I'm having difficulty getting my speedometer adjusted to read correctly.

I'm using Tunercat's Speed Calibration tool.

My question is: I've replaced the read end with a Strange 12 bolt rear end with 3.73:1 gears. It uses the stock driveshaft but a different rear u-joint. The rear u-joint has bigger caps for the rear end than the driveshaft. Would the Pulses per Driveshaft Revolution is different than the default stock 17 pulses per revolution?

 

It's been a while since I have used tunercats, can you take a pic of the screen that you are making adjustments and upload it here? If I had my laptop with me I would look at it myself lol.

 

It will be tonight or tomorrow before I can, we're on a trip.

Tunercat allows one to use tire size/tire diameter/rotations per mile as options. One can also set for auto/manual and input rear end ratio. The default is 17 pulses per driveshaft rotation which can be changed. Finally one can input observed speed (the speedometer reading I assume) and the actual speed (as per gps) which is what I normally do. All options give different calculations to apply.

Thus I was wondering if the driveshaft revolutions per rotation might be affected by the rear end and rear u-joint or if it's set at the transmission tail which is stock.

 

Here's a screenshot of the Speed Calibration Tool in Tunercat. It's pretty straightforward. I've been using the Speed Error method lately. #ad

 

Yeah that's what I used as well and it was pretty close just doing the rear end and tire size. How far is it off?

 

It's reading 88 when I'm doing 80.

 

Have you tried the speedometer scaler? I would try moving it one way or the other and see which way it moves you and then fine tune it from there.

 

so i thought i would share these numbers for the hopes someone makes a sticky or something to help with little tunes
so these are the numbers you need to put in your speedo tune program if you have this setup
255-50r16 tires
auto transmission
95z28
swapped in 3.42 gears

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these numbers will get your speedo dead on i used my GPS speedo and got it dialed right in .
hope this helps someone else .
Now pretty much just the top 3 boxes were making a difference in the speedo when i was playing around.
I found the 3rd box was the most important to move but only go up or down one full point at a time up raises if your under the correct speed and down lowers the speed.
thanks for reading .

Z is right if you adjust the speedo scaler scan tool number and for your speed 80 being 88 i would raise it 2 numbers so if its 43 go 45 or 55 go 57 you get my point

and yes i know i have diff gears and tire size but in the program the 3rd box is the most important and it doesnt care about your tires or gears it scans revolutions and going up or down a number or two you can dial in your correct speed

 

Thanks for the input guys. I've not had an opportunity to try some of the tips. Hopefully this holiday weekend I can get it dialed in.

 

Finally took time to work on adjusting the speedometer. I got it within 2-3 mph of my gps reading so I'm gonna be satisfied with that though my OCD wants it dead on. Thanks for all the suggestions.