A series of questions from a complete novice about replacing a brake chamber.

To start with: Hiring a mechanic's not an option, but also shouldn't be necessary since this seems like a fairly straightforward procedure.

I'm replacing a 3030 air brake chamber on an '89 F850 fuel truck. I went down to Napa and picked up a brake chamber that looked right, but my first question is - did I pick the right one? Here's a comparison of the old one (still on the truck) and the one I bought:






They're both 3030s with a 2.5 inch stroke, the old one has a 150 psi max pressure and the new one has a 145 psi max pressure. I've never seen the needle go much past 130, so that shouldn't be an issue.

Second question: How do I measure where to cut the new pushrod? I've watched a half-dozen detailed Youtube videos, and have seen a half-dozen different ways when they remember to show it at all, including some that involved specialized equipment. What I'm think of trying is: Install the cage bolt on the old one, remove it, install the cage bolt on the new chamber cranked down to the same degree as on the old, set them side by side, and that should give me a length on the old one to measure a cut on the new one, as both will be in the same position.

Third: Is it necessary to have the new chamber caged until I finish installation? I'm figuring it's probably safe just to do so.

This is going to be a field job, not in a shop, so the simpler the better.

 

Mechanic is always an option. If you have to ask on a fourm about how to work on safety equipment, you should not be working on said equipment.

Get someone in that knows what they are doing, and maybe learn so you can do it next time.

 

Why are you replacing it?

If the pushrod and bolted portion arent damaged,

stop your current plan, cage both chambers, then simply replace the halfback (if you cant figure that out from what ive said, then zvar is right, you have no buisness doing it at all)

At worst, cage the brake, pinch the supply line, and drive it to a mechanic. Loves will replace a chamber for 1 hr labor, less if its just a diaphragm or halfback

 

That chamber doesn't look very old. As other guy said you can replace just the back half or maybe just the rubber diaphragm.

What are your symptoms?

If you do need to replace the whole measure the pushrod length with the chamber NOT caged.

 

Screw the jam nut down on the pushrod past where you are going to cut. Cut with hacksaw, grinder, whatever. Then screw the jam nut off, it will clean up the threads

 

On cutting length, either cage or uncaged both and just cut the same length. It should get you close enough to work fine. Running nut past where is you cut is always a good idea.
If it's your first one, make sure cage bolt is locked in solid with both tangs grabbing, seen rookies think they cage it but not lock in bolt all the way and it pop out during disassembly.

 

The service (not spring) brake chamber is loudly venting a lot of air through one of the vent holes. So the diaphragm is likely shot.

And, after a long night of research, it looks like replacing the diaphragm takes about ten minutes, significantly less effort, and a fraction as much of (someone else's) money.

 

It actually isn't an option - the nearest air brake mechanic that isn't in-house for either a government, logging, or construction outfit is seventy miles away. Ironically, I work for the county, which has a big road department with qualified mechanics ... that they absolutely won't loan out to other departments. If I can't do it myself, it won't get done, and I've got a useless fuel truck.

Anyways, it looks like replacing the diaphragm is both what's needed, and 100x easier.

 

You can replace just the diaphragm if you like. But you really should replace both if one went bad the other one probably isn't far behind.

But if you are replacing the whole can really the right way to measure the pushrod is to mount the can where it mounts up bolt it up tight and then get a square and go from the rod that sticking out right up to where the center of your slack adjuster is. On the center of the camshaft there should be a little dimple there and that has to be 90° to where the pushrod is.

Online they have instructions how to measure back from the clevis pin and how much room you're allowed. As far as cutting it goes the best thing is to put the lock nut on and put another lock nut and when you have the right length lock them together and then cut it flush at the end of the nut.

If this is a new to you truck or you've never replace these before it's important that you use a square and you check all this because often times people put them on there and they cut the wrong length.

It's common that you'll take two of them off and the shafts will be a different length. This will throw your braking off so you need to make sure everything is exactly perfectly correct.

And some guys I supposed to replace just one can but if you're going to replace one he should replace both of them and the one that's still good keep that one for a spare.

With brakes and Brake Chambers and that sort of thing I say always replace in sets.