Downhill braking

[Iceni John]

And this is why I'm getting my Jakes to work right  -  they've never worked properly since I got the bus.   I want to keep my brakes as cool as possible at all times.   Heck, I would also mount a Telma if I could!   Mind you, even with Jakes I don't descend quicker than I would if I didn't have them  -  I don't ever want to get into a position that they're the only thing that saves me.   They're for slowing, not stopping, and definitely not an excuse to drive downhill like an idiot.

John

[TomC]

There is a real good reason Jake Brakes are built into engines now-because they work. Many engines like the DD13, 15, 16 and the Cummins ISX15 have dedicated cam lobes just to operate the Jakes-that work very well and very quietly. The trick going down any hill is to be geared down to a speed that the Jake brake can just about hold the speed with you tickling the brakes (light application for about 10 second [I don't believe in stabbing]) to bring the speed back down.
My bus weighs 31,000lbs and with my M/B in tow, weigh in at 34,750lbs. I can go down the Grapevine northbound at 35mph with just my Jake brake (8V-71) having to switch from two heads to one head to keep speed up-never touching the brakes. When I went exploring in the Sierra Nevada Mountains, I was down in 1st gear-which will lockup the torque converter when pulled down to 1st range. The Jake brake was very effective at those speeds. Good Luck, TomC

[Jon]

Clifford,

Here is some context for my use of the retarder and gearing.......

I know heat is the enemy and that the retarder has the ability to generate a lot. So my management of speed begins before the top of the hill. I am slowed down and geared down and in my 2 coaches I use 55 in 4th as my top speed. I crest the hill in 4th at 45 MPH or less. My retarders have the stalk on the steering column and from experience if I am on a 7% grade I can maintain my target speed or less using the 2nd retarder position and control my retarder output fluid temps to 230 degrees or less. If the speeds creep up I can go to the third position, but in addition to speed I am also self imposing a 230 degree temp limit. If I have to because the grade steepens and there is no flat spot in sight I do stab my brakes and take it back to 40 to 45 MPH, but that is when the grade is not constant but has steep sections and flatter sections.

I have been to Las Vegas twice using the route discussed with a 97 coach at 46,000 pounds and my 06 at 53,000 pounds. The 06 measures temps at a different location and has a more effective transmission cooler but the methods I used stayed the same with the same results.

[Tony LEE]

STAB braking is an entirely different concept and is used in emergency situations.

Stab braking: Use only on vehicles without anti-lock systems. Apply the brake all the way. Release the brakes when the wheels lock up. As soon as the wheels start rolling, put on the brakes fully again.
Using Air Brakes And Stopping Distance | High Road Online ...
www.truckingtruth.com/cdl-training-program/page46

SNUB braking is the widely-recognised technique for descending steep grades under control

Snub braking is now the recommended method of downhill braking. This method works by: first, choosing the correct gear for the hill; second, allowing the truck to speed up to the maximum safe speed as it descends the hill; third, applying the brakes hard to slow the truck down 5 mph; and then repeating this process to the bottom of the hill.

[kyle4501]

Who woudda thunk there was such a big difference between STAB & SNUB. 

For the benefit of those who aren't in the business, a clear & concise definition usually helps others understand.


I donno about " applying the brakes hard " . . . . A hard brake application for me is just shy of leaving skid marks 
A firm application is quite noticeable, but passengers aren't thrown against the seat belts.   

Does SNUB braking really want that version of hard braking?

[luvrbus]

Really doesn't make that difference with the newer stuff the ABS controls your braking anyways

[eagle19952]

Really doesn't make that difference with the newer stuff the ABS controls your braking anyways

How does ABS know if you are loaded, overloaded or empty 

i never was a fan of ABS.

[Jon]

The only thing ABS does is sense a wheel going slower than the others which it interprets as impending lock up, and the modulator valve closes the air path to the brake chamber, and exhausts the air in the chamber. As soon as the wheel speed matches the others the modulator valve closes the exhaust path and maintains open flow again to the brake chamber.

[luvrbus]

LOL you been to Bendix school also I just read the exact quote from my Bendix book 

[eagle19952]

The only thing ABS does is sense a wheel going slower than the others which it interprets as impending lock up, and the modulator valve closes the air path to the brake chamber, and exhausts the air in the chamber. As soon as the wheel speed matches the others the modulator valve closes the exhaust path and maintains open flow again to the brake chamber.

still don't like them 

[luvrbus]

I was reading where Honeywell and Wabco has made a lot of technology advances on the ABS systems in the last 2 years but I am not a huge fan of taking that much control away from a driver 
The Wabco system when the ECU detects a lockup then it will activate not before according to the Wabco manual section 1 page 3 I questioned my Bendix instructor on that one

[pabusnut]

When I read the title "Downhill braking", I thought DUH?  Of course it is downhill ---Who would brake on an uphill?! 

I know ---my sense of humor is strange 

Steve Toomey
PAbusnut

[lostagain]

Clifford, speaking of less driver control,the Freighliner Cascadia Evolution I was driving (I quit a couple of days ago, but that is another story not for this forum), has Adaptive Cruise Control. It senses a vehicle or an object moving slower than you in front and reduces your speed. If you get close enough, it applies the brakes. I didn't test it, but I assume that the ABS would take care of a lock up if necessary. Now with Lane Departure Warning, Automated Manual Transmission, GPS and other electronic doo dads, it is not such a big leap to driver-less vehicles...

JC

[eagle19952]

wheel holding nanny state, led by the insurance industry, litigation happy lawyers  and geeky programmers... i am so happy for me, having lived in the past and getting sorrier for my grand kids...

mini rant over, smh.

[luvrbus]

With no job now JC maybe see you in Jan @ Quartzsite ?