braking on big mountains...

Discussion in 'Experienced Truckers' Advice' started by elharrison, Feb 8, 2008.

  1. red_eye

    red_eye Medium Load Member

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    Dec 30, 2009
    belpre, ohio
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    Found this interesting.. excuse some of the run together words... I copied and pasted..and didnt want to edit it..lol
    if you want to read the whole thing http://deepblue.lib.umich.edu/bitstream/2027.42/960/2/82902.0001.001.pdf


    5.0 SUMMARY OF FINDINGS, CONCLUSIONS, AND RECOMMENDATIONS. The findings from the mobile dynamometer experiments, described in Section 4,indicate the following:*The snubbing (pulsing) strategy provides a higher cooling rate than that provided bythe dragging strategy. However, the difference is not large.*The dragging strategy is more conducive to the formation of hot spots than thesnubbing strategy when new linings are installed*The use of a snubbing strategy for mountain descents will not cause a common type ofautomatic slack adjuster to perform improperly.These findings all support the use of the snubbing strategy. The findings from themountain descent testing , described in Section 3, indicate the following:*The overall level of brake temperature per pound of brake drum will be nearly the same regardless of whether a constant dragging or a snubbinglpulsing strategy is used. The test data did not indicate that one strategy provided significantly better cooling than theother.*The snubbing strategy involves higher pressures than the dragging strategy andthereby tends to provide a more uniform temperature distribution from brake to brakeand from axle to axle. Through this mechanism, the snubbing strategy aids in making each brake do its fair share of the work even if there is a gross pneumatic imbalance.*Very high brake temperatures result if some brakes are not doing much work.Tractors and trailers need to be matched through pressure and temperature balances ifhigh temperatures are to be avoided in mountain descents. (The grade severity ratingsystem is not conservative in this respect since it lumps all of the brakes together as ifeach brake were doing approximately a fair share of the work.)*Significant losses in stopping capability can be attributed to misadjustment combinedwith pneumatic imbalance. Particularly poor stopping performance will occur aftermountain descents when the tractor's brakes are misadjusted and the trailer's brakesare very hot due to pneumatic imbalance, or vice versa with hot tractor brakes due topneumatic imbalance and the trailer's brakes misadjusted.*In some circumstances, with combined misadjustment and imbalance, the snubbingstrategy has been found to lead to hotter brakes for the misadjusted brakes, which inturn leads to an additional increment in stopping distance after a mountain descent.The findings from the mountain descent tests favor the snubbing strategy in that thehottest brake will be cooler if snubbing is used rather than dragging. However, thedifferences in average brake temperature are not large enough or consistent enough to favor
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    either strategy. The snubbing strategy appears to have an advantage over the draggingstrategy because the snubbing strategy causes each brake to come closer to doing its fairshare of the work, particularly if there is a pressure imbalance at low brake pressure.It is interesting to observe that a pressure imbalance can result in a situation that warnsthe driver that the brakes are overheating. If the brakes are imbalanced and the driver isproceeding at too high of a speed, the brakes doing more than their fair share of the workwill heat up first. If the driver sees smoke or smells these hot brakes, the driver can use theother brakes (the ones that have not overheated) to stop the vehicle safely.This situation was observed in practice many times on the mountain on 1-64, Thehighway has broad shoulders. On many runs down the mountain with the test vehicle,other heavy trucks with one set of smoking brakes were seen stopped on the shoulder. Thedrivers had apparently learned that they did not need to pull into the runoff ramps and getstuck. (The mountain has two runoff ramps, one at the middle and one at the bottom. Theone in the middle has been used about once a week since it was built.) The drivers chose topull over, stop, and wait on the shoulder for about 40 min for their brakes to cool.There is a danger that a tire might explode at the bead due to the nature of the heat flowwhile the vehicle is stopped. This is a particularly dangerous situation in that it may takeabout 10 min for the wheel to explode after the vehicle has stopped. The driver should stayclear of the wheels with hot brakes.The point to be made is that there may be circumstances in which some brakes overheatand the other brakes can easily stop the vehicle. This situation can be used as a safetywarning if the road has plenty of shoulder room to stop in. However, there is a significantloss of time while waiting for the brakes to cool. Nevertheless, drivers of vehicles withsome (but not all) brakes overheated should stop to let the brakes cool before proceeding.With regard to instructions in the Commercial Drivers License Manual, the results ofthis study do not show that dragging is superior to pulsing. With respect to the overallaverage temperature, the results indicate that either strategy is as good as the other. For agiven vehicle on a particular mountain, the total heat retained by the brakes after descendingthe mountain will be nearly the same regardless of whether a pulsing or dragging strategy isused. The important issue is to use a control speed that is appropriate for the slope of thedowngrade, the length of the downgrade, the weight of the vehicle, and the balance of thebraking system. A snubbing strategy that allows for approximately k3 mph speed variation about the control speed has been found to be reasonable and practical. The owners and operators ofcommercial vehicles should be made aware that the snubbing strategy will produce more
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    uniform temperatures throughout the vehicle, thereby leading to less brake wear overall andless frequent need for readjustment and relining. They should also be made aware that aftermountain descents misadjustment on one set of brakes can lead to long stopping distances,particularly if the brake system has a large pressure imbalance tending to reduce the workdone by the misadjusted brakes.Although the snubbing strategy has been found to have advantages over the draggingstrategy, the main conclusion from this investigation of downhill braking is that heavytrucks should proceed down the mountain at a speed (a controlled speed) that will be lowenough to prevent the brakes from overheating regardless of the braking strategyemployed. Given that a prudent control speed is used by the driver, the benefits of asnubbing strategy can be safely attained. These conclusions support the recommendedwording of advice for commercial vehicle drivers as presented in Section 1 of this report.Specifically, that advice is to go slowly in the proper gear and remember that a snubbingstrategy can aid in (a) making each brake do its fair share of the work and (b) reducing thetendency for hot-spotting of brake drums.
     
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  3. phroziac

    phroziac Road Train Member

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    Jun 16, 2009
    Gary, IN
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    how the hell is it your fault when your company is so unconcerned about basic maintenance?

    Anyway, that must be why the newer freightliners have a redesigned trolley valve. It's big, plastic, in the middle of the dash,and honestly it looks like a shifter. Spring loaded, springs back up when you let go. Impossible to check your brake lights with without jammin something in it. Poor design.
     
  4. notarps4me

    notarps4me Road Train Member

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    NASA HQ
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    If you don't have 60 lbs of air they will light up.:yes2557:
     
  5. HoosierHunter

    HoosierHunter Light Load Member

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    Jul 22, 2008
    Grabill,In
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    PrimeExample of a truck driver you are not.
     
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  6. striker

    striker Road Train Member

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    Aug 8, 2009
    Denver, Co
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    PrimeExample, remind me to never go to work for Stevens. And I must say that apparently Steven's training system doesn't work. I've seen many Steven's trucks sitting on the side of I-70 EB/WB waiting for their brakes to cool, as well as more than a few with signs of soot on the exterior of the trailer. Plain and simple, your people sound like the same ########## that were advising the town of Vail a few years back when they tried to ban the use of engine brakes on I-70. Thankfully intelligent heads with Colo. State Patrol, OOIDA, CMCA, and CDOT prevailed. I've driven trucks in the hills without jakes, it's definetly an aquired skill and not something you send a rookie out to learn. You send a rookie out in a truck equipped with a jake brake so that if they have a problem, they have a backup and to prevent accidents. I wonder, does Stevens also guarentee you a job if you loose it on the Mtn's and have to take the runaway ramp? do they also pay the tow bill and fines?
     
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  7. GasHauler

    GasHauler Master FMCSA Interpreter

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    Oct 23, 2005
    Vegas/Jersey
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    Good post Striker. How about the instructor that lets the student go down the hill with no engine brake and in the wrong higher gear to smoke the brakes to teach him? The way I feel is I'd fire that instructor and inform the student you never want to put a student in danger. What would have happened if the engine brake fail to come on when they needed to save their ###? Engine brakes do fail.
     
  8. kwray

    kwray Medium Load Member

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    Jun 14, 2009
    Pennsylvania
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    I'm having a little trouble understanding where this theory that "fanning your brakes will cause them to burn" came from. "Letting the air get at the hot shoes" and a few other things I've heard over the years really don't make a lot of sense. It's not like opening the damper on a woodstove. And the heat from the drums will dissipate out into the hub regardless of whether or not the shoe is contacting the drum.
     
  9. ironpony

    ironpony Road Train Member

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    Ask my GPS...
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    I came down Emigrant a couple of months ago (7th on the jake, thank-you) look in my rear-view, and here comes Stevens like a bat out of hell. Smoke coming off the trailer tandems and drives. I got over on the shoulder - he smoked those brakes all the way down, and never stopped - kept on going at the bottom.
     
  10. red_eye

    red_eye Medium Load Member

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    Dec 30, 2009
    belpre, ohio
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    Yea the old design was on the column.... an I just say it should have been my fault..since i was the one who pulled it out of yard..but after that ..if i could see up in there.. I looked.. that was freekin scary..lol..
     
  11. primexample

    primexample Light Load Member

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    May 16, 2009
    az
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    Sure it works if you do it right.no they dont send rookies out with jakes.thats why you may have seen some of our drivers sitting on the side of the road,and not crashed out because at least you should be able to pull over and stop, like they did.And Vail. driver in your 18 years of driving I can gaurantee you that you have never seen a Stevens truck west of Denver, CO on I-70 sorry choose another group of ********.I can tell you really rely on that jake so bad you get in a uproar if someone says they might ban it from you. maybe thats why we was taught without one.you make it sound like all stevens trucks dont have jakes. they do except for newbies out of training for 6 months.
     
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