LEARN­ING CURVES LEARN­ING CURVES

Diesel Power - - Top Tech Questions - Robert Strebb via the In­ter­net

QUES­TION: I’ve al­ways wanted a diesel, and now I have my first one: an ’08 Dodge Ram 2500 with a six-speed man­ual trans­mis­sion. I’m 23 years old and have only driven pick­ups with au­to­mat­ics, and I’m hav­ing a lit­tle bit of a chal­lenge shift­ing smoothly. Some­times I get a lit­tle gear grind. Could there be a prob­lem with the trans­mis­sion that is mak­ing it so dif­fi­cult—or is it the “young gun” be­hind the wheel? AN­SWER: Con­grat­u­la­tions on your first diesel! Step­ping away from an au­to­matic and mov­ing to a man­ual six-speed also de­serves credit. Many Dodge Ram own­ers have found re­plac­ing the G56 trans­mis­sion’s syn­thetic ATF with a syn­thetic SAE 50 lubri­cant and over-fill­ing by 1 quart helps im­prove shift­ing. (Be­ware that over-fill­ing a trans­mis­sion, dif­fer­en­tial, trans­fer case, or other com­po­nent that runs gearsets can cause aer­a­tion of the oil, and, as a re­sult, cause degra­da­tion of cool­ing). Oth­ers have found com­bin­ing a quart of Amsoil 5-30 Syn­chro­mesh with a syn­thetic 50-weight en­gine oil is a good com­bi­na­tion. How­ever, the lubri­cant in­side the man­ual trans­mis­sion is just a small part of achiev­ing smooth shifts with a Cum­mins/G56 six-speed pack­age. It’s the driver that re­ally makes the dif­fer­ence. Sea­soned own­ers of man­ual-equipped diesel pick­ups (and most race car driv­ers) know the se­cret to mak­ing smooth, slick shifts: dou­ble-clutch­ing. It’s a very ba­sic con­cept—let­ting the trans­mis­sion gears match the speed of the en­gine be­fore mak­ing that shift up or down. When you want to shift up, say from Third to Fourth, push the clutch in, lift off the throt­tle for a sec­ond, shift to neu­tral, let the clutch out, wait a brief

mo­ment, then push the clutch back in, and slide shifter into Fourth. That brief clutch in/out/in pe­riod al­lows the en­gine and trans­mis­sion gears to be closer to the same rpm they would by just try­ing to slam the shifter home in one mo­tion, which usu­ally re­sults in a lit­tle gear grind­ing. The same prin­ci­ple ap­plies to down­shift­ing: clutch in, shift to neu­tral, clutch out, blip the throt­tle so en­gine rpm comes up a cou­ple hun­dred, then clutch in and make the down­shift. Once you get the hang of it, mak­ing smooth shifts be­comes sec­ond na­ture—and fun. Driv­ers that are re­ally good at it can shift up and down through the gears with­out touch­ing the clutch once the truck is rolling, just like pro­fes­sional big-rig driv­ers. One other item of note to con­sider when driv­ing diesels with man­ual trans­mis­sions: Keep your foot off the clutch pedal when you aren’t shift­ing. “Rid­ing” the pedal tears up throw-out bear­ings. Keep your left foot on the floor un­til it’s time to shift, dou­ble-clutch while mak­ing the shifts, and you’ll be good to go.

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