Poor braking

You may end up saving money on this by just replacing the entire take system. I haven't a clue what it could be but it may be worth a thought

 

How much space is there between drum and shoe when brakes are adjusted in this fashion?

 

Sounds like and under leverage issue. What's the current adjuster arm span? If you have dual length adjusters and they are on the short length try moving to the longer hole.

Sounds like something in the system is the wrong part, as in assembled wrong from the factory. It happens.

TA

 

I finally have a theory.

Stay with me while I think this through. You get your braking power from your air tanks. Primary and secondary. Avoiding the details, I expect that the air brake system with it's hoses to the cans etc is pretty independant and self contained.

What I am thinking is this.

Is it possible you have airride under those axles back there and they are fed directly or as parasite via the primary and secondary tank? Mack Trucks usually had three tanks, two for the air brake and one for the airride and everything else. (This side of the air dryer)

If you are applying braking air, your truck noses down, raising the rear end on it's airride which causes it to get whatever air it can maybe stealing it from the same air you are trying to feed the brakes.

Does that even make sense?

 

Bumping this because its been near 9 months and I'm curious if this issue ever got solved.

 

I’m bumping this as well as we have a Mack tri axle dump truck with the same issue at the moment. Many mechanics and Mack have looked and still has the issue.

Even the spring brakes can’t hold the truck for a parking test.

6 years, 140,000 kms on the pads and still 3/4 linings left. That’s with all the stop and go short driving these trucks do.

I’m soon going to take the entire brake system apart and compare to the sterling dump truck we have as that truck stops really good and I just did the brakes on that one a few weeks ago.

 

While Mack thinks the cam is proper for this truck according to part numbers, I’m leaning on the cam being the wrong setup.

2005 sterling dump truck:
Q-plus meritor pads
16.5 drums
30/30 long stroke chambers
5.5 inch Gunite slack adjusters.
Cam, no part numbers at this point. I’ll be calling sterling next week for the part number for that truck.

Mack dump truck:
Q-plus meritor pads
16.5 drums
30/30 short stroke chambers
6 inch meritor slack adjusters
Cam, I have the part numbers listed in parts books but not in my head. I’ll have to check.

Both trucks have same brand front and rear drive axles.

The Mack’s front brakes and lift axle seems to do all the braking and I can easily put my hand on the rear drums while the lift axle is smoking a little.

The Sterling can stop almost as fast as a car while loaded and the whole load in the dump box will fly forward (likely have Mto very happy to write tickets for tandem steers being overloaded)