Air brake question

[Nel]

Hi all, I started the 4104 yesterday and it aired up fine, I noticed that when I went to push in the spring brake air release button, it would not stay down, air pressure was over 100 psi, thought maybe brakes were stuck but I was able to move the bus as if the spring brakes were released. put it up on ramps , shut it down and had my son push the service brake pedal and noticed the brake can on the pass. side would leak when brake was applied. so I know the service brake can on that side is bad but don't understand why the spring brakes are not holding . They usually held solid before.
Thanks in advance, Nelson

[DoubleEagle]

If the spring brake is not holding, either the spring is out of spec and the unit needs to be replaced, or the brakes need adjusting. If you have auto-adjusters, maybe they are not keeping up.

[Oonrahnjay]

... noticed the brake can on the pass. side would leak when brake was applied. ....  

    Air brake systems are complex and there can be many sources for a particular symptom but a leak like that is usually a sign of an internal failure within the brake can assembly.  A thing that strikes me as odd is that that's often that failure keeps the parking/emergency applied (i.e. the air pressure that's meant to release the spring brake leaks out without disengaging the parking brake -- no air pressure at the canister means the parking brake is on because of the effect of the spring).  It's pretty sure you have some problem in that leaking canister; I'd also check the brake release button and it's valve and air supply lines plus any quick-release valve associated with the release button.  If you change the brake canister and solve the obvious leak and that doesn't fix the parking brake problem and the release checks OK, then you're looking at tracing air lines, relay valves, anti-compounding valves, etc.
    I hope it's something simple.  

[Nel]

Thanks Walter and Bruce will replace unit and check

Also noticed the driver side slack adjuster has alot of side to side play on the shaft when brake is off, is that normal , lots of grease on it so cant tell yet what holds it in place

[eagle19952]

Thanks Walter and Bruce will replace unit and check

Also noticed the driver side slack adjuster has a lot of side to side play on the shaft when brake is off, is that normal , lots of grease on it so cant tell yet what holds it in place

simple answer.. no.

[TomC]

Slack adjuster bushings need to be replaced.

[eagle19952]

Slack adjuster bushings need to be replaced.

they're actually S-cam bushings...which when they wobble like you describe.. usually means the S-cams are shot too.

and will contribute to the early death of the parts you just installed, not to mention that all tyhe adjustment in the world is not going to make your braking as good as it was intended...

[Nel]

Thanks, I will be looking into it further soon, the play seems to be the slack adjuster sliding on the shaft like a retainer or something is missing

[eagle19952]

Thanks, I will be looking into it further soon, the play seems to be the slack adjuster sliding on the shaft like a retainer or something is missing

some small lateral movement on the shaft is ok, most have circlips or snap rings. it is orbital or oscillating movement of the cam that is not so good

[Nel]

Thanks Don

[bevans6]

There are usually shims or stroke indicators on the S-cam shaft that take up some of the lateral movement.  I suspect they often get left off when slack adjusters get changed.

[eagle19952]

There are usually shims or stroke indicators on the S-cam shaft that take up some of the lateral movement.  I suspect they often get left off when slack adjusters get changed.

agreed, or many don't know they belong there so do not order them with the new parts..

[Jim Eh.]

The cam washers (spacers) are installed on either side/both sides of the slack adjuster to loosely center the slack so it is in line with the brake chamber push rod.

[eagle19952]

The cam washers (spacers) are installed on either side/both sides of the slack adjuster to loosely center the slack so it is in line with the brake chamber push rod.

hence slight lateral movement

[chessie4905]

Disconnect and plug air lines to leaking chamber only. Now try to apply and release parking brake. It will probably work fine then. If so you should just replace both chambers while you are at it if they have been on coach a while since they are cheap. Of course take care of play, looseness and worn parts while you are in there. 4104's don't have big brakes anyway. 5 and 7.