Down-Hill Driving....Automatic

[Iver]

Those of us who live on the west coast of Canada are just now seeing spring weather finally arrive. So it is about time to get the coach out of hibernation and take it out for a good run.   Because of our location, unless we drive due south, we end up in a mountain pass. 

There has been recent discussion about driving automatics up hill and how to shift etc.  So far I haven't had a problem keeping up the rpm's and speed going up hill, but what about driving down long hills.  We have an Allison 5spd auto and a Jake (MCI-9).  We are planning a mountain test drive and were just curious as to what suggestions others might have.

I know this topic has been covered before with varied recommendations but maybe we could revisit it again to remind others like myself.
         Thanks,  Iver

[Sojourner]

A very good question.

May I ask you a question before yours?

Have you inspected of what condition is brake's lining & drum as well the adjustment?

With tow (or trailer) or no tow? Tow (or trailer) with or no braking control?
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The reason I ask is that I brought a MCI-8 in 1997 and without knowingly that my 2 front drum had a deep & wide groove to cause about 20% less braking. Being new about driving a large bus, I wasn't aware that it was stopping poorly until inspect my braking system.

Sometime seller won't tell you what you should know but to be careful.

More Later after your answers.

Sojourn for Christ, Gerald

[NJT 5573]

Iver,

Think you should adjust the brakes to be sure they are tight. My slacks are auto and they really don't do the best job of keeping the brakes snug. A jake is nice, but keep in mind that the coach brakes are adequate to stop it under just about any conditions. That said I think you should run some mountain grades without the jake first to be sure you have a good feel for the brakes that you may have to rely on in an emergency sometime. If I had a buck for every time my jake quit working I could easily take a nice vacation.

Another issue if you have a good Jake is that they will lock the drivers and kill the engine when its slick out. Buses have a tendacy to do a 180 when this happens especially if you are at much speed and in a curve.

You live in an area where there is plenty of ice for several months a year, so keep in mind if it kills the engine on the ice, you may also have a rough time with the power steering as you lose it as well.

If you keep your coach brakes adjusted and dry and your jake quits, you will never be in much trouble, but if you come to rely on your jake and let the coach brakes get wet without drying them or let them get out of adjustment and need them when the Jake stops working you may find you are on a thrill ride that will require a change of clothing or worse.

If I am running rain, I always ride my brakes until they are dry and keep them dry, sometimes that can be as often as every 1/2 mile or so in a serious downpour, but if you have to stop, and the brakes are wet, you will travel well more than 1000 feet before you get any brake action and then it will only be from the one that got dry first so its hard to say what direction they will pull you in.

The need for a Jake on buses is very small so don't fall into a trap of relying on the Jake and not having the foundation brakes always at the ready.

Don't read in this that I am not a big Jake fan, but I know how to do it the old way and thats what will keep you alive and you need to know how to do it both ways and know how to take care of and use the coach brakes first. The Jake is mostly a nice toy in bus application. I have pushed my coach brakes real hard a few times, and have never been able to smoke them, but I have never used the stab brake procedure either, because it really just don't work if you are heavy and are on a long steep grade. By the time you do the 3ed or 4th stab, you have a runaway where we live.

[johns4104s]

Great subjet,

I also have a Allison in my MCI 9, I have never driven the 9 in mountains. I remember when driving the 4104 I would be geared down before going down the grade. this with pulsating the breaks would keep me under control, I must say I never did like big grades.
With an automatic what Is the correct gear to be in or do you leave it in drive and use the brakes? Does the automatic slow you down at all??

John

[poppi]

  Once you smoke your brakes things start happening REAL fast.
So a few things to keep in mind.
    Keep your air pressure up you can't do that if the engine is idling so yes down shift
    before you start your decent.
    Some trannies have a high rpm upshift (so if it does) slow down so you can down shift again.
     once the tranny upshifts it can go from 35 to 55 in a very short period.

    Brake before the corner not at the apex. When you brake you have more G's on the front
    and if you hit gravel you'll feel the front end give  NOT GOOD

    If things start geting real bad start looking for a dumping place where you have some
    surviveability...looking down 200 ft drop offs makes your choices limited.

    When you do get to the bottom..........stop and walk around and check the tires and drums.

    Other than that enjoy the views and just keep it slow!

     BTDT
    Skip

[johns4104s]

Would you change from drive to 2nd or 3rd before you desend the hill?? By doing this will it help you to keep the speed down and stop the tranny from changing up?? Will stareting of in a lower gear ( automatic) Will this hold you back??

Thanks

John

[RickB]

When i bought my first bus 7 years ago a trusted friend gave me good advice for driving in the mountains.

Go down the grade in the same gear you would go up it.

Seemed like pretty good advice and it has served my family well so far.

Rick

[gumpy]

Would you change from drive to 2nd or 3rd before you desend the hill?? By doing this will it help you to keep the speed down and stop the tranny from changing up?? Will stareting of in a lower gear ( automatic) Will this hold you back??

Thanks

John

Absolutely.  Before you start down the grade, you should drop your speed and gear down. How much depends on how steep, and how long the grade is.

I frequently go down mountains in Colorado and Wyoming in 1st or 2nd gear at 18-22 mph, even though trucks are whizzing by me at 60 mph or more. I don't care. I put on my flashers and enjoy the ride, watching my speedometer and listening to the engine as it wraps up before applying slight braking to bring my speed back down into the low end of the zone. I don't have jakes, but if I did, I wouldn't do it much differently. I don't think the brakes on the MC9 are adequate enough to safely stop a 34000 coach on a 2 mile 7% grade without doing serious damage to them or seriously overheating the drums and risking brake fade and ultimately failure. I sometimes smell the brakes as they begin to heat up, and my feeling is that if you can smell them heating, they're already too hot.

Remember, as you heat your drums, they expand away from the shoes. At some point, they will expand past the available travel of the shoes, and you will experience brake fade. The shoes can no longer make sufficient contact with the drums to stop the coach, and you are then at the mercy of the gravity Gods. Your best bet is to slow down and gear down before you start down and don't use your brakes at all, if possible. Make it a goal to descend the grade with minimal brake usage. That way, you should not have to worry about having adequate braking should you have an emergency half way down.

[poppi]

Depends on......
  tranny, differential ratio and how tight your engine is.
  on mine L10 w/ZF I can do 45 mph in 2 up the hill
  but on passes like east side of McDonalds pass or Rogers pass here in montana
  2 going down isn't enough alone to hold you back.
  1 puts it so slow but less brakes required. Since that time
  I have hooked up the internal retarder but I have not tested it yet.
  (yes I'll admit it I've been spooked worse than running 30k 2t grain truck and having
    the front tire blow out at 60mph)
  Jakes are very handy maybe when I can save up the money

   The slowest curve on the pass is 45 mph big sweeping arc with my truck loaded
  I like going into it at 35. (dry road and winter sand cleaned off) slower otherwise.

    So one pickes the gear where max speed/rpm fall within that range and brakes to keep it
  below. (whether you are a pumper, stabber, or holder I won't get back into that debate)

   Hope this helps
  Skip

[PP]

After reading NJT 5573's response, I'm wondering if I don't put too much faith in the jake. It's never let me down (literally) but maybe I've just been lucky. I use it religously whether I'm in the mountains or in town. I don't think I would remember how to drive a beast like this without leaning on the jake to the degree that I do. The thought of it failing never occurred to me, Thanks, Will

[Iver]

Thanks for the responses.  Up until now I have been driving as Craig suggested.....low gear and slow.  I just thought I was being too cautious.  Lots of trucks pass me by downhill.  I can live with that I guess.

I am lucky to have a pit to work on adjusting the brakes so I take as much time as I need to make sure all the brakes are adjusted correctly.
As for the Jake, I don't think I would want to rely on it totally.  It works okay but it doesn't slow the coach down like the Jakes on the 4-strokes...

I can't say if I'm a "stabber" or not but I usually go slow enough to stay in control....
      Thanks,,,,   Iver

[RJ]

After reading NJT 5573's response, I'm wondering if I don't put too much faith in the jake. It's never let me down (literally) but maybe I've just been lucky.

Will (& Iver) -

A different perspective:  In my 29+ years in the bus industry, often averaging 80,000 - 100,000 miles per year, I only had one Jake brake failure while on the road.  And that failure was a broken wire on the fast idle buffer switch.  So don't panic over what NJT said.  If you do the routine maintenance on your coach on a regular basis, chances are you probably won't experience a Jake failure.   Not to say that it won't happen, just saying that, with a well-maintained vehicle, chances are pretty small.

A revenue service MC-9, with 44 passengers and three full baggage bins, equipped with a 6V92/HT-740 powertrain, will maintain about 55 - 60 on a 6% freeway downgrade w/o ever having to touch the brakes.  BTDTHTS

And to answer Iver's question - YES, an Allison WILL automatically upshift to the next higher gear, even if you've manually selected a lower one, when you bump it against the governor too much.

It is also a good idea, if you're not familiar with the hill, to downshift early, not late, for obvious reasons.  RickB's philosophy above is a good one, too - especially if you do not have a Jake.

FWIW & HTH. . .

[johns4104s]

RJ,

I am amazed but glad to know the Allison740/745 will still shift up a gear even if you purposely click it into a lower gear before you take the hill.

John

[Diesel_Gypsy]

Iver,

Great to hear from other Canadian Busnuts!

I'm new to this forum but not so new to driving. I made a living at it for 30 years and have logged over 3 million miles, driving in all kinds of conditions and on all kinds of roads. I've probably driven on the same highways as you are going to test drive your bus! (I used to haul cars from Annisis island in New Westminster all over western Canada)

That said, I have to disagree with some of the "advice" that's been given.

I agree that it is important to keep your air brakes in good condition and properly adjusted, but not using your Jake brake if you have one? That's just silly. Air brakes cost a lot of money if you use them a lot. Jake brakes work for FREE ! Also, using your Jakes will keep your engine temp up on a long grade, thereby helping your engine to last longer. Again saving you money.

Then there is the safety issue. When I went down a long grade, I would throw my Jake on maximum, turn on any other retarders I had, and maintain a speed where I only needed to touch the service brakes once in a while, if at all. (assuming there wasn't a sharp corner at the bottom of the grade) This saved the service brakes for when I really needed them. (like if the RV ahead of me spotted a bear cub or something in the bush and just had to stop for a picture  )

Another issue that NJT 5573 brought up is this idea that the Jake brake will lock up your wheels on icy roads. I have made many miles on ice that you couldn't stand up on and I will say that the best thing to do is not use any brakes at all. However I use my Jake on ice lots because it is MUCH SAFER than the service brakes. The reason is that if the Jake overpowers the traction (engine starts rapidly slowing down), I can recover almost instantly by stepping slightly on the throttle. The truck (or bus) will generally not try to to anything silly like 180 degree turns or anything else scary. This is because you have a differential and only one wheel is likely to be slipping. Service brakes (air brakes) are slower to apply and much slower to release so if you step on the brake pedal to the point where your bus starts to slide, you could be in a very bad way before the brakes release enough to regain control.

If NJT 5573 spent a little more time on maintenance of his bus (fixed the wiring), maybe he wouldn't be having so many breakdowns. . .

As far as "the need for jakes is very small", I guess if you don't mind sitting in the shop spending your savings on unneccesary replacement of brakes, then go ahead and use them. . .

As for me. I'll be the one passing you in the "hammer" lane with my Jakes on and a big smile on my face!

Later. . .
Jim

[PP]

Jim, welcome to the board. Are you sure you're not from England. You speak straight up like an Englishman. Refreshing, Will