Bus Conversions dot Com Bulletin Board
September 01, 2014, 02:08:21 PM *
Welcome, Guest. Please login or register.

Login with username, password and session length
News: 500 Members as of May 5th, 2006.  Smiley  3,499 Members as of October 21, 2012 Cheesy

   Home   Help Forum Rules Search Calendar Login Register BCM Home Page Contact BCM  
Pages: [1] 2 3 4 5 6 7   Go Down
  Print  
Author Topic: proper way to decend grade  (Read 22416 times)
ttomas
Full Member
***
Offline Offline

Posts: 128




Ignore
« on: August 26, 2007, 08:22:58 AM »

 most of us were not born in a bus. therefore, without instruction it would be difficult to know the proper techniques of driving a 30,000 lb rig. 
What is the proper technique to descend a major grade?
In my last rig, I would shift to low 2nd, let it pull up to max rpm, and brake back down. It worked, but I never could find out if this was the best way for my brakes etc. thanks Tomas
Logged
Jerry32
Hero Member
*****
Offline Offline

Posts: 726





Ignore
« Reply #1 on: August 26, 2007, 08:27:01 AM »

Yes to shift to lower gears but you need to have the lowest that will let you use the least brakeing. the brakes need time to cool between applications depending on how much braking was needed to slow to controled speed Jerry
Logged

1988 MCI 102A3 8V92TA 740
TomC
Hero Member
*****
Offline Offline

Posts: 6747





Ignore
« Reply #2 on: August 26, 2007, 09:49:36 AM »

This is the best argument for the use of a Jake Brake. 

A little history of the Jake brake. Clessie Cummins-the founder of Cummins engine company, invented the Jake brake-when he almost lost it a couple of times coming down steep grades.  Cummins did not have the capacity to make his new braking device in bulk so he awarded the Jacobs chuck company the rights to make and market the new compression brake-hence the Jake brake.  Cummins engine company still makes their own version called the Interbrake.

For those that don't know how the Jake brake works, here's the short version.  Most of the truck engines have an additional camshaft lobe and rocker arm that operates the unit injectors (whether it be mechanical or electronic).  The Jake unit sits over the rocker arms and when the system is activated, the unit is charged with oil pressure from the engine.  The pressure servo is then extended down to touch the cam side of the injector rocker arm.  When the rocker arm is pushed up from the camshaft, the pressure servo is also pushed up that creates pressure inside the Jake unit that causes a hydraulic cylinder over the exhaust valve to push the exhaust valves open on that cylinder.  So what you get is the exhaust valve opening when the injector is activated.  This happens at the highest point of compression, so all that built up energy is released into the exhaust pipe (hence the noise), and with the expulsion of that energy, causes the engine to act like an air compressor that makes the braking force.  For other engines that don't have unit injectors-like some Caterpillars, they will use other exhaust rockers from other cylinders for the exhaust Jake activation across the engine to another cylinder.

I drove for 21 years always with a Jake brake (I don't sell any big trucks without Jake brakes).  I have a very well adjusted (by Don Fairchild) Jake brake on my 8V-71 and can tell you it works extremely well!!  Coming down the north bound side of the I-5 Grapevine which is a 5 mile 6% grade.  The Jake is so effective I have to switch between one head and both head activation to keep from slowing to much, and not touch the brakes at all.

To those that don't have a Jake brake and have intentions on travelling west of interstate 25, going to Canada or Alaska, PLEASE have one installed.  It isn't a frivolous toy-it can and will save your brakes from smoking and possibly failing.  Good Luck, TomC
Logged

Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Busted Knuckle
Hero Member
*****
Offline Offline

Posts: 6447


6 Setras, 2 MCIs, and 1 Dina. Just buses ;D


WWW

Ignore
« Reply #3 on: August 26, 2007, 10:33:23 AM »

I agree with Tom about Jakes being absolutely worth the cost! I drove big trucks for yrs, some with Jakes and some with out! I'd never drive one with out Jakes again (unless it was just across town!) I don't have them on my buses but my Setra's come with transmission retarders that work very well, and the MCI my dad drives doesn't have them and he doesn't see it worth the $ to put them on it! Well as I said he drives it, and he does a very good job of it! Jakes are nice, and as TomC said if driving out in the Rockies or on the west coast I'd have them installed immediately (even on dad's bus wether he wanted them or not!), but out here in the mid west they are not an absolute necessity that we can't live with out!

Now back to the original question! As a general rule it is best to go down the hill in the same gear you came up it ! And also using the brakes off---on-off---on-off----on-off---- to allow them time to cool.

Now the one thing that has always stuck in my mind is what an old timer told me once when I was nervous about dropping off one of the passes out west (I don't remember which one) he told me "Son just remember you can go down many mountains, many times too slow, but you'll only go down one, one time too fast!"
Grin  BK  Grin
« Last Edit: August 26, 2007, 10:38:34 AM by Busted Knuckle » Logged

Busted Knuckle aka Bryce Gaston
KY Lakeside Travel's Busted Knuckle Garage
Huntingdon, TN 12 minutes N of I-40 @ exit 108
www.kylakesidetravel.net

Grin Keep SMILING it makes people wonder what yer up to! Grin (at least thats what momma always told me! Grin)
Songman
Guest

« Reply #4 on: August 26, 2007, 10:51:26 AM »

Great quote! I'll have to remember that! haha
Logged
Jerry Liebler
Hero Member
*****
Offline Offline

Posts: 1320




Ignore
« Reply #5 on: August 26, 2007, 11:30:23 AM »

I know it's controversial and I'll probably get flamed but here goes. Once in the correct gear so the engine is doing most of the braking.   The service brakes should be applied  continuously and just enough to maintain the desired speed.  This will result in the lowest temperature rise of the brakes.  Letting speed build up then braking to a lower speed and repeating will result in hotter brakes.  In other words riding the brakes, contrary to popular belief is the best technique.
Regards
Jerry 4107 1120
Logged
DrivingMissLazy
Hero Member
*****
Offline Offline

Posts: 2634




Ignore
« Reply #6 on: August 26, 2007, 11:35:21 AM »

Jerry, I have heard the same thing many times and have seen a few instances where a control was installed that allowed you to actually adjust the amount of air pressure that was applied to the braking system continuously. In other words, for example you could set it for 15 pounds of continuous air pressure. This was adjustable so you could set the correct amount to maintain the desired speed.
 
Two different thoughts obviously of proper braking techniques.

Richard

I know it's controversial and I'll probably get flamed but here goes. Once in the correct gear so the engine is doing most of the braking.   The service brakes should be applied  continuously and just enough to maintain the desired speed.  This will result in the lowest temperature rise of the brakes.  Letting speed build up then braking to a lower speed and repeating will result in hotter brakes.  In other words riding the brakes, contrary to popular belief is the best technique.
Regards
Jerry 4107 1120
Logged

Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body. But rather to skid in sideways, chocolate in one hand, a good Reisling in the other, body thoroughly used up, totally worn out and screaming:  WOO HOO, what a ride
gus
Hero Member
*****
Offline Offline

Posts: 3505





Ignore
« Reply #7 on: August 26, 2007, 11:46:25 AM »

Jerry and Richard are right. The on-off-on is not correct but I used to think it was and did it until I studied for my CDL and found out it was not correct.

The reason it is not is explained very well by Jerry.

I used the steady pressure along with the Jake on the 18 wheeler I drove and use it on my 4104 (No Jake). I've made three trips across the Rockies and Cascades and have not once overheated the brakes.

I don't shift down my 4 sp but I do make sure I start down a grade very slowly and don't ever let the speed build up over 55-60 until I'm sure I can see the bottom.

One little town in UT has a 35 mph speed limit right at the bottom of a very long, steep grade. That one got them a bit warm but still didn't overheat.
Logged

PD4107-152
PD4104-1274
Ash Flat, AR
skihor
Sr. Member
****
Offline Offline

Posts: 291





Ignore
« Reply #8 on: August 26, 2007, 04:48:17 PM »

My wife is a Certified CDL Examiner in Denver. She is also a driver/trainer for cars, busses, and semi's. She has 25+ years experience of city bus driving. According to the CDL manual in Colorado the ON-OFF-ON braking is the proper method. Section 2.16 of the Colorado cdl manual.. The truck driving school that she works for teaches the ON-OFF-ON technique as part of their state certified course.
 Constant steady braking, no matter how light the pressure, is a receipe for disaster on  a mountain grade.

Don & Sheila
Logged
Dreamscape
Guest

« Reply #9 on: August 26, 2007, 05:01:42 PM »

I have used the on off method because I thought that constant applied pressure would result in heating the shoes and drums, no matter how light. Now I wonder which is the correct way for our Eagle, 20 tons of flying metal and rust.

Paul
Logged
Songman
Guest

« Reply #10 on: August 26, 2007, 05:03:13 PM »

I think just point it down the hill and pray is a good way. Smiley

I think I have seen truck drivers doing that on Monteagle plenty of times!
Logged
Jerry Liebler
Hero Member
*****
Offline Offline

Posts: 1320




Ignore
« Reply #11 on: August 26, 2007, 05:13:43 PM »

Don, Shelia & anyone in Colorado.
     I said it was controversial!
    Apparently Colorado has it's own laws of physics and/or some very STUPID bureaucrats.  The correct method  is riding the brakes and has been proven over and over in experiments. Colorado and it's bureaucrats are NOT above the laws of physics, I'm sure glad I don't live there.  You should take on the challenge of removing this dangerous urban legend from your state.
Regards
Jerry 4107 1120
Logged
Tony LEE
Sr. Member
****
Offline Offline

Posts: 392



WWW

Ignore
« Reply #12 on: August 26, 2007, 05:24:41 PM »

Lots of versions around. My impression was that the on off system is not recommended because many drivers tend to use a too-rapid and too-heavy on-off brake application and it can run your air down low enough that the parking/maxi brake can apply.

Light constant braking for a long time was said to glaze the linings over and result in loss of brakes.
« Last Edit: August 26, 2007, 05:26:39 PM by tonylee » Logged

Dreamscape
Guest

« Reply #13 on: August 26, 2007, 05:31:31 PM »

Does anyone have a link to post on this subject? In other words a tested experiment that proves the proper method beyond a shadow of a doubt. Not biased by state laws, but by proven methods in the trucking industry.

Paul
Logged
Songman
Guest

« Reply #14 on: August 26, 2007, 05:32:45 PM »

As I have already said, I don't have much experience here so I have to go by what others say.

I will say that after some research, the 'experts' say that SNUB braking is the correct method and that is what CDL testing now calls for. Snub braking is off-on-off.

This article is most telling. It was written by a forensics expert who studied the reason for truck crashes and it appeared in Trucker's World magazine. I will quote the first paragraph here and interested parties can follow the link to read the entire article.

Quote
When the Commercial Drivers License (CDL) manual was first published, it recommended that a driver use a light and steady application of the brakes when descending steep grades. This recommendation was based on an old theory that heavy brake applications would generate more heat than light applications. This method (controlled braking) was commonly taught to drivers and, even after changes were made to the CDL manual because this theory was proven wrong, the method is still taught and practiced today.


http://www.johncglennon.com/papers.cfm?PaperID=36 - John C. Glennon Jr - CrashForensics.com

Every other state CDL site I looked at recommended snub braking without exception.

I still like the 'point n' pray' way! Smiley
Logged
Pages: [1] 2 3 4 5 6 7   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.18 | SMF © 2013, Simple Machines Valid XHTML 1.0! Valid CSS!