Brake chamber pushrod

You don't need zip ties to measure stoke. Your eyeballs work just fine.

Brakes released just look at the brakes. Gaps between shoes and drums. Adjust them.

Closed gaps won't have much stroke compared to open gaps. Brakes work better with a half inch gap over 2 inch gap.

You guys sure make things difficult when all you gotta do is look at the gaps.

 

I would say you have something going on inside the chamber you cannot see.

 

With service brakes you can apply up to the full air pressure in the system (105-140 psi).
With the spring (parking) brakes applied, the spring only gives about 45-60 psi equivalent pressure. So you will see less pushrod travel as there is less pressure being applied.
Although 1-1/2” difference does seem like a lot. So either the spring in the chamber is old and weak or could be broken in a way that it’s barely making contact.
So it’s probably worth changing out that brake chamber.

 

There's just not much there to go wrong. As long as you have no air bleeding into thr supply side (would assume not since only affecting one), and since it's working properly with service brakes, just change it.

 

Are the slack adjusters both mounted on the s-cams at the same angle and are at same angle when brakes are released? If so then the longer stroke on the one side is caused by slack adjuster bad and will not stay in adjustment, broken or worn spring in chamber, or a long stroke chamber was installed on that side and the other side has a short/standard stroke can. I have seen that mismatch happen when someone needs a can in a pinch and long stroke is all that is available. Same with trailers. Seen many get a standard when they need a long. That Causes weak brakes instead of overly tight brakes.

 

Spring is probably broken. Once in a blue moon they'll break in such a way that the slot for the caging bolt is still lined up with the access hole in the back. Give the chamber a few light smacks with a rubber hammer or your palm and you'll probably hear pieces of it rattling around in there.

 

That’s what mine did. They were broke, but couldn’t tell. Still had tension. That’s why they always cut the spring in two places to disable old ones for safe disposal.