED AT LOW AMBIENT TEMPERATURES (ABOUT 20 DEGREES F OR -7 DEGREES C OR BELOW)- VEHICLES BUILT AFTER 4/1/90

FORD:
1990-92 ESCORT, MUSTANG, TAURUS, TEMPO

LINCOLN-MERCURY:
1990-92 SABLE, TOPAZ, TRACER

LIGHT TRUCK:
1990-91 AEROSTAR, BRONCO, ECONOLINE, F-150-350 SERIES
1990-92 RANGER
1991-92 EXPLORER

ISSUE:
Mechanical speedometers may indicate higher than actual vehicle speed at low ambient temperatures (about 20~ F or -7~ C or below). This occurs because of insufficient lubrication at lower temperatures. The speedometer will indicate speed correctly after the vehicle warms up.

ACTION:
Replace the speedometer head with a service speedometer assembly. Speedometer part numbers are identified in the Parts Block/Application Chart. Refer to the appropriate Service Manual for removal and installation details."

Quted from said TSB on AllData

 

[iangoround]

Uhhh... how can an ELECTRICAL problem cause a MECHANICAL speedo to read "off"

Oh and BTW, on a 4x4 the transmission is irrelevant when discussing the speedometer, because the speedo cable is connected to the transfer case.

AD

I was a bit confused why an electrical problem would have anything to do with it as well, but what do I know?

 

[rusty ol ranger]

Ive had alot of older vehicles do that, my LTD used to, my dually does (sometimes), i just ignore it.

later,
dustin

 

[HLS]

Ranger Speedometer Reads High - When Cold

Just fixed my 91 Ranger speedometer. NO, you do not need to buy a replacement cluster, its a dry bearing issue. This is a mechanical speedo. It can only read high if something is dragging the needle up.

Remove the front of the dash (two screws at ash tray and then pry it up). Remove screws around plastic lens on the gauge cluster. Starting on the left pull up on the gauge (it simply plugs into the dash, no screws or wires). Next remove the next set of gauges on the left. Then pull the right side tachometer leaving the speedo in the middle. Now it is free to lift up so you can get behind it and push the flat part of the white plastic clip to release it. You may need to push up the speedo cable from under the dash to get it out far enough to push the release.

On the bench you will see how the speedo works. The speedo cable turns a shaft with a set of magnets attached. They fit inside a housing (open on the rear side) which in turn moves the speedo needle. The Speedo needle shaft fits inside the end of the rear shaft that ties to the speedo cable.

Using a light oil I simply lubricated the bearing where the front and rear shaft meet. Also make sure the magnets have not picked up any dirt or metal particles that may also be dragging on the needle. I used a small piece of paper to pass between the magnet and housing to ensure nothing was caught between them.

This fixed my issue with the speedometer going to 85 MPH in 1st gear whenever the temperature was below 35.

Total cost = $0. Total time to fix knowing what the problem is = 1 hour.