Replacing brake chamber

You don't have to cage. Disconnect slack adjuster and two bolts. Hoses of course.

 

A lot of those mounting holes for the cans are slotted for positioning. What are the chances it was just mounted wrong?

Push rod cut too short coupled with auto slack adjusters generally results in brakes adjusting with too much stroke.

 

how would you go about cutting new 30/30 push rods for a trailer? Or is it better to just get a welded clevis?

I installed brake safe a couple of days ago and noticed two brakes were off. They are on new cans installed earlier this year. I let my trailer shop in town do it, but they didn’t seem to understand how to cut the push rods right. I measured push rod travel before I left the shop, and it was decent but almost right at 2 inches. I noticed one of the ones that were out of adjustment was longer than the others so I cut it down to match the others, about 7 3/4 in. It’s barely in adjustment now. And I just read your post about push rod cut to short + auto slacks can equal to much stroke.

I remember hearing too, about when the brakes are set they should be at a 90 degree angle, mine, even after the cut, still seem at an acute angle. And with the brakes set you can see that it’s almost already out of adjustment and the parking brake isn’t a full brake application of course. But the out of adjustment moved in the right direction after the cut. Any suggestions? Go a little shorter or? ... (thanks in advance) the first 2 pictures are of the rod I cut. The 3rd picture is the brake right next to it. (It’s barely in spec too.)

 

Google push rod cutting procedure it will explain to you how to measure it so that everything is correct.

I tried to load the PDF but for some reason it won't let me load it.

 

Ok, thanks. I was reading it once, about measuring a 90, then going back a few inches. I wonder though, about after it’s already been cut, how to go about getting it right. I’d rather not re-buy new chambers when these are only 25,000 miles in.

I’ll go re read that though. Thanks

 

For Meritor slacks, you need a template. I think the trailer one is light brown.

 

The brakes should be set when I measure and cut right?

As far as procedure, Does this look about right? I can still measure center point from the push rod, where it makes a 90 across the center of the S-cam. Then measure back the inches it says on the bottom right of this procedure according to size of slack adjuster I guess? I just watched a one minute video on YouTube and he was like quick done and easy lol

 

You have to mount your chamber in its bracket first with the rod sticking out behind it. You do that with the brakes not applied. The measurements that you are going to make will give you the right distance for the stroke. Make sure that you have the can in the correct holes and that all the cans are in the same holes. Also make sure you don't have any buildup of rust where the can is being bolted up against.

When you take your Square set it on top of the rod and line the other side up with the exact center of where the slack adjuster is. After I had it lined up I used a marker and marked it right down the side of the square down the center of the camshaft just to make sure I had it perfectly in the center. There should be a dimple inside of the camshaft for dead center. Then I screwed the nut up to the square and I used the marker to exactly Mark the threads at the nut.

The instructions will show you how to measure from the clevis back toward the brake chamber. Read the directions and re read them if you have to but make sure that you have the right length for the stroke and the Clevis.

Look on the chart and it'll tell you what the stroke should be for the type of chamber that you have and just measure. Then you cut your rod and put your clevis in.

The way that I did mine was I ran a nut down along the shaft and when I put my tape measure against it I could turn that nut little by little to get exactly the right length and then I used a marker and I marked the shaft right against the nut. Then I turned the nut down towards the chamber and I had a perfect Mark for the right length. Also when you back that nut off the shaft it'll make all the threads perfect where you cut it and you'll have no problem putting the clevis on.

Make sure that when you cut it you figure for whatever the width of your air cutter is or your hacksaw or whatever you use. I think that you are allowed 3/16 for the shaft to stick out from the Clevis if you need to make any adjustments.

It's not in the instructions but when I did mine after I made all my marks after subtracting and everything else I measured directly from the can out to where that last Mark was (the cut mark) and I wrote it down so that I knew exactly what the length is supposed to be.

That way when you cut it you can make whatever adjustment you need with the Clevis and you can get that right down to the 16th of an inch.

When you get to the other chamber on the other side it should be the same but I still did the same measuring and everything just to make sure it was right.

I am pretty anal about stuff like that.

 

Its been such a long time since I replaced an entire chamber I honestly do no remember the correct procedure.