Disc Brakes

Well, i'm not from USA, but here in Europe there are disc brakes on all new highway trucks. They have pretty bigger stopping power, ordinary EU truck can stop from 80km/h to 0 in around 50m fully loaded (44t on 5 axles)

 

My advice is go with the drums, I had a CH Mack that had disc and I replaced them with drums. As far as them freezing up, dont know I didnt keep them that long, and as far as stopping power maybe if your gross isnt going to exceed 80,000lbs they might be alright, but I'm drums all the way!

 

Disc brakes are the best way to go in my opinion(the Feds too ). You will lose about 18# per wheel, stopping distance is unreal, no brake fade compared to drum & the ware and maintenance are great. You will still have s-cam & slack adjuster(same as always). Freezing won't be a problem because you won't have a drum to catch & hold the moisture. If you want more info just google air disc brakes.

 

I had a factory rep from paccar tell me that disc brakes are worse for stopping power than drum brakes. The reason is that there is more surface area on the drum brakes than there is on the disc brakes. This may sound stupid but I actually had proof of that three years ago, too bad I threw away that information.

 

The only reason there would be more surface area on a drum vs a disc in a truck is that there isn't enough room to get adequate SA. In a car, there is WAY more surface area on a disc than a drum taking up the same space.

Either way the Feds are going to require disc brakes anyway, do NOT attempt to dispute them with actual FACTS, you'll just get swept aside.

 

when drum brakes get hot they expand away from the pads

when disc rotors get hot they expand towards the pads giving greater stopping pressure

 

Haha, that is pretty funny. The most effiecent type of brake out there is a band brake. Then coming in number two is the drum brake followed by disc brake. The band brake had an efficency of around 87% for the amount of pressure applied in order to stop it. The drum brake had around 83% and the disc was around 72%.

I am in no way saying that all trucks need to have band brakes on them. What I am saying is that right now drum brakes work the best. You will get longer life out of them vs. disc brake. You could say that drum brakes will have brake fade. Sure but you will have less surface area on a disc brake to stop you vs. drum brakes. So you will go through more brakes pads per miles traveled plain and simple. In order to get larger disc on a semi rim and tire manufactures would have to go to much larger rims and tires thus increasing the cost of the brake package not including additional rotating mass of the new larger rims and tires. So in reality you would not gain that much more by going to a lager tire and rim package because you now have to stop that additional weight you put on there. Paccar has already investigated this trend and has descided that drums brakes are better and until a better braking system has evolved that can stop better I do not think that the feds are going to mandate a braking system that is less effiecent. Now you can get into the whole debate about regenative braking systems and say that you should put them on all trucks, but you don't want to go there as that particular trend has a whole different can of worms that I can open up on it.

 

The stopping pressure of the that the disc get come from the air pressure that is given to them from the brake pedal assembly. This air pressure then reacts on the surface area of the piston in the disc brake assembly. The bigger the piston the greater the force that you get against the disc. So in order to get more "stopping pressure" you need to increase the force applied IE get more air pressure to the piston in the caliper or buy a disc brake with a larger piston in it. The disc brake assemblies are intened to "float" so that they are mere thousands of an inch away from the disc. This is the way that they are designed. IF they were constantly touching the disc they would wear faster resulting in you replacing them more often. On drum brakes the slack adjuster tacks up for the expansion.