Brake temps in the mountains

[Ben10]

Enjoying a vacation in the Smoky Mountains. I have ceramic brakes on the front, and so far they have performed perfect throughout this area. How hot is reasonable? Drove down the main park road into Gatlinburg and stopped at the bottom. My C2500 had about 800 lbs of passengers, 50 ils of luggage, and 3/4 tank of fuel. Rotors were almost 500 degrees, and calipers were almost 400 degrees. Brakes worked fine, but am I overworking them? Thanks.

[rustyk]

Enjoying a vacation in the Smoky Mountains. I have ceramic brakes on the front, and so far they have performed perfect throughout this area. How hot is reasonable? Drove down the main park road into Gatlinburg and stopped at the bottom. My C2500 had about 800 lbs of passengers, 50 ils of luggage, and 3/4 tank of fuel. Rotors were almost 500 degrees, and calipers were almost 400 degrees. Brakes worked fine, but am I overworking them? Thanks.

Cooler is better (Obviously :) ). The truckers' technique, in addition to downshifting (which I do in my motorhome) is to use the brake periodically to slow to lower than the speed you want to run, then let the speed build up, and use the brakes again. This gives time for the brakes to cool between applications.

[Robyn]

As a commercial trucker that runs HEAVY STUFF :eek: 105,500 Lbs loaded
Let me quote some stuff that make a big difference between stopping and not.

First off the ceramic pads will grab and hold almost to the point that the rotors turn into a puddle and run out on the ground.

The heat from braking has to go somewhere and a lot of it is dissipated through the rotors and then to the air
A fair amount of heat will find its way through the pads and into the calipers/pistons etc.

The one issue to worry about is that eventually the piston seals can fail if hot enough, long enough.

Generally this is a worst case scenario though.

Large rigs like I run (if driven by a pro) will decend long steep grades in a gear that will allow for low brake usage.
The issue being that even sporatic use on a long grade will heat the brakes to a point that the frictional coefficient between the shoes and the drums will decline to a point that no amount of air pressure will stop the thing.

This is why they have runaway ramps on many Interstates.

The secret is not using the brake more than absolutely necessary.

Now here is where the Jake (Exhaust brake) comes in handy.

I can come off a 6% ++ grade at 105,500 and maintain a reasonable speed and use the service brakes little to none.

I shift the tranny into a gear that will allow the engine to run right up near max recommended speed with the Jake full on.
This gives me the maximum amount of absorbed Horsepower within the engine.

I can usually maintain around 45 MPH on the steep grades and will only touch the air if the speed increases above the desired point.

The test on air brakes is to do an application and see what pedal pressure (app gauge) is required to drop the speed say from 50 to 45. the next time you do it and with similar grade (same one) if it takes more pressure to get the same effect then your brakes are fading some.

This scenario will continue as the brakes get hotter and hotter until they are gone.

The Jake is a truckers best Buddy.

The Jake is best summed up as an electro mechanical retarder.
This device turns an engine into a power absorbing air pump

To state it simply without going into all the intricacies, the system works like this.

The piston compresses air on the compression stroke, the exhaust valves are popped open just before the injector would squirt and the compressed air is blown off out the stacks. ( injector never fires on throttle off times)

Ths leaves an empty dead hole and a piston that has to be pulled back down.
This offers no "rebound effect" to the crank. So every compression stroke
then becomes a power absorbing stroke.

My 500 HP cat will Jake out at about 400HP of braking effort.

Believe me, you dont realize what this is until you get stupid and Jake it on snow or other slippery surfaces.
The thing stops the wheels and can get really hinky to get them rolling again.

All brakes create heat, the trick is to keep it to a minimum and use brake friction materials that will tollerate it with the minimum amount of friction loss as that heat rises.

A rig thats towing is a very good candidate for an exhaust brake.

The REAL Jake brakes are not available for our little engines but there are flap type units that add quite a bit of retardation effect.

BD makes a brake that I believe will work on a 6.5.

The flap type units are no where near as effective as a JAKE but they do help.

500F is getting warm for sure. I have never checked the temps on the big rig but they do get very hot.

500F is above the temp your Missy cooks the Pizza in the oven at.

I am going to Hazard a guess that this would be close to upper limits for long term braking.

Ceramic pads are great "Grabbers" but will eat up a set of rotors real fast if used hard.

Used to use ceramic clutches because they would hold, now we use full dual disc Kevlar.

No wear on the plates at all and very smooth in tough hard starts.

Hope this helps some.

best

Robyn

[Hubert]

That sounds high but don't know. The race boys glow their rotors at what about 700F ish ??? Can't remember when steel turns red.

If they don't fade or sponge on you at all you are probably ok but if they start doing that then it might not stop going down hill.

What kind of grease and lube are you running. I think generic hi temp bearing grease is good for about 470F ish on a quick google search. What is DOT 3 fluid good for as a reference???

How are you measuring them?

[Ben10]

I am measuring them with an IR thermometer. If I downshift into a lower gear will i cook the transmission, or is it meant for such extremes? The upside to the mountains is that I am getting 20mpg on the interstate areas around here, since most times i am going up at 55mph, and down about the same. The interstates are too gentle of grades to either raise the engine temp or the brake temps, it's the backroads in the national park that make the 7% I-40 stuff look like flat land. One climb raised the engine temp from 176 to 206 at the top. Great views though. Anybody think I should downshift to let the tranny help the brakes? I don't get this fun in Florida.

Added mountains bonus. Last night I woke up at 3. It smelled like a skunk walked into our bedroom and blasted the joint. Nasty. Apparently the little gem got worked up next to the air intake outside and the heater spread it around the house. I really prefer the wild turkeys we saw the other day back there.

[DmaxMaverick]

No problem with compression braking. Run it up to the redline, and keep it there all day, if needed. Even better if you can keep the TC locked.

Yep. Skunks are foul. But, not as foul as the fowl you prefer. Careful what you ask for. Wild turkeys are like cats. Once they get comfortable (secure and fed), they'll move in. Once you have a dozen of them roosting around, you'll wish you had the skunk back. Seagulls are lightweights, compared to the turkeys. Good eating, though (turkeys, not gulls, although I've never had smoked seagull).

[Robyn]

Skunk is good eating too. :eek: :D

years ago when I was a youngster, I worked one summer off and on for an old couple and one eavening she fed us stew that was made from fresh garden Vegatables and a light wieght meat.

Hmm I had to ask ya know.
The old gal smiled and commented "Ya mean Y'all didn't see his little flag a hangin off the railing outside"

I looked and about messed my pants.
Now that said the stew was delicious and I did have another helping.


Missy

[jasondmann]

I'd say you are getting warm but not hot. After a 35 lap feature our super stock dirt track car will come into the pits with the left front at 600 to 700 (just starting to glow at 700). Definitely work on snubbing the brakes, a lot safer!