Truck vs car manual tranny

One major carrier was rumored to order road tractors without tachometers. We thought there must be some crunching at that company. We pitied them and took pride in being able to glance at the speedometer, glance at the tach, and skip a gear or two on a downshift. Then one day, I descended into Reno with a head-cold. The descent caused me to lose my hearing, and I could not shift that Tri-State Freightliner so save my butt. Watching the tach did not help at all. At least, my co-driver slept through it; but it was not pretty until my hearing returned about 30 minutes later.

 

No kiddin'?
Small world!
I had a similar experience whilst descending into Reno from Truckee.
Although I did not lose my hearing --- a good thing, as it turned out, ................. 'cause I lost my dad burned sight.
YuP!
Couldn't see a dang thing,................. but I could hear it all.

I just aimed that Marmon betwixt the screamin' and hollerin' and made it all the way to Sierra Sid's 76 Truck Stop in Sparks.

HuH?
Whazat?
Was I draggin' somethin' to make sparks?
NaW, just an old refrigerated flatbed. But it was rollin' along, OK.

OH!
Y'all are thinkin' I said "sparks"?
No. No!
I said
"Sparks."
You know,................... that town just east of Reno.

No problem gettin' there for me.
Plenty of practice doin' that in my sleep.
The only thing bad about it was when I pulled up on the
fuel island and got out of the Marmon and went inside
the building.

And walked straight into ol' Sid's Elvis collection display.
Hit it right about in the matching John Wayne Winchester Rifle area.
Bummers!

I WAS tryin' for the restaurant with the Big truck grills on the wall.
Probably a good thing I missed that isle though. I COULDA run smack dab into the Elvis finger ring and fancy wrist watch display case.

What mess THATA been!

 

Wow! I'm glad you survived to tell the tale, AfterShock. I have not been out there since 1969, and I was westbound when I lost my hearing. At that time, the truck route went down main street. I don't know if a bypass was ever built. Now, they say that Bill & Effie's Boomtown has been replaced with a Cabela's.

 

Cabela's is good.
Although, I'd probably leave more money there than
at a casino. But at least I'd have somethin' to show
for it.

Alright!
Who said "loser'?

BTW: The "bypass" is called I-80.

 

In a classic volkswagen service manual they say the best way to shift is to float shift. except when down shifting.

 

Downshifting is fine to float too- you just HAVE to understand that a downshift involves raising the RPM of the engine to match the new gear... whether you're using a clutch or not.

You should never use your clutch as a brake... that's not the point of downshifting.

I.E. you should never let the RPM drop below the next gear on an upshift, thereby "dragging" the motor back up to the correct speed, and you should never let the RPM rise above the next gear on an upshift, thereby "dragging" the motor back down to the correct speed.

On motorcycles we call this "lack of traction conservation"

 

I only use the clutch to take off, and when I am stopped. I agree, for a smooth execution of (float) shifting your speed and RPM got to be in that sweet spot.

 

"I.E. you should never let the RPM drop below the next gear on an upshift, thereby "dragging" the motor back up to the correct speed, and you should never let the RPM rise above the next gear on an upshift, thereby "dragging" the motor back down to the correct speed."

The above quote applies to cars. Heavy truck transmissions are different. If the rpm is not nearly perfect, the gears will not engage. Of course, there is such a thing as feeling a slight grinding while the rpm is changing and then "finding" the correct rpm for the gear change. With a heavy truck, most likely you will not get it into gear and then drag the motor to the required rpm as the clutch is engaged. Rather, you will engage the clutch as the transmission slips into gear, and the rpm is already correct.

My point is that with a heavy truck, if "the RPM drop below the next gear" or "the RPM rise above the next gear", it ain't going into gear.

 

"With a heavy truck, most likely you will not get it into gear and then drag the motor to the required rpm as the clutch is engaged. Rather, you will engage the clutch as the transmission slips into gear, and the rpm is already correct."

"Most likely" Exactly- my point is not in regards to actually slotting the stick into the hole, but rather once it's in the hole... how the driver treats it once it's there.

i.e. if you shift out at 1600 expecting a 500 rpm drop, you will end up in gear around 1100 rpm- however, if the driver were to have a 'brain fart' for some reason and kept the right foot off the accelerator and the left foot on the clutch and permitted the engine to drop that few hundred more rpm to it's idle speed before releasing the clutch, that driver would then 'drag' the engine.

not as likely on heavy trucks, because a) the driver is a trained professional, and b) much narrower powerband necessitates deliberate shifting without hesitation...

we're talking the same thing here, i think ... just tackling it from two different angles.

along these same lines with the 'dragging' is why so many 4-wheelers think it is taboo to downshift and/or engine brake... because no-one has ever taught them the correct method and they think dragging the clutch is correct when it is not.

on a motorcycle, lack of proper traction conservation can kill you in the blink of an eye on some bikes and in some conditions. if you drag-clutch downshift on a bike while braking into a curve, it's lights out... of course when you have something with a 13,500 rpm redline and a 7,500 rpm wide powerband, it gets even more exaggerated than in a 4-wheeler...

 

We are comparing apples and oranges, PTX. I understand points you are making; and on a bad day, have made some of those driving errors myself. I want to point out that it takes 45 lbs of force on the pedal to release the clutch of a heavy truck. The truck driver is more likely to complete the double-clutch motion quickly as in "boom-boom, boom-boom".

My second point about the difference between trucks and cars is that truck engines have heavier rotating parts with lots of inertia. The compression ratios of truck diesels make heavy parts necessary. "Dragging" the engine to the correct rpm with the clutch does happen by mistake, but the driver will resolve never to do that again. The heavier engine does not respond easily to being "dragged" by the clutch, and the result is always startling if not catastrophic. As teenagers, we used the phrase "popping the clutch". If you pop the clutch in a car, the tires will squeal. Popping the clutch of a truck by mistake could tear the center section out of the clutch, twist the drive shaft, destroy a U-joint, etc.

I understand your comment about the mistake of using the clutch as a brake when the engine rpm should be brought up with the accelerator before engaging the clutch. This is not to be confused with the "clutch brake". The clutch brake is to be engaged when the transmission is in neutral, and its purpose is to stop the input shaft only. With the transmission in neutral, there will be no "braking" of either the engine or the truck with the clutch brake that is applied when the clutch pedal is depressed against the floor.