tom1642 Posted February 9, 2013 Share Posted February 9, 2013 Speedometer Problem Not Working - Was having problem with speedometer not working , installed to sensor on the transmission and then the speedometer started to work but would not work until at leat going 40 miles per hour, below that was not working. Went to Mack dealer and bought new speedometer and installed with the dip switches on back of speedometer to exactly what was orginal. now the speedometer does about the same thing and you need to be going about 40 for the speedometer to register and miles per hour is not accurate . Looked at install manual supplied with new speedometer and did the calculation by the manual and changed the dip switches setting to the manual calculation, still nothing. checked and there is power to the speedometer , checked wiring connections and plugs and all seems to be fine. there appears to be no brokem wires. .PLEASE I NEED HELP TO SLOVE THIS PROBLEM Quote Link to comment Share on other sites More sharing options...
theakerstwo Posted February 10, 2013 Share Posted February 10, 2013 Pull the sensor out of the trans and lift up on the drive shaft and at the same time use a samll screw driver and go thru the sensor hole and see if you can turn the tone wheel on the yoke or shaft. If so then pull down and see why. Quote glenn akers Link to comment Share on other sites More sharing options...
57 bcr Posted February 10, 2013 Share Posted February 10, 2013 Thanks Glenn.I was just about to ask the same question as Tom did.A buddy has a '97 RD with the same problem.I told him last night ,I would ask someone on BMT,they'lll know! Al Quote IF YOU BOUGHT IT, A TRUCK BROUGHT IT..AND WHEN YOU'RE DONE WITH IT, A TRUCK WILL HAUL IT AWAY!!! Big John Trimble,WRVA Link to comment Share on other sites More sharing options...
tom1642 Posted February 12, 2013 Author Share Posted February 12, 2013 hello Glen thanks for the info , pulled out sensor and you can not turn the ring gear . i did notice a small acculmation of fine metal particles on the sensor magnet, cleaned and reinstalled and still no luck. went to the mac dealer here in florida and was told the ring almost never is a problem, and to repalce you have to buy the yoke assembly and the gear is pressed onto the yoke as an assambley. also rechecked all the electrical wiring. there are 5 lines to speedo, one is power , one is ground , one is for cluster light and the other two go directly to the sensor. all line schecked out ok. to go futher ran conunity check on the two lines to sensor and is perfect, also ran teat light from power to the two sensor lines to see if there was a short to ground. all wiring is perfect and all connections were cleaned and are making contact. so now i am reall confused and do not know how to fix this probem. any help is appreciated. note replaced new speedo and also sensor and no luck 1 Quote Link to comment Share on other sites More sharing options...
br549 Posted February 12, 2013 Share Posted February 12, 2013 roadranger or mack transmission, did the speedometer worked right before and this just started, Quote Link to comment Share on other sites More sharing options...
tom1642 Posted February 13, 2013 Author Share Posted February 13, 2013 hello the truck has a mack transmission. today i took out the new speed sensor to view the gear that is on the yooke, i believe called ring gear. it appears to be be ok and i tried with screw driver to see if i could move gear. the gear is attached sloid to the yoke , so is definetly turning when the truck is driven. i was thinking to attach multi meter with a spare connector i have attached to the speed sensor and see if it produces any current while i drive the truck. i have checked continunity on all wires and every thing checks out and also i checked for a grounded wire from speed sensor all is ok. i was looking at article on checking 2 wire speed sensor and when is working properly produces an ac current and you are suppose to be able to measure with mulitmeter, so i am going to try this tomorrow . the speedometer was working and just stopped. replaced with new speedometer and still i can not get the speedometer to work. i am totally baffled and do not know how to correct this problem. any help is much appreciated, sincerely Tom Quote Link to comment Share on other sites More sharing options...
57 bcr Posted February 13, 2013 Share Posted February 13, 2013 Yeah,Tom,my buddy's truck is doing the same thing.He said his gear was also not spinning when he put the new sensor in.Says it works fine for a few hours,then only reads about 20mph tops,for the rest of the day.He is also pulling out what hair he has left! Quote IF YOU BOUGHT IT, A TRUCK BROUGHT IT..AND WHEN YOU'RE DONE WITH IT, A TRUCK WILL HAUL IT AWAY!!! Big John Trimble,WRVA Link to comment Share on other sites More sharing options...
tom1642 Posted February 16, 2013 Author Share Posted February 16, 2013 finally fixed the problem today, after checking out all the wiring and connections everything was perfect. i took out the new speed sensor and decided to check the depth from the ring tone gear. much to my amazement the speed sensor threaded into the housing with finger preasure and then when it stoped as it was bottomed out to the ring gear. after checking the depth measure from ring gear to bottom of sensor there was an air gap of more than 3/8 of an inch. when i saw this i new this had to be the problem. the problem was the threads in the housing. ran tap into the threads until i hit ring gear, installed the new sensor and made adjustment to bottom out sensor on ring gear and then back off a half turn. started the truck and took for a ride and speedometer works perfect. the problem was too much air gap between the sensor. the threads in the hosuing were not letting the sensor go in all the way. thank god i found the problem was driving me crazy. Quote Link to comment Share on other sites More sharing options...
BrandonG Posted January 24, 2020 Share Posted January 24, 2020 (edited) @tom1642 Can you take a picture of where your speed sensor is, i have the same problem with the speedometer i haven’t worked on a Mack before and I just don’t want to mess it up thanks Edited January 24, 2020 by BrandonG Quote Link to comment Share on other sites More sharing options...
alex g Posted January 24, 2020 Share Posted January 24, 2020 Speed sensor should be located on out put shaft of rear of transmission Quote Link to comment Share on other sites More sharing options...
BrandonG Posted January 25, 2020 Share Posted January 25, 2020 Thanks Quote Link to comment Share on other sites More sharing options...
Khall Posted August 19, 2021 Share Posted August 19, 2021 Why do I lose engine RPM and power when my speedometer quits working periodically? Shut engine off for a few minutes and it clears up for a while. Quote Link to comment Share on other sites More sharing options...
Vmac3 Posted August 21, 2021 Share Posted August 21, 2021 On 8/19/2021 at 5:08 AM, Khall said: Why do I lose engine RPM and power when my speedometer quits working periodically? Shut engine off for a few minutes and it clears up for a while. I'm not sure what type of vehicle you have, but generally speaking, if the ecu detects a fault in the spedometer circuit, it will defuel the engine and put the vehicle in a limp mode, so the owner of the vehicle is forced to repair the speedometer issue, especially for older vehicles. A derating power option can be turned on or off for Etech engines. In case of a speedometer fault in newer vehicles they will register vehicle speed using the ABS. V Quote Link to comment Share on other sites More sharing options...
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