Grinding Gears

Wrong RPM'S is the usual cause.

 

I usually bump the pedal to bring the RPM's up, and when they are dropping, the shifter will hit the slot for me. It will take a while to figure road speed, and matching gears.

 

Your instructor should be able to coach you through this minor issue. Don't tell us your trying do do this without going to a recognized school, if so down shifting will be just a small problem in the long run.

 

The quick bump will work better if you're starting your downshift from a lower rpm, also. If you start your downshift anywhere from 1,000-1,300 (just for example), you've got a lot more "room" up top for the gear to slide in than if you start from 1,300-1,500... The higher rpm you start from, the closer you are to the engine's governed speed. Hope this makes sense...

 

Practice, practice, practice. School trucks are very temermental. They are usually old and take some getting used to, each one is different.

To get through school I over rev to about 1600 RPM and I gear fell in place when the rpms fell to 1500. I suffered though a ton of grinding because I was not reving enough.

 

Your truck will only let you do it one way, but sometimes it's the technique you use that makes the difference; when I went to school, one instructor made me only look at the tachometer, which works, but I spent so much time worrying about that that I would end up losing too much speed trying to be precise, while another told me to give "the bump", and catch it on the way down, which works also, allowing you're not grinding into the next gear. This technique worked for me, until I got to the point that I can bump it in with no resistance or "scratching" at all, it just drops in.

 

When I was a CDL instructor I used to tell students that the need to down shift is accompanied with need to synchronize the speed of the transmission, by engaging the clutch, with the trans out of gear, raise the engine RPMS, depress the clutch and go to the desired gear. Remember it is perfectly proper to go down two gears at once. The fewer times you down shirt, the fewer opportunities you have to make a mistake. Most trucks have have a RPM difference in gears of 5-700 RPMS. Hope that helps some. Remember no one achieves perfection over night, some never do.