Originally Posted by
handyman43358
It is possible that by changing your fluid, you could have disturbed many particles of crap inside the tranny that had been sitting calmly, if the fluid has a lot of miles on it. I can't tell you how many times I've seen people rack up 120,000 miles before they change the transmission fluid, and then after they do it, they start having problems. I'm not real sure about your 91, but I know 92 and on uses a sensor in the rear to determine speedometer readings, but I also think that it might use a sensor mounted on the side of your speedometer cable close to the tranny to determine speed there also. Not real sure, but that may be what's causing your problem.
he's right about the tranny fluid,if there is a lot of miles on the tranny and it hasn't been changed,Iv'e seen the same thing, people change there fluid and the new detergent in the new fluid cleans all the build up away and in no time it starts to slip or the clutches freeze up and it will try do go foward and backward at the same time,even in nuteral,and as for the speed-o-meter sending unit,it on the top of the rear end housing with a two wire plug,but most of the time when the speed-o-meter don't work the tranny shifts up and down really hard and all crazy,because the vehicle's ecm don't know what gear to shift to because it don't know how fast your going.