Colin Wood
Colin Wood Associate Editor
6/23/20 10:50 a.m.

Most modern passenger cars and trucks can come with anything from five- to 10-speed transmissions. Semi-trucks, on the other hand, are often equipped with 18-speed transmissions–like the one on this 2007 Peterbilt 379.

Sure, transmissions in semi-trucks function a little differently fro…

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z31maniac MegaDork
6/23/20 11:56 a.m.

That was pretty cool. I always wondered how those big monster transmissions worked.

Datsun310Guy UltimaDork
6/23/20 12:51 p.m.
Datsun310Guy UltimaDork
6/23/20 12:54 p.m.
Wally (Forum Supporter)
Wally (Forum Supporter) MegaDork
6/23/20 1:00 p.m.

My grandfather had a couple of these Macks.  At one point I knew how to do this:


outasite HalfDork
6/23/20 4:28 p.m.

In reply to Datsun310Guy :

I was driver/operator of a M 246 wrecker as a mechanic in the Air Force in the 60s. It had the 5 spd with splitter like this. Driving the old PA turnpike with a truck on the hook required 100% concentration.

einy (Forum Supporter)
einy (Forum Supporter) Dork
6/23/20 6:53 p.m.

Geez, and I thought driving a normal automotive 6 speed m/t well was a thing!

Datsun310Guy UltimaDork
6/23/20 7:08 p.m.

In reply to outasite :

I'm sure somebody today can do all that and still text.  LOL. 

outasite HalfDork
6/23/20 7:13 p.m.

In reply to Datsun310Guy :

No doubt, I had a student that could text with his phone inside his hoodie pouch. With one hand.

11GTCS Reader
6/23/20 8:56 p.m.

One of my high school friends used to run heavy equipment for a local excavation contractor.  One of 10 wheeled dump trucks was an International with a 549 cid gas engine that had a 5 speed main and a 4 speed auxiliary transmission.  Split shifts were done with your left arm through the steering wheel and left hand on the main stick while your right arm shifted the auxiliary.   It was quite impressive to watch.   I drove it once on a side road, took about 7 shifts to get up to 30 or so.    They eventually repowered the truck with an International DT 466 diesel and whatever transmission came with it out of the donor truck when parts for the gas job started getting unobtainium.    Not as cool to watch but way more useful. 

They had a Mack dump as well, I remember riding shotgun in that a few times moving equipment between jobs.   The exhaust stack was right behind the passenger seat and would shoot sparks if the engine had a good load on it,  fun at night.  No power steering, he got a workout driving it.  That one had a some variation of a road ranger transmission so the splits were done by an air operator on the auxiliary controlled by a switch on the side of the main stick if I’m remembering correctly.


buzzboy Dork
6/23/20 8:57 p.m.

I saw a vid on youtube years ago of an aussie driving a transmission that had like 4 switches or maybe a switch with 4 positions on the gear stick. Very unique trans that I can't find again.

The question I've always had about 18 speeds: How do you know what gear to shift down to after slowing? Like I can be going 80 in the bmw, brake hard down to 55 and know that 4th won't overrevv but will also be a good power gear to get back up to 80.

ShawnG UltimaDork
6/23/20 9:17 p.m.

Best sounding truck ever.

2-stroke Detroit 4/53 diesel.


outasite HalfDork
6/23/20 9:30 p.m.

In reply to 11GTCS :

I was going to mention the arm thru the steering wheel but was not sure if anyone would believe me.

03Panther HalfDork
6/23/20 9:43 p.m.

One of the guys that taught me a bit about shifting ( and backing one of the beasts) once hit a large pot hole while in the middle of a shift... steering wheel snapped hard enough to break his arm! But yes, common practice back then.

Also, a commenter on one of the videos said shifting 18 speed wore his left leg out... if your driving a big MT without syncro's,  ya only use the clutch from a dead stop. "float" shift, and you get a feel for what gear to hit on the way down.

Sidewayze New Reader
6/23/20 9:54 p.m.

When I did school for my class 1 license many moons ago (8 weeks full time back then), one of the trucks they had to learn on was a Mack with a 5 & 4.  It was a real experience to shift your way up a hill...... 

Pete Gossett (Forum Supporter)
Pete Gossett (Forum Supporter) MegaDork
6/23/20 9:56 p.m.

I took my CDL back in the early 90's in a borrowed grain truck with either a 15 or 18-speed. It was interesting to drive. Fortunately our company box truck was just a 5-speed though. 

chief8one Reader
6/25/20 8:13 p.m.
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