auto overdrive ratio question

[Mhannink]

ok well i have a bit of a freak truck its a 99 24v but i have the newer 48re auto my problem is i went to get the speedo corrected but the speedo still isnt right it seems to be off about 5mph at 65 so im really doing 70. im wondering since the tire size is right in the computer is the overdrive different in the 48 vs the 47? also the easiest way to get this correceted would be appreciated thanks. matt

 

[fox]

They are the same ratio.

. 69

 

[Mhannink]

what might my problem be then

 

[steved]

ECM programmed for other size tires??

steved

 

[JoeBioDiesel]

Maybe the Vehicle Speed Sensor makes a different amount of pulses/mile on the two transmissions. Any chance you have the old trans and can count the teeth?

Joe

 

[steved]

Maybe the Vehicle Speed Sensor makes a different amount of pulses/mile on the two transmissions. Any chance you have the old trans and can count the teeth?

Joe

Because the low speed is taken from the ring gear in the rear differential, there should be a jump in the speedo at around 30mph.



IIRC, the 99s use two speed sensors, one in the trans and the other in the rear diff.



steved

 

[Mhannink]

the comp has been reprogramed and there is no jump in the speedo that i can see