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Discussion in 'General Truck Forum' started by Moostang, Aug 13, 2008.
Why is S...H...I...F...T.... blocked by this dang system?
you forgot the f in shift
All class 8 trucks (Big rigs) have a non synchronized tranny. whether you double clutch or float the clutch must be engaged(foot off of clutch) in neutral in between gears so that the engine and gears inside transmission can synchronize. Double clutch goes like this. you start out in 2nd gear(1st is granny only used on steep hills) you get engine up to around 1600rpm push clutch in only half way shift to neutral let up clutch let rpm drop to 1300 rpm push clutch half way shift to 3rd and then let up clutch. downshift goes like this slow rpm to around 1200 push clutch 1/2 way shift to neutral pop clutch rev engine to 1500-1600 push clutch 1/2 shift to next lower gear let up clutch. Floating gears works almost the same you just dont use the clutch. floating takes a little practice but once you master its a piece of cake. either way in the middle of the shift clutch has to be engaged(pedal up) so that engine speed and input shaft speed are the same. otherwise grind!! clunk!! grind!!
I hope that helped. The following example is for 12.7 detroit with eaton direct drive 10speed 2.37 rear end gears in a freightliner century class. but pretty much the same for any big rig, just the rpm's might be different.
don't forget the high side of granny
a blast from the past thread?? dont know why i didnt comment on this one. and no, i dont drive rigs but can.
75 did have the point as to what setup you have. some rigs have a 5 speed tranny with 2 speed rearends. then some have 9,10, 12, 15 and 18 speeds where all your gears are either in the tranny or a combination between the tranny and the box on the output shaft. you will have a high and low side with the 9 and 10. 5 low holes and 4 high holes for the 9. the 12,15, and 18 are a little different. low range, mid range and high. the 15s and 18s, you usually dont use the low hole with normal driving. these are mostly used in the log woods as 3,4, and 5th gear respectively will not get you above 15 mph. most truckers start out in the first mid range gear. 9 and 10 speed trannys start out in 2nd.
tumbleweed mentions about downshifting through the gears. this is true however, some drivers do not do this but drop out of the hole and brake to a stop. the one at the house has 3 stage jakes and thats what that driver primarily uses.
guess this is better late than never. maybe someone looking for info to be a truck driver can find this oneday and apply it.
brad you are right 90% of drivers use only jake brake to slow down. and very little down shifting
I only use the clutch to start off in the work rigs. after that, It's just by listening and rpms..... you can slip between gears if you get it right. same as a pickup and or car