Author Topic: Air brake question  (Read 2145 times)

Offline Nel

  • Full Member
  • ***
  • Posts: 178
Air brake question
« on: May 24, 2016, 05:31:58 AM »
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
4104-4519
West Nyack , NY

Offline DoubleEagle

  • Hero Member
  • *****
  • Posts: 1060
Re: Air brake question
« Reply #1 on: May 24, 2016, 06:13:35 AM »
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.
Walter
Dayton, Ohio
1975 Silvereagle Model 05, 8V71, 4 speed Spicer
1982 Eagle Model 10, 6V92, 5 speed Spicer
1984 Eagle Model 10, 6V92 w/Jacobs, Allison HT740

Offline Oonrahnjay

  • Hero Member
  • *****
  • Posts: 3299
Re: Air brake question
« Reply #2 on: May 24, 2016, 06:50:57 AM »
 ... 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.  
« Last Edit: May 24, 2016, 08:53:03 AM by Oonrahnjay »
Bruce H; Wallace (near Wilmington) NC
1976 Daimler (British) Double-Decker Bus; 34' long

(New Email -- brucebearnc@ (theGoogle gmail place) .com)

Offline Nel

  • Full Member
  • ***
  • Posts: 178
Re: Air brake question
« Reply #3 on: May 24, 2016, 08:02:28 AM »
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
4104-4519
West Nyack , NY

Offline eagle19952

  • Hero Member
  • *****
  • Posts: 3764
Re: Air brake question
« Reply #4 on: May 24, 2016, 08:16:15 AM »
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.
Donald PH
1978 Model 05 Eagle w/Torsilastic Suspension,8V71 N, DD, Allison on 24.5's 12kw Kubota.

Offline TomC

  • Hero Member
  • *****
  • Posts: 8651
Re: Air brake question
« Reply #5 on: May 25, 2016, 08:55:32 AM »
Slack adjuster bushings need to be replaced.
Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.

Offline eagle19952

  • Hero Member
  • *****
  • Posts: 3764
Re: Air brake question
« Reply #6 on: May 25, 2016, 10:35:31 AM »
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...
Donald PH
1978 Model 05 Eagle w/Torsilastic Suspension,8V71 N, DD, Allison on 24.5's 12kw Kubota.

Offline Nel

  • Full Member
  • ***
  • Posts: 178
Re: Air brake question
« Reply #7 on: May 25, 2016, 12:56:51 PM »
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
4104-4519
West Nyack , NY

Offline eagle19952

  • Hero Member
  • *****
  • Posts: 3764
Re: Air brake question
« Reply #8 on: May 25, 2016, 02:37:37 PM »
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
Donald PH
1978 Model 05 Eagle w/Torsilastic Suspension,8V71 N, DD, Allison on 24.5's 12kw Kubota.

Offline Nel

  • Full Member
  • ***
  • Posts: 178
Re: Air brake question
« Reply #9 on: May 25, 2016, 07:43:39 PM »
Thanks Don
4104-4519
West Nyack , NY

Offline bevans6

  • Hero Member
  • *****
  • Posts: 6006
  • 1980 MCI MC-5C
Re: Air brake question
« Reply #10 on: May 26, 2016, 05:04:58 AM »
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.
1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Allison MT-647
Tatamagouche, Nova Scotia

Offline eagle19952

  • Hero Member
  • *****
  • Posts: 3764
Re: Air brake question
« Reply #11 on: May 26, 2016, 09:00:18 AM »
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.. >:(
Donald PH
1978 Model 05 Eagle w/Torsilastic Suspension,8V71 N, DD, Allison on 24.5's 12kw Kubota.

Offline Jim Eh.

  • Hero Member
  • *****
  • Posts: 743
  • Excess in moderation
Re: Air brake question
« Reply #12 on: May 26, 2016, 09:20:39 PM »
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.
Jim Eh.
1996 MC12
6V92TA / HT741D
Winnipeg, MB.

Offline eagle19952

  • Hero Member
  • *****
  • Posts: 3764
Re: Air brake question
« Reply #13 on: May 27, 2016, 12:59:24 PM »
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 :)
Donald PH
1978 Model 05 Eagle w/Torsilastic Suspension,8V71 N, DD, Allison on 24.5's 12kw Kubota.

Online chessie4905

  • Hero Member
  • *****
  • Posts: 2826
Re: Air brake question
« Reply #14 on: May 27, 2016, 02:32:33 PM »
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.
GMC h8h 649#028 (4905)
Pennsylvania-central