Big Rig question

Hey, you guys are smart. Someone should know this.

Do tractor trailers have ABS? If not, why not?

jg

In reply to JG Pasterjak:

Based on this site, it appears new ones are required to have them:

http://www.thetruckersreport.com/facts-about-trucks/

I didn't know they were required, but I can tell you the last International straight truck with airbrakes I drove had them.

The trailers or the trucks? Our shop's '87 Peterbuilt does not have ABS (sometimes it doesn't have any brakes, eek!) and neither do our tandem mid-70s vintage trailers.

How else would you do wicked highway lock-up jack-knifes?

I could clarify that was an '03 International 4600.

Newer school buses have it.

The current Peterbuilt specs claim that yes, they come standard with ABS

http://www.peterbilt.com/trad389.4.aspx#7

Jay wrote: Newer school buses have it.

I doubt newer school buses have air brakes.

I wonder how they do ABS with air.. considering Airbrakes work opposite of how hydraulic brakes work. When it senses lock up, does it apply air to the system?

I know we have some truck drivers (or ex-truck drivers) on here...question, this "floating" shifting technique, is this like the clutchless technique you can use with car transmissions? (stay on gas (well, it's really a "load match"), come out of gear, match revs, go into other gear)?

That is how I did it, except I would let up on the throttle just enough to keep the revs from rising.. timed right, it was just like butter

Yes, newer rigs can be had w/ ABS. Clutchless shifting is hard to do, I've never gotten the hang of it. I fear beating up my trans to practice too much.

I'd wondered about the ABS thing. Seems like it would be a good idea, but a difficult implementation with air brakes. Then there's the additional complexity of the trailer and the fact that one tractor may tow any number of different type trailers.

As for shifting, I'd imagine it has to be tricky going back to a car considering how complex the shifting process is in a multi-range rig. What with the pedals, levers, buttons... how do you guys ever have time to look down shirts?

Why would air make implementing ABS difficult? Aside from having to add air pressure to release the brakes they work just the same as any other vehicle. Pads squeeze metal and make heat, too much squeeze makes lockup, momentary pulses of less squeeze allow the driver to maintain control.

Air brakes work by releasing air from the system, not applying it. The ABS systems can pulse the system quite well.

Yes, ABS has been available for trucks for quite some time. When I used to work for a transit bus manufacturer, we built vehicles as far back as 1984 with ABS and traction control. It wasn't a standard, but was an available option.

JG Pasterjak wrote: I'd wondered about the ABS thing. Seems like it would be a good idea, but a difficult implementation with air brakes. Then there's the additional complexity of the trailer and the fact that one tractor may tow any number of different type trailers. As for shifting, I'd imagine it has to be tricky going back to a car considering how complex the shifting process is in a multi-range rig. What with the pedals, levers, buttons... how do you guys ever have time to look down shirts?

never found it that hard... once you were rolling. It was getting up to speed that took a lot of effort. LOTS of shifting.

and no... getting into ANY car after driving the truck was like belting yourself into an F1 car..

Yep all current trucks and trailers being manufactured have ABS per DOT regs. I believe it has been mandatory since 2000 but may be wrong on the date. The systems are very efficient at applying and releasing the pressure to modulate wheel lock up. You guys are both half right in air application as the primary air lines are all ways pressurized in order to do their job, but air still needs to be applied through a service line (i.e brake pedal) to apply the brakes. Most ABS control units only control the air in the primary side of things though. The ABS system works just like a cars system through a series of sensors and rings to detect lock up. Also there is a only a handful of brake manufacturers (Bendix, Meritor, Wabco, etc...) so a majority of trucks are running what is essentially a pretty standardized braking system, makes parts availability and servicing a lot easier and cheaper.

With up to 5 air tanks at 120 psi (3 on tractor, 2 on trailer) the system should never be at a loss of pressure.

As far as floating gears it's pretty darn easy. As with every transmission there is "sweet spots" where the gears line up perfectly. I drive a '08 Peterbilt everyday and in my particular truck I bring it out of gear under load at 1600 rpm and as slide back into gear at 1200 rpm.

Saw one slam on his brakes in trafic tonight. There was a little light on therear corners of the trailer that flashed. It had a sign that said ABS on it. I guess the light flashes when the ABS activates.

Old trucks didn't need em.' The cowboys that drove them were exceptional or died quick.

Always fun to lock up 8 our of 10 wheels.. when empty those trucks can stop amazingly quickly.

What is scary about locking the rears.. the ride gets amazingly quiet AND smooth when that happens. The exact opposite of what happens in a car

Appleseed wrote: Old trucks didn't need em.' The cowboys that drove them were exceptional or died quick.

that was before the navitron autodrive

I have met some great truckers. I remember getting advice before backing down into an underground loading dock. It was noon out and without a cloud in the sky, you could not see a thing until your mirrors hit the shade.

"keep backing until you hear breaking glass or screams" was the advice I was given

mad_machine wrote:

Jay wrote: Newer school buses have it.

I doubt newer school buses have air brakes. I wonder how they do ABS with air.. considering Airbrakes work opposite of how hydraulic brakes work. When it senses lock up, does it apply air to the system?

Every full size school bus I've seen in the last ten years has had air brakes and ABS.

I don't know if the newer ones are any better but the biggest problem we had with ABS and airbrakes is that airbrakes don't release as fast as hydraulic brakes so you would lock a bit, then roll a bit more and repeat this until you hit something, but slower than if you had just skided into it. It was an incentive to drive slower in the snow as the last thing you want is unpredictable brakes.

driving slow is the one thing school buses do well around here. I think they are all governed to 35mph