naked Posted July 10 Share Posted July 10 i I have 2014 mack pinnacle mp8 and mdrivre tranny that is giving me a lot trouble sometimes when is on low gear rpm jump and don't want change like jerking and when is on 12 speed sometime rpm lock and stay still on 12 rpm and truck don't accelerate and do anything for like 15 second onto I keep driving like normal I do it like 3 or 4 times a day now is like 10 or 15 time a day..I'm desperate I need help Quote Link to comment Share on other sites More sharing options...
The Heinz Posted July 10 Share Posted July 10 Do you have an air leak on the transmission anywhere or in the bellhousing area? mDrive's are air operated, so if you have any kind of leak at all, it won't shift correctly. When's the last time you changed the air dryer cartridge? We see progressive failure all the time due to the air dryer not being serviced. 1 Quote Link to comment Share on other sites More sharing options...
fjh Posted July 10 Share Posted July 10 1 hour ago, The Heinz said: Do you have an air leak on the transmission anywhere or in the bellhousing area? mDrive's are air operated, so if you have any kind of leak at all, it won't shift correctly. When's the last time you changed the air dryer cartridge? We see progressive failure all the time due to the air dryer not being serviced. yup these are real sensitive to air leaks on the clutch slave! How many miles on the clutch it may be due for the works ! Fly wheel slave and a new clutch! 1 Quote Link to comment Share on other sites More sharing options...
Nickdieselz Posted September 27 Share Posted September 27 It sounds like you're dealing with a combination of shifting and acceleration issues on your 2014 Mack Pinnacle MP8 with the mDRIVE transmission. The behavior you're describing—jerking in low gears and RPM locking in 12th gear—suggests there may be a problem with the transmission control system or related sensors. Here are a few areas to check: 1. Transmission Control Module (TCM): The TCM could be malfunctioning, causing improper gear changes or locking the RPM. Try performing a reset or updating the TCM software if available. 2. Clutch Calibration: mDRIVE transmissions rely heavily on clutch calibration. If the clutch calibration is off, it could cause jerking or inconsistent shifting. 3. RPM/Speed Sensors: A faulty sensor could provide incorrect data to the transmission, leading to improper gear shifting or locking in a specific gear. Check the speed and RPM sensors for proper function. 4. Wiring and Connectors: Since this issue happens intermittently, there could be a loose or damaged wire, especially around the TCM or transmission. Inspect all connections and wiring harnesses for wear or poor connections. 5. Hydraulic System (if applicable): If the transmission relies on hydraulic actuation, ensure that there is proper hydraulic pressure and that no leaks are present. 6. Fault Codes: Even if the dashboard isn’t showing active fault codes, plug in a diagnostic tool to check for any stored or pending codes that could give more insight into the issue. If the problem persists or worsens, you might want to consider taking it to a specialized shop that deals with Mack transmissions for a thorough diagnostic. Quote Link to comment Share on other sites More sharing options...
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