Update on driving a semi tractor

I'd recommend tracking down one of the "rent our truck for your CDL test" places that has a semi with one of the automatic (really semi-automatic) transmissions for your road test. They will have the proper insurance for everything and having the auto truck will make things less stressful as well as giving you more points available to potentially miss on the test and still pass. You can't grind gears (or run over curbs) on the test, but once you have your license you can grind the gears on your truck all you want (and everyone runs over curbs it seems). The test truck rental places also know the test routes and will guide you through the actual test route for practice before you take the test. It's well worth the $500 or so they typically charge for what is typically half a day of their truck and driver's time.

Pete, what are those semi-automatic transmissions, exactly?

I do agree with you, as a matter of fact, about renting something like that.

I only have direct knowledge of the Eaton that was on the Kenworth T2000 I tested on, but essentially they are a regular manual semi transmission (like 14+ gears) that is under computer control.

There is a clutch that you use when starting and stopping the truck, but outside of that the computer handles the shifting. There is a transmission shift that looks a bit like an automatic, but has no PARK mode and has up/down buttons on the handle as well. Park is handled with the normal air brake controls which is why there is no PARK on the shift.

Basically you press in the clutch and shift the lever to D (drive). The computer will clunk the transmission into gear for you (normally second gear) and you start moving with the clutch and accelerator like normal. After you have let the clutch out you just forget about it until you are coming to a stop. The computer will cut power (electronic throttle) and power shift for you as you accelerate. There is a display that shows the current gear it's in. The up down buttons on the shift lever can be used to force it up or down much like some "sport" cars with automatics.

When you are coming to a stop you brake normally and let the computer downshift for you as you slow down. When it is down to low gear (second) you finally push in the clutch as you come to a stop and hold the clutch down as normal if waiting at a light, or if you are parking you shift to N (neutral) and set your air brake park control.

They are really quite nice and remove that extra bit of distraction while trying to merge into traffic on an entrance or exit ramp. Certainly after you have been driving a manual for a few years that isn't much distraction, but it is still some and certainly more for new drivers. From what I read the autos are becoming more common in the big fleets too.

Just check VERY carefully. Many states put restrictions on for various items (glasses, hand controls and such) I know one of those used to be Automatic transmission ONLY. IE if you couldn't drive a stick you got a restriction saying that you could only drive automatics.

You're learning at a better age than myself. I started driving truckloads of wheat to the elevator at 14. Dad told me to never go on the highway. Of course, I ignored that. I forgot to down shift at the top of pleasant grove hill. When the brakes wore out, I tried to down shift and missed it. That old truck was doing 80 at the bottom of the hill. I was lucky to see 15. But, I've never forgot to down shift again.

Karl

Just about time, I would say. Thanks for a great explanation.

As far as I know, it only applies to air brakes.

I have found a golden guy, an honest mobile mechanic, I will have him check my brakes out.

Iggy, just in case you don't alread know, NEVER go down a hill in a gear higher than you go up it. Downshift at the top. No matter how good the brakes are, it won't stop 80,000 lbs. I just told you how i learned this.

Karl

And the same lesson will kill you in a car, too. I ALWAYS downshift one notch on hills and stay off the brakes as much as possible, even if I'm not overloaded or towing and the brakes are minty-fresh.

You have to keep the brakes cool enough to get stopped when you need to. If you were riding them down the hill to scrub off speed there may not be enough reserve brake power left to get stopped before they heat-fade into nothing-ness - then you are well and truly screwed.

Young dumb kid in a 1962 International Scout 4X4 (maybe a half-ton) with the 152-CID Four and the stock Girling drum brakes towing WAY too much unbraked trailer over a moderate canyon grade - Malibu Canyon from US-101 to Pacific Coast Highway.

Got way dicey getting it stopped going down the hill, and that's with pulling over several times for the brakes to cool down after I could feel them fading away - more than once with Both Feet mashing that one poor little pedal Fred Flintstone style.

Couldn't get enough engine braking out of it in Second without grenading the engine, and I had a line of honking cars behind me when I tried it in First. And that was the flattest route to the beach.

The trip home was after dark and traffic was lighter. First gear all the way down the backside and SCREW 'EM - Honk all you want, I'm getting this rig back to the barn in one piece and Never Again. I'll hug the shoulder, you go around.

If I'd have tried that same trick on Kanan Road (and this was long before they put in the Runaway Truck gravel pit in the median) there wouldn't be any graceful recovery - I'd have been a splat on the Hillside at the Tee intersection with Pacific Coast Hwy...

... For about two seconds max, then *(if by some miracle I made it across the intersection unscathed the first time) I'd get T-Boned by the 4-lane 55-MPH through traffic on PCH. If one didn't kill ya, the other one certainly would.

-->--

Karl, I am aware of this, yes. I think that proper brakes are enough to slow down downhill and to switch to low gear, but I am aware of the brake fade phenomenon.

I am studying that stuff and will take theoretical CDL exam as soon as practicable.

I will use this dump truck and the 15k trailer, in lieu of a bigger semi tractor/trailer setup, since I already have this dump truck and a

The problem is not the brake fade, the problem is if you do not do your downshift before you go over the crest of the hill, you have very poor odds of being able to successfully complete the downshift on the downgrade. What happens is you get it out of gear and then you are unable to get it into the lower gear and often you can't get it back into the previous gear as well. This leaves you on a downgrade in neutral with *no* engine braking at all and your service brakes won't do the job. It's runaway truck ramp time if you are lucky enough to find one.

OK, I will bite, why would the service brakes not do the job and stop the truck, at least once?

They MIGHT - under ideal conditions - if applied and held. Let off once and re-apply and all bets are off. Are you willing to take the chance????? Engine compression braking - and better yet a Jake or exhaust brake, are the much safer "bet".

Of course they will stop the truck when they are cold. The problem arises when you use them on a long hill to control speed, rather then the engine. In a surprisingly short time the brakes get hot and braking efficiency drops, amazingly.

-- Cheers,

John B.

I do not think that I have a Jake brake. Thanks. What you say makes sense.

Mainly because by the time you realize that your NEVER going to get back into gear you have already stabbed the brakes a half dozen times trying to slow down and they are now HOT. If they were stone cold when you hit them they would probably stop you once, they would likely burn up from the heat and maybe set your rig on fire but they would stop you. When they are HOT, you may as well head for the wall/bank/run off ramp. They lose a LOT of braking power once they heat up and start out gassing then they start glazing over then it's game over. Glazed brakes are about as effective at stopping as a block of jelly is at stopping a chainsaw.

With an unloaded truck, they probably would. With a semi-loaded truck, they might. With a fully-loaded truck, they would burn up in the process. Think power-to-weight ratio. The weight requires so much force to be put on the shoes/drums that they can't release the heat in time to work effectively.

First you experience brake fade, where it takes more and more force on the pedal to slow you down. Then you feel as if you've lost the brakes altogether. About this time, you usually see smoke coming from your axles and you occasionally lose a tire to bursting from the heat generated by the brakes, transmitted through the wheels. (Retreads are the quickest to do this, and I've seen/heard dozens pop on I-5 where I'm living now, on a mild downgrade!) Then you see actual flames coming from the axles, where the brake shoes have caught fire inside the drums. I've seen all of this on the road, which I'm sure many will now attest to. My buddy Phil has been driving portable TV stations around to the sports events and has told me some real WOW! stories. He survived losing his brakes; his truck (tractor) didn't.

-- It is characteristic of all deep human problems that they are not to be approached without some humor and some bewilderment. -- Freeman Dyson

They might... if you have not picked up too much speed before you realize you are in deep doo-doo and you apply them solidly in one emergency stop.