[HRLand]

I've never owned or even driven a truck with air brakes but I found one I would like to buy that has them. Is there any drawback to them as far as maintenance , replacement or cost? I would guess that they would be better considering all bigger trucks have them.

[Paul]

All you need to adjust the brakes is two wrenches a 1/2" and a 9/16" open end. They are much simpler to repair, and last much langer.

[HRLand]

Does this hold true for Japanese trucks as well?

[Bill Schwab]

Japanese trucks typically use an air over hydraulic system. Same as a Iveco. The drawback to this system is a brake job can cost $4,500.00, and most of that is all parts. Another very bad system to stay away from is what is called "wedge brakes" Tow truck guys tend to favor these. The problem with them is when it comes time for a brake job, you have to torch most of the moving parts off.

Air brakes are the best invention known to man when pulling heavy loads. And, if yor truck has a Jacobs brake on it, you can use the compression of the engine to stop the truck..

I would call the dealer of whatever brand truck you buy just for yucks, tell them what it is, and you are looking to put brakes on it...If they need specifics, then evert to the question now you got me curious, what is the apporximated cost of this going to be...

Intermediate Mack trucks made by Renault were ridiculously expensive too...

[Robert T]

the only issue with air brakes is the air system.It HAS to be maintained or you will pay! Brake linings and hardware can last up about 60,000-100,000 miles. Service the air drier once per year. this is the best way to catch problems before they get to big,
Is the truck located in your area? if so you can get the Vin # and get any parts info you want. I would ask them what dealer they used for service and get a history report from the dealer.

What kind of truck is it? and what is the engine make?

[HRLand]

The truck I'm looking to buy is 95 mitsubishi fk with a new roll-off system. The brakes are all air, not air/hyd. The place that's selling it buys box trucks from rental co's and converts them to dumps, I don't think they would know the service record.

[dan deutekom]

Air brakes are great and they last a long time if you look after them. Check the adjustment frequently. They are easy to adjust and it only takes about 5 minutes. Drain the air tanks daily! You may have to get used to driving with them because they stop better than hydraulic brakes but if you are one of those drivers that are always touching and feathering brakes when maneuvering in tight areas you can overrun the compressor. Here in Ontario you have to have a special endorsement on your Drivers License to drive air brakes and only a licensed mechanic is allowed to work on the brake system including the adjustment. (strange to get the endorsement you have to know how to adjust the brakes but legally you are not allowed too!)

[diginahole]

A lot of newer air brakes have automatic slack adjusters. Regardless you are required to verify adjustment daily on your inspection report.

I have to disagree with comments about air brakes being faster or better than hydraulic. It simply just cannot be true. Hydraulic brakes are both faster and stronger as well as being less prone to brake fade. Simple high school physics teaches us that air can be compressed and liquids cannot. It is my belief that air brakes are commonplace in commercial vehicles is for the ease and reliability of coupling trailers.

[Robert T]

the reason most hydo brake systems don't have fade is because they use rotors on at least one axle. its not because air compresses. Large trucks use drums all around. When drums get hot they expand causing brake fade. There are government requirements for vehicals that they must stop in a certain distance. air is the most reliable and safest way to acomplish this.
Another reason air is used is for saftey if a truck looses all its air Psi then the E- brake sets. any Axle with a maxi chamber will lock up and stop the vehical. If a hydo brake fails then you either manualy set a park brake (if its not froze up) or run out of kenetic energy. I.e cut power and roll or hit something.

[diginahole]

No argument here Robert, the expansion of overheated brake drums is what leads to fade. I think air systems are more prone to overheating because of the lack of feedback to the driver because of air's compressability. Stopping distance is increased with air because of the delay from the time it takes for air to travel from the pedal to the brake chambers. Air brakes simply don't react as fast as hydraulic. Hydraulics are there already, pushing on one end creates an instant reaction at the other. Both air and hydraulic systems on newer vehicles have dual brake systems so that you need to have two failures before e-brakes become necessary. In air systems the driver has no control over the e-brake, it is fully on or fully off. Heavily loaded vehicles will have an increased stopping distance because not all wheels have e-brakes. Lightly loaded vehicles may skid out of control because wheels lock up. Hydraulic systems use a manual e-brake which can be controlled by the operator. The shortcomings inherent to air brake systems are the reason we need special licencing to drive airbrakes.

[dan deutekom]

Blair makes some valid points. Air brakes are used only on the heaviest of trucks. Trucks that had air brakes regularly even only 10 years ago now have hydraulic brakes which shows how far braking systems have come in the last few years. But once you start hitting the 30000 pound class you only see air. Hydraulics get limited by size and number of brakes. Air can go to any size and number of axles. Also trying to stop a loaded truck with an manual e-brake is a pretty iffy thing but if the e-brake comes on in air brakes the wheels are locked and all axles but the steering axle will be locked. Air brakes have also come a long way in the last few years with automatic adjusters and disk brake systems.

[Robert T]

In the States you don't have to have a special license for air brake vehicles. CDL license is for vehicles over a weight of 26000 almost every vehicle over this weight has air brakes because they are the only system that can meet the stopping requirements set up by the Government. Some smaller truck also have air brakes and don't require a CDL endorsement. Air doesn't have to fill all the lines from the pedal to a brake chamber to work almost all lines are full of air. a signal line from the treadle (foot valve)to the relay valve is what opens a port to supply air from the relay valve to the brake chamber. All air is routed thru the foot valve because it is also a proportioning valve. The learning curve involved with air brakes is because when the brake is first applied a large volume of air quickly applies the brake and an operator needs to release some of the psi to control braking force. with hydro you feel more feed back thru the pedal. For example if your rotors are warped you can feel the pedal pulsate. with air brakes you get little feed back because you are suppling a constant air pressure thru a supply line that operates everything.
As far as both systems on a dual braking system having to fail this is not the case on the two vehicles I am familiar with. Both the Mack midliner/freedom series and the UD trucks are a air over hydro and if either one of the systems fail then the brakes fail.

[diginahole]

What would be the point of a dual braking system if only one could disable all service brakes?

Forgive me if I am using the wrong term here, but by dual braking system I mean similar to the dual master cylinder system employed in modern automobiles.

[Robert T]

I am not 100% sure but I think it is to increase the application pressure.
Normal hydro systems produce about 3500 psi
International have an electric over hydro to increase the pressure
On Large construction Equipment like articulated trucks and loader they have air over nitrogen charged actuators those actuators are charged at 6500 psi.
On class8 trucks it only takes 30-60 psi of air but the leverage on the slack adjusters multiplies the force so many pounds for each inch of leverage.

[diginahole]

Ah see that's not the dual system I meant. Built into all modern vehicles is a failsafe which would require a double failure of braking systems to entirely disable it. Air/hyd vacuum/hyd and electric/hyd are all simply power assit mechanisms to reduce pedal effort.