How to drive a steep downgrade?

[brokedown]

We call it stab braking but it's really just "brake hard in short bursts" meant to get your speed down quickly and back off the brakes to let them cool. Maybe a bigger deal on hydraulic setups where braking down big hills can boil your fluid, but overheating the drums on your air brakes is something worth avoiding too.

When I was rolling up and down the mountains around our northwest states, I spent a good amount of time in "2" going down hills. AT545 FTL.

[Dapplecreek]

Originally Posted by brokedown

We call it stab braking but it's really just "brake hard in short bursts" meant to get your speed down quickly and back off the brakes to let them cool. ...

DirtDoctor: thanks for the links! On one of your links, the next page discusses how to use one's air brakes and it is consistent with what I believe is being advocated here. We may be using the phrase "stab braking" as a handy description when in fact it may be a technical term for something else.

This is what I plan to do:

1. Use the engine's compression if at all possible, always.
2. Pick a target speed for your descent.
3. When you hit that target speed, brake to drop speed by 5 mph - should take about three seconds, and does NOT involve locking up the wheels (which I think is what "stab braking" means in the trucking world, after reading your links).
4. Let speed increase to the target speed.
5. Repeat.

[EastCoastCB]

https://www.youtube.com/watch?v=aNgeu7i6eOk

Here's me coming down monteagle southbound in a bus I'd just picked up in Kentucky. 466 with 643. went down at 45mph easy breezy.

https://www.youtube.com/watch?v=W5PZvtSvp9s

[CE42]

Originally Posted by EastCoastCB

Here's me coming down monteagle southbound in a bus I'd just picked up in Kentucky. 466 with 643. went down at 45mph easy breezy.

Thanks for the video's EastCoastCB !!!

I live in Monteagle and go up and down the mountain at least once a week (one side or the other - depending on which Walmart we are headed to<g>).

I've been here over 10 years and have seen a lot of trucks and buses go up and down (as well as drove my own bus fairly often).

The smart ones who never let their speed get too high (especially the trucks loaded heavy) almost never get into trouble unless there is an equipment failure.

Then there are the stupid ones (or those fresh out of truck driver training who don't seem to understand that the warnings about the grade % and suggested speed limits by weight are SERIOUS about what lies ahead). They are the ones that end up in one of the two runaway ramps or over the side of the mountain.


I've seen some of them less than a quarter of a mile out of the truck inspection area and laying down a blue cloud of smoke from going too fast and laying on the brakes too long.

When I see one of those I know it is time to go a little faster (or slower) and get the hell away from them. They are an accident waiting to happen.

Monteagle is a heck of a rock with some steep grades to be sure.


However a few years ago I drove a truck pulling a heavily loaded trailer to Alaska (up the route from Seattle). As I recall there were a couple of 10% grades out there! They were straight as an arrow and as expected there were some idiots who were letting it go wide open (or at least far over the recommended speeds).

We eased on down at about 35-40 Mph and had a wonderfully boring and uneventful trip down with plenty of time to admire the scenery.


I used to drive OTR many, many years ago and ran the country from coast to coast and all up into Canada. As others have said, the worst times were trying to maintain maximum safe speed on an unfamiliar highway. Of course back in those days our GPS was called "Rand McNally" and "Google" was still what rubberneckers did as the passed by an accident!


These days I just tell people to "slow down, enjoy the scenery and arrive alive!".

[Brad_SwiftFur]

As a professional driver, I learned the hard way to *NEVER* ride the brakes going downhill, even in a low gear. Yes, I cooked the brakes but thankfully was going slow enough to stop and descend the hill in a very low gear. Ever since, my downhill braking method was to allow the truck to coast (engine brake) to 5 MPH above my target speed, give the brakes moderate pressure, enough to slow me by 5-10 MPH, and let it engine brake until it picks up speed again. If I am hitting the brakes too often, then I am in too high of a gear.

[05FrieghtlinerThomas]

personally I’m doing all that is mentioned here in my 40’ Thomas but I’m also looking into an after market jake brake. barrelling down a mountain at 100 mph is not how I intend to pass into the afterlife!

[brokedown]

You slow down a bit faster if you scream the whole time!

[Dapplecreek]

Originally Posted by brokedown

You slow down a bit faster if you scream the whole time!

[...writes note to self...]

[cowlitzcoach]

Originally Posted by Dirtdoctor

Stab braking is wrong for air brakes.

WRONG!

Stab braking is exactly what you want to do while going down a grade regardless of the kind of braking system you have.

You have to remember what exactly is happening when you apply your brakes. The friction of the brake material on the rotor/drum changes speed into heat. If you stay on the brakes the build up of heat can get hot enough to catch the brake friction material on fire.

By using the stab method when you let off the brakes you allow the heat to dissipate.

With air brakes, by letting off of the brakes you allow the compressor to build air pressure back up again.

If after you let off of the brakes you almost immediately have to reapply the service brakes then you are in at least one gear too high.

Ideally the engine and transmission braking will be such that you only have to occasionally stab the brakes.

[05FrieghtlinerThomas]

Originally Posted by cowlitzcoach

WRONG!

Stab braking is exactly what you want to do while going down a grade regardless of the kind of braking system you have.

You have to remember what exactly is happening when you apply your brakes. The friction of the brake material on the rotor/drum changes speed into heat. If you stay on the brakes the build up of heat can get hot enough to catch the brake friction material on fire.

By using the stab method when you let off the brakes you allow the heat to dissipate.

With air brakes, by letting off of the brakes you allow the compressor to build air pressure back up again.

If after you let off of the brakes you almost immediately have to reapply the service brakes then you are in at least one gear too high.

Ideally the engine and transmission braking will be such that you only have to occasionally stab the brakes.

and safely stopping to allow brakes to cool on a long grade is a good idea too.

[Dapplecreek]

Originally Posted by cowlitzcoach

WRONG!

Stab braking is exactly what you want to do while going down a grade regardless of the kind of braking system you have....

Cowlitz - are you recommending repeatedly just-barely-locking-up-the-wheels, or repeatedly braking significantly, in which one would drop 5-10 MPH over three seconds or so?

[EastCoastCB]

Originally Posted by 05FrieghtlinerThomas

personally I’m doing all that is mentioned here in my 40’ Thomas but I’m also looking into an after market jake brake. barrelling down a mountain at 100 mph is not how I intend to pass into the afterlife!

A jake requires a modified cylinder head among lots of other stuff. You'd be in it for tens of thousands.

However- you can get a retarder for your bus. Lots of them in CO came with them from the factory. Retrofitting one would be a lot cheaper and simpler.

[05FrieghtlinerThomas]

Originally Posted by EastCoastCB

A jake requires a modified cylinder head among lots of other stuff. You'd be in it for tens of thousands.

However- you can get a retarder for your bus. Lots of them in CO came with them from the factory. Retrofitting one would be a lot cheaper and simpler.

I’ll check it out, I have a price for a jake brake from a reputable Thomas certified bus dealer for approx $2K.

[EastCoastCB]

Originally Posted by 05FrieghtlinerThomas

I’ll check it out, I have a price for a jake brake from a reputable Thomas certified bus dealer for approx $2K.

Maybe they're calling a retarder a jake generically. Maybe they have some sort of exhaust brake.

Or maybe I've just never seen a regular school bus with a real jake.

[family wagon]

It might also be that they're conflating compression release ("Jake") brake and exhaust brake. Until about a year ago I didn't understand the difference in the two, so I certainly won't throw any stones on that topic.

As I understand it an exhaust brake is relatively easy to add because it's just inserted in the exhaust stream. The Jacobs engine brake on the other hand requires cylinder head modifications as ECCB pointed out.

It's not unlike the braking terminology -- to some of us "stab" braking means firm pressure for a few seconds; today I've learned that to others the same word means heavy brake pressure almost to the point of locking up the wheels.

[Iceni John]

Originally Posted by EastCoastCB

Maybe they're calling a retarder a jake generically. Maybe they have some sort of exhaust brake.

Or maybe I've just never seen a regular school bus with a real jake.

My bus has a Jake. It works well: it will hold my bus at about 40 MPH in 3rd gear down a 6% grade without touching the brakes at all. I came down Cajon Pass and didn't use my brakes once all the way down.

My friend's Gillig tandem has a 3-stage Jake - when we went up to Wrightwood ski resort a few years ago (we had to slow for the curves going uphill!), on the way back down he just toggled between the three settings, hardly using the brakes at all. Impressive!

Jake brakes are compression-release, as opposed to exhaust brakes that merely act as exhaust restriction. Jakes and Telmas can be used indefinitely without overheating, so they're the best for serious mountain driving. Jakes actually maintain some heat in the engine, useful if you're descending long grades in very cold weather.

John

[EastCoastCB]

Originally Posted by Iceni John

My bus has a Jake. It works well: it will hold my bus at about 40 MPH in 3rd gear down a 6% grade without touching the brakes at all. I came down Cajon Pass and didn't use my brakes once all the way down.

My friend's Gillig tandem has a 3-stage Jake - when we went up to Wrightwood ski resort a few years ago (we had to slow for the curves going uphill!), on the way back down he just toggled between the three settings, hardly using the brakes at all. Impressive!

Jake brakes are compression-release, as opposed to exhaust brakes that merely act as exhaust restriction. Jakes and Telmas can be used indefinitely without overheating, so they're the best for serious mountain driving. Jakes actually maintain some heat in the engine, useful if you're descending long grades in very cold weather.

John

You don't have a normal bus, dude.
Most of us can't afford those fancy retro buses. Hell I'm in FL. I've never seen a Crown or Gillig school bus.

[Iceni John]

Mine's not abnormal here! Until CA's older Crowns and Gilligs were recently outlawed due to smog control (their engines can't be retrofitted with all the latest gizmos to clean their exhaust), it was normal to see some still in service here, even a few older than mine. And because my bus was originally from Mid-Placer Schools in Auburn CA up in the Sierra foothills it was set up from the factory for mountain driving, i.e. with a Jake for the long grades there (it's 70, yes seventy, miles uphill on I-80 eastbound to Donner Pass!), and a Quick Start ether injection system for cold mornings. It never had a block heater, but I'm going to install one just like it could have had from the factory.

Don't all school buses in CO have to have an extra brake by law? I've seen some there with Telmas, not something you see anywhere else. Heck, if I could find a Telma for a decent price I'd install it - you can't ever have too much braking capacity!

John

[EastCoastCB]

Originally Posted by Iceni John

Mine's not abnormal here! Until CA's older Crowns and Gilligs were recently outlawed due to smog control (their engines can't be retrofitted with all the latest gizmos to clean their exhaust), it was normal to see some still in service here, even a few older than mine. And because my bus was originally from Mid-Placer Schools in Auburn CA up in the Sierra foothills it was set up from the factory for mountain driving, i.e. with a Jake for the long grades there (it's 70, yes seventy, miles uphill on I-80 eastbound to Donner Pass!), and a Quick Start ether injection system for cold mornings. It never had a block heater, but I'm going to install one just like it could have had from the factory.

Don't all school buses in CO have to have an extra brake by law? I've seen some there with Telmas, not something you see anywhere else. Heck, if I could find a Telma for a decent price I'd install it - you can't ever have too much braking capacity!


John

There are buses not from CO with retarders. But yeah CO has em on any mountain route buses they buy.

You have what used to be a normal bus in Kalifornistan. Now you have a rare collector object of bus-lust.
The rest of us have Thomas, BB, IC, and the occasional Wayne, Ward, or Carpenter.