brakes or low gear on long hills

[dieselcrawler]

I will be moving to a new house in a few months. Nice place, really big, but at the top of a nice long hill. I'll have to climb and decend this hill daily to get to work. It's about a mile long, not sure of the grade, but it rises about 500 feet in that mile. I have lighter duty 3/4 ton brakes on my dually K-30, both front and rear. Should I use the brakes, pumping them, and letting off to alow them to cool for a second or two, or just hold the trans in first gear, and let the motor try to hold the truck back. It does ok useing the trans to hold it back, it just ends up revving quite high. What will using the trans hurt, in the trans, and for the motor, to be revving at high RPMs w/o any throttle for the trip down the hill?
I want to use the brakes in such a way as to not warp rotors left and right (no pun intended) but also not ruin my trans or motor.
Thanks,
Greg

[HammerWerf]

Crawler:

To get to and from some ranches near where I live, I have to go up and down similar but longer grades. Both grades are in the 5 - 9 percent range. The shorter one is 1/2 mile (paved), and the other is about 1 1/2 miles long. The longer one is Dirt.

What I do is when decending the longer on with the suburban, I put it in 4wd low range 1st gear. Nice and slow. Actually have to press the go pedal to get the speed to 5mph. 2nd low provides better speed that is very controllable.

In my 83CC, I pull the tranny into 1st gear, then stab at the brakes to keep the speed between 10 -15mph. I try and let the engine/tranny do as much work as possible. On the paved grade, I pull them both down to 1st gear, running the A/C to create extra retard load, then stab the brakes.

The 84 has a manual tranny, put it in lower gear, run the A/C then stab brakes when necessary. My brakes on this one are similar to yours.

Have fun. At these speeds, we get a real good look at the wildlife.

Hope this helps.

HammerWerf

[dieselcrawler]

I think my bigest concern/question is this: How does forcing the motor to turn at high RPMs w/o being fed with fuel affect it? What does this do to the EGTs? Is it possible to over-rev the motor this way, as in, it has a rev-limiter built into it some where that works when accelarating, but what happens in this situation?
Naturaly, I'm smart enough to do as I have been, and as sugjested, and use both the trans and brakes to keep speed in check... but it all just got me thinking, and I want to know what ever I can about it.

Thanks,
Greg

[jcomp]

Your EGTs will be lower going down the hill. My EGTs can be around 1000 at the top of a pass and then back down to 300 by the bottom. I've noticed on mine that the tranny temps will go way up if I'm engine braking, might be something you want to keep an eye on.

On hills I use the engine as my primary means of keeping my speed under control and try to use the brakes as little as possible. Its best to use them in short pulses of hard braking, never ride the brakes down a long hill.

The most important thing is to just not be in a hurry and keep your speeds low.

[Colorado Kid]

To answer your other question, the TH-400 will eventually shift up rather than overspeeding your engine to death, but you won't want to go fast enough for that to happen becasue if you do it'll take a BIG brake application to get it slowed down enough for it to shift back down.

Iterestingly in 6 years of mountain driving school busses we were always given advise almost exactly opposite jcomp's. Use the lowest gear possible and then light steady pressure to keep it from shifting up. Maximum engine braking effectiveness is at maximum RPM. The purveyors of this advise claimed that by making maximum use of the available engine braking the light-steady pressure put less heat into the brakes than even short hard applications. In fact we were told that if we had to make a short, hard application while decending a grade (to avoid a deer, for example) we were to come to a complete stop and wait 45 minutes :eek: for the brakes to cool before proceeding. Bus brakes are a bit more massive than pickup truck brakes, but the point is that they take like forever to cool once you get some heat into them.

[JeepSJ]

jcomp - you may want to look at adding a manually operated switch to control your torque converter lockup. Coming down the hills in lower gears the converter will be unlocked and the slippage generates heat. Lock it manually and you will see temps go down and you will get better engine braking.

To throw my 2 cents into the braking conversation - I know 2 professional truck drivers and they both say the light steady pressure is the way to do it. Follow a big rig down a grade and watch the tail lights.

[Mark Krieger]

Originally posted by jcomp:
The most important thing is to just not be in a hurry and keep your speeds low. It seems to me that the physics of the situation is this: Slower is better. Here's why...

For a given amount of drag created by the brakes, the power released is giong to be proportional to the speed squared.

In english, this means that going HALF as fast down the hill while riding the brakes will create only 1/4 of the heat generating power. The power you're robbing with the brakes will directly influence the temperature of them.

Or, going TWICE as fast down the hill will create FOUR times heat generating power! Going THREE times as fast down the hill will generate NINE times the power.

[jcomp]

I used to drive a pickup/trailer for a company, they told us during training to apply the brakes in hard pulses going down a grade and not to ride them. Our truck (1-ton Ford) and trailer weighed 19K lbs and we traveled all over the northwest USA. We went down quite a few steep grades and never had any braking issues. I don't know much about big truck brakes, maybe the big drums of a semi or school bus need light continuous braking and the disk brakes of a pickup work better the other way? But then we also had drums on 3 axles and disks on only 1. :confused:

JeepSJ- I think you are right, a manual lockup switch will reduce the temps. It's on my list. smile.gif