replacing brake chamber - issue

I thank so but open for correction. Believe you are KW and would have Halidex slacks. They seam to be a bit more to tolerant to different rod lengths than some others. Rockwell auto slacks have a jig to line up on the three pins and are quite sensitive for proper operation.
The difference in length I was speaking of is between the clamps at the diaphragms. They were all 2.5 inches for years. That is the reason for the max travel of 2 1/2 travel on a #30 chamber. The chamber travel would end at 2.5 inches and no pressure is applied to the shoes.
As I answer this I question my own answer. However if you look at any Freightliner made in the last 10 years or so you can visually see the different length between the clamps and those on older and or other equipment.
Just don't mix them up and sounds like you are great.

 

Looking at the pictures I don't think the old can is fully extended. If that is the case the new can is cut too short. That would explain not enough threads. 34 years as a mechanic I have never needed to cut threads on a brake can. Something is not right. Dig the old can out of the trash & air up the service side to see if the pushrod extends further. Is the yoke jam nut hitting the can with the brakes released?

 

Maybe I'm wrong, but I thought if the adjusters reached a 90 angle, the DOT would shut you down.

 

90 degrees (or slightly less) is the best angle for maximum torque multiplication. As long as the applied stroke does not exceed 2" (bear with me I haven't worked on truck brakes in about 6 years) then you shouldn't have any issues with DOT. Typically a correctly adjusted brake has about 1.5" to 1.75" of applied stroke.

 

Rollin'....do what you want but if they are all the same age and one failed, the others aren't far behind. Kind of like headlights that are the same age....replace all of them when the first one fails. It likely saves you time, aggravation and money in the long run.

 

You beat me to it.
Have at least a spare chamber ready.

 

Looks like you got 'er figured out. You bought the wrong brake can, but you used a die to cut threads farther up the rod. You could've just re-used the old rod (with the new spring) in the new can...which is probably what I would've done rather than trying to track down the right size die.

 

With the brake manually caged, a broken spring can keep the rod from coming out all the way. You can also measure with the brake uncaged and insert a welding rod (or something like it) to measure the the length you need. The rod and slack adjuster need to be at less than 90* for maximum effectiveness. The laws of physics. When replacing 1/2 of a brake chamber make sure you know which clamp to remove. I vote to replace the whole thing. KW uses more than one brand of slack adjusters. The lowest bidder gets the honors.