Hot Brakes

Sooooo...how 'bout dem COWBOYS!!

If low pressure constant braking ISN'T enough to slow the truck, then you snub brake.

Why? Didn't they say the two methods put the same amount of heat in the brakes?

Tests have shown that either method will result in approximately the same average brake temperature at the bottom of the mountain as long as the same average speed is maintained.

So why would you use one method under certain circumstances but switch to the other when they're producing the same amount of heat and doing the same amount of work?

Now I'm done.

Totally glad I stayed out of this one.

Anyone know if having to use an "escape ramp" is still a firing offense at most larger companies?

Rick

I was told it was but I think they are taking it case by case. Our first month solo a friend took a downgrade in too high a gear. We were told NOT to downshift on downhills.... That it couldnt be done. Found out later that you can, the fear was that a new driver wouldn't be able to shift properly and wouldn't get back in gear. Staying in neutral they would lose all control.

My friend used the escape ramp but safety did not fire him. They put him back out with a trainer. The fact that he did not freak out and was able to think to use a ramp showed them he wanted and had every intention to do the correct thing and thought about it. He just needed more instruction. An experience driver? I expect would be fired.

As far as the rest of the conversation... I think part of the debate problem is that trainers who have been driving for decades still use the old method and teach it. Funny Stevens transport was mentioned because a friend of mine went there last year and this is what she was taught...to feather. A friend of mine whose been driving and training for a loooooonnnggg time and now trains at prime (and worked and trained at Stevens) still uses/teaches the feathering. They both do the brake adjustment with the pedals...I asked about that on a thread here and basically was told that was before self adjusting brakes and old methods.

I learned the snubbing but was told it was the stabbing method. Never heard the term snubbing til this thread.

Thanks Brett for the explanations of the mechanics involved. It helps newbies understand the kinds of things to look for and what could go wrong. I had a valve problem too and got it fix immediately.

I take my truck into the shop every six weeks or so. For company drivers the mechanics are very thorough and look for all warranty items that need replacing. They adjust my brakes and give me tid bits of info every time I go in. I'm not a mechanic so I rely on them.

Since I just hit 100,000 miles in this truck, I asked about my brake wear. They have the depth recorded in their records and the mechanic compared the current to the time I got it. He was impressed and said most new drivers put more wear on their brakes.

Point is...go downhill in the lowest gear necessary. Monteagle was mentioned in this thread and in another Robby started. That downgrade has an inspection station at the top of the southbound side. The speed limits for weights are listed. So under x weight the limit might be 45mph but weighing 74,000 might be 25mph. Ignoring this limits would be a drivers first mistake. Not getting in proper gear would be the second.

Braking during curves was mentioned...brake before curves..its in the CDL manual.

I would expect newer drivers to have hot brakes not experienced ones. Since I didn't experience it as a newbie, I know it can be avoided with the snubbing method, low gears, proper Jake control, and slow speeds. I'd rather go slow and be in control than land down the side of a mountain.

Anyone know if having to use an "escape ramp" is still a firing offense at most larger companies?

I'm sure Farmerbob has the answer.

I took the time to thoroughly read the 100 page report from the University of Michigan that has been referenced numerous times and argued about in this thread. The report is written in plain English and moderately difficult to read even if you are not an ME. Worthy of note; the test was conducted on trucks with uniform pressure balance, unbalanced pressure, properly adjusted brakes and varying degrees of brakes not properly adjustment (you can read the report if you want to know every criteria tested). Point being, the results of the tests considered a multitude of pressure balance and adjustment variables which rolled up to net the Basic Findings.

Basic Findings:

The basic findings of these tests and experiments involving heavy vehicles with air-actuated brakes are as follows:

*The average temperature per 100 lb of brake drum is practically equivalent whether the light dragging or the snubbing strategy is used for controlling the speed of heavy trucks on long steep downgrades. (Mobile dynamometer experiments show that snubbing results in slightly lower temperatures than dragging but the difference is not large.)

*The hottest brake will be cooler if the snubbing strategy is used. (Even though the average temperature is approximately the same, the snubbing strategy provides for a more even utilization of all brakes compared with that attained by the light pressure involved in dragging.)

*On short (approximately one minute) downhill descents, the dragging strategy will result in a higher level of martensite formation than that formed by a snubbing strategy. (The formation of martensite can lead to drum fragmenting and it is a problem involving new brakes or recently relined brakes.)

Although the snubbing strategy has been found to have advantages over the dragging strategy, the main conclusion from this investigation of downhill braking is that heavy trucks should proceed down the mountain at a speed (a controlled speed) that will be low enough to prevent the brakes from overheating regardless of the braking strategy employed. Given that a prudent control speed is used by the driver, the benefits of a snubbing strategy can be safely attained. These conclusions support the recommended wording 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 snubbing strategy can aid in (a) making each brake do its fair share of the work and (b) reducing the tendency for hot-spotting of brake drums.

Here is what the report recommended to DOT regarding downhill braking techniques:

"The right way to go down long grades is to use a low gear and go slow. Use close to rated engine speed to maximize drag. If you go slowly enough, the brakes will be able to get rid of enough heat so they will work as they should. The driver's most important consideration is to pick a control speed that is not too fast for the weight of the vehicle, the length of the grade, and the steepness of the grade. Drivers who are unfamiliar with routes in mountainous regions need to select a low speed to be safe. Ideally, the driver should be familiar with the route and should be prepared by knowing the appropriate speed of descent for the vehicle as loaded. However, if the driver is not familiar with which grades are long ones, the driver needs to proceed with caution-perhaps at a low speed of no more than 20 mph on long grades.

If at all possible, the driver should plan ahead and obtain information on any severe grades. Often severe grades are well marked ahead of time by highway signs, and the driver of a heavily-laden vehicle needs to heed these warnings because overheated brakes will result from travelling too fast for the severity of the mountain and the condition of the vehicle and its braking system.

To control speed going down a mountain, some people favor using a light, steady pressure to drag the brakes while others favor a series of snubs, each sufficient to slow the vehicle by approximately 6 mph in about 3 sec. The snubbing strategy uses pressures over 20 psi for heavy trucks while the light drag may involve pressures under 10 psi. Tests have shown that either method will result in approximately the same average brake temperature at the bottom of the mountain as long as the same average speed is maintained. However, the snubbing method, due to the higher pressure involved, will aid in making each brake do its fair share of the work. Hence, the snubbing method will result in more uniform temperatures from brake to brake and thereby aid in preventing brakes from overheating. Furthermore, light, steady pressure at highway speeds on short grades of roughly one mi in length can lead to problems with "hot spotting" and drum cracking and fragmenting if the brake linings are new. In summary, the most important considerations are to go slow enough and use the right gear.

Remember that compared to a strategy based upon a light pressure dragging, the snubbing strategy will aid in making each brake do its fair share of the work and reduce the tendency for hot-spotting and drum-cracking of new or recently relined brakes."

Those are excerpts from the report relevant to this thread (no content editing was done). Draw your own conclusions. For me personally I see nothing to indicate that I should change my current downhill braking strategy, it's confirmation.

Anyone know if having to use an "escape ramp" is still a firing offense at most larger companies?

I'm sure Farmerbob has the answer.

Actually, no, I do not.

Tractor Man, I respect you, but I'm a little bit irritated that you are trying to bait me like this.

You appear to have taken offense to my knowing what I'm talking about when I say I know what I'm talking about.

If you watch how I phrase things, If I am not confident about something, I commonly say that I'm "not sure", or "I've heard" or other phrases that indicate uncertainty.

When I do say I am sure about something, it means that I am going to be very hard to convince otherwise, and you are going to have to present cold hard facts that actually disprove me. In this case, some people think they have done so, but they have not, because the study quoted does not say what they think it says.

Occasionally, I do not use equivocations and might sound like I am being firm, but will back down when pressed. That's clearly not the case here.

The DoT teaching recommendations may have changed, but not for the reasons some people believe they changed. Think about it. This is the same DoT that thought having a 34 hour break require two periods between 0100 and 0500 was a good idea.