Brake chambers keep breaking after trailer rebuild

We had a demo trailer that flopped years ago. Finally sent it to the frame shop and ended up putting everything new on the axles as well as new airlines and brake valves. Everything works well, but we've had 3 chambers break internally between the parking and the service side which sends air back into the service valve and wont release the parking spring on that one chamber. I'm pretty confident we matched all old valves and chamber rod lengths. -Standard 3030 short stroke threaded rod chambers -065437 SR-5 Parking valve -103028 R14 Service valve We sent one of the broken chambers in for warrant and they said something about the rod lengths must have been incorrect to have that failure.

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Are you sure it didn't have long stroke air chambers to begin with, identifiable by the fact the threaded ports are cast square instead of round.

Im pretty confident the chambers were originally short stroke

Well it's the park brake side that broke, what brand of chamber is it.

You've got geometry wrong somewhere, it's not normal for those things to break. And not a hard fast rule, but rather, typically, short stroke chambers are used with self adjusting slack adjusters where long stroke are typically used with manual adjusters.

willie59 said: And not a hard fast rule, but rather, typically, short stroke chambers are used with self adjusting slack adjusters where long stroke are typically used with manual adjusters. Click to expand... It's definitely not a hard fast rule. Freightliner has been installing long stroke chambers with auto slacks at factory for about the last twenty some years. But that said, I ran through a batch of Alliance chambers that broke the park brake puck or leaked through park side to service side. * What would or might help is a couple of photos showing slack geometry with brakes set and released.

My thoughts exactly.

Plus we don't know if only piggyback park chambers were installed, in that case the service side of chamber plus rods would still be the same as before. If not were the rods cut to correct length for slacks with correct yokes. And if chambers were complete units were those installed in correct mounting holes for a straight shot.

Truck Shop said: Well it's the park brake side that broke, what brand of chamber is it. Click to expand... I don’t recall the brand, but I have others with the same brand and batch in my fleet, so it has to be a geometry issue on this trailer Truck Shop said: Plus we don't know if only piggyback park chambers were installed, in that case the service side of chamber plus rods would still be the same as before. If not were the rods cut to correct length for slacks with correct yokes. And if chambers were complete units were those installed in correct mounting holes for a straight shot. Click to expand... we changed out the entire chambers when rebuilding the trailer Truck Shop said: What would or might help is a couple of photos showing slack geometry with brakes set and released. Click to expand... I’ll have pictures uploaded shortly

View attachment IMG_9467.jpeg View attachment IMG_9469.jpeg Both pics are of rear axle, which are the only chambers that keep breaking. First is parking brakes released, second is parking brakes set. I measured strokes (1st Measurment: parking brakes released, 2nd measurement: parking brakes released and Johnny bar applied). For both chambers on my rear axle they were over 2” of stroke, while my front axle was just under 2” of stroke. I’m assuming that is my whole issue here. Do I need to get new rods/chambers and cut the rods longer?

It's not that far off, if anything the rod would be shortened slightly, main thing is slack doesn't travel past 90 degrees. But those are Gunite style auto slacks and like all use a templet to set proper adjustment stroke. Those are stroke sensing slacks not drum sensing. Nothing in that photo looks to be that far off. I added a PFD file to look at, pages 7, 8. * https://www.accuridecorp.com/sites/default/files/resources/2020-08/WE3.001 Rev. 2 ASA Manual_low res.pdf

We put a square on the rod and slack and both rear axle chambers were past 90°. We adjusted the clevis’s in slightly and got them at/ under 90°.

And the mystery remains, nothing jumps out as a red flag there. But just an aside, that setup with those gunite self adjusters look like they would work with welded clevis short stroke 30/30 chambers. If so, would take the guess work or template work out of cutting brake chamber rod to proper length.

willie59 said: And the mystery remains, nothing jumps out as a red flag there. But just an aside, that setup with those gunite self adjusters look like they would work with welded clevis short stroke 30/30 chambers. If so, would take the guess work or template work out of cutting brake chamber rod to proper length. Click to expand... I’ll keep that in mind. Thank you for the help.

I don't know how many I've seen with auto slacks with too long of rod, over center and never broke a park brake puck. The long strokes are designed to do just that-go over center. I enlarged the image of chamber and bladder, can see which way can was installed by all the damage, but looking closely at weld area on puck--it was a less than adequate weld. Looks like two defective standard 30-30 brake chambers IMO, and not impossible with the quality of parts these days.

Wait, there's such a thing as quality of parts now days?

If the mystery remains it's said---and it really isn't an issue of geometry--then what's it left too, poor construction. Actually it is common for pucks too break, don't know how many I've found through my years, didn't know at any time I would need to keep track of that particular failure. Fact is it's the weakest part of a break chamber--total force pinpointed. And findings/experience depends on just how many break chambers a person in this business replaces in a career. What might seem abnormal to some is normal to others.