Turbo Diesel Registry
Issue link: http://read.uberflip.com/i/594528
24 www.turbodieselregister.com TDR 90 AISIN TRANSMISSION SHUDDER My truck is a '15 Turbo Diesel 3500, single rear wheel (SRW), Crew Cab, 4x4, with the Aisin transmission and 3.42:1 axle ratio. It is equipped with factory installed rear adjustable air ride. I am experiencing what I call launch shudder. It occurs only when towing my 12,000-pound fifth-wheel trailer and the trailer is well within towing and payload capacity of truck. Usually, the only time I feel the shudder is when towing up an incline at low speed when the transmission automatically shifts from 2nd to 3rd gear. The shift to 3rd gear lowers the engine speed to 1,200 to 1,400 rpm, as best I can tell, and it appears to me the transmission shifts into 3rd gear with the engine speed too low and it's lugging the engine. It occurs both in and out of Tow/Haul mode. If I manually shift back to 2nd gear, the shudder immediately disappears. All the latest transmission flashes have been successfully completed. Horseman-AR, AR I suspect that what you're feeling are engine torsional vibrations. The torque from the engine is not constant. It fluctuates or pulses due to the individual cylinders firing. These fluctuations in torque are called torsional vibrations. The amount of fluctuation increases as engine speed drops, and also increases as the overall torque increases. The worst situation is at low engine speeds when requesting high torque (which is what you have described). It is possible that these torque pulses are extreme enough to cause the Torque Converter Clutch (TCC) to momentarily slip. If that happens, it creates a shudder. The TCC is slipping and grabbing, slipping and grabbing, repeatedly. Each torque pulse that exceeds the TCC capacity breaks it loose again, then as the torque subsides, the TCC grabs again. If the vibration is primarily something you hear, then I suspect it's the engine torsional vibrations. If you feel a shudder, then I suspect TCC slippage due to high engine torsionals. So either way, torsional vibrations are likely the cause. The fix, as it seems you've already figured out, is to back off the accelerator pedal to lower the torque, or manually down shift the transmission to raise the engine speed. Either one will reduce the level of engine torsional vibrations. TransEngineer, Grass Lake, MI I continue to experience these torsional vibrations, and I assume by your explanation, I'll always experience them. Would replacing the TCC help or is this something I must live with? Horseman-AR, AR Some torsionals are indeed normal when operating at low engine speed with high torque, but if you are experiencing rumble strip-type vibration TCC shudder, you may indeed need a new torque converter, assuming you are running the original factory programming. Demonstrate the torsional vibrations for the dealer since it sounds like maybe your TCC capacity is too low. In the meantime, shift your transmission manually when towing at heavy throttle, so you can delay the 2-3 upshift and avoid the shudder. Using Tow/Haul mode should help. TransEngineer, Grass Lake, MI Yes, it's the "rumble strip" vibration in both Tow/Haul and not in Tow/ Haul. I have not modified the engine programming. The only time it occurs is when towing up a steep hill. In order to demonstrate the shudder to the dealer, I must hitch to my trailer and find a steep incline. Horseman-AR, AR Are you sure about your engine speed? I just checked the shift schedule for the Aisin, and the lowest engine speed you should see after a 2-3 upshift, unless you're at very light or closed throttle position, is about 1,365rpm. TransEngineer, Grass Lake, MI I have the Longhorn instrument cluster with three or four marks between 1,000 and 2,000rpm. When the vibration starts, it's always above the 1,000rpm mark, and the indicator needle covers the second little mark, if I remember correctly. I'm guessing that's about 1,200rpm, but there is no way to tell if it's really 1,200 or 1,300rpm. It could be 1,365rpm, but isn't easy to tell. I really have to "put my foot into it" to get the transmission to shift back down to 2nd gear, so I always manually shift it. It always seems like the Aisin is trying to determine whether it should be in 2nd or 3rd gear as if there's a little glitch in the programming. It never occurs when not towing. Horseman-AR, AR I think if I were you, I would simply hold the transmission in 2nd gear (Manual Mode "2") when towing up a steep grade, until the engine reaches about 2,400rpm, then tap shifter tab up to "3", and back to "D". At that point, the engine speed should be around 1,600rpm after the 2nd to 3rd gear shift, which will hopefully avoid the shudder. TransEngineer, Grass Lake, MI Someone mentioned that these transmissions adapt to driving style or is it just the 68RFE that adapts to the driver's driving style? If he continues to allow the Aisin to lug his Turbo Diesel, will it eventually learn a new shift point? Newsa Coverage of 2010 and newer Model Trucks. Web Site Correspondence Edited by Bill Stockard.