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RonF
Top Member
867 Posts |
 Posted - 01/16/2019 : 04:54:49 AM
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I have been fighting this issue on buses with the drivers for the last 15 years or so and can't get a good answer so maybe here we can figure something out.
Air brakes:
It happens on IC, BlueBird and Thomas from pretty much year ranges 1999-2019 models.
When you apply the brakes whether moving or sitting you get a loud clunk from any wheel at particular times. I have had this happen while driving as well and sometimes the bus would pull hard at that moment and that moment only. While inspection the brake system, everything is adjust and nothing is out of specs.
Some years ago I had a Haldex instructor tell us that if the drivers will push the brake pedal with full air pressure 3-4 times during pre trips, that this will stop that and for the most part it has. He explained that it is the adjusting pawl teeth hitting together just before adjustment.
Again, this is happening on all types of buses, including brand new ones.
Any thoughts???
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wwinters
Senior Member
USA
114 Posts |
Posted - 01/16/2019 : 05:13:29 AM
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| Over the years I find that the S cam roller is not working properly when this is happening, you may want to check that. I clean and use a emery cloth to smooth S cam when installing new rollers, I do not put anything on it due to collecting brake dust causing more problems. I have also found on customer trucks the S cam sticks due to lack of greasing S cam but not so much on School Buses due to more intense servicing |
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RonF
Top Member
867 Posts |
Posted - 01/16/2019 : 05:44:07 AM
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quote:
Originally posted by wwinters
Over the years I find that the S cam roller is not working properly when this is happening, you may want to check that. I clean and use a emery cloth to smooth S cam when installing new rollers, I do not put anything on it due to collecting brake dust causing more problems. I have also found on customer trucks the S cam sticks due to lack of greasing S cam but not so much on School Buses due to more intense servicing
That all makes since and I have found issues over the years, but the ones that are troubling are the new buses and by new I mean less than 1000 miles on them. That has me thrown and it's not just one bus either. It has done it on both IC and BB when new. |
US Army retired CMBT |
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Bluenozer
Top Member
Canada
644 Posts |
Posted - 01/16/2019 : 07:25:41 AM
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| Here in Nova Scotia by law we do a annual brake inspection, tear down , check, lube, replace whats needed so I haven't heard that noise since I left the stealership and that brake apply session is part of our pre-trip to pump down air until button pops so every day the adjusting pawl is adjusted |
OEM trained in wiring and all engine platforms for over 20 years
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671Fan
Active Member
47 Posts |
Posted - 01/16/2019 : 08:03:07 AM
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| We get that one regularly. For us it is a collection of brake dust and other lovely stuff creating a speed bump of sorts on the s cam. Sometimes the roller seizing will contribute also. Pull the drum, check the roller surface and action, run some emery over the s cam to smooth it out and it should be fine. I assemble the rollers to the shoe dry as any wet lube collects brake dust and turns into a sticky mess and stuck rollers. |
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RonF
Top Member
867 Posts |
Posted - 01/16/2019 : 12:39:53 PM
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quote:
Originally posted by Bluenozer
Here in Nova Scotia by law we do a annual brake inspection, tear down , check, lube, replace whats needed so I haven't heard that noise since I left the stealership and that brake apply session is part of our pre-trip to pump down air until button pops so every day the adjusting pawl is adjusted
Pulling the wheels and an annually wouldn't help with this particular bus from this morning. We haven't had it a year yet. I am however going to pull the wheels tomorrow and have a look before I send it to the dealership. |
US Army retired CMBT |
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Poolguy7250
Active Member
USA
11 Posts |
Posted - 01/16/2019 : 7:09:42 PM
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| Do your wheels have backing plates on the brakes. |
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RonF
Top Member
867 Posts |
Posted - 01/17/2019 : 03:39:11 AM
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quote:
Originally posted by Poolguy7250
Do your wheels have backing plates on the brakes.
Some do some don't. The one I'm working on this morning does not. |
US Army retired CMBT |
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slippert
Top Member
USA
630 Posts |
Posted - 01/17/2019 : 04:11:38 AM
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I support the the roller/s-cam sticking issue on the clunk you describe, happens here also..... I have to pull wheels clean and lube rollers on mine anywhere from new to 20,000 miles the first time also....
I replace smooth roller with a knurled roller, when I pull wheels for this problem.... that seems to cure my issue for the life of brake lining, since I started doing this about 10 years ago.. so far have seen no adverse effects/wear from using the knurled roller in my fleet... |
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RonF
Top Member
867 Posts |
Posted - 01/17/2019 : 08:25:51 AM
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Alright I just finished working on the latest bus. A 2019 Vision, gas with air drum brakes. Driver complaint was a clunk in the rear when applying the brakes.
I removed the wheels and drums. I had smooth rollers, so I replaced them with knurled ones. There was nothing on the cam. Put it back together, road tested and no clunk.
Time will tell
Thanks all. |
US Army retired CMBT |
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Bluenozer
Top Member
Canada
644 Posts |
Posted - 01/17/2019 : 08:34:10 AM
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| I wonder if over adjusted brakes would cause a clunk grabbing a shoe and lifting it off an anchor pin and then bouncing back down |
OEM trained in wiring and all engine platforms for over 20 years
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krmvcs
Advanced Member
362 Posts |
Posted - 01/17/2019 : 10:30:54 AM
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quote:
Originally posted by slippert
I support the the roller/s-cam sticking issue on the clunk you describe, happens here also..... I have to pull wheels clean and lube rollers on mine anywhere from new to 20,000 miles the first time also....
I replace smooth roller with a knurled roller, when I pull wheels for this problem.... that seems to cure my issue for the life of brake lining, since I started doing this about 10 years ago.. so far have seen no adverse effects/wear from using the knurled roller in my fleet...
Ditto. Most likely the smooth rollers are "skipping" on the s-cam as it rotates. |
-Ken- |
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Mechan1c
Top Member
USA
853 Posts |
Posted - 01/17/2019 : 12:35:53 PM
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We hear it a lot on the front of CE's from 2006-12. We also started hearing it right off the bat with low miles.
I was getting on a bus in the yard one day and putting my first foot on the stepwell I had one pop on the RF just from that. Like it was bound up just barely and all it took was just a little (200lb!) weight on the bus step.
We've pulled them apart looking for flat spotted rollers and never really found one...
I've not heard it on a transit, and first started hearing about it when we got conventionals from drivers. Back in the old days it wasn't unusual to find flat rollers when doing a reline, but I don't remember driver write-ups about pop noises. |
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Poolguy7250
Active Member
USA
11 Posts |
Posted - 01/17/2019 : 4:50:50 PM
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| With the backing plate off. You can turn the wheel outward and with a light look into the wheel and see the s-cam and roller. I back the slack off and spray penetrating oil in on the roller. Careful not too much, it drips. Work the brakes and get the oil to work in. Adjust the brake and road test. If it goes away you have a choice. Pull it apart or let the driver have it. It’s not a cure all but a diagnostic tool. |
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JoeHEB1
Advanced Member
498 Posts |
Posted - 01/30/2019 : 11:37:27 AM
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| Seen this once before in this forum but I can't find it for some reason, but I lubed the roller and anchor pins and problem solved. I lubed them with anti seize. We lube all pins and rollers on every brake job. |
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Brake clunk
