Need help with downshifting please (LA area)

Raise those RPMs and she will slip in. That's the key.

If it's grinding, you don't have a sync match.

Those lower gears are probably geared to where you're gonna have to give it a tad more.
If 6 and 7 are slipping in at 1400-1500... and 4 down are grinding, try bumping your tach to 1600-1700. AND DEPRESS THE CLUTCH FULLY.

 

If you allow the rig to drop to 1K RPM you will find there is too much fuel you are throwing onto her. You only need at that point maybe 1400 and she should fall right in.

That introduces a new problem lugging. You are hurting her by failing to shift before she falls below say 1250. Then you can rev to 1650 and she will fall right in the next gear down.

Quit grinding. She wont go in. Go back to the gear you were in before or try the second gear down if the roadspeed fell off too much while keeping the rpms between torque and horsepower.

Never come out of gear downgrade. some mountains are worth your life if you flub a shift on them.

 

I would say try lowering the RPMs in low rang. Like down shift at 1000 RPMs even 800 RPMs. In low rang it hard to match the gears. So the lower RPMs you downshift the more easy it will be.

Generally it 400 RPMs step between gears. So if you wait to 800 RPMs it should go into next lower gear at 1200 RPMs. Slow to 1000 RPMs next lower gear would be at 1400 RPM. Because you are downshifting you probably don't need the power, your looking to make the shift easy and smooth. So the lower the RPMs the smoother and more easy it will be. So I would try waiting to 800 RPMs and it should go in next lower gear at 1200 RPMs. You could do 1000 RPMs and 1400 RPMs but you will need to match more at 1400 RPM.

Remember in low range you don't need much power to keep pulling so the lower the RPMs the more easy it should be.

I would say your not lugging the engine because your slowing down. Your not pulling and demanding engine power. The engine has a lot of power in low rang. You won't need 500HP to pull trailer if light turn green.

 

Brandt is right, I do shift at those very low RPMs in ice. The kind you fall down on. But in the same coin, the amount of fuel being applied to the engine is very little at the pedal. Just enough to keep it turning without nosing down or bucking and bouncing or worse stalling the drive tires.

I prefer to stay in the band between torque and HP.

The problem with low range is the deep reduction, you multiply so much power down there you will find that being gentle with it works wonders. I can go on to fill the forum with more thoughts but I think that's quite enough.

 

So you are worried about a simple road test. That tells me you already have a CDL and all that.

Ease the nervous energy by deciding you are going to give so and so a ride in the fun big rig. Its fun to give rides today in the wonderful weather.

Come up through your gears to top gear memorizing the RPM numbers you shift at.

When the tester tells you go go back down through all the gears to stop I suppose, just start from the top gear and go through each gear the same way all the way down, remembering two things.

First your heart is a useful timing clock, two beats gets you next gear. SOME engines Fall down slow in REVs or some engines drop like a dead man to 600 before you see it.

Second the closer you get to low range and especially towards first gear, get really light on your fuel and touch. You don't need but a fingertip and she will fall right in. (You will discover floating where you don;t need a clutch at all... in due time)

Its a test. You can practice all you want when you get your first truck.

When I was taught to drive my pa's manual, I managed to destroy the transmission in someway. Thinking back on it it was a waste. I did learn in a big rig and so there is that. You could not destroy those by grinding. But you can hurt them bad. there is like 40 ton sitting on those two tiny gears against huge horsepower at the other end of it. Its amazing we don't shred the whole box.