Trailer Brakes

[Jim B]

So I was driving home today from West Chester, PA, on I-476 & I-81; and I must have passed about 20 to 25 trucks from Seaborne Intermodal or Seaway Intermodal, or something like that; and they were all pulling three axle container trailers with either a 20ft or 40ft container.  While that in and of itself isn't all that exciting, I did see on one of the trailers something that looked like a warning sticker.  I think it said "Disk brakes.  35% Shatter Rate."  This can't be right, can it?  It doesn't seem right that the DOT, or the Canadian equivalent as these trucks were from Canada, would allow brakes with a 35% failure rate on a vehicle.  Maybe I read the sticker wrong, but it does seem strange. 

Edited March 18, 2017 by Jim B

[mdlbldrmatt135]

I just did a little google searching.  It seems that the disc brake (besides being more $$ per axle)  has a 25-40% smaller surface area of pad contact.  That doesn't seem like a good idea on bigger vehicles.

[PierreR89]

If they are maintaned properly the shattering is not a problem as the brakerotors will have been replaced long before it reaches that limit.
Also the shattering happens most on trucks and trailers that have ventilated brakerotors. The ones that have solid rotors dont shatters easily.
Volvo FH series uses mostly solid rotors that are something like 48mm thick new and they are to be replaced once they reach 36-38mm.

The ventilated rotors have the same thickness but once they start to get close to the minimum thickness (same as the solid ones) they will have stresscracks in them and if they are not replaced by then they will enentually shatter.
The rotors are allowed to have stresscracks but they are only allowed to be 3cm long, not start/end at the edges and must be less then 1mm deep, over that = replace
I have had to replace drakedrums on 5 wheels on a 4 axle trailer because the brakelinings got loose from the brakeshoes and they then got wedged on something in there and kaboom went the drum..
The drum also took out the airbag, tires and damaged the controlarm that the airbag sits on, it did even manage to dent the frame at that wheel.

I have also had to replace brakerotors that have shattered and took out the brakecaliper to. When the rotor shattered the brakepads got thrown out, then what was left of the rotor hit the pistons inside the caliper and bending them and causing the rest of the rotor to fall off.
If the truck was unloaded the wheel would just have stopped turning but this happend one a fully loaded (65ton) in a downhill so the weight helped to push on and destroying even more.
 

Edited March 18, 2017 by PierreR89

[olsbooks]

Seems air discs are an on again/off again trend of late.  Kelsey Hayes tried HARD HARD in the late 80's/early 90's to go this route.  The size of the contact area of the shoe obviously matters but fiction, heat dissipation and (obviously) performance vs cost matter most.  Airplanes immediately come to mind as well as railroad passenger cars.

Even if disc brakes on semi's was/is better, it is going to be a tough sell.  "Everyone" knows and is set up for  drum brakes on big rigs.  Tools, parts, quirks, etc are in place meaning a huge learning curve/tool up costs.  It is like the size of trailer kingpins or glad hand connections.  There may be better things out there but the cost/benefit simply is not there in the grand scheme of things......yet. 

If/when we get point of using electric motors at the drive wheels, 3 phase motors not only can handle stalls (hill holding) but take a vehicle down to virtually 0 mph.  "Freq drive" meaning frequency modulation drive is just around the corner and already common place in locomotives, cranes, mining and heavy construction/farming equipment.  Siemens, GE and Mitsubishi are a few big names that have solid track record 20+ years and supply the components to outfits like Caterpillar, Deere, Kubota, etc.  The point being, brakes would be probably about 1/10th the size and used only below 2 mph and parking

One thing for sure..the drive lines/brakes that have been around for so long surely do seem on track for a major change in the next few years.

Peace 

 

 

 

Edited March 19, 2017 by olsbooks
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