Recovry4x4@aol.com wrote:
> List members; anybody out there have a 2 1/2 or 5 ton tractor? My question
> is this, air/hydraulic systems use air to apply the hydraulic brakes,
> correct?
On the trailer, yes. On the tractor, I think the air is just used in a
brake booster, much like vacuum in a car's brake booster, but with the
atmosphere on the "vacuum" side.
> Can one of these tractors pull a trailer with straight air brakes?
Yes, I think it should, as long as it has two glad hands at the rear.
One should be marked "service" and/or should be color-coded blue, and
the other should be marked "emergency" and/or be color-coded red. My
1972 2.5-ton van has both glad hands, and the fittings at the rear
work just like the ones in an air brake system, even though the actual
brakes in both my truck and trailer are hydraulic.
> Doesn't the air in a straight air brake system release the brakes?
There are two hoses in a straight air system: One is pressurized only to
apply the service brakes, and the other is pressurized all the time to
release the spring brakes. In a commercial truck, there would normally
be a pair of air supply knobs on the dash; one for the tractor, and
one for the trailer. You would leave the trailer knob pulled out when
driving a bobtail, and otherwise push in both to drive, and pull out
both to park.
My 2.5-ton van has air fittings at the rear, but it does not have
controls to apply the trailer's spring brakes (if it has any) from the
cab. But then, it's not designed to pull a very heavy trailer. It does
not have a handle on the steering column to apply just the trailer
brakes, either. By the way: that handle, when it's there, is ONLY for
testing the trailer brakes with a tug test; you should never use it
when driving.
My 1.5-ton trailer uses the emergency supply to charge an air tank.
When the emergency supply line drops suddenly (like, if the trailer
gets loose), a diaphragm valve dumps that air into the service brake
side to apply the service brakes. Because that air will leak out
eventually and release the brakes, this would only be useful to apply
brakes if the trailer got loose. It's not a parking brake, and I need
to use the mechanical parking brake levers when I uncouple the trailer.
> Reo M-275 tractor (not home yet)
Good luck!
Check your state's laws to find out if you need a commercial driver's
license and/or an air brake certification to drive that truck on the
road. In California, you would need at least a class B CDL, and
possibly an air brake certification, just to drive the tractor,
regardless of intended use. You would definitely need a class A CDL
and air brake certification to drive the tractor/trailer combo. Laws
in other states may very, and federal laws are mixed in, too, just to
keep things confusing.
I hope this helps!
-- Mark J. Blair, KE6MYK <mblair1@home.net> PGP 2.6.2 public key available from http://www.keyserver.net/ Web page: http://www.qsl.net/ke6myk/ DO NOT SEND ANY UNSOLICITED COMMERCIAL EMAIL TO THIS SITE PLEASE SEND PLAIN ASCII TEXT ONLY -- NO HTML OR QUOTED-PRINTABLE
This archive was generated by hypermail 2b29 : Mon Feb 05 2001 - 07:13:52 PST