Detroit DT12 shifting problems

A similar problem was discussed over in the Freightliner forum on this thread. Dt12 transmission air problems. I am just re-posting the information I posted over there as its the same transmission just in different chassis. The diagnostic steps are pretty short.

For Engine RPM flare during up shifts, first you need to make sure you at least 100 psi air pressure to transmission and don't have air leaks. If you have air leaks fix before going on. Next do road test with Diagnostic Link log Actual Engine Speed, Countershaft Speed and Actual Gear engaged. After test drive you review the log file and if the engine speed flare is there. Next steps is to remove the transmission and rebuild the Counter shaft brake.

For those who are having the engine rev during up shifts I am attaching the diagnostics steps that the transmission manual says to do for engine rpm flare during up shifts. Seems like the diagnosis would be inexpensive. The cost would be in the repair.

 

I having the same issue. Did anyone resolved this problem?

 

Check your transmission air lines for leaks. You may have to spray with soapy water. Also, your check valve may not be keeping enough pressure. Make sure you’re at 120 while driving.

 

I had my clutch, actuator and clutch brake replaced January 2023. Around May or June it started displaying characteristics of the Split Shift Rod issue, dropping to Neutral and hesitating when upshifting from 9 and would typically drop into 11 at around 1100RPM when clearly it should be in 10th. Then around September it started also exhibiting the DDC-SVC-MAN-0140-15.1 Engine RPM Flare during upshifts. I contacted the dealer inquiring as to why they didn't check the Split Shift Rod when they had it in January, convinced they'd overlooked it. But they showed me a Daimler record of my truck receiving the titanium collar in 2017. They added that they'd never seen one fail. I took it in to have a road test and computer disgnosis and they said they took the screen out and they found metal filings. At 879,000 miles, they're advising that the transmission needs replacing.

 

Hey brother did you ever resolve the issue with the trans

 

I've replaced mine but I've also gotten in touch with the company that will rebuild my core. They're going let me know what they find inside and as to the metal found in the screen. If it's just clutch material and brake debris I'll consider sueing

 

Oh okay thanks for the reply