Has anyone run a GPS to check their speedo?

[scrambled]

I just bolted on my 37 goodyears on Trail Worthy Fab recentered humvee wheels (awesome!!!!) and went for a spin with my Tomtom to check the speedo. I am only 3 MPH faster than the needle at 45. How far under was I before with the little 235/85s?

Has anyone run a GPS to verify the speedo in their 1008? I am too lazy to swap the tires back over and go for a spin.

Thanks,
Travis

 

[donalloy1]

never been down that road. sounds like fun though! my speedo is all over the place due bad cable i think. cant wait to get steady reading. dml2 sends...

 

[K9Vic]

My speed reading is off and slowly increases as I go faster per my GPS speed. When I am going like 65 my speed shows as about 85, but when I am going like 30 it shows at about 38. I have a brand new cable, so I suspect the speedometer is what is bad. I have an extra one, but the miles is 54k and my truck only has 31k. So when I am on the highway I just use my GPS for my speed.

 

[wikallen]

never been down that road. sounds like fun though! my speedo is all over the place due bad cable i think. cant wait to get steady reading. dml2 sends...

The speedo gear in the transfer case on my 88 suburban was plastic. I assume it is the same on the m1009. Easy to replace. Take the cable off the transfer case, pull the end off the transfer case, slide the gear off, and slide a new one on.

 

[rnd-motorsports]

Just put in a power outlet to run tomtom I have 750 / 16 daytom tires and was shocked to see speedo is about perfect with the tom tom very cool!

 

[hovenga67]

I have and with my 315/75r16 (basically a 35) my speedo is dead on according to the gps. So evidentally it was off before hand.
Brent

 

[91W350]

My speed reading is off and slowly increases as I go faster per my GPS speed. When I am going like 65 my speed shows as about 85, but when I am going like 30 it shows at about 38. I have a brand new cable, so I suspect the speedometer is what is bad. I have an extra one, but the miles is 54k and my truck only has 31k. So when I am on the highway I just use my GPS for my speed.

It should be directly proportionate to your speed, say it reads 66 on the speedometer and it is actually running 60, at half that it should be 33 and 30. Ten percent in this example. There are some exceptions though, if the cable is binding and snapping forward, the needle will read much higher than speed as it is kicked up by the faster pulses.

All three of mine read faster than they are actually running. It may be where some of the M1009 guys are saying they run 75 and the engine sounds fine, because mine are both way off. Good for the 6.2, let them think they are running 75-80 while it is quietly humming away at a much lower rpm.

Oddly though, the odometers are very close. On my M1008 it takes about 35 miles to gain a 1/10th of a mile on the Interstate. When I came home from Utah, I knew my speedometer was way off, but I could not find error in my odometer.

Glen

 

[Shop Rat Fab]

Here are the results of the lifted trucks I've had with bigger tires:
33 inch tall, speedo read about 3MPH slower than I was going
35 inch tall around 5MPH slower
37 inch tall aound 6-7 MPH slower
I never regeared the axles or speed gear just left them alone and just added larger tires. Keep in mind the odometer will register lower miles than you actually travel.

 

[Jimma]

No but I have thought about doing it on my deuce. Just have not done it yet.

 

[ohfisherman]

7mph off at 65. 84 m1009 with 31x10.5 tires. shows 72 and i am really doing 65.

 

[AndrewH]

I run a gps in the M1009 most of the time. The speedometer has gotten an additude and onlt works when it wants to. Usually reads about 8 percent slow. Did a 150 mile trip this weekend and the odometer difference between the GPS and truck was about 10 miles. Completly stock truck. Except the 12V outlet...... And winch... and...