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Originally Posted by lee
Could someone explain how this error could happen by a swap?
My understanding of the speedo setup is that a gear is driven from the right side axle, which in turn does some magnetic signaling that gets decoded and sent on to the speedometer.
My point is the speedo, since it's driven by axle revolutions, should register exactly the same (good or bad) before & after, regardless of the ratio installed.
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You got me thinking on this 'cause on a typical Front engine/rear drive car, the speed sensor senses transmission rotations and is independent of the final drive ratio. I did some research and found a copy of a tech document concerning our 4eat transmissions published by Subaru at this site
http://www.ravensblade-impreza.com/t...ssion/4eat.pdf I'm now quoting from this document:
Vehicle Speed Sensor #1
Vehicle speed sensor #1 is mounted to the transmission and is basically electrical governor pressure. It is used to detect vehicle speed and it effects shift points, lock-up, and line pressure. In FWD transmissions the speed sensor reads parking gear rotation at the front output shaft. In AWD transmissions it senses the transfer clutch drum rotation at the rear output shaft.
Vehicle Speed Sensor #2
Vehicle speed sensor #2 is built into the combination meter. In FWD units, it is used as a back-up for speed sensor #1. In AWD units, it is used as the front output shaft speed sensor.
If I'm reading this doc correctly, #1 takes a reading from the rear output shaft while #2 takes a reading from the front output shaft before the front differential. I took a look at the wiring diagram for my 1992 SVX and it shows that the speedometer is driven by Vehicle Speed Sensor #2. Neither speed sensor would be affected by final drive ratio, so speedometer readings would naturally be inacurate after changing the final drive ratios.
I emailed the tech guy at
http://www.terf.com/SpeedChangerPage.htm. He indicated that the SpeedChanger box would work with the Subaru electrical system, but I'm concerned that if it wasn't wired into the correct spot on the harness it could cause the TCU to think that the front wheels would be turning at a different speed than the rear and cause a whole pile of problems.
Any Thoughts?
Steve