Hey there! My odo recently stopped working and I can't seem to figure out why. I switched out the entire dash cluster and it still did not fix it. My MPH works but is 5MPH to fast. Any other possibilities as to why it stopped working? It stopped at 90,999.0 so basically half way to 91,000.

 

Its probably the stepper motor. That's what mine did, got a used one off of eBay and it works fine now.

 

Ahem. It would be rather helpful to include your model year in your profile.

 

That's a good problem to have! It will never hit 100,000 miles....

 

Profile says it is an 87 (Maybe it got updated this morning?) But yes, people are much more inclined to weigh in with advice if the year car is included in the request for help. (Leaving the year out is pretty common over on the Buick Century forum)


The odometer assembly is a mechanical "clock" whose basic design goes back 60 or 70 years. For years these odometers were driven by the speedometer cable, but back in the 80's were adapted to be driven through a stepper motor and several plastic gears (to generate the torque to roll the ones, tens, hundreds, etc drums each time the preceding drum reaches "9".) The problem being, age, heat, and possibly the lubricants used on the gears cause the plastic to eventually soften to the point that teeth strip off of the gear (usually the one that drives the tenth's gear on the "clock".)

At this point a visual inspection is in order. IF you find a stripped gear on your original odometer assembly, a used replacement can be had on eBay for $25 to $35 dollars and I have seen "new" ones with a lifetime warranty for around $50. I won't venture to guess what the problem is on your replacement cluster since I don't know it's pedigree. Since the speed is off and the odo doesn't work, I'd look into returning it.

While you are on eBay, I'd look for a used Factory Service Manual also. The manual would have paid for itself right off the bat by steering you away from buying a cluster you didn't need.

 

The cluster I had was sun faded and I could not read ANY of the numbers. The new cluster was rebuilt with new LCDs and motherboards/bulbs. From what I could see with polarized sunglasses, the old cluster was off by 5mph just like the new one. Which tells me a sensor is misreading?

I will look into a new stepper motor and that'll hopefully fix my issue. I appreciate the responses!

 

Check your tire size compared to the specified tire listed on the tire placard on your door jamb. If your effective tire diameter is different from stock, your speedo and odo will be off. Many online tire vendors will list revolutions/mile and approximate tire diameter for each tire listing. A tire around an inch and a half taller or shorter is enough to throw you off by 5mph. Example: Pi x 24" = 75.398 inches per revolution. Pi x 25.4" = 79.8" per revolution. The difference in distance travelled is 4.4 inches. If a 24 inch diameter tire makes 860 revolutions per mile (5280 ft), then a 25.4 inch diameter tire will travel 439 ft further, or 5719 ft in the same 860 revolutions. That's 1.083 miles. At 60mph indicated, you will actually be traveling at 65 mph despite an indicated speed of 60.

 

I did double check the tire size on the door and I do have matching tires all the way around. I did hear of that being an issue though. What else could cause the MPH to read 5 miles faster on two different clusters?

 

Rear axle ratio is not stock.

VSS has wrong gear in it.

 

That or trans has been swapped and speedo gears didn't get changed out. Either way, changing the speedo gear in the trans tail shaft housing will get you reading correctly. Check out this website: http://www.transmissioncenter.org/GM...eter_Gears.htm

For more insight, you can also do an advanced search here for "Driven gear", just restrict your search to the C4 Forum.