Help with Speedometer adjustment.

My 2004 Freightliner Classic XL speedo is roughly 5% off. If I'm going an actual 65mph my speedo reads 68mph.
I don't have any trouble judging my speed since I know this but, my odometer is also off. Every hundred miles I'm showing an extra 5 miles or so. This adds up rather quickly.
Is there an easy fix? A dealer said they could adjust the dip switches but he didn't really know how.
What do you suggest?
Thanks for the help.
Mack

 

how worn down are your drive tires when my tires get about half worn it will be about 3 mph off. that isnt really that far out of wack. if that isnt the problem then you can readjust the speedo. when i reratioed my truck i had cat adjust the speed in the ecm. yours might be the same way.

 

Drive tires are a bit worn, probably 1/2 tread but I really don't see much difference when they are new. It is always off roughly 3mph. Perhaps it isn't enough to be concerned with. It just drives me nuts thinking "I'm driving 600 miles but I'm logging 630".

 

you could have it checked but i will bet there isnt anything wrong with it all speedos are not 100% accurate 100% of the time.

 

This is what I kind of expected but I had to ask.
Thanks again.

 

heck look at it this way at least when you think your doing 68 you are actualy going 65 no tickets that way!!

 

Actually as you described it, the miles driven would be the opposite. If speedo is reading 68 you would do 680 miles in 10n hours, but actual is 65 so 650 miles in 10 hours.

Some companies set their trucks up this way...to save 10% on the excess miles on a lease.

 

didnt think about that. does that mean if i readjust my speedo i could save on logbook hrs?

 

If I wanted to save it would have to be the other way. Now I am paying road taxes etc. for 680 miles when only actually going 650. I'm racking up a ton of miles on my odometer that I'm not driving but I have to log it as if I am. Hence my concern.

 

That would be opposite again....and actual miles is figured by odometer or hub meter.

And in answer to the earlier question...the speed/miles is in the ECU, if you are off 5% it means that the tire size is wrong in the ECU set up...any dealer can adjust to get accurate tire rotation to the speed and distance traveled.