How do you know drum brakes are working perfectly?

The linings may have glazed over from too much hard use and the heat it generates.

 

Nothing that gets onto a big truck is "Illegal"

Oil in the tanks? That tells me that either the tanks are never drained each night (No air dryer?) or the oil etc has compromised the rubber dividing the Spring and the Service air chambers of your brakes.

I don't know about the rest of it without seeing everything first hand. There is a range of possibilities.

 

It is winter time here.
I noticed this in the winter, for me it was just the wrong kind of grease being used in the Slacks and s-cams. Too heavy grease caused a delay in the reaction Time, caused by a slow rotation of the s cam.

 

A shiny inside of the drum ( can be seen once those guards fall off) says it's working.

 

Warped drums. There's no way to see it without putting them on a machine to turn them. Which I don't think exists for truck drums.

I had a truck that took 60 plus pounds and still sucked. Then it got new brakes and drums. Stopped on a dime afterwards. With only 15 pounds.

I had a 76 Plymouth duster that was the same way. Brake pedal felt like hitting a brick wall. Machined all 4 drums. Worked like a champ.

Mechanics talk valves and replace but problem never gets fixed. But new drums always does the trick. In every truck I've gotten new drums with.

 

Oil is messing up your valves If it's spewing oil into air lines.. IN cold weather they can gum up so bad from oil they freeze and trailer won't air up properly

 

You can likely eyeball them and clearly see if they are warped that badly. Jack a wheel up. Set something close to the drum, spin and watch the warps.

 

If you can see that. Your truck is probably falling apart every time you hit the brakes.

Only way to see it is on a machine. Grinding the surface down till it's perfectly round. Or flat if rotor.

Drums and rotors warp. That's just normal. Nothing anyone can do. It's caused from uneven heating and cooling. The thinner they get. The worse the warp. And drums and rotors do get thinner from every day use. Just like brakes get thinner.

Course. Your probably shaking your head and rolling your eyes. But hey. I used to do brake work for a living before changing to steering wheel holder.