Is it possible for the Speedo and the Odometer to be out of synch? The last owner replaced the dashboard/speedo/etc in my truck. I haven't been able to check the speedometer but I think it's correct. I decided to check my odometer to see if my MPGs were really 16.5. I noticed that it was off by 1/10th of a mile at every mile marker (oh well, at least I'm really getting about 18.5 mpg). So I am wondering if the speedo can be right while the odometer is wrong?

 

I would think they are tied together... However, I am not sure about that.

If you have available mile markers that are accurate, hold at 60mph and check it against a watch/clock that has a second sweep hand (or stopwatch). That should give you enough of an indication to see what your next step should be....

 

If the odo is off, so is the speedo.

 

Ok - sounds reasonable. So, if I am running 235/85/16 (stock) tire size could the dash be out of another Ram with different stock tires?

The tag on the rear end gears says "3 54" so those are 3.54s right? I think I am running about 2000 rpm at 70MPH. Does that sound right? Is 18+ mpg about average for that setup?

- THANKS -

 

The speedos are all the same. The drive gear for the VSS may be wrong, though.

With the same size tires mine runs about 2100 at 70, but the OD on the auto is taller by a good bit. Somebody with the same setup as you will have to tell you what RPM you ought to see.

 

everyone probably already knows this, but here goes anyway. drive down the road and compare the milemarkers to your odometer, to see how much its off. Older mechanicals are easier to check in just 1-2 miles. For digitals you may have to run 2-3 miles before you get off by an even 1/10th. To check your speed, get on a flat road and hold exactly 60 mph. If you pass a mile marker at exactly every 60 seconds, its reading correct. If you are off 3 seconds, that 5%. 6 seconds is 10%. That much difference can lead to a speeding ticket. Odometer and Speedometer should be off by the same amount. Like the post above said, the calibration in your 92 is probably controlled by a gear in trans ?? The newer ones are computerized with no gears, all programming. My 01 is off about 3 sec, covering 1 mile in 57 sec. That causes my odometer to read about 5% short, my speedometer about 5% slow, and my mpg about 5% less than actual - all due to bigger tires, which look good. oh well.

 

it will give you speed and distance, then check that against your speedo.