There is no 18 wheeler transmission that has synchros, the torque/inertia of such huge and heavy drivelines does not alllow for it, so yes big rig drivers have to rev match and double clutch evry shift. They wil also engine break all the time, since the weight of their rigs would fry their brakes otherwise.

I would love to learn how to drive one of those, just for the hell of it, (and to learn to handle a transmission like that) I heel and toe almost evry downshift, but have never been able to double clutch.

 

Sign up for a truck driver's school. :-)

My understanding is that shifting those big rigs isn't hard. I've only driven one once, bobtail, and didn't have trouble with the gears. I think the hard part is learning how big it is with a box, making turns without running anyone over, and backing them up.

For double clutching downshifts...first try it without heel and toe. In the 8 go about 40 mph in 4th and take it down to 3rd, double clutching. You'll go from 3000 rpm to 4000, and it's a straight push forward. It's really sweet when it slides right in without any effort, and there's no jerk when you let the clutch out.

Driving on the street there are not many times where you *have* to heel and toe, so kind of spiral out from 4-3 at modest speed til you get the hang of the shifting/clutching part. Then start doing it with heel and toe.

Ken

 

Actually I spent about a year driving tractor-trailer rigs, long story, but basically I was taught by a driver with about 30 years experience, like this:

Starting off from a standstill -- in the lowest gear, pop the clutch with the engine at idle, then apply accelerator. Lowest gear is RIDICULOUSLY low so this is OK. First upshift will usually happen at 3 to 5 MPH.

Upshifts -- accelerate until engine hits governor ('redline", typically 2200 RPM), ease off on throttle while pulling shifter toward neutral. When load is off the gears, shift will effortlessly fall out of gear without using clutch. Apply gentle pressure toward desired higher gear. Engine RPM's will fall slowly once truck is in neutral, and when rev-matched for next desired gear, gears will engage with only a slight nudge, again without use of clutch. Sounds bizzare if you've never done it, I know, but it works.

Downshifts -- a bit trickier. If already decelerating, apply slight accelerator while pulling shifter toward neutral. Again, when load is off the gears, shift will effortlessly fall out of gear without using clutch. Then while in neutral, apply gentle pressure toward desired lower gear, rev engine, and when rev-matched for desired lower gear, gears will engage with only a slight nudge, again without use of clutch.

Coming to a stop -- deceleate using engine ("Jake") brake, air brake, and gears as needed. When moving suitably slow and under control, release clutch and shift into neutral just as engine is at or slightly above idle speed (typically 200-300 RPM if I remember right). Then stop using air brake only. Those air brakes are AWESOME.

If badly screwed up with either upshif or downshift, clutch can be used, but likely with some embarrassing gear grind. Good driver will use clutch only for starting or stopping. It's actually just a bit more complex than what I wrote, the trucks I drove were Cummins diesels with 13-speed transmissions involving a high/low range selector which worked with compressed air. But, it sure made me understand the concept of rev-matching. Later I tried it on an old air-cooled VW Beetle which had little if any synchros left, and sure enough I was able to shift smoothly without using the clutch, using the same technique I had leaned in the trucks.

 

all the time!

 

I've been doing it for about 6 months, including two track weekends. It's a "must have" skill for the track. IMO you must use it all the time if you hope to use it at the track. It has to be so instinctive that you don't even think about it. When you're approaching a turn at >100 mph, an 80% chance you'll get it right is not good enough!

 

http://www.renkucorp.com/garage/shifting.html

 

I learned to heel-and-toe on my FC. I got pretty good at it - I've never done any sort of racing, so I'm not claiming to be that good - but I could downshift 5->2 smoothly enough that my girlfriend wouldn't even notice.

I've been having a tough time of it with my RX-8, actually - mostly because the accel. on the 8 is *much* more responsive than on the old FC. Applying the same pressure that got me 1k RPMs on the FC gives me 2-3k on the 8, so I'm having to re-program my muscle memory to adapt to that. I've had the 8 about a month now, and I think I'm making reasonable progress.

I actually figured out how to do that on my FC, as well. I was cruising down a street at 45 in 5th gear (low RPMs/low load), fiddled with the shifter (I do this all the time), and it just popped out of gear! Started experimenting with it, found I could pop it out of any gear at any speed. After thinking about this phenomenon, I realized what was happening and realized that, by the same principle, I could pop the tranny *into* gear without clutching. I got to where I could upshift 3->4->5 without the clutch - 1->2 I never tried, and 2->3 was kinda jerky/lurchy so I didn't use it much.

I still shift 3->4 and 5->6 w/o clutch in my 8 when I'm accelerating in traffic. The brand-new shift boots are a little too stiff to let me go 4->5 without grinding most of the time.

 

You got it, dr_ishmael. When in gear there is a point called "float" when you are neither accelerating nor decelerating, so there is no load either way on the gear teeth. Indeed, some transmissions exhibit a distinct "float" noise in this state. When at float, the shifter will effortlessly "slip" into neutral. I don't consider that to be the same as "popping" out of gear as happens under load and usually means gears are either mis-aligned or not fully meshed.

To effortlessly slip into gear, the mating gear set must be perfectly rev-matched. If you can do that, then you truly "get" rev-matching.

My RX-8 is not a 13-speed diesel truck. So, while I occasionally do "float" the gears to drop into neutral while in motion and don't feel like moving my left foot, I would not attempt to rev-match into gear without using the clutch.

BTW for me, the fancy double-clutching is for smoothness while cruising, but it does lose a few fractions of a second. When driving hard I am more than happy to let my synchros do their job.

 

Shifting without your clutch isn't very good for your transmission, even if you do it right. It's more strain on your synchro's.

 

Agreed, although if you do it right the synchros aren't really doing anything . . . However, if you do it WRONG, you could chip a few gear teeth.

 

Where are you getting your information? It puts more strain on the synchronizers because there's a **** load of resistance they have to overcome to stop the gear and allow it to slide in without grinding. This has been discussed many times on many different forums. It's not good for your tranny, whether you're doing it right or not.

 

If the gears which are about to mesh are already spinning at the exact same speed, what work is there for the synchros to do? Why would you want to "stop the gear" to "allow it to slide in"?

 

Hah, yeah. You draw a good point, but I guess it's a good thing that i'm more aware of it than ya think. Thus, I practice a lot more than i used to. I'll be moving out of town during the summer. I'll be about 40 minutes from Racers Ranch, and maybe an hour from that H3R or something like that (tracks). I can't wait for that I'm hoping I can meet other 8 drivers so we can all be like to the other cars, heh