why cant i downshift my 18 speed without grinding

Downshifting rules are the same as upshifting with a splitter.

pre-select and shift

Splitting gears down shifting is not really necessary unless just settling into a power range for climbing a hill. You can still do it but it is not necessary.

You can drop a gear and half as well. Like from 6 OD to 5 direct. I have always used a 200 rpm gap for the split gears. So this shift would be a 600 rpm gap.

So, you are driving along in 8th direct and you lug it down to 1000, clutch in, out of gear, clutch out, throttle up to 1400 rpm, clutch in, shift into 7th direct, clutch out. Or float them without the clutch.

So, if you are in 8th OD and you want to drop a gear and half, drop rpm down to 900, flip the splitter, and pull out of gear, throttle up to 1500 rpm and slide into 7th direct.

Each truck and transmission combination will be slightly different but this is roughly how I do it. Maybe somebody can explain it better or point to a flaw in my process.

 

You don't need the clutch. Just reverse the process you used to upshift. Move the splitter, let off the throttle, it will come out of gear, give it throttle and it will go back in.

 

You are probaby driving at the wrong road speed either too fast or to
Slow for a good shift. Big difference between a 9 and a 18 speed as you
Found out. Keep practicing and it will get eaiser.

 

Bobtailing or empty, I'd not worry about splitting, personally. I don't in the 13 I have. Never been in an 18 but would figure it's not much different.

I do know when I was with the County here and was "training" new hires on getting their CDL, a couple just couldn't get the 13 down...splitting gears etc.... So I just had them avoid splitting, as they would not be ever driving as part of their job anyhow. But they had to have a CDL nonetheless.

 

I got a 13 in my W9. I can float up the dial fine but haven't quite got the hang of floating down - but I can do downshifting perfectly with the clutch. I get the RPMs down to 1000 or even 900 and then pull her out of gear, let the clutch out, shot of fuel, push the clutch and she clicks perfectly into the next lower gear. I did find out that running the jakes caused my timing to be off too, but I am working on finding someone local to take a run with me and see what I am missing floating DOWN the dial...

Practice Practice Practice!

 

An 18 speed dont shift any harder than any othe trans. If you dont use the splitter it shifts the same as a 9 speed. An 18 is not a pain in the but.

 

Use the tach and listen......

Feel for the gear to "slip" in.....I use two fingers to shift....Manhandling will only damage the tranny.....

Running down an on ramp you might have to skip shift......

 

As far as the spliter goes dont use it down shifting till you get the hang of the main trans first. after you get good with the main trans start to try useing the spliter on the down shifts. The reason your having a hard time isnt the trans but the engine. you need to figure out how to work the fuel petal to get the right RPM to get the trans to shift. Most shifting problems are engine timing probs. not trans probs. Whole gears are 400 to 450 RPMs. Split gears are 200 to 225 RPMs. USE YOUR TACH! Practice 200 and 400 RPM revs. Learn the throtle responce of the engine. Thats where your problem is.
As far as splitting something I tell any one that ask how to do it is.... Up shifting let up on the fuel petal. Down shifting, step down on the fuel petal. You actually need to let up just for a split second to let the splitter out of gear the rev up to down shift. Dont bother with the clutch when splitting.

 

what type of engine?, cats shift alot slower then a cummins, I don't mean to sound like an ### but if you can't shift a KW your in trouble, they are the best shifting truck I ever drove, yes I know the trannys are all the same but the make of the truck seems to make a difference.
P.S. if you shift better double clutching sounds like you are just moving the stick too fast when floating, the foot movements slow down the way you move the stick, just pull the truck out of gear, pause as if you were pressing the clutch then slide it into gear