So as my trek into Jeep repair continues, I've got a new issue. The speedometer is wrong by like 10 or 15 MPH or so. Now, this Jeep (a '94 Wrangler YJ) was in a pretty bad accident a while back, and had a lot of repair work done to it... after which, the speedo started reading incorrectly. I haven't learned anything about the speedometer system on a Jeep yet, though I have seen that it's electronic, so I'm hoping the manual (when it arrives) will give me details on recalibrating it, but here's my concern... it dawned on me that perhaps the rear end was swapped out as a part of the repairs (entirely possible), and that the new one that was put in, for some reason, had a different gear ratio and that's causing the massively incorrect speedo readings. Now if this is the case, that'd be just fine unless the gear ratio in the front differential did not match, correct? It seems to me that if the front and rear differential gear ratios do not match up, engaging 4WD would quickly break something if you were to drive very far on anything but the loosest of gravel.
I don't have a way to ask the repair shop if the rear differential was changed out in any way, and the normal trick of rotating the wheels while the vehicle is elevated and counting the rotations of the driveshaft doesn't seem to be working as the differential is a bit too loose for that and it just spins the other wheel in the opposite direction (turning the driveshaft and counting wheel rotations isn't working either). Is there any sort of trick to figuring out from casting marks or ratio tags on the differential housings what the internals might be? Or if it's the same assembly that came with the vehicle originally? Judging by the amount of yuck on the housing I'm guessing it's the original, but then that doesn't explain the huge speedo discrepancy. Maybe someone out there knows how the speedo system well enough to explain how this could happen. Thanks in advance for any suggestions!
Bryan