I have a D6N that shifts very hard from reverse to forward whether it's cold or hot. Cat mechanic did a transmission fill calibration, he had a difficult time getting the transmission oil hot enough for the computer to do the calibration. The required temperature is 167° f. Once he was able to get it hot enough and did the calibration it shifted beautifully. I did not use it at that time and the next time I did it was shifting hard again. We replaced the modulation valve, it has not made a difference also. The cat mechanic seems to think transmission temperature sensor is not the issue, I am looking for other opinions. The transmission temperature always seems quite a bit cooler than what it should be. Even after running it in hot weather, pushing hard it doesn't get much over 130° f. If my transmission temperature sensor is reading cooler than actual would it cause this hard shift? Thank you
It would be easy enough to check with a hand held infra red thermometer. Point it at the sensor and compare the reading with what’s on the gauge. What sort of temperature does the coolant normally operate at.? Also what type & weight of oil do you have in the transmission.? Lastly please post up a Serial Number to help in locating technical information.
Serial number: CAT00D6NJMG500913 Oil type: Cat 8T-9572 SAE 30 Transmission and Drivetrain Oil (TDTO 30) Engine coolant temperature is typically around 180° f. I've been running it all day, torque converter outlet temperature is reading 175-180° f. Transmission temperature is reading 130-135° f. Using an infrared thermometer on the transmission housing shows 155-165° f. It's looking like my transmission temperature is consistently 25-30° lower on the machine readout then actual.
It certainly looks that way. It might be worth checking the wiring harness plug for security and/or corrosion/dirt/green crusties before shelling out for a replacement sensor. The sensor is #10 on the attachment. It seems as though these sensors were susceptible to water ingress and were improved but that only happened a few years after your tractor was built. For your climate I would suggest Cat TDTO-TMS as an alternative to TDTO if a replacement sensor does not provide a 100% fix the harsh shifting issue. It is a multigrade TDTO and has the benefit of being thinner in colder climates such as I imagine you have in MN, while still giving the performance of an SAE30 TDTO at higher ambient temperatures. https://www.petersoncat.com/sites/cat/files/downloads/Cat%20TDTO-TMS.pdf
At that temperature the thermostat is probably only just open. the spec is for it to start opening at 176F. It not supposed to be open fully until the coolant temp reaches 201F.
Thank you for the help, I'll do some more digging on that temp sensor.
How did this problem start.? Getting worse for a while or symptoms appeared suddenly.? I guess the other question that has not been asked yet is regarding how exactly the reverse to forward shift is performed. For example:- Is the decelerator used.? What speed in reverse (2nd, 3rd?) to what speed in forward.? Is the tractor allowed to pretty much come to a complete stop before engaging forward speed.?
I bought this dozer on an auction, and it's been shifting hard like this since I purchased it. It was shifting so hard, that whenever I would shift from reverse to forward I would brake to a complete stop and the deaccelerate completely before I shifted to forward, I replaced the temperature sensor this morning, and it was almost 100% better, did a transmission fill calibration and and it's mint. The new temperature sensor read 30° higher than the old one. Thanks again for your help.
Excellent news. If the shifting becomes more harsh when the weather turns really cold then the next step would be a change to a mulitgrade TDTO oil. You could buy the equivalent of Cat TDTO-TMS from a major lube oil brand. Cat-branded oil is nothing that special, it's produced by Mobil IIRC. The Mobil equivalent is Mobiltrans AST, the option I would go for in your type of climate is the 5W-30 option.