Extremely Fast Odometer

[ttcole1254]

Well this is something I've never seen before.. on my 1988 Full size 351, the odometer reads VERY fast, as in it's reading 300 miles when it should be 30 or so. The thing looks like a slot machine ticking away the miles. Is there anything that can cause such a thing? My speedometer is accurate, so I don't think it could be that.

Thanks

 

[Skitter302]

I think you got one of them "limited features" /

In all honesty it sounds like something broke and it might need to be replaced. And considering the the speedo works like it should, its not on the transmission end.

 

[ttcole1254]

Haha "feature" sounds like it  /emoticons/[email protected] 2x" width="20" height="20" /> 

I got the truck with 67k miles on it.. looked at it a few days ago and it jumped all the way to 72k! Oops. I was planning on pulling apart the whole dash and checking everything, but was wondering if anyone knew of anything to check first. Tried googling and couldn't find anything about it going crazily fast. Now my speedo does seem to "hover" or bounce on lower speeds plus and minus like 3 or 4 mph. The bouncing quiets down at about 30, and then its steady the rest of the way up. Any idea what that could be? I forget if it was something normal on these older trucks.

 

[Skitter302]

Now that I'm in front of my computer, it sounds like the worm assembly to the odometer has bound up with the cable assembly and that is what is giving your odometer the fast speed. That requires a professional rebuild to repair.

Speedo bounce is caused by a dirty cable 9/10 times.

You have to reach under the dash to the back side of the spedo unclip/unscrew the cable.

Then unscrew/unclip the cable from the transmission.

From the top half or the cable, pull the core out 2-3 inches and spray a **** down the cable. Don't use a high foaming **** because that will make a mess. (as a last resort you can use 3in1 from a bottle)

At the bottom of the cable spray lub up the cable a lil' and let drain for 1-2minutes.

Clean the area near the cable connection on the transmission to avoid contamination during reinstall.

IF all that cleaning doesn't help then you might have age bounce.

Push the core back into the cable and reinstall to the speedo.

Then *****/clip the cable back to the transmission.

 

[miesk5]

Yo Tyler,

As Skitter advised!

Here is a reply to same issues;

How_do_you_fix_a_speedometer_on_an_88_f-150_and_will_this_fix_the_odometer_and_trip_meter

http://wiki.answers.com/Q/How_do_you_fix_a_speedometer_on_an_88_f-150_and_will_this_fix_the_odometer_and_trip_meter

F 150 speedometer/Odometer is same

Here is the Speedometer Accuracy TSB 89-02-07PUBLICATION DATE: January 25, 1989
 

FORD
1989 and prior All Car Lines
LINCOLN-MERCURY
1989 and prior All Car Lines
LIGHT TRUCK
1989 and prior All Truck Lines
MEDIUM/HEAVY TRUCK
1989 and prior All Medium/Heavy Truck Lines

ISSUE The accuracy of speedometer/odometer readings may be influenced by several vehicle components or systems. The information in this TSB article is intended to assist technicians in speedometer/odometer concern diagnosis. ACTION Use the following supplemental information to assist in speedometer/odometer diagnostics.

Operation

A mechanical analog speedometer displays vehicle speed and the odometer displays total distance traveled. The speedometer/odometer assembly is cable driven by either a transmission or a transaxle. All speedometer/odometer assemblies, except for police vehicles are the same with respect to the speed accuracy tolerance used during calibration. The odometer gear ratio is fixed so that all are identical and have no error in the speedometer head.

Electronic digital operation is similar. It could use a drive cable or a speed sensor to drive the speedometer/odometer. An electronic signal is sent from a speed sensor to the digital speedometer/odometer assembly. The speed sensor is driven by a transmission or a transaxle, similar to a cable.

Several areas of concern that may affect speedometer/odometer readings are tires, axle gear ratio and speedometer/odometer drive and driven gears.

Tires

Improper tire rolling radius and inflation pressure, temperature and size may contribute to inaccurate system readings. System accuracy testing should be performed after the tires are set at the correct pressure as shown on the safety compliance certification label. The tire should be warmed for a short period. Best results are obtained on smooth, dry pavement while driving at a constant speed within the posted speed limit.

Axle/Transaxle Ratio

The gear ratio of the rear axle or the final drive ratio of the transaxle must be known to select or check if the proper speedometer/odometer drive and driven gears are present. Various gear ratios are available, but usually are not a concern when dealing with speedometer/odometer concerns unless the gear ratio has been changed.



WARNING:

NEVER CORRECT SPEEDOMETER READINGS BY CHANGING GEARS UNLESS THE ODOMETER IS ALSO OFF.
Drive/Driven Gears

The speedometer/odometer drive gear is located inside the transmission, transaxle or transfer case and is not easily accessed for change. The driven gear rotates the speedometer cable. Rear wheel drive vehicles have several driven gears with various numbers of teeth available to correct input to the speedometer/odometer head. Front wheel drive vehicles generally do not offer different gears for correction.

General Description

The maximum allowable odometer system accuracy error is ± 3.75% of the actual distance traveled. Ford Motor vehicles are well within those limits.

The speed indication is biased high, except on police vehicles with certified calibration speedometers/odometers. As a general rule, the indicated speed is equal to or greater than the actual speed. This is intended to protect the consumer against violating speed laws. Most customer concerns are related to speedometers reading too high at true speeds between 50 MPH and 65 MPH (80 - 105 Km/h). At that speed range, the worst case errors may indicate a speed that is 10% greater than true speed.

The speedometer head is an instrument which processes information sent to it by the rotating speedometer cable. If the system components send the wrong number of revolution per mile to the speedometer head, an inaccurate speed reading and amount of distanced traveled will be displayed. Since there is no error in the fixed gear ratio of the speedometer head odometer, start by checking the accuracy of the odometer even if the customer concern indicates a speed accuracy problem. Odometer accuracy can be checked by using roads established at mile increments or a known local course. If roads with mile markers are used, a five mile stretch is recommended to allow for inaccuracies. If an error is greater than 3.75%, a change to the transmission drive/driven gear selection, tire size, or tire inflation may need attention. The odometer should be checked again to verify any corrective action. If the indicated speed error exceeds 10% between 50 MPH and 60 MPH (80 - 105 Km/h), replace the speedometer/odometer assembly. Vehicles with transfer cases that have fluctuating readings may be due to slippage of drive gears, parts not splined or loose yoke nuts.

If the vehicle has speed control, the speed accuracy can be checked using the verified odometer vs. time. The formula is as follows:

3600 divded by TIME (seconds to cover one mile) = TRUE MPH(Km/h)
EXAMPLES:

60 MPH (96 Km/h) requires 60 seconds to cover one mile
55 MPH (88 Km/h) requires 65 and 3/4 seconds to cover one mile
----------  If I recall correctly; damage gear teeth will cause higher than actual speed and odometer readings (higher miles travelled than actuals)