Jalisurr

Hey All,

So I've done a few track days / HPDEs with my 1990 ZR-1 now at River's Edge road course here in BC. This course is known for being hard on brakes apparently and man am I seeing that. Here's what's happened so far (all on Nitto NT05 tires in stock sizes on stock 17" salad shooters).

1st HPDE: I had Hawk HPS pads and normal DOT4 fluid. Boiled the fluid. Replaced with Castrol SRF.
2nd HPDE: Cooked the Hawk pads - replaced with G-Lock R10 front / R8 rear setup
3rd HPDE: All good on the braking front but had a transmission fluid leak so had to stop about halfway through
4th HPDE: This happened:


Looks like my front left caliper actually bent a significant amount and was sitting crooked on the rotor. I guess this is the caliper spread I hear about.

So, I'm looking for suggestions on a rock solid braking system for track use. I'm now slightly leery of the sliding caliper setup if it allows this to happen so thinking of something opposed if possible. That said, I really don't want to have to pay way more than OEM for rotors as they are wear items on the track, so something that works with stock corvette rotors of some form would be ideal. Wilwood calipers with the C5 adapters maybe?

I'm also assuming that I'll be needing to go up to 18" wheels, unless anybody knows of a really good setup that will handle this kind of abuse and fit inside 17" rims?

Thanks in advance!

c4cruiser

Going with 18" wheels would make it easier to install Wilwood brakes as a package for the front. With the later C4's having the parking brake as part of the caliper, it may be just picking the right pads for the rear. A C5 front conversion may not get you much more that the current J55 setup you have. But the C5 front brakes (calipers and rotors) should fit with the OEM 17" wheels. It's possible that you may have to grind off some of the height of the fins on the caliper to fit OEM wheels. When I had my '87, I installed a C5 front brake conversion and used aftermarket 17" ZR-1 style wheels and they fit with no problem. I had to add a different brake bias spring because of the C5 calipers,

Do you have any ducting to get cooling air to the calipers? That may help some and not cost a lot to do. There are aftermarket air dam kits that have openings in the dams and come with flex hose.

Jalisurr

Ah, I should have mentioned that, yes I do have the air dam kit from mid america motorworks and have directed the hoses right up to the inside of the rotor near the caliper. The reviews on it have been mixed but I figured it was better than nothing. I can't say for sure how much of a difference it made as I also swapped the pads to the G-Lock and added braided steel lines at the same time.

Going to stock C5 brakes seems like an insufficient upgrade over the J55 brakes (slightly smaller to be worth it to me. I'm wondering if C5 rotors with the Wilwood SLC56 calipers would work well enough?

I don't think I need to change out the rear brakes unless I do something really drastic - my rear brake pads were only worn down to 50% in the time the fronts were almost completely used up.

Tom400CFI

Dizwizz needs to see this thread. This is why the standard J55 "ain't all that". Those calipers are about the flimsiest caliper out there.

The C5 caliper is thicker and has a lot more meat on it...and won't do that as easily. The C6 base/Z51 calipers have more meat than the C5 to resist flex and bending even further.

Still, none of these is what I'd call "bullet proof" for track duty....especially with the ZR-1; you've got more hp to generate more speed...and then you've got more weight to slow down. I agree with your goal of a fixed caliper with 4 or 6 pistons.

Change your brake bias spring too, if you can, to increase rear braking. All 4 corners should wear at about the same rate.

Jalisurr

Good call, I'll grab one of the DRM brake bias springs to increase rear bias.

For the fronts, this is what I've currently put together for options:
1) C5 Brakes - I don't think this would be worthwhile
2) C6 Z51 Brakes - Big! But still sliding calipers and won't fit inside any 17" rims
3) Wilwood SLC56 calipers with 13" rotors (C5?). - 4 piston fixed caliper. May fit inside 17" A-Mold (for my street tires). Will this be sufficient?
4) Wilwood 6 piston calipers with 14" rotors (C6 Z51) - Should be plenty of braking for anything. I'll have to replace all my rims and tires.

Any suggestions or opinions are always appreciated. There's a big world of brake options out there but nothing has jumped out at me as perfect.

0Todd TCE

Few thoughts:

1. There is now a full late model C4 rear kit with four pot caliper and second parking brake caliper.

2. The SLC56 parts are very nice and easy to fit calipers. They however are not intended to be a competition part. They fit only smaller 12.8" rotors and run the thinner of the two 74 series pads: 7416. There are ample compounds in that spec if you wish to try it but I think you'll find you'll overheat things quite quickly. Great street product, onesy-twosey track day maybe but not a poor man's bbk by any standard. It will be a somewhat lateral move given the small rotors.

3. The advent of the C6 rotor and 18" wheels begin to show their value. 13.4 and more ideally 14" rotors lead to much beefier Aero6 calipers with more thermal capacity and 20% more cubic brake pad as well as a greater swept area. Efficiency plain and simple. *Now of course if your heart is set on 17" wheels you'll have little choice but to down size in the rotor department and pay the price for durability.

Jalisurr

Thanks Todd,

I'm not competing with this car per se, these are lapping days / HPDE events. That said, I drive the car hard and fast (and generally can keep pace with some significantly newer machinery). I would ideally like to keep the ability to run the 17" A-Molds as I have nice new all season tires on my set of those and I like how they look for the street, but I'm not willing to sacrifice having sufficient braking for repeated hard track sessions in order to avoid needing to replace them.

I've heard many stories of people with stock C5 brakes on C4 corvettes being very happy with them on the track with the right pads, and surely the SLC56 will be an upgrade over those at least in resisting spreading due to the different design? However, there are also many stories of people with J55 brakes doing track time with no issues and obviously I'm harder on the brakes than they are. It's difficult to evaluate.

Would you say that if going to the Aero6 setup, it would be enough of a change that upgrading the rear would be necessary to remain balanced?

For the Aero6 setup, can you use stock C6 Z51 brake rotors? How about the rear, can those calipers be used with OEM rotors instead of the wilwood units? The wilwood rotors are lovely looking and I'm sure are quite light but I don't fancy paying that price on a continuous basis when track pads eat them up.

Thanks for your input

ChumpVette

Kevova

The 1996 grand sport j55 caliper is more resistant to spreading than the standard j55 caliper.

ElisTwoCents

EXACTLY. I recently posted about the C5/C6 upgrade in a separate thread where advice was sought and although it won't beat down a say 3k aftermarket system, it also won't cost nearly as much, so there has to be a point of diminishing returns - While many agree it's a reasonable upgrade for the cost there are still a few skeptics that swear by the C4 brakes. My C4 has the C6 Z51 brakes and they bite as hard or harder to be frank than the brakes on my C5 Z06, maybe I should do a stop test sometime to compare but not sure how truly comparative the results would be due to the different platforms/wheels/tires/vehicle weight/brake bias (spring pressure vs electronic through ABS) so might be a moot point.

Sorry to hear about the failure but try the C5/C6 stuff or go to the big brand aftermarket brands.

Jalisurr

Really? That's both surprising and very intriguing. I figured that setup would be too bit for sure

Jalisurr

I've heard that, but it's been very difficult to find Grand Sport calipers for a reasonable price and I assume it's only a fairly incremental upgrade. Thanks for the info though!

0Todd TCE

I think you have a clear grasp of most of my comments. Yes the SLC56 would be an improvement over the current parts due to the fixed design and more rigid body. Benefits of top loading and improved pedal response/feel. My only concern is that you'll remain "rotor challenged" no matter what caliper is used. Gauging your success is a shot in the dark here. If you use the car primarily for street you'll be golden, it you run a dozen track days a year I suspect you'll find it still a challenge to keep things under you.

With regard to the Aero6 kits they fit both the 13.4 and 14" rotors with the supplied stud spacer. And yes having more rotor mass is now good. That said someone suggested the 13.4 (J55 I believe) will fit inside a 17 and while that may be true of the oe caliper I don't think you'll be so lucky on the Aero6 part. You'd have to check the wheel fit diagram to see what the barrel size requirement is.

Doing both at one time is nice but not overly crucial. There's not a huge bias change from your 12.88 to a 13.4" rotor here. You're talking a 1/4" radius. But more mass. And adding that tiny bit up front is where its going to get the most bang for the buck anyhow short of going nuts on size differences.*Also I cannot speak to fitment of the C5 parts onto the C4 with adapters. Stands to reason that if you can do it with oe parts you should be able to do so with the kits.

Two piece rotors do look nice. And save weight. To do the rears you'd have to keep in the C4 family.

At the end of the day this is really going to be a wheel decision. If you want better brakes, more durability and longevity you need larger parts. That in turn means larger wheels. Some guys do well on smaller brakes and the use of 17s...that's cool too. And I think the smaller cal kits are a plus. And in fairness there are some other options out there also using 13" rotors and aftermarket calipers. Not wanting you to buy the SLC56 parts to be your end all of brake issues on track then suggesting the product is not up to the task.....it's more about picking the proper tool for the job.

dizwiz24

Jalisurr

That would be the GS calipers, yeah. I've been told they are a slightly different casting that's more resistant to spreading, though I imagine the difference is fairly small due to the similarity to the regular J55.

Couldn't say for sure! I don't have GS calipers available to me or I'd try and bend them too :P

calvinlc

I don't know if Doug Rippie still sells the GN3 Wilwood kit, but I bought it years ago and it has paid for itself. It has the 6 pot GN3 calipers that take huge pads that are 0.8" thick and because of their commonality I can buy any level of Raybestos pads for about $190. They have 13" 2 piece rotors that are 1.375" thick and are made by Coleman racing so the replacement rings are only like $200 each. They fit under the ZR-1 style 17" wheels. The biggest key though is get yourself a set of spindle ducts and run 3" brake hose. I have a mod that works for this with Home Depot parts and still allows you to turn lock-to-lock. This combo allows me to run about 8 track days on one set of brake pads. When you combine this with the spring that Doug Rippie sells to modify the brake bias a bit the stock rears work fine with this combo when using the same pad compound as the front. With NT01 tires my braking deceleration is about 1.2 to 1.3 g's and never fades with Motul RBF600 fluid. I have at least 2000 track miles on this setup and see no need to change it. I can send pictures if you want them of any of it.

Jalisurr

That's good info, thanks! What spindle ducts are you using?

VikingTrad3r

formula80_ca

I see that this thread is a year and a half old but I just found it. I'm in the middle of putting together a C4 race car and am very interested your set up with the GN3 calipers. Do they still make them and can you still get the bracket to adapt to the C4? Also very interested in your home depot parts cooling duct photos.

formula80_ca

I know I'm resurrecting a year and a half old thread but I'm very interested in what you ended up doing for a brake upgrade on your C4 track car?

I'm currently building a 1990 C4 race car for the Area 27 GTU series. I have a Z51 package car that has the J55 13" brakes and need to make a decision on an upgrade.

Thanks in advance for any advice.