Another brake upgrade option

[belize1334]

I've spent the last day or so searching for rotors that have the same total height and discard thickness as our stock rotors (front and rear) with the idea that they could be used in an OEM big brake kit where the stock calipers are retained but used with larger rotors and new brackets. I came across a few interesting things.

For reference, the dimensions of the stock rotors are:

Front:
diameter - 10.86"
height - 1.77"
thickness - 0.886"

Rear
diameter - 10.45"
height - 1.94"
thickness - 0.33"

Now, the rears are the real headache since they need to be solid but with a relatively low height since they don't have an incorporated drum. The only thing that even comes close is from an Audi A6.

A6 rears:
diameter 11.88"
height - 1.934
thickness - 0.393"

Now, obviously the bolt pattern will be wrong so I assume the need to drill a new pattern. But, aside from being slightly too thick it's a pretty good match with a diameter upgrade of about 14%. I don't know if the added 0.063" will fit down into the caliper gap but I assume that if not it could be "resurfaced" down to the appropriate thickness.

For the fronts we're looking for something in the 12.3" range to keep the bias the same as stock. I thought it would be easy but it turns out that our fronts are relatively thin for their size and I was getting discouraged by all the options that weren't QUITE right. Until, I found the 2004 Montero Sport

04 Montero w/ 16" wheels:
diameter - 12.365"
height - 1.78"
thickness - 0.882"

Whats even better is that the images of the caliper for that car look identical to ours (rockauto.com) but with a different bracket. It may be a direct swap for the front as opposed to a "make a bracket" deal for the rears. But, what has me concerned is the "L mounting type" vs. "K mounting type" that most cars see. Is that just a distinction between car and truck (with the larger center bore)? The bolt pattern is 4.25" so it should have room to accomodate a 114.3mm pattern and a spacer disc to make it hub-centric.

The other option that I found is the rear from an Audi A8
A8 rear:
diameter - 12.2"
height - 1.66"
thickness - 0.787"

Now, that's about 0.1" thinner than our calipers and also about 0.1" shorter so it'd mean that the piston would be further extended to make the pad contact but the rotor should fit inside the caliper with stock mounting position (laterally). I don't know if the reduced thickness will have a big effect on performance.

The last option is 3000gt front rotors (2G) which are perfect in diameter and height but are 1.15" thick instead of 0.886". I doubt they'd fit as are and I don't think it wise to machine down a vented rotor or it could be unsound... Does anyone know how wide the stock calipers can be pushed? It is possible that they would accommodate a 1.1" rotor as is?

 

[belize1334]

Update... I found that napaonline offers the caliper-bracket from the '04 Montero. It seems to be identical to ours but designed for a bigger rotor.

click

Looks to me like this could be swapped in to move the caliper out and sit perfectly over a 12.3" rotor. Now it's a question of exactly how thick a rotor the stock caliper can accomodate. Anybody have an extra front caliper lying around? It'd be nice to know exactly how wide the gap is with the piston fully recessed.

 

I have a pair of calipers lying around. I, however, happen to be ~300 miles from home. If no one else steps up to the plate I can get those dimensions for you tomorrow.

 

[89Mirageman]

I might be wrong about the Montero caliper but I know some of the other newer twin piston calipers (like the 99+ V6 Galants and 97+ Diamantes) have a wider bolt pattern where they mount to the knuckle. I want to say that the GVR4 bracket is about 6" from the center of each bolt hole. I can't remember what the other brackets were, maybe 7".

Also for front rotors did you think to check out the newer 350Z parts or were they too wide? I know a guy on Tuners is using rotors from a crown vic that are 12" in diameter, maybe a little more. 5 x 114.3 too.

 

[vr4play]

This is some good information. Thanks for all the work. I have been planning to build my own wilwood brake kit but I was originally going to use 13" cobra rotors but can't get them to fit behind my wheels. I was going to buy new wheels but the car business has been a little on and off lately so my car fund is low. If I can get some that are a bit bigger than 12" I think I can make it work for now and just make new brackets later.

 

[belize1334]

I'm not sure about the size of the ears on the Montero Calipers. I know that the Outlander calipers of the same era are a direct bolt-in affair. Unfortunately they only accomodate an 11.6" rotor which is a measly 7% bigger than stock. I'm contemplating going that road and not doing the backs at all. But, I'm CONVINCED that balance is very important so if I increase the front lever arm without decreasing the clamping force then I need to do the same to the back. Especially given the fact that factory cars are typically front heavy for safety anyway and I want my stopping distances to go down, not up.

Now, there's another option in the works. Alot of people are doing the cobra front brakes using the '99-'04 calipers which feature 40.5mm pistons. Doing the math on a 13" rotor you get about 17% increase in torque at the front. BUT if you use the '98 calipers they have 38.1mm pistons. With the same rotor that amounts to only 1% more front clamping. That means you could upgrade to cobra 13" rotors and calipers with less than 1% change in overall bias. Now, I expect that the rears would look silly with those massive fronts up there but looks aren't everything. And as far as I know fade is basically a non-issue in back so this would improve overall fade resistance without unbalancing anything. It's not bolt-in like the Outlander setup but there are kits out there. Then if you later decide that the rears are lacking you can either do a custom setup as I described above, or use the Corvette rears.

As for the Corvette rears. It turns out that with the piston sizes and 12" rotors you get a 50% bump in rear torque. That means that, depending on whether you use the 38.1mm or 40.5mm front calipers you get either 67% or 65% forward bias. Thats WAY too rear biased for a high-cg car like ours. If you use the camaro rotors instead they're only 11.5" so the bias shifts to either 69% or 68% depending on the fronts. Still too rear heavy. So, I'm thinking as of now that the camaro calipers just aren't a good option unless you use an even bigger front kit. The same 13" rotors with 3kgt calipers (40.4mm and 42.8mm pistons) gets you more like 71% forward bias when used the the smaller camaro rear rotors and corvette calipers. Evo front brakes would be even better with their 40.4mm and 44.3mm front pistons. So, I'm thinking that for the ULTIMATE big brake kit you'd want the corvette rears with the smaller camaro rotors and then THE BIGGEST FRONT SETUP YOU CAN FIND to achieve a good overall balance.