speedo not reading right... blowing my mind D:
09-25-2012, 09:07 AM
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speedo not reading right... blowing my mind D: okay i swapped a 3 channel open diff rear for a 4 channel posi. my car came with posi 3.23's i looked up the RPO codes... and the car i pulled the rear from had the same codes. except it had TCS. i expected the 'brake' and 'abs inop' lights on due to 4 channel system, but my speedo its reading about 1/2 the speed it should (stays at 0 until about 40 mph and ive got it to 35 so far which was about 80). now, given one of the rear abs speed sensors is out because i damaged it trying to pull the c clip so i could replace the axle seal. i assumed that would be a possibility on throwing off the speedo. but have almost ruled it out because i unplugged both rear speed sensors assuming it would make the speedo dead or maybe right. but it stayed the same as with both sensors plugged in and one working. so the only thing i can think of to finish ruling that option out is to go have the computer flashed and take off all the codes, and while keeping both sensors in the rear unplugged, see if the speedo then re-calibrates itself. but another possibility is that when pulling the rear, the driveshaft fell out. and i slid it back up in. idk if it has to go a certain way? and is there anything on the rear of the transmission that is vulnerable that i could have hit or something? also the last possibility to me is the actualy gauge itsself. i took out my cluster last week because i got new needles. all other gauges work just fine. but do you have to be super careful taking off and putting back on the needles? i could have maybe put it on at a different angle and thats why its off 35-40 mph? if anyone could rule out any of these possibilities for me or confirm one that be super helpful!
09-25-2012, 08:18 PM
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Don't know about A4s, but when I changed the rear in my M6 Camaro, I knocked the speed sensor plug loose from the tail of the trans while installing the torque arm. When I went to drive it later, the speedometer didn't work at all, and the mechanism that is supposed to lock you out of reverse during normal driving didn't work-found that out the hard way 
09-26-2012, 02:02 PM
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Don't know about A4s, but when I changed the rear in my M6 Camaro, I knocked the speed sensor plug loose from the tail of the trans while installing the torque arm. When I went to drive it later, the speedometer didn't work at all, and the mechanism that is supposed to lock you out of reverse during normal driving didn't work-found that out the hard way
09-26-2012, 11:10 PM
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well i got under the car and inspected really good. i dont think i would have hit the sensor... and technically its still works. it climbs smooth just as it should only about 35-40 mph to what it should. and im no expert on sensors... but if it were somehow damaged i would assume it wouldnt work at all... im starting to think its the needle itself. if it were how would i fix that? take out the gauge cluster and start the car placing the gauges back in without the face and pin the needle at the speed i know it should be reading?
