proper way to decend grade

[cody]

It looks like the debate on this could be very involved and seems to depend a lot on a persons own comfort level of what the different experts opinions and studies would show, for every expert in one area, you can counter with another expert that shares a different opinion.  To me, the best solution would be to have a back up system that would allow for variables that would be more easily controlled, my comfort level would tell me that if a jake helped as a back up system, it would be worth the added expence, that is the direction I'm leaning here.  I have no doubt that each area of study here has merit but the variables a person would encounter would make each one inconsistant based on the individual equipment and the condition of it, wow, I never knew I could use those big words all in a row, I have to thank Slow Rider for that lol.

[RJ]

All -

Folk are overlooking an important point from all these various sources regarding controlled constant braking vs snub braking techniques:

Being in the RIGHT GEAR when you start down the grade!

Too high a gear puts additional stress on the service brakes to keep speeds under control.

Engine braking, regardless of whether equipped with a Jake or not, is an essential part of keeping the service brake temps manageable on long downgrades.  Vehicles equipped with a Jake can usually descend using a higher gear than those who are not blessed with this additional safety device.

The old adage "Come down in the same gear you go up" still has merit, especially if you are unfamiliar with the terrain and do not have a Jake.

The extra time needed to descend a grade in a lower gear is well worth it compared to the potential for disaster by being in a hurry.

FWIW & HTH. . .

 

[Devin & Amy]

Hi all,

We just got back from a 5500 mile round trip to CA from MN. We went through some of the toughest ranges in this country, and while I have very little experience in the long term sense , this is my take on it.

I used both the off-on-off and the constant pressure methods.
I think that as I got a little more used to the grades I used the constant pressure technique more.
I am fortunate to have a four-spd with which to control my descent, lending to the constant pressure method.
But, there was a range in Wyo. (Bighorn Mountains, Hwy. 14A) which dropped 3600' in 10 miles (10% grade).
I think I used every bit of my three years driving exp. in the bus to get to the bottom of that hill. It just wouldn't quit.
I did get to the bottom safely, and there was no real smoking of the brakes. It did take more than an hour though.

Lessons learned:
Check your brakes before every trip, and often during.
The go down in same gear as you went up is a good rule.
I will be installing a jake system.
Driving techniques are not something you can learn from reading, unfortunately.(so get out there and practice!!!)

My $.02 worth

Devin

[bobofthenorth]

Thank you Russ - you have reinforced the point I was about to make which is that kinetic energy rises as a function of the square of the velocity.  What that means in english is that, if you are going twice as fast you have 4 times the energy.  In other words, if you descend a grade at 60 MPH instead of 30 MPH you have to dissipate 4 times the heat through your brakes in order to slow to a stop.  The only safe way down a hill is slowly.  Jakes help but they don't work miracles.  You can argue all week about stab braking vs. steady applications and it won't change the underlying physics which is not about dissipation of heat in the brake drums but rather about speed and its relation to energy.  Go slow and it won't matter how you brake.

[TomC]

Many loggers (the heaviest, steepest, hardest trucking) use windshield washers at each tandem position.  They plumb the hose to dump on top of the drum (not in it) to cool the brakes coming down big, steep grades.

The brakes on our buses (especially the transits and those with tags) are bigger than on trucks.  Also, most of us are not near the maximum gvw rating of the bus since we are not hauling people (I'm 5,000lbs from my gvw).  With properly adjusted brakes (tighten down, then back off 1/4 turn) and a little common sense coming  down grades, there shouldn't be a problem.  The vast majority of buses still use drum brakes-just like what we all have now (maybe a very few with air discs).

I still advocate having Jake Brakes!  In my opinion being able to descend a 6% grade without brakes at 60mph with the Jakes slowing the bus down, is almost miraculous.  Good Luck, TomC

[Busted Knuckle]

Not trying to flame anyone, as I for one have no clue what I'm talking about! I only have 20+ yrs of commercial driving experience in which I have driven tow trucks (cleaning up wrecks), dump trucks, equipment haulers, Reefer Units (chicken hauler), and Buses. I have been coast to coast top to bottom many times and have crossed many if not all of the worst passes this great country has to offer! And I did it safely to be around to tell about it today! I always used the same gear down as I went up, with the occasional on-off----on----off method. The trick is to let the engine do the work while occasionally touching the brakes to help maintain that low speed desired! I agree with TomC 100% Jakes do make it a lot easier to come down in the proper gear with out touching the brakes at all in a bus! An 80,000+ lb tractor trailer still requires a little assistance from the brakes.
But as I said before the advice given to me by an "Old timer" has always stuck in my mind any time I'm driving in the mountains!
"You can go down many mountains, many times too slow, but you'll only go down one, one time too fast!"

[Chaz]

Ok, maybe a dumb question but........... should I pull the automatic trany down a gear when going down hill??
 No on has made the distinction of a manual over an auto, so i just want to be sure. It just kept sounding like you guys were talking about manuals.

   Chaz

[tekebird]

the same gear down as up is a bit dated........as with 450HP and higher engines some units can climb grades at much higher speeds while brake technology has not advanced at the same rate.

I have only found one grade where I would have liked a Jake.....the trans retarder didn't cut the mustard and it is a road most of you would have never been on.......I was being paid to drive there and was the victim of poor pre trip planning by my client

[Busted Knuckle]

Ok, maybe a dumb question but........... should I pull the automatic trany down a gear when going down hill??
 No on has made the distinction of a manual over an auto, so i just want to be sure. It just kept sounding like you guys were talking about manuals.

   Chaz

First off Chaz the only truely dumb question is the one not asked, until it's too late!
Second off when I say come down the hill in the same gear you went up in, it means just that! Auto, manual it doesn't matter if your automatic trans had to go down to 1st or 2nd to pull the hill then that is what you should use to descend the hill! FWIW
 BK  

[ttomas]

Thanks Chas for asking the question about the auto trans.. This is my first automatic transmission.  Tomas
   

[Sojourner]

Keep in mind while I am slow typing this...many more good posts came. So here goes my 2 cents worth.

Snub braking and riding braking is two kinds of braking.
Snub braking is applying brake until speed is reducing about 5 mph and repeat after it gains 5 mph.

Brake riding is a steadily applied pedal pressure to maintain safe speed without “cooling” and “building up of compound” relief.

The reason “snub brake” is safer is 3 reasons:
1)   Drum expands due to heat, about 0.010 inches per 100 F. At 600 F, a drum could grow by 0.060 inches. Multiply that by the mechanical advantage (leverage) between the slack adjuster and the cam, and you could need an extra half inch of brake stroke. The hotter the drum, the more extra stroke you’ll need. Also, if temperatures get too hot, the bond holding the friction material in the brake shoes starts to weaken, and the shoes become less effective. So by brake snubbing, it cool down drum some in-between braking.
2)   Lining material is only good as long it below fading temperature. Shoe’s heat is being reduce while released to allow cooler ambient air enter gap & shoes.
3)   Whenever apply brake produce wearing compound from shoe’s lining & drum. So by having off & on shoe contact to drum will release its compound to roll off before next braking. Otherwise it will build up hard spot on lining to cause lesser fiction and brake squealing later.

I would NEVER, NEVER ride with a so call truck driver that rides their brake going down hill. I learn these in early years of driving on truck farming. Had many close calls and it is avoidable by driving smart. It never fails after tried two difference type of braking. Snub braking keeps me in control every time.

Link about temperature of fading:
http://www.e-z.net/~ts/ts/Brakfade.htm

Caution to anyone who have purchase a used bus or vehicle. Please inspect drum’s surface for deep groove…my bus had about 1” wide groove with a new set of lining already on. I didn’t do the inspection thinking the seller (charter Bus Company) said it ok to drive 5000 miles trip. Yes I should know by the way of stopping power but only happen when I was in emergency. That when I learn that it was not good. It was after the trip home that I learned about deep grooves in both front drums. Then I learn why not happy the way it stop. Also make sure you have matching air cylinder assembly for left & right of each axle. Otherwise uneven braking. Mine was unmatched from charter company.

Bottom-line is Not to follow any vehicle that can stop quicker than yours. In other word stay off that truck’s lane or stay way, way back behind them. Or you may be victim of serious injury or death.

Another bottom-line is Never to gamble on yours brake stopping power whenever you are near border line of fading braking temperature. You can only tell when it starts smoking while drum is expanding larger and it usually already too late. So never mind what others are passing you…either they have ADS (disc brake) or they are gambling. Take your time going down hill even if it 5 mph while you’re ahead in the long run.

Link to CDL controlling speed: http://drivingrules.net/cdl/cdlsecb/b6speed.htm

About transmission…if youre driving on level hwy then have to go down hill always slow vehicle and shift to next lower range….then if it very steep like 7%...then shift to lower still and be careful not over rev your engine by snub braking till safer. BK quotes is ok if you are climbing same grade as if you go down. I know he mean well.

FWIW

Sojourn for Christ, Jerry

[Jerry Liebler]

Sojouner,
    None of your reasons for 'snub' braking are valid.  The facts simply are that, for the same time to descend a given hill, more heat is generated by 'snub' braking.  The only reason for 'snub' braking is that it is more likely to distribute the heat to all brakes rather than concentrating it on the one(s) that are applied first.  On the other hand all of your reasons are reasons for going slow enough.  Simply slower is safer.
Regards
Jerry 4107 1120   

[Songman]

I love all you guys... I really do... But I am still going with the guy with the degree in Automotive Technology whose job it is to study truck crashes and figure out what caused them. We can say his reasons are invalid all day long, but he has teams and labs running tests to prove what he says. I need more than 'that is invalid' typed on a forum to make me see why I should ignore him and trust some typed words on the internet.

If all these things were invalid, why does the expert say otherwise, and why did every state change their CDL requirements? I'm not being a smartass. I just find it hard to believe that every expert is posting things as tested and proven fact that are 'invalid'. Please show me some tests that back it up. The guy started his article by saying 'This is the method that everyone always believed was right but now we have proven scientifically that it is wrong."

[JackConrad]

Chaz,
   We downshift our MC-8 with 8V71/740 automatic. I have found that if I downshift to 3rd and the hill we are going down is steep enough for the speed to build, the transmission will still shift into 4th to prevent over revving the engine. So, the technique we use is to downshift and use enough brake to keep engine RPM low enough to prevent shifting.  Jack

[zimtok]

Read the article in this forum very carfully.

If I understand it correctly snub braking is preferred to constant braking because on a tractor trailer setup there is a good chance that the braking pressure between the tractor and trailer may not be balanced.

A bus is different because it is not swapping trailers. Does this mean that the brake system on a bus is more likely to be balanced? (maybe)

Testing and numbers don't lie, but the DOT may be following a wide average based more on tractor trailer rigs then looking at buses as a different animal. (was there a braking test done on buses?)

I am confused,,,, but will defer to the "low gear brake as necessary method."