Driving In Mountains

We are taking our first long trip and I need some advice about driving in the mountains. We are making our way from Fort Myers, FL to Cincinnati via Hilton Head. (It is so nice here in Hilton Head it is hard to leave.)

From Fort Myers to Hilton, the hills are mostly overpasses. From Hilton Head to Cincinnati the hills get larger.

I assume going up hills is just stand on the gas pedal and let it do its thing.

I'm more concerned about coming down. We are in an H3-45 with transmission retarder (no jake brake) and towing a 4,500 lb car. How do I determine how far to downshift and how much retarder to use? I realize the size of the hill really matters so I guess I'm looking for general advice.

Thanks for your help.

Terry

Hi..with the transmission retarder you will not have any problems. We drove it up and down many hills.

Terry, With planning the retarder is a great way to manage speeds on the downhill side of a mountain.

Going up we put our transmission im performance mode, and in some cases where we know the hill is steep I downshift into 5th early and just hammer down.

The retarder is most effective in lower gears and mine automatically drops a gear when it is engaged. Traveling out west where some grades were 6 and 7% and warning signs posted those grades I would put the retarder in the second position and drop my speed before hitting the downhill to below my 4th gear top speed which is 55. If the speed approached the 55 point I pulled the lever into the third retarder position and left it there until my speed dropped back to 50 or so. In all cases I was able to manage my speeds and keep the transmission oil temps to a maximum of 230 degrees. All this without touching the brakes.

I initially was concerned about if I would pose a hazard to the trucks behind me until I realized they had slowed to the same speeds I was going.

If you don't monitor your transmission fluid temps they can get hot, but the computer will take away the retarder if they reach 300 degrees. I prefer to limit my transmission oil temps to 230 which is very conservative but easily done.

I have come down Black Mountain on I 40 in North Carolina with a 30 foot stacker behind the bus(71,000 total) with a retarder and never touched the brakes and the transmission temps never went over 225.

A rule of thumb is "you go down the hill in the same gear that you climbed it in". The retarder and/or Jake brake will help control the speed. Watch for the posted safe speed limit signs and stay 5 mph below that speed. It is a conservative method but a safe one.

Terry anticipate the hills and down shift to keep the RPM's in the optimal range, don't wait for the transmission to do the shifting. But then I only have an old 8v92.

Thank you for the input. I feel more confident and ready to take on the mountains. We are thinking about heading to Alaska next summer so I'd better get comfortable in the mountains.

Thanks again.
Terry

The key to all of this is you as the driver have to participate. You can't sit there and expect the retarder to do the work for you. You have to actively manage the retarder and the gears to maintain your target speed. It is when you allow things to go beyond your target speeds or temperatures that you go from being a driver to a passenger. Like Jack points out the retarder is more than capable and Denny's post is right on target. Don't let anyone try to intimidate you into going faster than a safe speed.

I drove a dump truck during college so i am ok with actively participating in driving. I have also subscribed to Jon's school of thought when it comes to speed. I set the cruise at 67 or 68 and don't worry much about what is happening behind me. I imagine going down the first longer steep grade will be a bit slower until I get the feel for the transmission and retarder.

There's an old truckers saying - you can go down a hill too slow a thousand times....but only once too fast...

Ok, so how about a few more lessons in driving down big hills, with ONLY the JAKE brake and transmission to control your speed?

I don't have a transmission retarder to help me.

At the top of the hill going say 35mph, do you downshift into 2 or 3rd and maximize the Jake brake to cruise slowly down the big hill? And will that be enough to maintain a slow speed without over reving your rpm's?

Gary S.

Hi Gary. I would find the seed at which you are comfortable depending upon the grade. Usually 4th or 5th works but I would still use the jake.

Gary,
There are three factors involved in controlling downhill speed. You mentioned two but don't overlook your brakes; they are a necessary part of the safe speed equation. Depending on the hill the Jake brake and transmission may not control the downhill speed. As speed is increasing, use the stab method of braking. Apply the brakes to reduce the speed to at least 5 mph under the speed limit then release the brakes. Allow the Jake and transmission to hold you back until you gradually reach the speed limit again. Then apply the brakes to slow you down to 5 mph under the speed limit. Keep repeating this process until reaching the bottom. Again, you go down the hill in the same gear that you went up it in. Depending on the downside, you may have to go to the next lower gear. It is a trial and error method to control the speed. Don't ride the brakes or they will overheat and they won't be there when you need them. Plus the smell of overheated brakes stinks.

With a jake and a big hill select a gear that will hold you back with the engine RPM close to 2000 rpm. As Jon said stab the brakes to control speed. If the jake is not holding you back get on the brakes hard to slow down then select a lower gear. As I drive the big hills I use the jake and save the brakes for the guy that may pull out in front of me. In the mountains saving the brakes is key. Here in western Colorado one sledom drives on level roads so I rarely turn off the jake until there is a lot of flat ground.

There are a couple of things folks need to know about the downside of hills and Jake Brakes.

First, a Jake is not going to have the ability to hold back the bus that a retarder has. A typical Jake only develops about 1/2 the horsepower of the engine. So when working a Jake you need to slow down at the crest and be in the lowest gear suitable for the speed.

A Jake works best at high RPM and hardly at all at lower RPM so downshifting is important.

If the Jake will not hold the speed you want then you must apply the brakes. Typically apply the brakes at your target speed and slow the coach down about 10 MPH before releasing them. DO NOT PUMP THE BRAKES BUT APPLY CONSTANT PRESSURE TO SLOW DOWN. DO NOT "RIDE" THE BRAKES. Our brakes require air to work and pumping the brakes depletes the air supply. Riding the brakes heats them as Denny points out and hot brakes are less effective. Apply the brakes firmly to get slow and then let the Jake take over.

If you have selected the right speed and proper gear it is possible the Jake at the highest setting will actually slow the coach without the use of brakes. When that happens you can toggle between the Jake settings (high to low and back again) to keep your speed in the desired range.

We have had both the Jake Brake and a retarder. Both require you to participate, selecting the proper gear and speeds. Each has its benefits and shortcomings. What is critical to remember regardless of which system you have is that bringing 50,000 pounds safely down a hill requires the management of energy and that starts at the top of the hill with the correct gear and speed. If you wish to maintain normal driving speeds down a hill understand that your already long stopping distances are going to increase significantly and you are placing your safety solely in the ability of your brakes to do their job. Don't do that. Be safe. Use the Jakes and retarders to help you.

Today I drove east down Monarch Pass (US50) in Colorado. The speed I wanted was the speed that allowed the Jake to hold me back without using the brakes. For the top 5 miles or so that was 3rd gear at 2000 rpm. I never touched the brakes for the five miles but did lightly touch the throttle when jake began to decrease my speed. Just a light touch of the throttle turns th jake off but also allows the jake to come back on the instant the throttle is released. Works great for me. As the grade became less steep I unshifted to 4th gear.

There's some good info in this article that closely relates and supports the advice in the Post/Article on using the Transmission Mode Button. http://forum.prevostownersgroup.com/...N-TRANSMISSION

As pointed out in both posts, the main thing is learning how/when to punch that mode button or the up and down arrows. Fortunately, with the Allison transmission, it is smart enough to do most of this by itself, but there are advantages to knowing how to do it yourself.