no drive brakes, will not adjust

Discussion in 'Trucks [ Eighteen Wheelers ]' started by freightlinerman, Jun 16, 2012.

  1. freightlinerman

    freightlinerman Road Train Member

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    Maybe you can help, I have a bus with DD3 springer chambers. Yes, they are air brakes.

    I bought the bus where it was towed at least a year ago. Drive shaft was pulled and I believe the tow driver backed the brakes off. I had a mechanic, who worked in the truck shop try to adjust the brakes by airing the bus up, releasing the park brake and giving a full service application, at which point he began to adjust. We tried twice and no luck.

    The shoes will adjust and make contact with the drum and he back's them off to make the adjustment. All seem's well till you try to test the brakes out, the parking/emergency and service brakes are non functional because they are so out of adjustment. This is a gray bearded mechanic who was doing this awhile. I even called a bus mechanic who walked him through and did everything.

    Has anyone ever had this problem before? It is not in revenue service, it is just something I bought for fun and is parked in a different location now. The mechanic even watched as a full service application was made to make sure they rotated freely, they did.
     
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  3. Pedigreed Bulldog

    Pedigreed Bulldog Road Train Member

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    Sounds like maybe the S-cams/bushings could be worn so that there is slop in them? The excess motion there would basically be absorbing the stroke of the slack when the brakes are applied (whether by spring/parking or air/service), preventing the shoes from pressing against the drums with sufficient force to hold/stop the vehicle.

    That's be where I'd start...
     
  4. bender

    bender Road Train Member

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    Sounds like the brakes have been adjusted backwards to the wrong side of the S-Cam. This will cause the brake shoes to go away from the drum when the brakes are applied.
     
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  5. Pedigreed Bulldog

    Pedigreed Bulldog Road Train Member

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    I'm not sure that would even be possible....

    dsl-d25.gif

    If you back them off too far, they won't get tighter....the rollers just hit the S-cam and you can't back it off any farther. Meanwhile, the shoes would be so far off of the drum that you'd know there was a problem.
     
  6. bender

    bender Road Train Member

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    It is possible and it happens when people don't pay attention to direction of S-Cam rotation when adjusting brakes.

    When they get mis-adjusted backwards the shoes hit the drum before the roller gets all the way to the backside pocket of the cam.
     
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  7. lv gn

    lv gn Heavy Load Member

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    Do they have the release pins installed for when it was towed and the driver never removed them??
     
  8. freightlinerman

    freightlinerman Road Train Member

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    I did read back in the DVIR report from over 10 years ago, one driver complained the parking brake was not holding good. As far as the theory on backing them the wrong way, the mechanic adjusted them once and was not happy, this was before we realized they were not functional. Then, I called bus mechanic who spoke to the mechanic and walked through everything and still no dice. I'm pretty sure the mechanic tried forward and backwards, he was puzzled as to why they weren't adjusting.
     
  9. freightlinerman

    freightlinerman Road Train Member

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    PS, is it possible the wrecker drive could have damaged them some how? Not sure IF he backed them off, OR how he backed them off. OR, if they can even be damaged by backing them off the wrong way. Please advise, thanks. I'm not sure if DD3 chambers can be caged, but if they were caged would the mechanic be able to tell?

    When you push the knob in, you can hear the DD3 chambers moving around.
     
  10. Pedigreed Bulldog

    Pedigreed Bulldog Road Train Member

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    You'd have to back the brakes off awful far to reach that point. Even if you AREN'T paying attention, you should realize something is wrong before you get them that far backed off....and the shoes would back off the drum until you eventually tucked the roller up into the cup of the S on the S-cam and you wouldn't be able to back them off any more. The shoes would be so far off the drum at this point that there would be no way anyone with any business adjusting the brakes on the truck would realize something wasn't amiss.

    The only way I could see what you're saying to be even a remote possibility is if someone were to have installed the wrong S-cams...but even then there would be significant clues that something is wrong. Any style of auto slack is going to fight you while backing it off...whether you're hearing the ratcheting mechanism or have to pull out on a button to get the screw to turn...and if you're experiencing that while snugging up the brakes prior to backing them off instead of only while backing them off, it's a pretty good clue something isn't right. Maybe with the old manual slacks, it would be possible...if you didn't know your left from right....but if you don't know what you're doing adjusting the brakes you've got no business driving a truck with manual slacks.

    Now if the brakes have EVER worked since the last time the S-cams were replaced, you can pretty much rule out the "wrong S-cam" as a possibility....so I just don't see how what you're stating as a possibility could realistically be what is wrong.
     
  11. smokincamels

    smokincamels Bobtail Member

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    Check the bolt that is used to cage the spring.
     
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