Speedcal Calibration help!!!

When I installed the built '03 Cobra IRS in my Bullitt, there were FRPP 4.10's installed in the carrier which was awesome because I wanted 4.10's and was going to get them installed regardless.

Anyway, I bought a used Brothers Performance Speedcal from a respected member on Corral, and installed it last week. I checked out Dallas Mustang's Speedcal chart to see where my dipswitch settings should be set, and took the car around the block. The speedo worked fine, but was about 10-15 mph off. I double checked all my wiring, and my dipswitch settings, then called Dallas Mustang. He suggested I take a 10 mile ride and clock it with my trip odometer as well as my GPS, then call him back with the difference. It was way off. I spent about an hour combined time between many phone calls and trial dipswitch settings, and none of them worked.

I guess my question is, who has 4.10's and what are you dipswitch settings? He assured me that the Brothers Performance unit was the same as the Dallas Mustang unit so thats not the issue, and I know my wiring is correct because he even said if one wire wasn't right, there would be no movement in the speedo at all. I don't wanna be putting excess miles on the car that aren't real and I really want this fixed!!

wmburns said:

The 96-98 Model years use a VSS sensor. The 99-04 Model Years use an OSS sensor. The sensors are different and the outputs are not compatible with each other. The type of sensor used needs to match the transmission harness and PCM.

Normally a Speedcal is used to install a OSS style transmission in VSS style car.

For a 99-04 Model Year car with a OSS style transmission already installed, the gear change can be handled with a PCM update. This method of updating rear end gears is vital in an automatic application for proper automatic transmission operation.

Are you sure the Speedcal unit you have is compatible with your MY?

What percentage is your speedometer off by?

Click to expand...

Hmm, to be completely honest, I don't know what my "MY" is. I would say the speedo is probably 5-10mph SLOW right now. It currently has the "2" and "7" switches in the up position and the rest down.

I had them in the position that Dallas Mustang says on their website from 3.27's to 4.10's, did the 10 mile drive, and the trip odometer said 16.4 miles traveled according to the 10 miles recorded on the GPS. I then called Dallas Mustang and Justin their Speedcal tech suggested putting "1" and "7" in the upright position and the rest down. This cause it to be MUCH higher. I was doing maybe 50ish according to the speedo when I was really doing about 15-20mph.

Again to be honest, I don't know that much about the 99+ models since they are much more electronically controlled than my old '95 which I had for years.

How would I know if the Speedcal is compatable? Brothers Performance doesn't even sell them anymore so I can't even call them to ask. I know for a fact its the same unit as the Dallas Mustang one.