Quote:
Originally Posted by huck369
OK, Wheel size isn't exactly what I was saying, but thought that would get the point across...
The Circumference of the tires that the tranny came with will be the difference, because all trannys DO NOT turn the same output at the speed sensor location, as the Subaru Manual Trannys are still set up to drive a cable driven speedometer which they had up untill the mid 90's, and there is a gearset inside the tranny that is matched to the final drive ratio and the tire circumference Do yes, he's running the same tires before and after his swap, but the TRANNY is NOT running the same tires it was set up for, the Speed sensor just converts the rotational output of the transmission into a digital signal so no matter WHAT speed sensor you install it will not read correctly, there are aftermarket setups that adjust the digital signal between the speed sensor and the speedometer, but without that you either need to find lower profile tires to try to match the transmissions original tire size (and if it were a tranny set up for 13's you'd probably have to run just the 16" rim with a strip of rubber around it  ) or you would have to open up the transmission and install a different speedometer gear drive set.
A bit of a plus is the SVX (as most cars) stock the speedometer is off to the slow side, saying you are going faster than you really are...so some tranny swaps actually work out to a more accurate reading, some make it worse,,, |
I was under the impression that the speed sensor on the tranny simply read the rpm of the half-shaft. That leaves the actual speed calculation up to the interface between gauge cluster of the car and the sensor. So, for example, the transmission and can be identical between a Legacy and an Outback, but the Outback's gauge expects the larger tires that come on the car, and therefore the speedo reads correctly on both cars with the mechanically same transmission.
I figured, the OP's problem was simply using the wrong speed sensor, which reports an incorrect rpm to the cluster, resulting in being off by 10 mph. If the issue were related to diff ratios and tire sizes, then the speedo wouldn't be off by 10 mph across the board, it'd be off by some percentage of the actual speed, like off by 2 mph @ 30 mph, 5 @ 60 , 10 @ 90, etc.
I was under the impression that when doing a 5MT swap, if you simply re-use the SVX's speed sensor in the 5-speed, your speedo is as accurate as it ever was before the swap. Having not done a 5MT swap myself, I can't really claim to know what I'm talking about, but I'd be surprised if there were mechanical differences between every transmission related to the size of the tire that was expected to be attached to that transmission. It would be so much simpler just to draw the lines on the gauge in different spots and/or use a different speed sensor.