Brakes. Driving correctly

bw1974

Member
Feb 7, 2020
16
NC
I tow a ten foot Starcraft StarFlyer XL with a much heavier 96 Ford Bronco and find that at least taking it out overdrive and into 3rd on even interstate downhills is much easier drive on the downhill. I have also noticed that shorter wheel based vehicles are more likely to have sway from the trailer trying to push the TV around that sometimes it helps to manually put on some trailer braking before applying the regular brakes if you can. Even with the little Tent trailer we have I can get sway going down hill if it's not packed perfectly... So it's very nice that the starcraft has Trailer brakes.
Very easy to add an anti-sway bar :)
 

rdyck

Member
Dec 3, 2017
35
Victoria, B.C.
Different scenario, but my tow vehicle is a 2016 GMC 2500 Savana van with 6 speed automatic transmission. There is a button for towing that changes the shift points on the transmission, and also engages engine braking when going down steep hills.

Also, remember that the big commercial trucks use engine braking, Jake Brakes, when not in residential areas. :)
 

stierheim

Member
Apr 22, 2013
59
A modern TV has four wheel disc brakes - you ain't going to hurt them in a hurry - but there are absolutely some downgrades long enough and steep enough to get the pads very hot - I have seen it and smelt it happen on other vehicles. But hot disc brake pads wll still work ok, unlike brake shoes-drums.
This is not quite right (... hot disc brake pads will still work ok, unlike brake shoes-drums).

Disk brake pads run at higher temperatures than drum shoes do under normal operation. It's simple physics. For the same weight, downhill altitude change, speed, and time to descend, a disk brake and a drum brake must dissipate the exact same amount of heat energy.

A disk brake pad has a much smaller surface area than the drum brake shoe has and therefore must run at a higher temperature at the pad surface to dissipate the same energy as the brake shoe which has a much larger surface area. This is why disk pads are 4 times or so thicker than a brake shoe, while they both last about the same amount of mileage. This is also why disk brakes run at much higher pressures between pad and disk than shoe to drum pressures do. Disk brakes uses greater than 3 times the pressure that drum brakes use between the friction material and the rotating disk/drum.

Where disk brakes have the advantage is that over 75% of the disk friction surface is spinning in free air which allows for very good heat dissipation. A drum brake has around 20% or so of the friction surface exposed to air, and that air is trapped inside the drum so it can't easily dissipate heat out of the brake. Most of the heat energy dissipated in a drum brake must travel through the thick steel drum and exit on the outside surface of the drum - this is very inefficient and results, with braking on a long downhill, with overheating the brake shoes.

Their good ability to dissipate heat is the reason why disk brakes are preferred over drum. But is doesn't mean you can't overheat a disk brake, it just takes longer (more energy must be absorbed before it over heats). And if you can dissipate this energy in any other way, like engine braking via downshifting, it allows the brakes to work longer and at a lower temperature on a downhill.

Regardless of disk or drum technology, neither will work once a critical temperature is reached. Brake fade, as it is called, happens when the surface temperature of the friction material reaches the boiling point of the binder (basically glue) used to hold the pad or shoe friction material together as a rigid block. Once at the boiling point, gas is given off (like steam from boiling water) and this gas layer between the friction material and the steel disk/drum prevents contact and results in a significant loss of friction. This condition will persist until friction material temperature drops below the boiling point of the binder.

And one final point on downhill braking:

A vehicle (or vehicle/trailer combination) has a specific amount of potential energy based on its weight and altitude (this cannot be changed). When altitude decreases, the potential energy is converted to kinetic energy (this also cannot be changed in any way).

If vehicle speed is the same at the top and bottom of the hill, then as the vehicle or combination descends, 100% the kinetic energy that results from the altitude drop must be converted to heat, it cannot be retained in the vehicle at the lower altitude.

The amount of energy which must be dissipated during the descent is a fixed unchangeable value. The speed of descent has no impact to the amount of kinetic energy which must be dissipated. The only control the driver has in dissipating this kinetic heat energy is TIME. The longer the descent takes (i.e., a slower speed), the longer time the brakes have to dissipate the heat into the air and as a result will operate at a lower temperature. This is why speed means everything on a descent while protecting the brakes from overheating. It is also why diverting some of the kenetic energy away from the brakes via engine braking helps keep brake temperatures lower.
 

RandyP

Member
Dec 11, 2020
23
Tumwater, WA
There is a reason that the national MUTCD (Manual on Uniform Traffic Control Devices) has a standard sign warning of steep grades, and an accompanying "plaque" (smaller sign) that often goes with it that says "TRUCKS USE LOWER GEAR."
 

Lonewolf55

Going NoWhereFast
Mar 25, 2015
59
Statesville, NC
Wow, Its always interesting all the ideas people have concerning proper driving techniques and safety measures. Drum brakes vs Disk Brakes. Drum brakes on the front have wheel bearings. If you use your brakes too much,(front brakes are 60% of braking) you will over heat your bearings, burn off the grease and possibly loose a front wheel. That is one of the reasons front brakes are now mostly disks. Disk brakes have a separate "rotor" from being part of the axle shaft, but it is still tightly attached to it. So they can transmit a lot of heat to the axle and bearings. I burned up the bearings in a ford Taurus back in 2003 with too much braking on many hills. Brakes fail on long down hills because the pads (Or shoes) get so hot they transmit the heat to the brake cylinders (the things that push the pads into the disk/drum) and will get the brake fluid hot enough to boil inside those cylinders. Once they heat up the brake body hot enough to boil the fluid you are braking with air (No braking), and it will boil for 3-4minutes after you stop braking, and the fluid is ruined. And most likely the cyclinders have enough pressure to cuase the seals to fail and spray oily brake fluid all over your brake shoes/pads. So now you have cooked your bearings, over heated and warped your disk/drums, oiled your brakes so they have no friction to stop you, ruined your brake fluid, and are going down a hill at 80mph. I would make sure you have a bible in the seat next to you.

My Father was the transmission designer for Chrysler, (A small auto manufacturer in the 70's-80's). He always said you wreck a transmission with the accelerator, not by the using it without power. Worst thing for an automatic transmission is heat. If your going downhill at 4-6000rpm in 90-100deg F temps, watch your temp gauges and realize your tranny is over heating with your engine (same with going up hill). But let your Brakes rest until you really need them. They can save your life.

This is assuming of course you have hydraulic brakes and not mechanical ones like a bicycle. I will totally agree with the statement about electrical cars use regenerative braking, except that regenerative braking is a setup where when you use the brakes, they operate a small generator like system that recharges the batteries, so braking in an electric car is a good idea in most cases.
 
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ccarley

Active Member
Sep 23, 2014
231
I've heard that brakes are cheaper than a transmission, however that doesn't add up when your brakes fail and you can't stop. Using the engine to control the speed to a point is ideal, and then using the brakes to make adjustments works well and you have emergency braking available still.

Towing our Starcraft with my '00 F-350 you would think this wouldn't be a problem (but we're like 13k pounds or more combined and loaded). I've got big brakes on the truck, and the Starcraft has brakes as well. I still downshift to maintain speed and use the brakes at times to make adjustments to speed. Actually, I save more fuel that way as the computer shuts off the injectors when going downhill with the converter locked... My wife's 2017 Explorer actually will downshift on it's own (automatic) when going downhill...

Just some thoughts.
Clay
 

tombiasi

Super Active Member
Sep 1, 2012
6,764
Northwestern New Jersey
Never EVER put it in neutral going down a hill. If in neutral, you lose an aspect of control. As above, use a lower gear. Former truckdriver here, and we had a trial run of disc brakes for trucks circa '85-89, and the key to disc brakes is to apply firmly, then let off to cool. If you stay on them, the rotors will overheat and warp with heat.In the switch to 4 wheeling, I'm known to verbally apply my "jake brake" down the hills!!
Your truck responds to voice commands?
 
Dec 26, 2014
14
Yes, downshift to a lower gear when driving down a hill, just as you would downshift when going up a hill. The same applies to vehicles with automatic transmissions, select a lower gear when going down, or up a hill. Most vehicles have a tachometer, so use that as your guide for which gear to select (do not overrev your engine).
The other benefit of downshifting to a lower gear (whether you're going up or down a hill) is the increased engine speed helps circulate water faster through the radiator, helping to cool the engine. Older vehicles, with non-electric fans, also benefit by forcing more air through the radiator when engine rpms are increased.
Keep an eye on your tachometer and coolant temp, and you'll save both your brakes and automatic transmission.
 

1380ken

Super Active Member
Nov 7, 2013
2,973
Mass
I like all the over thinking and deep brake physics. I can almost understand someone who only drove an automatic their whole life not having a feel for gears and engine braking. Can't understand how you can drive a manual and even ask the question.
 

Rick Thomas

New Member
Jan 26, 2020
1
Just as an FYI, I own a Chevy truck with the Diesel Engine. If you leave it in gear, on the downhill, the Engine brakes "kick in" saving the wheel brakes from wear. Truckers have been using this method for more years than have been on this planet. I was always taught to use a lower gear and save brakes. They are expensive and take time that you could use for better activities (fishing, hiking, camping, etc). Hate to say it but, I really think you need to get a new theory...
 

jeepster04

Active Member
Nov 23, 2010
294
It is interesting reading/hearing what other people think works best. Just the other day, a coworker said he once popped a brake line and to slow down, he put it in neutral... I was like, what? He said "yeah, I didnt want the engine pushing me...."

My Jeep has very good engine braking. I rarely have to use the brakes when going down hills while everyone else either rides my butt or is hammering on their brakes in front of me. Some people just dont know.
 

rikichef

New Member
Jul 23, 2016
6
Interesting reading. Being in Wyoming and going over many 10,000 ft passes with our Toyota Hylander Hybrid towing our Palomino TT (while hubby was pulling his butt up and over these passes on his road bike), he informed me early on to put it in a low gear when going down hill so I wouldn't have to ride the breaks. Always worked great for +8 years of cycling tours with just needing to tap them here and there.
 

phowardtx

New Member
Nov 18, 2019
1
I nearly melted my brakes coming down Sandia Mountain. In retrospect I should've unhooked the trailer before going up, but on the way down I could definitely tell they were starting to fail. I stopped and let them cool off for about 30 minutes or so before continuing because they literally started smoking. I have a 2005 Z71 with quality ceramic brakes and a Fleetwood camper without the trailer brakes hooked up. Next mountain pass I'm going to have the trailer brakes operational.
 

tfischer

A bad day camping beats a good day at the office
About 20 years ago my wife and I went up Pikes Peak with her little Saturn sedan. That car only had a "Drive" and "2" on the automatic selector. On the way back down, the car in front of us was riding their brakes the whole way down. I was driving, and trying not to use the brakes, but in "2" gear I just wasn't getting nearly enough engine braking to stay behind the vehicle in front of us, which decided they needed to go like 15mph down the entire mountain.

At some point they had a "brake check" where you stopped and they would take the temperature of your brakes. Unsurprisingly, both the car in front of us, and us, were pulled aside and told we had to wait a half hour.
 

1380ken

Super Active Member
Nov 7, 2013
2,973
Mass
Coasting in neutral is dangerous on flat ground . You need to be in gear to accelerate to avoid accidents
 




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