Brake rotor for extreme duty on a big rig.

So I've finally hit the point where I need to do some research on brakes.
98xj, 5.3/4l65e, 35x12.5", WJ Akebono fronts and KJ drilled/slotted rears, around 5000lbs on most days.

Setup is more than adequate for the stuff we normally do (street, and low speed wheelin') but yesterday I finally found my Jeeps stopping limits. Spent about 8 or 10 hours on a mountain we'd never been on, most of it is relatively high speed (top end of 4th (a bit faster than 5th in the AX15, cause auto)). On our way back down the mountain we started experiencing an odor that is new to my Jeep. Smoking brakes. As we got to the very end of the trail and to the road, the fade hit and I had to gear down, pull the e-brake, and try to slide around in the gravel to get stopped. Front pads/rotors were smoking like a mutha and both wheels were too hot to touch - Oops.

Now to give you an idea though, my shocks (12" bilstein 5125's) were also too hot to comfortably touch. We were moving pretty fast and it was a fairly hot day, and I was about 5100lbs, but still. I figure if I can't descend a mountain trail at around 50-65km/h, I'm not super confident in my ability to descend a mountain highway at 110km/h for 20km (A few years ago, I smoked my brakes on a hill I'm about to be driving next week).

So that said, the front WJ rotors are just boring solid rotors, while the rear KJ's are solid drilled and slotted. Yea, the rears don't work as hard, but in 4L with 5000lbs, and no prop-valve, they're working PRETTY hard, but they weren't smoking.

I know a bit about rotors, and I understand that in terms of cooling capacity, they go something like:
* Solid
* Vented
* Slotted
* Drilled
* Vented/slotted/drilled

I know a vented/drilled/slotted rotor will run between 100-200f cooler than a solid rotor, but know nothing about just plain old vented, or a solid drilled/slotted.

I've always stayed away from drilled/slotted for off-road application, 1. Because they get noisy very fast due to mud/sand intrusion, and 2. drilled rotors are more prone to cracking. But, at this point, I need an upgrade in the front at very least, and I'm more concerned with reliable stopping power than I am ninja stealth .

So that in mind, should I just be looking for a good vented rotor, or assuming I go with a well manufactured rotor, should I be looking for vented/drilled/slotted?

Centric premium rotors seems to be the consensus

Johnnie Walker said:

Centric premium rotors seems to be the consensus

Click to expand...

Is that a solid or vented?
I ask because regardless of manufacturer, the physics remain the same. A solid rotor of the same size will radiate heat at the same rate regardless (for the most part) of alloy chemistry. I suspect a vented rotor should do the trick, but I'd like to be confident about this before dropping $ on my 5th set of rotors in 2 years (lots of upgrades/axle changes/stuff).

I'm also wondering if the drilled/slottedness of the rears (otherwise solid) is actually doing anything, or if I'd be better served by a simple vented rear as well.

They come in a few varieties.

Unfortunately, Centric doesn't list specs with their P/N's on their website. Fuuuuu.
Anyone happen to know a PN for a regular vented (Centric Premium) rotor for a front 03 WJ, and a rear 03 KJ?

Check the black magic brakes site to see if they post a PN.
I'll do a quick search to see if I can help you out.

Summitracing.com lists some rotors

120-67022CRY
Front WJ

18363-05215739
rear KJ from partsgeek.com

Well crap. I'm an idiot. My fronts ARE vented. Still insufficient. So, what do I do from here besides adjust driving style, slow down, and/or lose some weight ?

Have you upgraded your brake Master Cylinder?

No, but the MC isn't at all the issue. My stopping power is ridiculously good considering the 35's and 5000lbs. I stop faster than my GF's civic (which has 4 wheel disc, vented/slotted/drilled). I can JUST lock up all 4 wheels on dry pavement under ideal traction conditions. The only issue I'm having is with heat, and this is the first time I've ever had a problem.

That said, my rotors do heat up quite a bit even just at a cruise on the highway, so it's possible they're rubbing a bit much at all times, which could definitely contribute. I've never actually checked my roomies brake temperature (at a cruise) to see if his heat up as much as mine do. Checking for brake drag I suppose is my next task here, and man I'll feel dumb if this overheating was just caused by brake dragons.

I'm hoping Cal will chime in here as I'd be interested to hear what he's running on the KOH, and how well it holds up. I'd imagine the KOH run has gotta be working the braking system pretty hard.

vented does not brake better or cool faster (according to the experts). Less mass = less heat sink.

We run WJ centric premium rotors (no slots or holes) with black magic pads.

The key is the pads. They don't fade when they get warm the way other pads do (think Formula 1 compounds), but they also bite when they are cold.

If this is the first time you've encountered this, I'd probably replace them with new centric/BMB stuff and not give it a second thought, unless you plan on racing down that mountain a lot more - if that is the case, call up Blaine at black magic and consult with the master.

Hahahaha. Well, long story short, I think this XJ is about ready to be laid to rest. Apparently messed up a few things last night. Will take the brake info into consideration when I start the new build.

Uni finally tweaked a little too far the other day and did a lot more damage than I thought. It all surfaced today on the way home from the lake. Rear passenger shock mount (behind seat) tore right out and I didn't notice because it'd stuck in place. Was squeaking. When I checked it out and discovered it'd ripped out, the engine being funky today made sense as well as my battery ground went into that mount No idea how I was getting any ground at all.
T-case chain started slapping on the way home and had to pull the front DS, but only had an 8mm wrench, which works for the t-case side, but not the axle side. Took the axle side u-joint apart and discovered that one of my bolts on the t-case side was stripped, so I had to break the double cardan joint out (with furious anger).
Then realized my hatch didn't want to open or close. Must've shmucked a tree a little harder than I thought. Uni is done.

Cal, I'll be asking you all about your cage shortly. How it was put together, how hard you've beaten on it, and how well it's held up . Next project is "project unbreakable".

the centric premiums are vented.

I'm going to disagree with Cal on the venting not increasing cooling. the vented rotors have more surface area, and thus cool better. that's simple physics, a solid rotor simply cannot cool better, although they may have more mass to absorb the heat, without the venting, there is nowhere for that heat to go.

however, he is correct that heat is not the only issue. unless you are getting so hot that the fluid is boiling out of the lines, what you are experiencing is heat fade in the pads. a big reason to switch to the Black magic stuff.

rockclimber said:

the centric premiums are vented.

I'm going to disagree with Cal on the venting not increasing cooling. the vented rotors have more surface area, and thus cool better. that's simple physics, a solid rotor simply cannot cool better, although they may have more mass to absorb the heat, without the venting, there is nowhere for that heat to go.

however, he is correct that heat is not the only issue. unless you are getting so hot that the fluid is boiling out of the lines, what you are experiencing is heat fade in the pads. a big reason to switch to the Black magic stuff.

Click to expand...

When yall are talking about "vented" are you talking about vented as in the difference between a stock front rotor for an XJ and a stock rear rotor for a ZJ? Or are you talking about vented as in a bunch of holes and slots etc in the rotor?

iluv83vettes said:

When yall are talking about "vented" are you talking about vented as in the difference between a stock front rotor for an XJ and a stock rear rotor for a ZJ? Or are you talking about vented as in a bunch of holes and slots etc in the rotor?

Click to expand...

venting refers to the gap between the 2 contact surfaces.




a rotor with slots and holes is a slotted and drilled rotor. not a vented rotor.

rockclimber said:

the centric premiums are vented.

I'm going to disagree with Cal on the venting not increasing cooling. the vented rotors have more surface area, and thus cool better. that's simple physics, a solid rotor simply cannot cool better, although they may have more mass to absorb the heat, without the venting, there is nowhere for that heat to go.

however, he is correct that heat is not the only issue. unless you are getting so hot that the fluid is boiling out of the lines, what you are experiencing is heat fade in the pads. a big reason to switch to the Black magic stuff.

Click to expand...

yup. i read and typed 'vented' but my inside voice said 'slotted' every time.

if it said slotted, i would have been accurate, as usual.

So I found the thread on JeepForum about the Black Magic pads. EPIC thread. mrblaine seems like a stand up guy for sure, and I dig how he's gone well out of his way to 1. Prove his pads do as he claims by firing out samples to unbiased third parties for testing, and 2. Makes sure any issues that do arise get resolved immediately.

I was just asking him about pad temps and at what temp his compound starts to break down. According to him, they won't start fading out until around 1500*f. I haven't seen any direct evidence to back this up yet, but from the 20 pages of dialogue on the thread, it sounds like some pretty knowledgeable Jeepers seem to confirm they can run substantially hotter than other pads, and actually grab harder as they warm up.

That said, I'm an idiot and my front rotors are in fact, vented. I suspect my fade was in fact, simply pad fade and that no fluid was boiling, and that my next step is indeed, to try a higher temperature pad. Oh the amount of money I spend on a problem that has only bit me twice in my life... But ya know... It's brakes.



Has anyone else got KJ rear discs and have a somewhat functional e-brake? I've never managed to dial mine in to the point that it'd hold my weight on even a very slight incline, and they certainly won't do shit for me in an emergency. They seem to be adjusted bang on, they're dry (brand new rotors and shoes), and I can barely pull the lever past 3 or 4 teeth, but just won't hold my weight. I know some ZJ guys have said they have no problem with the e-brake, and ZJ's are slightly smaller than the KJ shoes.

Maybe try lightly scuffing the surface of the e-brake shoes and the inside of the drum with some 30-40 grit to increase friction? I adjust mine to 3-4 clicks as well.

last resort would be to ditch the ebrakes all together and go full hydraulic parking brake like this...

http://www.speedwaymotors.com/Park-Lok-Hydraulic-Brake,1970.html

Johnnie Walker said:

Have you upgraded your brake Master Cylinder?

Click to expand...

The WJ has a 1" master cylinder. No need to change out the stock one as it is already 1"

blistovmhz said:

Has anyone else got KJ rear discs and have a somewhat functional e-brake? I've never managed to dial mine in to the point that it'd hold my weight on even a very slight incline, and they certainly won't do shit for me in an emergency. They seem to be adjusted bang on, they're dry (brand new rotors and shoes), and I can barely pull the lever past 3 or 4 teeth, but just won't hold my weight. I know some ZJ guys have said they have no problem with the e-brake, and ZJ's are slightly smaller than the KJ shoes.

Click to expand...

Yep and yep. Another Mr. Blaine product:

http://naxja.org/forum/showpost.php?p=246240698&postcount=116

I read most the thread but found myself going back to your 1st post! YOU said your front pads and rotors were smoking like a mutha! I don't know if I'm correct but, With that statement it leads me to believe that you are not getting correct proportioning from your system! Were your rears hot? They will remain relatively cooler but should still be pretty warm if the fronts were burning up!