Speedometer jumping

From : james

Q: my dad has a 96 2500 with the cummings and has had a problem with the speedometer jumping below and above the actual speed. he was told that it would cost around $800 to repair. this quote was from the local dealer. anyone know if this amount is accurate it sounds high to me. james .

Replies:

From : tom lawrence

my dad has a 96 2500 with the cummings c-u-m-m-i-n-s speedometer jumping below and above the actual speed. he was told that it would cost around $800 to repair. this quote was from the local dealer. anyone know if this amount is accurate it sounds high to me. sounds pretty high to me as well. usually this is a sign of a bad sending unit. on the 96 its in the tailshaft of the transmission if its a 2wd or at the back end of the transfer case if its a 4wd. the unit is a $40 part and takes all of 5 minutes to change. now if its not that it could be a bad instrument cluster. just the circuit board is about $90 while the whole unit is close to $300 junkyard would be a good approach in this case. again the most common cause is a bad sending unit. id start there. .

From : james

pardon me... cummins. i drive a 79 trans am with a olds 403. i am not up to date with todays vehicles. still living in the past. my dad has a 96 2500 with the cummings c-u-m-m-i-n-s speedometer jumping below and above the actual speed. he was told that it would cost around $800 to repair. this quote was from the local dealer. anyone know if this amount is accurate it sounds high to me. sounds pretty high to me as well. usually this is a sign of a bad sending unit. on the 96 its in the tailshaft of the transmission if its a 2wd or at the back end of the transfer case if its a 4wd. the unit is a $40 part and takes all of 5 minutes to change. now if its not that it could be a bad instrument cluster. just the circuit board is about $90 while the whole unit is close to $300 junkyard would be a good approach in this case. again the most common cause is a bad sending unit. id start there. .

From : nirodac

pardon my ignorance but from this post am i correct in assuming that the flex cable that used to drive the speedo in the older vehicles has been replaced by an electronic version that gives the same failure indications. i still live in the past were i can fix anything on my 75 d200 at a reasonable price. ray my dad has a 96 2500 with the cummings c-u-m-m-i-n-s speedometer jumping below and above the actual speed. he was told that it would cost around $800 to repair. this quote was from the local dealer. anyone know if this amount is accurate it sounds high to me. sounds pretty high to me as well. usually this is a sign of a bad sending unit. on the 96 its in the tailshaft of the transmission if its a 2wd or at the back end of the transfer case if its a 4wd. the unit is a $40 part and takes all of 5 minutes to change. now if its not that it could be a bad instrument cluster. just the circuit board is about $90 while the whole unit is close to $300 junkyard would be a good approach in this case. again the most common cause is a bad sending unit. id start there. .

From : tom lawrence

pardon my ignorance but from this post am i correct in assuming that the flex cable that used to drive the speedo in the older vehicles has been replaced by an electronic version that gives the same failure indications. correct. up until 98 the output shaft either trans or transfer case drives a pinion gear in the sending unit which in turn generates an electrical signal that tells the computer or the instrument cluster directly how fast the vehicle is moving. this gear is what people swap out with slightly larger or smaller gears to compensate for changes in tire size. starting in 98 the vehicle speed comes from the rear wheel speed sensor originally used solely for the anti-lock brake system. this is a magnetic sensor that sits very close to a tone ring looks like a gear with many teeth thats bolted next to the ring gear in the differential. the teeth of the tone ring passing close to the sensor generates an electrical current. the computer counts the number of these pulses and can determine rear axle rpm. by applying the tire circumference to that measurement the vehicle speed is calculated. i still live in the past were i can fix anything on my 75 d200 at a reasonable price. and with a reasonable set of tools usually consisting of 6 sockets and wrenches and maybe a flat-head screwdriver. yeah sometimes i miss the past too .

From : rm

so my 99 1500 with 4.10 axles from a 3500 on 36 tires must be confusing the hell out of it! starting in 98 the vehicle speed comes from the rear wheel speed sensor originally used solely for the anti-lock brake system. this is a magnetic sensor that sits very close to a tone ring looks like a gear with many teeth thats bolted next to the ring gear in the differential. the teeth of the tone ring passing close to the sensor generates an electrical current. the computer counts the number of these pulses and can determine rear axle rpm. by applying the tire circumference to that measurement the vehicle speed is calculated. .

From : garnie garnieatsaskteldotnet

hey buddy. suffered the same thing for years on my 1991 diesel. as well my speedometer reads fast by about almost 5 mph. i had dodge replace the sender assembly in the mid 90s and i ended up with a still-jumping needle and the speed was still reading high. i finally figured out the jumping needle was due to a poor electrical connector on the sender. sooooooo every once in awhile id crawl under and wiggle it around and it would work good for a month or an hour. finally had dodge replace the connector and not a problem now in about 16 months the contacts are very cheap and flimsy. i never found out why the speed reads fast ... i even did the math years back from the crank to the rear tires to see what the rpm should be. although i forget what number i came up with it didnt match the tach. now its been so long since the tach crapped out i dont recall exactly but i think it was running around 1750 +- at a real 60 mph. timewise at a guage reading of 60 mph it was taking about 64 seconds to go one mile 56.25 mph. go check yer connecter fella. garnie on thu 18 sep 2003 163427 -0400 james jrhx@bellsouth.net wrote my dad has a 96 2500 with the cummings and has had a problem with the speedometer jumping below and above the actual speed. he was told that it would cost around $800 to repair. this quote was from the local dealer. anyone know if this amount is accurate it sounds high to me. james correct at and dot in the address to reply. .