mack88 Posted June 2, 2008 Share Posted June 2, 2008 Hi there great site. does anyone know why my 12speed grinds in the top two gears up or down but not in the bottom three. split shift or strait shift.truck has close to 500,000 K.M on it. i changed tranny oil there were some fillings in there some small metals to. I have read that these would grind but i don't know if it should grind when you split shift,using the jake helps on the strait shifting. Ithink mack is one of the best trucks around i just don't know about there trannys,but it could just be me to,kind of green on driving truck after 22 year delay.thanks again Quote Link to comment Share on other sites More sharing options...
HK Trucking Posted June 2, 2008 Share Posted June 2, 2008 Hi there great site. does anyone know why my 12speed grinds in the top two gears up or down but not in the bottom three. split shift or strait shift.truck has close to 500,000 K.M on it. i changed tranny oil there were some fillings in there some small metals to. I have read that these would grind but i don't know if it should grind when you split shift,using the jake helps on the strait shifting. Ithink mack is one of the best trucks around i just don't know about there trannys,but it could just be me to,kind of green on driving truck after 22 year delay.thanks againLook here:http://www.bigmacktrucks.com/index.php?showtopic=3805 Quote "If You Can't Shift It Smoothly, You Shouldn't Be Driving It" Link to comment Share on other sites More sharing options...
mack88 Posted June 2, 2008 Author Share Posted June 2, 2008 thanks for that link,like i said great site.o by the way i am from up in canada,Saskatchewan. Quote Link to comment Share on other sites More sharing options...
Coalbucket Posted June 3, 2008 Share Posted June 3, 2008 The reason it is always the top shift that grinds is that it has more rpm to change.The output shaft is connected to the driveshaft. The faster you go the faster the mainshaft goes.Shifting at 2100 rpm from 11th to 12th, the input shaft changes rpm from 2100 to 1632 rpm or 468 rpm. 10th to 11th is 373 rpm. 9th to 10th is 298 rpm.That's also why you can make shifts from first over to second under on a TRQL2220 Quadraplex by moving both sticks at the same time, the gears are going around so slow they just clunk into place. At higher speeds you have to get just right or it scratches. Quote Link to comment Share on other sites More sharing options...
fjh Posted June 3, 2008 Share Posted June 3, 2008 thanks for that link,like i said great site.o by the way i am from up in canada,Saskatchewan.By the way Don't pre select the split!If your going to split bereadyto do so don't select and wait!It plays hell on the shift fork!And if its and rd it is not a nice thing to repair!The last split is a bear too do try the tricks in the last link they may help some. Quote Link to comment Share on other sites More sharing options...
mack88 Posted June 4, 2008 Author Share Posted June 4, 2008 The reason it is always the top shift that grinds is that it has more rpm to change.The output shaft is connected to the driveshaft. The faster you go the faster the mainshaft goes.Shifting at 2100 rpm from 11th to 12th, the input shaft changes rpm from 2100 to 1632 rpm or 468 rpm. 10th to 11th is 373 rpm. 9th to 10th is 298 rpm.That's also why you can make shifts from first over to second under on a TRQL2220 Quadraplex by moving both sticks at the same time, the gears are going around so slow they just clunk into place. At higher speeds you have to get just right or it scratches.I thought i should change the tranny oil in it.I wasen't surprized to find filling and some small chuncks of metal stuck to the drain plugs,so maybe that is why it grinds,but sometimes it will slip ever so nicely into 11 but grind abit into 12th. Quote Link to comment Share on other sites More sharing options...
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