Speedometer wrong

[doain]

I recently purchased a 2002 Monaco Signature General. While driving the coach back to my home, the speedometer was reading 70-75mph yet traffic was flying by me like I was standing still. The dash radio had a screen that showed engine information so I turned that on, and the GPS based speedometer showed that I was only driving about 55mph when my coach speedometer reads 70mph.
Any idea on what is causing this? How do I repair the inaccurate speedo. The coach shows 60,000 miles on the odometer, I wonder how accurate that is as well.
Any help would be greatly appreciated.

Dwayne

[Flagelpater]

FWIW My friend had a Dynasty that was off by 10%, speed and odometer. If it is simply the wrong setting for the tire size it is a simple setting change. I don't know how to do it but I am sure someone will chime on in here with the answer. In the mean time you need to know if both the odometer and speedometer are off the same amount.

[Twomed]

Easiest way to find out if odometer and speedometer is close is doing the measured mile and time. Run several at 60 indicated then do the math to find the difference. Speedos are set with dip switches on the back of the speedo head. Monaco should be able to tell you/fax you an adjustment sheet to obtain the proper readings once you do the math. Not rocket science just tedious. The larger problem may be the adjustment sheet, but if you can at least get the manuf of the speedo head you should be able to contact the manuf for that info. The biggie is did they change suppliers every time they changed colors/faces on the dials or can they supply the info.

[Jim Stewart]

I know this is a stupid question, but was it a Canadian MH and it is reading KPH instead of MPH?

[Eaglesview]

If it is a Beede speedometer go to beede.com

Determine your exisiting dip switch settings and exact speedometer error. They can give you appropriate dip switch settings. Or you may be able to access the table of settings in their technical support section.

My 05 Dynasty has a Beede unit and was able to fine tune the settings.

[wa8yxm]

There are a couple of things that affect speedo-accuracy

one is the tires.. It is imparative that the tires be the original size and that they be properly inflated.. If for some reason the prior owner put on smaller tires (Cost less for example) the speedo will read high since it's really reading RPM of the tires.

Another is worn out speedo at least back in the old days.. The new electronic ones are not supposed to do that

Gear splitters... If your rig has an after market Gear splitter.. Some of them will read fast if in LOW range (they should read proper in high)

The one in my car is up to 5 mph off at speeds less than 20.. at about 20MPH the needle and the GPS become.. "Synced"

It's a mechinical.. The electronic one on the motor home

If I'm moving fast enough to register.. The GPS confirms the dash.

[Rick Long]

Look at the bright side.... Your coach may have far less miles on it than the odometer is showing.

[mahon1993]

I had kind of the same problem with my speedo. My local Cummins service center had a chassis dyno that we put the MH on. It was real easy to adjust the speedo on the dyno by flipping the right switches the right way. A lot easier and a whole lot more accurate than doing it on the freeway. I know, because I tried it that way. If you don't have a convient Cummins service center call around to large truck repair centers and see if they have a chassis dyno. You will also be able to get a horse power reading there.
Greg

[a k]

If you have the Cummins and the Allison Trans you have to have the ECM flashed with the right codes. They go off of the trans output and they set the gear ratio and rev's per mile of your tire. Mine is set for 4:33 ratio and 451 rev/mile. Have them check it with a Quickcheck 5100 or Insite program.

[doain]

Thanks for all the great responses....

I checked and it is set for MPH....

I cannot seem to find anyone that has any manuals to check the correct DIP switch settings

The tires are the same size listed as the original owners manual spec sheet.

My "local" (80 miles away) Cummins dealer did say he thought he could readjust the speedo electronically, so I will try to have them check it.

Thanks again!!

[DP01]

Take a look at: http://www.egauges.com/pdf/vdo/0-511-011-348.pdf

It may just work for you… or not.

Dennis

[EngineerMike]

The Cummins software has a setting some of the tech's call "revs" for revolutions per mile. I'm not sure that's exactly how if is input. But to adjust that parameter you give the shop (or have the shop measure, which is more tedious & time consuming) the tire circumference as it rolls. I mark the tire where it hits the ground, and the ground, roll the coach forward a ways & count the revolutions (10 tire revolutions is a good # if you have that distance clear to do this like in a parking lot or straight piece of road). Mark the ground where the tire mark hits. Measure the distance and divide by # of revolutions. This is the rolling circumference of the tire. W/that & a calculator the shop can reset the parameter.

With that said, the difference between speedo & actual in this case is pretty large. Not likely a reset of the tire size/"revs" unless the reset was a blunder by the tech. There may be other gearing that needs to be reset as discussed above on trans also. Note this to the service writer when checking in- the difference is way too large to be explained by tire size alone unless the currently set tire size is clearly stupid.

[pipedream2]

Dwayne
A lot of dash gauges will "pin" to full scale if ground is lost or read high if badly grounded
There should be 2 grounds...one for the instrument lights daisy chained together and one for the spedo itself Just something to check

[dbbob]

I have the same story ,2002 38 ft monaco windsor ,but my tires were changed with larger 22.5 it was off about 15 mph ,any how being me i said i can fix it ,so i took the dash out found the dip switches but their are 12 not 10 like others ,I did fix it, it took about 20 stop and change number and try again I'm about 1 mph off so i say good I went from 20 under to 40 over ill tell you how if you need , and you need a gps or someting to do it ....bob