Transmission (Auto)

The revolution sensor is nothing more than a speed sensor. There is a toothed part that is moving past a stationary sensor. The sensor can count the teeth as they pass. From this the computer is able to determine the speed of the revolving shaft.

What color is your fluid? If the band wore out, the fluid will turn darker from the friction dust that was worn away. Transmission shops should be able to put a scan tool on your vehicle, and determine if that band is applied or not, Possibly read the signal from the revolution sensor. good luck.

Thanks Bod c for the reply back. I thought there was a speed sensor and a revolution sensor. Double checked the Exploded view and i did see the Speed sensor. I think there is a check for the speed sensor and a revolution sensor but will have to go back and look. It is interesting but I checked the fluid when this happened and didnt see a change but I just check it after driving it around(my delivery truck) It is dark and there was gray matter on the stick.. UGH. This trany was rebuilt 100k ago. the last trany (original) lasted 169k.. But this trany had shifted hard from day one and never had engine braking. I found out why that was when doing the checks. was able to fix that. So you thinking its a band? and which one?? braking band on the forward clutch pack? or should I just rebuild this one again? The brake band behind the pump looks easy to replace. rebuilding the whole trany myself I dont think Id be comfortable doing. I did all the checks on all the electronics and all but the revolution sensor check out. had 1.5 volts with increased voltage as the car was moving but the book sez there should be 1.0 volt at 19 mph and should increase voltage as speed increased. I didnt know how the revolution sensor affected the shifting of the trany not going into 4th when it seemed it would affect all gears. But I am not an expert nor a trany guy even tho I have rebuilt a few older tranys and did some mods on a few. any help anyone?

I am not familiar enough to tell you all that you might need to know about your transmission. But, there should be a pressure tap that will allow the reading of most, if not all of the hydraulic components that are applied and released for all of the "gears" Do you have a good overhaul manual for the trans? One that will explain which clutches and bands are applied in each gear? If the same band that is used for engine braking is also used for fourth gear, that could be your whole problem. But if that fluid is that dirty, likely all of the friction components have worn, and it would be wise to do it once, do it right, and be done with it. The first thing I would suggest is to check the fluid pressure at the pressure tap that tells when the piston or band needed for fourth is applied.

It could be that because the speed sensor is not signaling sufficient revolutions, that all of the lower shifts were forced by the engine governor signaling the trans to up-shift. That could be the reason why there is no command to up-shift. It might up-shift if the engine reaches governed speed in third. This is not what I would want to try doing. Vehicle speed would be high.