Allison MD 3060 / WTEC-2 Has Gone Bye-Bye
I have posted a number of times over the past few years regarding issues with the Allison MD 3060 / WTEC 2 Controls that was supplied in 1997 with our FL-60. Matched up to a Cummins C8.3 Mechanical Engine it visited all 49 States. About 10 years into ownership, problems began to appear:
1) Inconsistent shift patterns
2) Error codes
3) Intermittent retarder operations
Over the past 10 years the following were replaced with periodic moments of success:
1) Main wiring harness from the transmission to the firewall / bulkhead connection replacement
2) Throttle position sensor replacement
3) Output speed sensor replacement and resistance checks
4) Valve maintenance and internal inspection at Allison Service Center
Maintenance over the life of the unit included:
1) Routine replacement of filters
2) Conversion to Allison Transynd Fluid two years into ownership
3) Installation of all Allison ECM Software and Firmware upgrades by Allison Service Center
4) Installation of Allison ground isolation modification
In the fall of 2018 the Allison began to randomly shift out of gear at high way speeds, hesitate to shift, perform extremely hard down shifts, and fail to shift into gear from neutral. It would occasionally throw various speed sensor / speed synchronization codes. This resulted in leaving one stranded on the side of the road - fairly inconvenient when one resides in Alaska and cell service is at best intermittent.
All Allison trouble shooting was followed for the various trouble codes with no conclusive improvements. The ECM was sent to Texas for test and evaluation and was determined to be in perfect working order. A change-out of transmission filters after 2,000 miles of operation showed black fluid and significant wear material (clutch material per Allison Service Center).
After all of this maintenance and trouble-shooting effort during the fall of 2018, the unit ran acceptably for approximately 100 miles before shifting out of gear during a left turn in front of on-coming traffic, it was a very close call. . . . .
After consulting with Allison engineering and aftermarket specialists it was apparent that these issues pointed to intermittent electrical problems, most likely in the wiring harness'. The wiring harness' were examined for obvious fraying / cuts / abrasions, etc - nothing abnormal was found with an installed inspection. All truck grounds were checked, cleaned and re-installed. The alternator was tested and found to be providing a clean / steady output voltage.
Replacement wiring harness components are no longer available, secondary market harness can be custom manufactured but are prohibitively expensive. Replacement transmissions shipped to Alaska exceed $10,000 and effectively do not carry a warranty.
With relatively low miles on the engine, no oil consumption, etc., a 6 speed Eaton Road Ranger manual transmission (fully synchronized) was installed. Clutch hardware and hydraulic linkage was obtained from later model Freightliner Business Class units. A very talented truck repair shop performed the necessary firewall modifications to contain the clutch hydraulic master cylinder.
Results to date:
A) Bobtail mileage has increased to 14.5 mpg from 10 mpg
B) Towing performance is improved.
C) Towing in city traffic is more challenging.
Root Cause of Transmission System Failure / Demise
As near as I can tell both the transmission wiring harness within the cab and from the transmission to the firewall connection failed (2 separate harnesses) failed due to wiring insulation failure. The failure was not readily visible until the harness was removed and un-bundled. It appears that the wiring insulation is polyimide (Kapton is the DuPont brand name). Do a google search on Kapton and you will have plenty of reading opportunity.
If you are running an older Allison set-up or are considering getting into one - check the harness wiring very carefully. Wiring insulation from the late 90's and into the early 2000's was not known for high quality / long life with respect to computer signal integrity and prevention of erratic signals.
Hope this helps a few folks on the forum. . . . .
97 FL60 / Cummins C (Mechanical) / Eaton 6 Speed Mid Range Road Ranger
97 Teton Royal