Which rear brake diaphragms

[Rogue1bus]

I’m pretty sure my rear brake diaphragms are going bad.. I can hear them hissing when applied at a stop light etc, and the compressor seems to run a lot. So I’m planning on changing them out. I called the international dealership and they told me I need “30s” in the rear. The problem is I don’t know if I need 30s with 2.5” stroke (seems standard) or 3” long stroke diaphragms assembly’s? Anyone know how to tell which diaphragms I need?

Thanks!

[Johnny Mullet]

You will have to look at the brake chambers to determine if it's standard or long stroke. If your bus is older, it's most likely standard. Long stroke chambers have square nipples where the air hoses connect. Got a pic of yours so we can verify?

[Rogue1bus]

Thanks!

[Johnny Mullet]

Looks like long stroke chambers to me.

[Rogue1bus]

Thanks I really appreciate it!

[Rogue1bus]

Turns out it’s actually the front brake that’s leaking. Refer to the pictures below. So I need to figure out what part it is also.

[Johnny Mullet]

Can't tell for sure, but looks like Type 24 chamber maybe? There is no long or short stroke on steer axle single can brakes.

[sojourner]

The brake chambers should have an ID plate on them that tell you the make and part number to get replacements. On the front service chambers, if not rusted up, you can easily change the diaphrams and save a good bi of money. Rears (spring brake) are another story altogether and should be changed as a complete assembly. DO NOT try to service a spring brake chamber!!

[Rogue1bus]

Thanks! I changed the fronts(which were leaking at least in the drivers side). And your right the old brakes did have a tag indicating the type. I haven’t changed the rear ones yet. Should I wait till I get a leak or change all of them out together?

[Johnny Mullet]

You kinda need to know what you are doing so not to hurt yourself.

[Rogue1bus]

Originally Posted by Johnny Mullet

You kinda need to know what you are doing so not to hurt yourself.

I got the entire assemblies, so the procedure should be; chock the wheels, measure the stroke distance, cage the diaphragm assembly, remove old diaphragm assembly, cage new assembly, cut stroke bolt to match the old assembly, and reinstall new assembly.

[Brad_SwiftFur]

For the rear, you can get an "Air Brake Chamber Half Kit" (one listing referenced a "Piggyback"), which is the sealed parking brake half, new service brake diaphragm, and springs. The above procedure still applies - *DO NOT DISASSEMBLE THE OLD ONE UNTIL IT IS CAGED!* For older buses with parking brake assemblies clamped - *DO NOT DISASSEMBLE THE CLAMP!* (parking brake side). It WILL come apart with tremendous explosive force since there's a huge eff'ing spring behind that cover - this is the spring that keeps the brakes applied when you park. The new ones are usually pre-caged, and it avoids all the hassle of having to cut the pushrod to length, and remove/reinstall the clevis and slack adjuster.


There have been a few folks severely injured and killed over the years taking brake chambers apart - which is why the parking brake halves are now pressed together instead of clamped. But the service side still has springs and when parked still has the parking brake spring pushing, so even the service brake half will have some pressure if it's not caged.


Typical failure point in these is one or the other (or both) diaphragms begin to leak, due to deterioration of the rubber. The springs will also eventually fail and break (usually rupturing a diaphragm in the process), leaving that wheel without a parking brake (and an air leak if the diaphragm is ruptured).

[HazMatt]

Not that ought be required, but:
^ 2X ^
Inertia's a bee-yotch, and pressure is a flat-out killer!

[Johnny Mullet]

The 30/30 Piggyback mentioned above is the way I would go.
Chock the wheels so the bus won't move.
Build air pressure to 100+ psi.
Release parking brake.
Back off slack adjuster all the way until pushrod retracts to stop.
Cage chamber if possible with caging bolt.
Set parking brake.
Remove air hoses marking "Service" and "Emergency" sides.
Remove or cut one clamp bolt.
Pry clamp off and chamber will come off.

Transfer any brass fittings to new chamber with pipe dope or thread tape.
Make sure new fittings face in same direction.
Assemble new clamp with one bolt threaded half way.
Install diaphram and then piggyback and hold it centered.
Use other hand to fumble with clamp and bolt squeezing clamp tight and tighten clamp nut.
Evenly tighten both clamp nuts with a socket or wrench.
Install hoses in proper arrangement.
Release parking brake with 100+ psi and listen/check for leaks.
Adjust slack adjuster all the way tight till brake shoes engage drum.
Back slack adjuster 1/4 to 1/2 turn.
Have assistant step on brake normally (not hard) and check stroke.
Pushrod stroke should be about 1 1/22" and check for leaks with brake pedal applied.
Adjust all other brakes accordingly.