Air Brakes versus hydraulic/Electric Assist

SnoJob67

Senior Member
Location
Illinois
From the driver's seat, how do air brakes work? I was told once they are a bit tricky to get used to, but that was not from an experienced driver.

Anyway, it is NOT a federal requirement for a vehicle with air brakes to be CDL, contrary to popular belief. States must meet federal regs, but some states obviously have their own regulations that are more strict.

I have heard air brakes are a big plus for stopping power. Any comments regarding how tricky they are to operate would be appreciated. I have never seen an air brake setup and don't even know if you still use a pedal on the floor (that is how little I know on the subject). :eek:

I know a few of you guys have a variety of the bigger trucks and may be able to help.
 

Pelican

2000 Club Member
The brake pedal is in the normal position, depressing it opens a valve which directs air from a storage tank to the wheels. At the wheels there are a few different set ups but the most common is the S cam.

Here there is a sealed chamber with a heavy rubber diaphram that fills with air from the pedal. As it fills, the diaphram pushes a rod which activates a lever that rotates the S cam. There are rollers that ride the S cam on the end of the brake shoes, this is what forces the brake shoes against the drum.

If properly adjusted, you get more braking force than you ever will from hydraulics. You don't pump the brakes on this system as you do hydraulics or you'll run out your air. The only tricky thing is making sure all wheels are adjusted the same, or one will lock much sooner than the others, risking a skid.
 
OP
SnoJob67

SnoJob67

Senior Member
Location
Illinois
Pelican-

Thanks for the reply. That was pretty easy to understand.

It sounds like a truck with air brakes would work just fine for us. I already have a cdl cheater with hydraulic brakes, but didn't want to rule out a truck equipped with air brakes if the right opportunity presents itself.

Thanks again.
 

Chuck Smith

2000 Club Member
Location
NJ
Snojob, we have one truck that is non cdl by weight regulations, but it has air brakes. Here in NJ, you need an air brake endorsement to drive a vehicle with air brakes. It kinda defeats the purpose of it being non cdl...

Stop by your local DMV and pick up a CDL Driver Manual. It should have a full explaination of air brakes (though Pelican summed it up pretty good).

As far as them being tricky to get used to, in a way that is true. They are "touchy" compared to hydraulic brakes.... especially when the truck is empty.

There is a built in saftey feature. When the air pressure drops to a certain pressure, the parking brake pops, locking the brakes. Before this happens, an alarm sounds alerting you that the pressure is low. If you ever hear that alarm, PULL OVER.

I am pretty sure this was the cause of a nasty accident here in NJ a couple of years ago. An 18 wheeler tanker was stopped in the center lane of a highway with his brakes locked, and a second tanker didn't see him until it was too late. They collided, and it was on a bridge. The fire was so intense that the heat warped the girders of the bridge and had it closed for months while it was reconstructed.

Pelican, you may have heard about it, it was on RT 80, and all over the news.

~Chuck
 

SLC1

Senior Member
I have heard with plowing with Air brakes it sometimes doesnt give a chance for the air to build up from all the stop and go in a parking lot, on a road there would be no problem but for a parking lot you can use up all the air and it might not have a chance to build up pressure, This is just what i have heard and is not from personal experience. Just my two cents
 

cat320

2000 Club Member
Location
stoneham,ma
That would be kinda true ,unless you have a real big lot and your pushing in such a way that it's like your plowing a street and just driving.But if in a small lot that your required to go back and forth it could ear up your air supply.
 

Pelican

2000 Club Member
Chuck, I do remember seeing that incident on the news.

I understand the comment about stop & go in a parking lot running out the air, but I question the efficiency of having a truck that size in a lot that small. I've only done street routes with air brakes, so I have no experience, but I don't think I'd want to horse a big 6 wheeler around a tight parking lot.
 

CT18fireman

Banned
Location
Western CT
I remember seeing that on the news as well. Also a lot of changes in thought and practice in terms of fighting such a fire came from experiences from that incident.

Off the topic but it was a bad accident.
 

GeoffD

PlowSite.com Veteran
I never had a problem doing lots with a truck that has air breaks. When you think about it, you shouldn't need to use the breaks that much. Most truck's air compressors build enough air so that the system can recover fast enough, even in a plowing enviroment.

Geoff
 

mattman2112@aol

Junior Member
Location
SE connecticut
yes you do still have a pedal. the main difference is the "feel". with hydraulic brakes, when you push the pedal, the pedal pushes brake fluid and the brake fluid pushes the shoes against the drums, in other words, YOU supply the pressure. with air brakes, when you push the pedal, the pedal opens a valve, which lets compressed air push the shoes against the drums.
 

LoneCowboy

PlowSite.com Addict
Location
Longmont, CO
Air brakes rule. To stop a big heavy vehicle, nothing works better. I can stop my 80,000lb semi faster than I can stop my pickup with a 10,000lb trailer on it.

Air doesn't work the brakes. Springs work the brakes. The air holds the springs back off and as you press the treadle valve (brake pedal) you release some air and the spring push against the cam which applies the brake shoes. Air doesn't actually push against it, the springs do. (which is why they are called spring brakes).

Air brakes fail on, hydraulic brakes fail off. Which means if you lose air pressure on an air brake truck, the brakes come fully on (the parking valves come pop out, and the springs are full on) and you aren't moving. (which is why the warning light/bell comes on at 60psi, to tell you to get over before you lose the ability to control your truck completely. On hydraulic brakes, if you lose hydraulic pressure, you have no brakes.

You do need an air brake endorsement on your CDL to drive an air brake equipped vehicle commercially. (and you are driving commercially, just go get the CDL). You can get a CDL without air brakes. (although most people don't).

More to go wrong on air brakes, and some more maintenance and checks (esp when cold/humid) but really very simple and at the end, they simply work, and they work like you can't believe. There is a lag time between pressing the pedal and something happening, and that does throw people initially, but after that, it's amazing.

I don't know how that would work plowing, you will lose pressure if you continue to pump them. Driving down a road plowing (like city/county/state trucks) wouldn't do it.

CDL class A (combination vehicles), air brakes, doubles/triples, tanker endorsements
 

Mark Oomkes

PlowSite Fanatic
Location
Grand Rapids, MI
Well shoot, might as well stir up some more controversy, maybe we can get wisdom from a certain member here too.

LC, hate to disagree with ya, but if a truck is under 26,000 GVW you do not need an air brake endorsement for THAT truck. Just had this explained by a truck cop regarding tanks.

If the truck doesn't require a CDL, you don't need one. You can't get an endorsement on a normal operator's license. So therefore, it is impossible to have an endorsement for something that you can't get.

Makes sense. Also, guy I know had it out with the Indiana folks at their weigh station regarding this matter. He won.

Just ticks me off because I wish I would've gotten my F800 with air instead of the crappy hydraulic brakes that are way more expensive to repair.
 

LoneCowboy

PlowSite.com Addict
Location
Longmont, CO
That's interesting, but I don't know
I got it explained that you couldn't run air brakes truck without the endorsement (which I agree I don't believe you can get without a CDL).

Remember though, ask 3 DOT guys/cops the same question, you'll get 3 different answers. :rolleyes:

And you should clarify your answer, because if you had a 19,500 truck with a 14,000lb trailer, you would need a class A CDL. (although not with a 10,000lb trailer, in some states).
It's all way more confusing than it should be.


Also interesting on the hydraulic brakes being more expensive to repair. That's your experience?
 

Jay brown

PlowSite.com Addict
Pelican;49088 said:
The brake pedal is in the normal position, depressing it opens a valve which directs air from a storage tank to the wheels. At the wheels there are a few different set ups but the most common is the S cam.

Here there is a sealed chamber with a heavy rubber diaphram that fills with air from the pedal. As it fills, the diaphram pushes a rod which activates a lever that rotates the S cam. There are rollers that ride the S cam on the end of the brake shoes, this is what forces the brake shoes against the drum.

If properly adjusted, you get more braking force than you ever will from hydraulics. You don't pump the brakes on this system as you do hydraulics or you'll run out your air. The only tricky thing is making sure all wheels are adjusted the same, or one will lock much sooner than the others, risking a skid.

it's been awhile since i've taken the cdl test, but i don't think this is the way the brakes work........ directing air from the storage tank to the brakes releases the brake, releasing the air from the brake chambers applys the brakes
 

Jay brown

PlowSite.com Addict
LoneCowboy;595952 said:
That's interesting, but I don't know
I got it explained that you couldn't run air brakes truck without the endorsement (which I agree I don't believe you can get without a CDL).

Remember though, ask 3 DOT guys/cops the same question, you'll get 3 different answers. :rolleyes:

And you should clarify your answer, because if you had a 19,500 truck with a 14,000lb trailer, you would need a class A CDL. (although not with a 10,000lb trailer, in some states).
It's all way more confusing than it should be.


Also interesting on the hydraulic brakes being more expensive to repair. That's your experience?

hydro can be more $$$$$ to repair on fords because they have that hydro system set up like air brakes and the booster tanks are expensive to replace
 

BigLou80

Senior Member
LoneCowboy;595952 said:
That's interesting, but I don't know
I got it explained that you couldn't run air brakes truck without the endorsement (which I agree I don't believe you can get without a CDL).

Remember though, ask 3 DOT guys/cops the same question, you'll get 3 different answers. :rolleyes:

And you should clarify your answer, because if you had a 19,500 truck with a 14,000lb trailer, you would need a class A CDL. (although not with a 10,000lb trailer, in some states).
It's all way more confusing than it should be.


Also interesting on the hydraulic brakes being more expensive to repair. That's your experience?

I think in my state you need an air brake endorsement even if its the family minivan. As for trailers if the vehicle israted for 17,000 lbs and 10,000 of towning they want a class A CDL even if the trailer is only rated at 2,500 lbs
 

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