i have a speedometer that reads slow....43 mph = 55, 48 mph = somewhere around 60...the dodge guy ask if i had changed tire size...they are different ....these are 245/75/16....he says the sensor on the transmission (5 sp 4x4) might be bad.......but it reads........it doesn't bounce and is consistant with the speed just slow.......question if it is electronic with the sensor...isn't the sensor going to read the rpm that the trans is turning internally.....if you change tire size you are going the same speed only the drive line is turning more rpm or less rpm to get the same speed......i guess what i am asking is if the sensor ...is...reading rpms is it bad......the dodge mechanic wasn't sure how to get it to read correctly and is going to have to research it as this is an old 92 model.....

is there a gear in the trans that runs off the drive line to compensate for tire size ...like the old cable speedometers had for this trans..........any information or coments are appreciated.....you hate to buy unneeded parts they get awful expensive........ie bought a crankshaft sensor for $100 and it turned out to be the computer...........not the sensor ....


HELP......joebuzz

 

the 92s still used cable driven with a gear with an electronic pickup for the OD. all you'd have to do is swap gears or put stock tires back on. if you ran a taller tire and the tranny turned the same rpms. you're going to move faster because the tire can cover more ground. all the sensor does is read the output speed of the tranny or Tcase. if you throw taller tires on it the truck will move faster than what the Tcase output is there for causeing the senser to read slower than what the truck is moving. if you run shorter tires the truck will move slower but since it takes the tires more revolutions to cover the same amount of ground the speedo will read faster than what the truck is actually moving..the sensor won't read ground speed. just whatever the output shaft of the Tcase or Tranny is putting out.

 

thanks for your comments................i will probably crawl up under the truck this weekend and count the # of teeth on the gear......i only hope dodge continues to have the gears where you can get one..........best i can tell the speedometer is about 20-22% slow....from the actual speed of the truck.............so i count teeth and get one that has the closest to 20% less teeth.....ie if the gear has 15 teeth i need one with 12.........

dodge seems to obsolete parts faster than ford does .....i could still get parts for my 84' ford and they (dodge) had discontinued the computer for my 92.....i had to get my own remanufactured....where is a good source of dodge aftermarket parts.....ie L&m,jc whitney,local junk yard........................joebuzz

 

The other thing you can do is get a speedo cable reducer box made, but it'll cost you about $100 or so. It just screws inline with the speedo cable and adjusts the cable RPM to be accurate. The best way to get it accurate is to pick a milepost on the freeway, set your trip meter (if you've got one), then drive exactly 10 mileposts and record your tripmeter distance. Repeat going the other way to double-check (sometimes they're not accurate). Then you've got your factor. I went from a 235/85r16 to a 35x12.5x16.5 and instead of being 10% off it was really only about 5%.

 

What are you driving? A 92 what with what engine? If you need help with finding the gear, lete me know. Stevo

 

hey guys...........it is a 92 dodge p/u with the 5.9 cummins....5 spd manual.....4x4......i crawled up under the truck and looked to see what i had and didn't find a cable..........did find an electronic sensor......i took it out and there is no gear just a little shaft that looks like an allen wrench.....so i am back to square one.............help!!!!...............joe