Keep Those Trannys Rolling - September - 2023

AS69RC Slips When Towing

In this issue of Keep Those Trannys Rolling, we are going to take a look at a 2018 Ram 4500 Cab & Chassis Flatbed Tow Truck equipped with a 6.7D engine and an AS69RC transmission that was experiencing a slipping concern when carrying heavy loads or towing a vehicle. We first became aware of this vehicle when our local tow company towed in a vehicle for a transmission repair. After dropping the vehicle off in our yard, the tow truck driver entered the office to take care of the paperwork. While taking care of the paperwork, the driver commented that he was experiencing a lack of power or possibly a transmission slipping concern while towing vehicles. He said the truck runs great while it’s empty, but as soon as he hooks another vehicle to it, the truck seems to lose power or slips while driving down the road. The driver also indicated that the “ck engine” light would sometimes flash, but it was not staying on. We contacted the tow company’s dispatcher and requested permission to inspect their tow truck. With the tow truck driver standing by, we began our initial inspection.

Initial Inspection:

We began our initial inspection by performing a “walk-around,” looking for any obvious concerns. We opened the hood and checked for damaged harnesses or connectors. We inspected the battery and connections. We checked the fluid levels. The fluid levels were up to their proper levels, but the transmission fluid looked dark and smelled burnt. We lifted the vehicle on the rack to inspect the underside of the vehicle. We inspected the suspension, engine, transmission, driveshaft, and differential. Everything looked good. We connected our scan tool to the data link connector (DLC) to check the computer systems for codes. During the code check, we found codes P0734 (4th ratio), P0735 (5th ratio), and P0729 (6th ratio) set in the transmission control module (TCM) memory, but no codes listed in “pending” or “current codes.” We cleared the ratio codes from the TCM memory, connected a pressure gauge to the line pressure port, and prepared for our initial test drive to see if we could duplicate the driver’s concerns.

Initial Test Drive:

With the pressure gauge connected to the line pressure port and the scan tool connected to the data link connector (DLC), we were ready to head out for our initial test drive. After warming the vehicle to normal operating temperature, I checked the transmission line pressure and rise in each range. The line pressure in “D” (drive) was around 100 psi and would rise to 280 psi during a stall, which was within specifications. With the driver in the driver’s seat, we started the test drive with an empty tow truck and headed out on the road. We drove several miles through city streets and then headed towards the freeway. The driver accelerated onto the freeway at full throttle while I paid close attention to line pressure rise during acceleration. During hard acceleration, the line pressure increased to 280 psi., and then settled down at around 200 psi. while at a cruise. This was well within specifications. While driving the truck through city streets and then out on the freeway, we experienced no problems whatsoever, so we returned to the shop to load a vehicle onto the flatbed for the extra weight and prepare for our second test drive.

Second Test Drive Duplicates the Problem:

After test-driving the vehicle for several miles with no problems whatsoever, we returned to the shop to load a vehicle onto the flatbed (for the extra weight) and prepared for our second test drive. Before heading out for our second test drive, I checked the computer systems for codes, and there were none. With the tow truck loaded with another vehicle, we headed out for our second test drive. Again, we drove through city streets for several miles and then headed for the freeway. As we accelerated onto the freeway, everything seemed to be okay. The transmission shifted from first to second and then to third with no problems whatsoever. As we continued accelerating, the transmission flared into fourth, fifth, and sixth gears. The driver immediately said, “There it is,” and the “ck engine” light illuminated within just a few moments. I paid close attention to the line pressure gauge during the flared shifts into fourth, fifth, and sixth gears. The line pressure stayed between 200 psi. and 280 psi., depending on the accelerator pedal position. With the slipping concern duplicated, it was time to head back to the shop and diagnose this concern.

Back at the Shop:

After duplicating the slip concern on the test drive, it was time to diagnose this concern. While monitoring the pressure and rise while driving the vehicle and during the slipping concern, we could confirm that the pressure control system could produce the pressure and rise needed to operate the transmission properly. This is one of the most important tests you can perform to diagnose a transmission concern. With the pressure control system working properly, you can eliminate internal transmission problems, such as filter, pump, pressure regulator, and pressure control solenoid. You are also able to eliminate external computer control problems such as the accelerator pedal position sensor (APPS), mass air flow sensor (MAF), and manifold absolute pressure sensor (MAP). With the pressure control system working properly, we knew we were heading inside the transmission. After unloading the vehicle from the flatbed, we made arrangements for the driver to be picked up, so we could continue with the transmission diagnosis.

Transmission Diagnosis:

We started our diagnostic routine by checking all the onboard computer systems for codes. We checked each system individually to make sure we did not miss something during the “scan all modules” procedure automatically performed by the scanner. The only codes found were P0734 (4th ratio), p0735 (5th ratio), and P0726 (6th ratio) as “current codes” in the transmission control module (TCM). We raised the vehicle on our heavy truck rack to remove the transmission pan. With the transmission pan removed, we found the fluid burnt and clutch material floating around in the bottom of the pan. It was obvious that this transmission was going to need an overhaul. We contacted the Tow truck company and requested authorization to continue with the transmission repair. With the tow truck company’s authorization, we removed the transmission from the vehicle and began our inspection.

Transmission on the Bench:

With the transmission on the bench, we removed the valve body and air-checked each clutch component with 45 psi. of regulated air pressure. Each of the components air checked with no signs of leaks. We removed the torque converter from the transmission and began the transmission disassembly procedure. We removed the pump assembly. We removed the K2 and K1 clutch assemblies from the transmission case. We immediately noticed that the K2 clutch drum was discolored, as if overheated, but the K1 clutch drum was okay. We continued to disassemble the transmission for inspection. No other components were damaged or worn. We separated the K2 clutch drum from the K1 clutch drum. We found the K2 clutches were burnt, and the K2 clutch hub was damaged. After further inspection of the K2 clutch hub, it looked like the K2 clutch frictions had worn into the k2 clutch hub, damaging the K2 clutch hub (Figure 1). It was apparent that we would need to replace the K2 clutch hub during the transmission overhaul.

“Houston, we have a Problem”:

We contacted our local Dodge dealership parts department the next morning to order parts. According to the parts department, “There was a problem.” The parts department could order the torque converter, a new valve body, and an overhaul kit and “have them here tomorrow,” but the K2 clutch hub was on back order with no estimated date of arrival. We ordered the parts we needed and began searching for a new K2 clutch hub. After contacting several shops and suppliers, it became apparent that the K2 clutch hub was having problems.

According to the shops and suppliers we contacted, the OEM K2 hub is made from soft, stamped steel that allows the clutch pack to dig into the hub splines, ultimately hanging and burning the clutches. Replacement OEM hubs are available but often begin to fail again in as few as 15,000 miles”. So, with this “top secret” information in hand, we ordered a “new and improved, hardened” aftermarket K2 clutch hub (Figure 2). Parts should arrive tomorrow.

Parts in Hand:

It would take a couple of days to get all of the parts in hand. So, we cleaned up the case and components so we could assemble the transmission once the parts arrived. Once we had all of our parts in hand, we started reassembling the clutch packs and stacking them into the transmission case. We replaced the K2 clutch hub with the aftermarket K2 clutch hub and installed the pump assembly onto the transmission. We air-checked all components with 45 psi of regulated air pressure. All components air checked with no signs of leaks. We installed the new valve body onto the transmission case and torqued it to specification. We installed an OEM filter and installed the transmission pan. We partially filled the torque converter and installed it onto the transmission.

Close to Completion:

With the transmission assembled and ready to be installed back into the vehicle, we raised the vehicle and began the transmission installation. The transmission installation went pretty quickly. We lowered the vehicle, partially filled the transmission with five quarts of MOPAR ASRC ATF fluid, and started the vehicle. With the vehicle running, we added six more quarts of fluid and allowed the transmission to reach normal operating temperature. We rechecked the fluid level with the transmission at normal operating temperature and added another quart of fluid to top off the transmission. We installed the transmission and topped off; it was time for our final test drive.

Final Test Drive:

With the transmission installed and topped off, it was time to head out for our final test drive. We contacted the tow truck company and requested the driver accompany us on our final test drive. The next morning, the tow truck driver arrived. We requested to load another truck onto the flatbed to duplicate the same conditions we had before. After loading the truck onto the flatbed, we headed out for our final test drive. We drove several miles through city streets and then headed for the freeway. I requested the driver to “hold the pedal to the metal” while getting on the freeway and during the upshifts. The transmission shifted into first, second, third, fourth, fifth, and sixth perfectly— no signs of slipping. With a flawless test drive, we headed back to the shop for our final inspection.

Final inspection:

With the transmission working perfectly, it was time for our final inspection. We rechecked for leaks; there were none. We checked all of the vehicle fluid levels and topped them off as needed. We checked all of the onboard computer systems for codes, and there were none. It looked like we had this one whooped. We released the vehicle back to the tow truck driver, and he has been out on the road for a couple of weeks now without any problems.

Well, there you have it. With the help of your local Dodge dealership parts department and your local aftermarket suppliers, you, too, can repair an AS69RC with a K2 clutch hub concern and keep those trannys rolling.