Installing YellowBox Speedo Box
- Thread starter 7TH_SIGN
- Start date
Contacted Unitrax via email. But until I hear back....
Ok, need some help.
My Viper's speedo has been off since I purchased it. I confirmed this via satellite navigation. At 50mph of actual traveling speed, the gauge would read approximately 10mph faster then actual speed of travel. So at 50mph it reads 60mph.
I couldn't believe that a car with only 805 miles had the stock rear end switched out. So I started looking over the car to try and maybe find a calibration box that may have been installed. Did not find it by the PCM.
Last night I decided to take the front dash out and inspect behind it. Well I found it! It was installed behind the speedo gauge on to the harness that connects to the gauge harness.
I don't know why they didn't install it at the PCM and why they would hide it somewhere you would have to remove the dash to adjust?!?! So I relocated it behind the driver side knee panel.
The switches where obviously wrong, so I did some research and found the switch sequence for 3.55 gears (assuming thats what the car has). The speedo is now off by only 5mph. So at 50mph of actual vehicle speed travel, it reads 55mph. Close but not perfect and I'm OCD.
The box appears to be the old Unitrax RB2120 calibration box. Does anyone know what switch sequence I need? Or maybe what gears could be in the car?
Thank you.
Here is a pic of the unit when I found it.
Ok, need some help.
My Viper's speedo has been off since I purchased it. I confirmed this via satellite navigation. At 50mph of actual traveling speed, the gauge would read approximately 10mph faster then actual speed of travel. So at 50mph it reads 60mph.
I couldn't believe that a car with only 805 miles had the stock rear end switched out. So I started looking over the car to try and maybe find a calibration box that may have been installed. Did not find it by the PCM.
Last night I decided to take the front dash out and inspect behind it. Well I found it! It was installed behind the speedo gauge on to the harness that connects to the gauge harness.
I don't know why they didn't install it at the PCM and why they would hide it somewhere you would have to remove the dash to adjust?!?! So I relocated it behind the driver side knee panel.
The switches where obviously wrong, so I did some research and found the switch sequence for 3.55 gears (assuming thats what the car has). The speedo is now off by only 5mph. So at 50mph of actual vehicle speed travel, it reads 55mph. Close but not perfect and I'm OCD.
The box appears to be the old Unitrax RB2120 calibration box. Does anyone know what switch sequence I need? Or maybe what gears could be in the car?
Thank you.
Here is a pic of the unit when I found it.
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I would contact Unitrax. I wonder if your car has 3.73's in it? if you adjust to that ratio it may be close enough. Also, assuming stock wheels and tires, sometimes you can get a little bit of variation between wheel and tires sizes.
Called Unitrax today and they were a BIG help. Extremely nice and informative. I got a couple different dip switch sequences I am going to try. They told me I may have 3.45 gears. I will try the sequences out and report back.
Devin at Unitrax is the man! I have never seen customer service like he provided me. I didn't even purchase the product from him and yet he treated me like his own customer. He dug through his old documents (as this device in from the mid 90s) and found the needed information. Who ever the previous owner got to do the install, it was incorrect. With Devin's help, I was able to install it correctly.
Back when not much was known on the Viper when they were first released, the speedo recalibration box was installed right behind the speedometer, splicing in to the actual gauge instead of the PCM. In my case, the unit was not fully installed, why? I have no idea. I know the unit was purchased from a shop named TNT Motorsports as I found papers in the car with their name on it, the company is no longer in business.
Finished the install. Devin provided me a couple dip switch sequences to try out to get the mph correct. On the very first sequence which was 1,3,4,6,7 turned on and the rest to off, I confirmed the speedo to be dead on now! This confirmed that the prevoius owner had the stock 3.07 gears replaced for 3.55.
Mission accomplished.
For archive purpose should anyone else run in to this issue,
Unitrax RB-2120 was produced in the 90s and is no longer made. For 3.55 gears, the correct switch sequence is 1,3,4,6,7 on.
If you input those numbers and the speedo is still off, you can try 1,2,3,4,6,7 on....... or 2,3,4,6,7
Also I am now an expert at removing the dash since I had to do it three damn times to fix this issue and I hope never again.
Back when not much was known on the Viper when they were first released, the speedo recalibration box was installed right behind the speedometer, splicing in to the actual gauge instead of the PCM. In my case, the unit was not fully installed, why? I have no idea. I know the unit was purchased from a shop named TNT Motorsports as I found papers in the car with their name on it, the company is no longer in business.
Finished the install. Devin provided me a couple dip switch sequences to try out to get the mph correct. On the very first sequence which was 1,3,4,6,7 turned on and the rest to off, I confirmed the speedo to be dead on now! This confirmed that the prevoius owner had the stock 3.07 gears replaced for 3.55.
Mission accomplished.
For archive purpose should anyone else run in to this issue,
Unitrax RB-2120 was produced in the 90s and is no longer made. For 3.55 gears, the correct switch sequence is 1,3,4,6,7 on.
If you input those numbers and the speedo is still off, you can try 1,2,3,4,6,7 on....... or 2,3,4,6,7
Also I am now an expert at removing the dash since I had to do it three damn times to fix this issue and I hope never again.
vancouver-gts
Viper Owner
I got the Unitrax calibrator through JonB in 2011. Previous owner swapped the gears to 4:10 in my 99 GTS in 2001. Bought the car in 2010 so for ten years my speedo and odometer was way out of whack, raking up excessive miles on the odometer and inside the ECM. Not planning on reselling the car but bugs me that it wasn't corrected right away. Wonder if the newer versions of Unitrax units have dip switches too because it seems to be still out of a few miles going faster, according to GPS.
Are you saying your current calibration box is not adjustable? It should have the switches on the inside.
That's what motivated me to get it fixed. With the stock wheels and tires, my car was off by 10mph! With my 18" CCW wheels and drag raidals, it was off by 5mph. Luckily my car only has 1,500 miles on it so the mileage isn't that far off. The bad thing about my setup is that because the calibration box is connected to the speedo and not the pcm, the pcm is recording 5mph off but at least the mileage on the speedo is correct. I plan on getting an AEM EMS one day anyways.
Devin informed me that Unitrax now makes a new unit that has a digital display on the outside and dip switches on the inside. I can't remember what the digital readout is for but if I remember correctly it is the set gear ratio from the dip switches.
Unitrax, Devin and Jerry.
These guys are a class act and understand any and everything about Viper gearing and LSD's. I have used them since 1994.
These guys are a class act and understand any and everything about Viper gearing and LSD's. I have used them since 1994.
vancouver-gts
Viper Owner
Not saying the box isn't adjustable. When I ordered it, Jon asked me what gear ratio I have and Unitrax set the dip switches for it as I understood it. I didn't open the box when I spliced it into the ECM but now I'm thinking of opening it and see if I could change the switch settings with the right combination. Just ran the car tonight with GPS along and the speedo reads about 4 miles faster .
My tires are almost new so the tire's diameter is right.Not saying the box isn't adjustable. When I ordered it, Jon asked me what gear ratio I have and Unitrax set the dip switches for it as I understood it. I didn't open the box when I spliced it into the ECM but now I'm thinking of opening it and see if I could change the switch settings with the right combination. Just ran the car tonight with GPS along and the speedo reads about 4 miles faster .
Oh man that's an easy fix. Yeah just pop the box open and adjust the switches. Give them a call and they will give you the correct dip switch sequence.
vancouver-gts
Viper Owner
Talked to Devin today. He suggested my switches should be turned on 3 6 for 4:10 ratio. If it isn't try setting at 1 4 5. Opened the box a few hours ago and found the dip switches turned on 1 2 4 7. I also have a diff box from yours since there are two dip switches in the box. One marked as test switch with four fingers with all of them turned off. The main switch has 9 fingers, yours have 8. I've tried 3 6 and 1 4 5 as Devin suggested and the speedo wouldn't move at all. I've changed the setting from the original setting of 1 2 4 7 to 1 2 3 7 and it seem to changed the calibration somewhat to be closer,out by only 2 miles. So it isn't cut and dry hence Devin wants me to call him back with results.
vancouver-gts
Viper Owner
Got two numbers from Devin to try. Switch now set to 1-2-7 , speedometer is dead on with GPS.Thanks Devon.
Got two numbers from Devin to try. Switch now set to 1-2-7 , speedometer is dead on with GPS.Thanks Devon.
Awesome brother! Devin does it again! Glad you got it perfect now.
