Poor braking

Just for ##### 'n giggles, when unloaded have you tried popping the yellow valve while moving in a large, empty parking lot? Obviously at a low rate of speed so you don't lose control. Doing that should give you about the equivillent of 60-90 PSI on the service brakes. If that locks up the drives or feels more powerful than braking with the pedal, the foundation side of your brakes are likely fine and your issue is ABS or air related. If the braking power is just as crappy, you most likely have a mechanical issue in the foundation side.

 

I know this was mentioned already but 9/10 times mechanics overlook the simple stuff. What is the applied stroke on the chambers? I have seen trucks where the pushrods were cut too short, which makes the auto slacks adjust them with too much chamber stroke. Drums heat up and expand and brake fade occurs. Properly adjusted I believe should be 1.5"-1.75". Standard chamber stroke is I believe 2.5".

 

How much psi do you get on your pusher brakes?

Has anyone disconnected a slackajuster from the aircan and moved it by hand?(to see if you don't lose force there)

Can you fit bigger diameter cans on your brakes?

 

Maybe worth a shot if you can find a good place to try it and willing to....
Get up to around 15 and apply parking brake the springs should be applying enough pressure to lock you up... Could let you know if it's a air issue mechanical

Nevermind see @NorthernMechanic beat me to it

 

The idea of spring braking being crappy scares me. A truck factory will have to be seriously incompetent bordering on sabotage if you cannot get spring brakes to essentially lock everything down.

I wonder if the ABS senses air pressure only or does it use what I consider to be more accurate rotational wheel information combined with possibly even a downward firing radar device designed to proved your ABS system knowledge of road speed actual. So that if one or more wheels lock up and radar shows you moving along at 50 or whatever then it's time for it to use the ABS.

My post here is a simple wandering post thinking out loud. Cams are beginning to make some sense and I resist the idea that the push rods are too short. Surely the factory that built the beautiful truck are not that stupid? (Im not insulting, Im simply expressing choosing a word closest to a mental lack of thinking required to build trucks properly so that the freaking thing will stop.)

 

I'm amazed they can't figure it out.

Mine has disc brakes and stops on a dime.

 

Curvature. Not enough contact with drums. You think there would be contact end to end across the pad.

You must have huge drums on that truck. Do drums come in different sizes maybe? It's a new truck. Sorta...

Ok accepting the fact you can stop at 25 psi and generate a hard stop.

I remembered something... from the ashes of long ago trucking.

I wonder if the axles in your truck to which your wheels, drums are attached to at the hubs are rotating forward when you are stopping, robbing your entire rig of stopping power by coming off the brake pads trying to apply braking pressure? Or actually the axles are hung from your body and frame and rotating itself on each one back there trying to stop and robbing the contact area the pads are trying to achieve?

Bad air ride suspension ride height adjustment maybe? or something else?

Im just thinking out loud. But this is really something. What a mystery.