XJ Front Brakes, BIG Brake Options

[CobraMarty]

Here's the pics finally,
Early Knuckles, Late Hub, 14" GT500 Rotors and 2014 GT dual piston calipers-

 

[wacho4]

Shur is purdy.

Been following your thread, Like where you're going with this.

 

[Root Moose]

Maybe it's a bad scaling thing in the picture, maybe it's the style of caliper used on the Mustang GT, or maybe it is just my personal bias...

That caliper doesn't look nearly as impressive as the WJ caliper. Not a lot of material in it?

FWIW, just another option, I'm running WJ calipers, an old WARN 5 on 5.5 hub kit for a TJ with a CJ7 rotor. I basically copied Mark Hinkley's old ORGS setup years ago. This was back when the WARN kit was still ~$600 and good weekend project, bolt-on scale value.

I've got lots of brakes but I wouldn't advise anyone copy it as I think the front rotor could use some more thermal mass to be ideal. That said, when used as a Jeep is normally used it is awesome. I have no real regrets other than the requirement of custom outer axles... shipping time when they get broken is a PITA (Bt/dt).

When I do the next major brake maintenance on my Cherokee I may try upgrading the rotor to a Scout II rotor (roughly 1/2+ ton size rotor, much larger than what's currently on there). If that rotor can work it would be a fantastic setup.

Between proper steering geometry and big brakes the normal 4 on 4.5" WJ setup is a straightforward, high value setup that has been done to death so there is lots of help out there. Y-links and T-links are crap and should be avoided especially in a high performance setup. The WJ steering setup is a revelation compared to the stock steering. Helps turn in feel immensely, no dead spots...

IMO, until you have been attending HPDE/ lapping your Jeep every weekend for a few years there is no need for anything more than WJ brakes and some decent pads. There are soooo many way over built vehicles relative to driver skills at lapping days... Hell, even lapping the first half dozen times stock brakes with decent pads are probably more brake than a n00b will be willing to use.

As for cost, WJ setup is not that expensive either if you scrounge used parts.

2¢

 

[GrimmJeeper]

That looks like the pad is only contacting ~70% of the rotor face, what's the point of a bigger rotor if you're not using it all?

 

[hawkeye 1]

That looks like the pad is only contacting ~70% of the rotor face, what's the point of a bigger rotor if you're not using it all?

Right, it's pointless, completely defies the purpose.

 

[yossarian19]

It gets better leverage, doesn't it? Less swept area than it could be taking advantage of, but I'll take a mostly swept 14" rotor over a fully swept 10 any day.

 

[GrimmJeeper]

that's going to look pretty sweet when the inner inch of that rotor flash rusts and never gets wiped clean by the brake pad.

 

[rockclimber]

Theoretically he is still getting more braking area. Larger circumference means more surface area.

Theoretically.


Cobramarty Do you have a pad measurement on that?

 

[Root Moose]

I went through a bunch of combinations and permutations on my rear axle and had a similar layout at one point (i.e. lacking full coverage of the rotor). I ended up backing away and using a matched rotor and caliper set.

I couldn't deal with the mismatch. It's the kind of thing that would make me nuts inside every time I looked at it.

If one is to spend all this time to try different things instead of just buying a kit one should end up with something ideal at the end. There has to be a better "ideal" combination. Making something work because it is cheap to obtain is not necessarily the best reason to make something work, especially if it brings compromises.

 

[CobraMarty]

The Mustang GT pads measure 4.3" x 2.0" overall but have a 0.6" gap in the middle. Bottom edge is slightly angled,

So I would say each pad has 2 blocks of 1 7/8" x 2".

So it looks like 7.5 sq. in. per pad, x 2 = 15 sq. in. pads each wheel.

14" Rotor pad sweep area is 13 7/8" outside, 11 7/8" inside.
151.20sq.in. - 110.75sq.in = 40.45 sq. in. x 2 each side = 80.90 sq. in.

 

[CobraMarty]

WJ Knuckles '93-98 12" rotors dual piston calipers 5x4.5 pattern. These can and have been used by many as an upgrade but requires different/modified steering and track bar modification as well as welding on a spacer to the knuckles. Can't just use the lower steering bracket because it will cause significant bumpsteer because it is 3/4"-1" lower than stock XJ. Gets expensive when include the steering and track bar mods.

corrections-

ZJ Knuckles '93-'98 11" rotors, single piston calipers, knuckle with brake pad mounts/ears, like XJ

WJ Knuckles '99-'04 12" rotors, dual piston calipers, mounting lugs for calipers, different lower ball joint than XJ, passenger side knuckle with high mount steering arm, 5x5" bolt pattern, to be used on XJs- requires spacers to be welded to knuckles, different steering linkage, modification to track bar mount and coil and sway bar area, need to redrill rotors from 5x5" to 5x4.5" pattern

 

[yossarian19]

So, are the Mustang brakes mounted to the RaceJeep yet?

 

[CobraMarty]

Most everything that I have read about brake fade talks about heat soak and heat sink/heat dissipation as the issue. The fix seems to be heavier and more mass to the pads, calipers and rotors. That being said, I weighed a few parts that I have.

10.8 pounds -2014 Mustang GT Caliper with pads
20.8 pounds -2014 Mustang GT 13.2" OEM rotor
24.6 pounds -Mustang GT500 14" Centric rotor

I need the weights for-
XJ Caliper with pads and rotor
WJ Caliper with pads and rotor

 

[cdawall]

Interesting I was thinking about the sport trac brakes and I have an old set of knuckles in the garage.

 

[kastein]

To actually compare brake surface area / effectiveness you really need to do some calculus, you can't just say "2x4 inches at a radius of 6.5 inches" or whatever and have it work out. You need to calculate the brake torque that will be applied by every spot on the pad/rotor interface (including the effects of the brake pad backing plate flexing due to the caliper pistons not covering 100% of the back of the pad, for best accuracy) summed up, i.e. an integral of some sort, I'm not thinking it all the way through because I'm lazy. Comparing using area of pad and diameter of rotor is approximate at best and misleading at worst.

It's a lot more work mathematically but you'll actually get usable numbers.

I'm not sure I'm comfortable at all with how you're mounting the caliper to the knuckle but would have to see a 3d model to really decide, and even then, I'm not a mechanical engineer, just an amateur with decent-ish gut feeling for when something looks weak mechanically.

 

[CobraMarty]

I'm just taking measurements and sharing the numbers.

The general consensus that I have read in most brake discussions is that 15" rotor brake better than 14" rotor which brake better than 13" rotor which brake better than 12" rotor which brake better than 11" rotors. It doesn't matter who is saying it, Porsche, BMW, Brembo, SBC, Wilwood, OEMs, etc, they all put out there that bigger diameter rotors brake better than smaller diameter rotors.

Pad composition seems to make more braking difference than actual pad size.
Pad size seems to have more to do with heat rejection ability and fade resistance.
Rotor diameter is related and proportional to braking ability.
Rotor thickness and mass/weight has to do with fade resistance and flexing.

I am bolting the caliper to a 1/2" steel plate with grade 8 bolts and also with grade 8 bolts, bolting the steel plate to the same mounting lugs which the OEM Jeep bolts their caliper to the knuckle.
Just to compare, other Big Brake Kits mostly only use 3/8" steel, I have even seen kits with 1/4" steel plates. Still some others use aluminum mounting plates. Even others cut off part of the knuckle and drill holes in areas of the knuckle not originally intended or stressed for holes and use other mounting bolts originally designed for other purpose not brake related. Right, wrong, different.

I will be testing the stock and upgraded brakes. My plan is for drive around town for ?10 minutes to get everything warm and then 4 consective 60-0 runs. Stock and with big brakes.
I read elsewhere (not jeep related) where with 4 consecutive runs, stock was like 140', 160', 170', 180' and Big Brakes was 128, 125, 130, 128. About 10% shorter distance and more consistent and no fade.

This is an interesting article, 22 cars brake 60-0 under 100 feet. Nearly all have 15" rotor front brakes. www.motortrend

 

[Talyn]

I don't see a problem with the mounting I would make sure that the bolts are very snud in the knuckler and/or have a shoulder to fit tightly in the knuckle's holes. . A larger rotor may lead to better braking, but you are also adding un-sprung weight which can decrease handling (not much on the XJ as the front axle is already heavy) but also slow you rig down.

As stated the small caliper/pad is an issue that could be addressed. Both for more pad contact and an ugly rust ring.

Does the knuckle have a provision for an ABS sensor? It looks like it might.

 

[CobraMarty]

Paint the rust ring area or machine the rotor face 1/2" and paint for those who don't like the look, good tight fitting bolts, used HDPE and different thickness stacked washers for mock up and getting the spacing right. Cutting the brackets out of 1/2" cold rolled steel and having the spacers machined to the necessary dimensions also out of steel. Yeah adding unsprung weight but there are tradeoffs, better braking and no fade. The added unsprung weight added with big brake kits hasn't seemed to adversely effect handling of other cars, I guess the centralized location has less effect. 35" tires add unsprung weight at a peripheral location.

Funny you ask about the ABS sensor.

We are picking up an ABS module for the XJ, we don't have ABS, and it looks like it is self contained with ecu and could possibly be retrofitted to a non ABS equipped XJ. Most take off their ABS module and we are looking at putting it on. We have the wiring diagram and it's nothing unusual.

 

[Talyn]

Paint the rust ring area or machine the rotor face 1/2" and paint for those who don't like the look, good tight fitting bolts, used HDPE and different thickness stacked washers for mock up and getting the spacing right.

Why not just use the correct caliper? While HDPE may seem good for a mock up it isn't really dimensionally stable. I recommend getting the bracket cut out of steel then use a stronger material for the spacer's final dimension mock up. Maybe even have the steel bracket milled flat. The next issue you will encounter is if you have the spacers welded to the bracket.

We are picking up an ABS module for the XJ, we don't have ABS, and it looks like it is self contained with ecu and could possibly be retrofitted to a non ABS equipped XJ.

How are you going to retrofit the 8.25 axle for ABS?

 

[urban yan]

Paint the rust ring area or machine the rotor face 1/2" and paint for those who don't like the look.

So you're just going to paint over your problem.

We are picking up an ABS module for the XJ, we don't have ABS, and it looks like it is self contained with ecu and could possibly be retrofitted to a non ABS equipped XJ. Most take off their ABS module and we are looking at putting it on. We have the wiring diagram and it's nothing unusual.

I only know of one individual that did it successfully. If it was as easy as you claim than most everyone would be doing it. The problem with you guys is that you take everyone's hard work/projects/advice AND make a mockery out of it.