C4 Front Brakes Alternative
06-27-2010, 03:11 PM
#1
Burning Brakes
Thread Starter
C4 Front Brakes Alternative
i keep the J55 brakes on my '96 in tip-top shape. i think the brakes act and feel quite good on track, but i can't even get 2 laps at 10/10ths before the pedal height change and fade conspire to keep me from heel-and-toe corner entries. pads wear pretty fast too. in traffic they're generally fine, since traffic means a significantly slower pace.
since i have an investment in 2 sets of race wheels (17x11.5 and 17x11), i didn't want to get a bbk that would require me to buy new wheels. the wilwood C4 13" SL6R front kit fits under my CCWs, but i found it a bit unpalatable that i'd be using a rotor that's even smaller than stock. (wilwood uses a 12.88"x1.1" rotor for their C4 kit. granted, it's a better rotor and not a significant difference in size, but i really wanted a bigger rotor, at least C5-sized.)
i started comparing the contents of the C4 and C5 wilwood kits and didn't see any significant issues in adapting a hybrid kit to the C4. i did some careful measuring and was pretty sure the C4 hat with a 13.06"x1.25" rotor from the C5 kit would fit. the hat bolt patterns matched, making it easy. i also realized the calipers were externally the same, just the C5 caliper fit the thicker rotor. the remaining fitment issue was that the thicker rotor meant the caliper would need to move inboard slightly.
unfortunately the radial-mount bracket for the C4 mounts outboard of the spindle ears, or the adjustment would be as easy as using spacers. instead, i took the C4 brackets and had a competent machine shop mill .150" off the mounting pads that face the spindle:
turns out .150" was .010" below the surface of the bracket body, but it's still plenty strong, and the machine shop chamfered all the edges nicely. (had i to do it again, i would ask them to mill .140" so the surface is completely flat, given that i ended up using some of the supplied shims to center the caliper perfectly.)
here's the rotor from the C5 kit on a C4 hat. the J55 rotors look big until you see this:
the tightest clearance is against the steering arm on the spindle. everywhere else clears by a lot, but here i measured .070" clearance (the picture is deceptive, it looks like a good amount of clearance to the naked eye):
i think that's enough clearance, but maybe not, not sure how much the rotor assembly flexes. the steering arm has plenty of meat there, i can shave off .050" no problem if i have to, but i'll try it like this. IMPORTANT NOTE: i have rod-end tie-rods, not the stock tie-rod ends. the stock tie-rod ends might poke out past the edge of the spindle steering arm. so if you do this, you might need to get the baer bumpsteer kit to make it fit. (you want that anyway, right? i got my bumpsteer curve perfectly zero from 1.5" droop, through ride height, all the way to the bumpstop with that kit.)
here it is, all installed:
it took 2 of the supplied shims under each mounting pad to perfectly center the caliper over the rotor. it only took one of the supplied shims on each stud to put the edge of the brake pad with the edge of the rotor bevel. it was trivial to make it all work, just with the machining of the radial-mount caliper bracket!
with my 17x11.5 CCWs, which don't have good clearance for brakes compared to more modern wheels:
those calipers in this configuration give excellent clearance to the wheels. the tightest spot to the wheel spokes measured .700".
i contacted a knowledgable dealer to bounce my ideas off of an expert before starting down this path. (i knew him from another forum, but he's a member here too.) he did some checking and confirmed it would probably work. even better, he put together a kit for me with the C5 rotor and caliper, C4 brackets, lines, and hats, for the same cost as the shelf C4 kit. the total price was fantastic. (PM me for details, i don't think he's a supporting vendor.) i would probably not have risked this purchase on the merits of my own measurements without his input.
-michael
since i have an investment in 2 sets of race wheels (17x11.5 and 17x11), i didn't want to get a bbk that would require me to buy new wheels. the wilwood C4 13" SL6R front kit fits under my CCWs, but i found it a bit unpalatable that i'd be using a rotor that's even smaller than stock. (wilwood uses a 12.88"x1.1" rotor for their C4 kit. granted, it's a better rotor and not a significant difference in size, but i really wanted a bigger rotor, at least C5-sized.)
i started comparing the contents of the C4 and C5 wilwood kits and didn't see any significant issues in adapting a hybrid kit to the C4. i did some careful measuring and was pretty sure the C4 hat with a 13.06"x1.25" rotor from the C5 kit would fit. the hat bolt patterns matched, making it easy. i also realized the calipers were externally the same, just the C5 caliper fit the thicker rotor. the remaining fitment issue was that the thicker rotor meant the caliper would need to move inboard slightly.
unfortunately the radial-mount bracket for the C4 mounts outboard of the spindle ears, or the adjustment would be as easy as using spacers. instead, i took the C4 brackets and had a competent machine shop mill .150" off the mounting pads that face the spindle:
turns out .150" was .010" below the surface of the bracket body, but it's still plenty strong, and the machine shop chamfered all the edges nicely. (had i to do it again, i would ask them to mill .140" so the surface is completely flat, given that i ended up using some of the supplied shims to center the caliper perfectly.)
here's the rotor from the C5 kit on a C4 hat. the J55 rotors look big until you see this:
the tightest clearance is against the steering arm on the spindle. everywhere else clears by a lot, but here i measured .070" clearance (the picture is deceptive, it looks like a good amount of clearance to the naked eye):
i think that's enough clearance, but maybe not, not sure how much the rotor assembly flexes. the steering arm has plenty of meat there, i can shave off .050" no problem if i have to, but i'll try it like this. IMPORTANT NOTE: i have rod-end tie-rods, not the stock tie-rod ends. the stock tie-rod ends might poke out past the edge of the spindle steering arm. so if you do this, you might need to get the baer bumpsteer kit to make it fit. (you want that anyway, right? i got my bumpsteer curve perfectly zero from 1.5" droop, through ride height, all the way to the bumpstop with that kit.)
here it is, all installed:
it took 2 of the supplied shims under each mounting pad to perfectly center the caliper over the rotor. it only took one of the supplied shims on each stud to put the edge of the brake pad with the edge of the rotor bevel. it was trivial to make it all work, just with the machining of the radial-mount caliper bracket!
with my 17x11.5 CCWs, which don't have good clearance for brakes compared to more modern wheels:
those calipers in this configuration give excellent clearance to the wheels. the tightest spot to the wheel spokes measured .700".
i contacted a knowledgable dealer to bounce my ideas off of an expert before starting down this path. (i knew him from another forum, but he's a member here too.) he did some checking and confirmed it would probably work. even better, he put together a kit for me with the C5 rotor and caliper, C4 brackets, lines, and hats, for the same cost as the shelf C4 kit. the total price was fantastic. (PM me for details, i don't think he's a supporting vendor.) i would probably not have risked this purchase on the merits of my own measurements without his input.
-michael
06-28-2010, 10:29 AM
#2
Safety Car
Nice...
When I (eventually) get back into the racing mode, this was one of the first things I wanted to address with my '91.
How is the bias? Did you use the Rippie bias-spring yet?
When I (eventually) get back into the racing mode, this was one of the first things I wanted to address with my '91.
How is the bias? Did you use the Rippie bias-spring yet?
06-28-2010, 01:52 PM
#4
Burning Brakes
Thread Starter
the bias is shifted more to the front, since the SL6R caliper has a higher piston volume. (this is the case with the shelf C4 kit too, C5 and C4 kits have the same piston sizes.) it's not a difference i can really tell driving on the street, so final analysis will have to wait for my next track event. i do have the different bias spring already.
brian, do the 18" CCWs have a different shape to the center? the clearance issue with mine has always been to the spokes, not out to the rim, so i had always assumed having 18" CCWs wouldn't make much difference. also, don't the parts you bought use the stock rotor? the stock rotor has less offset than what the C4 wilwood hats buy you, i guess wilwood did this to help insure caliper clearance. and, with the thicker rotor, my config puts the caliper even further inboard. that said, the total difference in caliper placement between my setup and using a stock rotor with the same caliper is less than .250", so your setup should clear by roughly half an inch.
edit: i misread your 18" wheel comment, i see now you said rotor size, not caliper clearance.
-michael
brian, do the 18" CCWs have a different shape to the center? the clearance issue with mine has always been to the spokes, not out to the rim, so i had always assumed having 18" CCWs wouldn't make much difference. also, don't the parts you bought use the stock rotor? the stock rotor has less offset than what the C4 wilwood hats buy you, i guess wilwood did this to help insure caliper clearance. and, with the thicker rotor, my config puts the caliper even further inboard. that said, the total difference in caliper placement between my setup and using a stock rotor with the same caliper is less than .250", so your setup should clear by roughly half an inch.
edit: i misread your 18" wheel comment, i see now you said rotor size, not caliper clearance.
-michael
Last edited by MSR; 06-28-2010 at 01:54 PM. Reason: clarification
07-22-2010, 10:52 PM
#7
Burning Brakes
Thread Starter
still only street use so far, being a new daddy has kept me from making any track events the past couple of months. i'm running an event the weekend of August 14, though, and an autocross the weekend before then, i'll definitely post feedback after that.
07-23-2010, 09:10 AM
#8
Le Mans Master
So let me see if I got this right for parts:
c4 brackets, mill the mounting holes until flat (.140 in)
c5 calipers
c4 hats
c5 rings
Just a question cause I know the hat/ring combo is better, would the stock c5 rotor work?
Ballpark cost for all these parts?
I'm not killing my J55's yet, just rebuilt the whole system and even CMP isn't causing the problems you had.
Guess I'm still not going fast enough to wear out the brakes, I'm still running a set of carbotechs I put on the car in April.
c4 brackets, mill the mounting holes until flat (.140 in)
c5 calipers
c4 hats
c5 rings
Just a question cause I know the hat/ring combo is better, would the stock c5 rotor work?
Ballpark cost for all these parts?
I'm not killing my J55's yet, just rebuilt the whole system and even CMP isn't causing the problems you had.
Guess I'm still not going fast enough to wear out the brakes, I'm still running a set of carbotechs I put on the car in April.
Last edited by jaa1992; 07-23-2010 at 09:12 AM.
07-23-2010, 11:25 AM
#9
Burning Brakes
Thread Starter
your parts list is correct. the dealer who helped me basically sold me the C4 kit with a free substitution of the C5 calipers and rings. he also included the brake hoses, and the AN adapters to make the hoses work.
you could probably make the stock C5 rotors work, at the expense of losing caliper to wheel spoke clearance. the C4 vs C5 hat has a pretty large difference in offset. in that case, instead of milling the brackets down, you'd need some pretty thick spacers (and possibly longer bolts). i'm not sure at what point that extra spacing ceases to be kosher in terms of load on the bolts (which are in single shear), so that's something to consider. the extra spacing would need to be on the order of 0.5", very roughly.
also, i'm not sure how much more expensive those wilwood parts become if not purchased as a kit, so you may not be saving much. also need to weigh the cost of the rings and their longevity vs the stock C5 rotor. but, it could be a great way to go.
i'll PM you on the pricing.
-michael
you could probably make the stock C5 rotors work, at the expense of losing caliper to wheel spoke clearance. the C4 vs C5 hat has a pretty large difference in offset. in that case, instead of milling the brackets down, you'd need some pretty thick spacers (and possibly longer bolts). i'm not sure at what point that extra spacing ceases to be kosher in terms of load on the bolts (which are in single shear), so that's something to consider. the extra spacing would need to be on the order of 0.5", very roughly.
also, i'm not sure how much more expensive those wilwood parts become if not purchased as a kit, so you may not be saving much. also need to weigh the cost of the rings and their longevity vs the stock C5 rotor. but, it could be a great way to go.
i'll PM you on the pricing.
-michael
08-08-2010, 09:32 PM
#11
Burning Brakes
Thread Starter
i ran my first autocross with the new brakes, today. let me preface by pointing out that i was using street pads, not track pads. this means the rear (oem) calipers had carbotech panther plus pads, and up front i used the wilwood pads that came with the kit. this was my first time running wilwood pads, so some of my experience is due to the difference in pad material, fwiw.
one thing i noticed, driving on the street, was that the pedal was a bit longer than with the J55s. the pedal might not move much further once the resistance is there, but it drops a bit more before it gets to that point. even knowing that, i was disappointed after my first run, as the pedal height was inconsistent (albeit never unworkable). the second run was somewhat better, but i was experiencing some fade by the end, which really surprised me. i thought i had bedded the new front pads pretty well before the event, but apparently did not, as they were smelling and smoking. after a cooldown, the pedal was very consistent on the subsequent run, with little or no apparent knockback. the overall f/r balance seemed no different than before, and there were certainly no complaints about modulation and outright power. the old brakes worked really well in this arena too, but the wilwoods have a definite edge in modulation, making the J55s feel like they work in steps.
so far, then, i'd say all wins excepting a pedal that's a touch longer than before.
next weekend is on track, with XP12s, i'll have much more significant input after that. in the meantime, here are a couple of my runs from today:
Run 1
Run 2
one thing i noticed, driving on the street, was that the pedal was a bit longer than with the J55s. the pedal might not move much further once the resistance is there, but it drops a bit more before it gets to that point. even knowing that, i was disappointed after my first run, as the pedal height was inconsistent (albeit never unworkable). the second run was somewhat better, but i was experiencing some fade by the end, which really surprised me. i thought i had bedded the new front pads pretty well before the event, but apparently did not, as they were smelling and smoking. after a cooldown, the pedal was very consistent on the subsequent run, with little or no apparent knockback. the overall f/r balance seemed no different than before, and there were certainly no complaints about modulation and outright power. the old brakes worked really well in this arena too, but the wilwoods have a definite edge in modulation, making the J55s feel like they work in steps.
so far, then, i'd say all wins excepting a pedal that's a touch longer than before.
next weekend is on track, with XP12s, i'll have much more significant input after that. in the meantime, here are a couple of my runs from today:
Run 1
Run 2
08-09-2010, 09:26 AM
#13
Le Mans Master
Are you running xp12 front and rear?
I'm all ears to see how they work on track!
I'm all ears to see how they work on track!
08-16-2010, 02:27 PM
#14
Burning Brakes
Thread Starter
did MSR-H, clockwise, in 100+ degree weather. i used a pre-bed set of XP12s, front and rear. they were really good right off, but took about 2 hard laps to really come on hard. here are some general observations, mostly stream of consciousness since i haven't had time to sort out my thoughts:
brake balance seems good. fronts go into ABS sooner if really pushing it in a straight line, yet there's still enough rear bias to help trailbrake pointing the car in. i didn't find anything wrong with balance that would cause me to use XP10s in the rear over the XP12s.
power was excellent. modulation and control were so good that i was able to achieve higher peak decelerations than with the J55s. (seat of the pants, don't have an accelerometer.) there always seemed to be a bit more when i needed it. interestingly, i perceived the ABS worked better, more efficiently and with less intrusion. it's hard to quantify something like that, and it could be my imagination.
pedal height was good. it sits a bit lower than before when coming into a corner, so i have to hold my foot a bit differently than before to heel-toe, but it's not worse, just different. i was happy to see that knockback was not an issue, the pedal remained consistent. this is on relatively new hubs, but no change over the weekend with very high heat and V710s.
i never experienced fade, but did eventually boil the fluid. first time the pedal went a bit spongy, i thought, crap, knockback! next corner it went almost to the floor, and i recognized it as fluid boil. a bunch of bubbles bled out in the pits, and the pedal was rock hard again. next session went fine since the calipers had relatively fresh fluid, but i boiled them again yesterday. a fellow forum member and old friend gave me a temp label to stick on a caliper. turns out the outside edge of the front caliper was hitting almost 450 degrees. since i had an oem-type Ate fluid in it, i can totally believe fluid boil at those temps. i guess some motul 600 (or maybe SRF) is in my future.
at certain (lower) speeds and short of super hard braking, there's a vibration in the pedal. it's much higher in frequency than the usual pulse from rotor warps or transfer layers. i'm guessing it's the slots in the rotors interacting with the XP12s, the wilwood pads don't do this. not at all a bother or limitation, it just surprised me.
i'm generally too critical to be ultra happy with purchases, but this setup got me where i wanted to be. assuming i can keep the fluid from boiling, i've taken brakes out of the "things i need to drive around" catergory.
Here's a few laps, this is the early morning red session, significantly cooler and no fluid issues. i'm not too happy with the perspective of that camera, though. it creates a nice effect, being so extremely wide-angle, but it kills any perspective on how close the cars are in front.
brake balance seems good. fronts go into ABS sooner if really pushing it in a straight line, yet there's still enough rear bias to help trailbrake pointing the car in. i didn't find anything wrong with balance that would cause me to use XP10s in the rear over the XP12s.
power was excellent. modulation and control were so good that i was able to achieve higher peak decelerations than with the J55s. (seat of the pants, don't have an accelerometer.) there always seemed to be a bit more when i needed it. interestingly, i perceived the ABS worked better, more efficiently and with less intrusion. it's hard to quantify something like that, and it could be my imagination.
pedal height was good. it sits a bit lower than before when coming into a corner, so i have to hold my foot a bit differently than before to heel-toe, but it's not worse, just different. i was happy to see that knockback was not an issue, the pedal remained consistent. this is on relatively new hubs, but no change over the weekend with very high heat and V710s.
i never experienced fade, but did eventually boil the fluid. first time the pedal went a bit spongy, i thought, crap, knockback! next corner it went almost to the floor, and i recognized it as fluid boil. a bunch of bubbles bled out in the pits, and the pedal was rock hard again. next session went fine since the calipers had relatively fresh fluid, but i boiled them again yesterday. a fellow forum member and old friend gave me a temp label to stick on a caliper. turns out the outside edge of the front caliper was hitting almost 450 degrees. since i had an oem-type Ate fluid in it, i can totally believe fluid boil at those temps. i guess some motul 600 (or maybe SRF) is in my future.
at certain (lower) speeds and short of super hard braking, there's a vibration in the pedal. it's much higher in frequency than the usual pulse from rotor warps or transfer layers. i'm guessing it's the slots in the rotors interacting with the XP12s, the wilwood pads don't do this. not at all a bother or limitation, it just surprised me.
i'm generally too critical to be ultra happy with purchases, but this setup got me where i wanted to be. assuming i can keep the fluid from boiling, i've taken brakes out of the "things i need to drive around" catergory.
Here's a few laps, this is the early morning red session, significantly cooler and no fluid issues. i'm not too happy with the perspective of that camera, though. it creates a nice effect, being so extremely wide-angle, but it kills any perspective on how close the cars are in front.
08-16-2010, 03:18 PM
#15
Drifting
Michael, I boiled my Motul RBF at an indicated 550 on my calipers (when I couldn't get the stupid active handling to shut off!!!). I was amazed at how much difference the brack cooling ducting made on my caliper temps when I installed it Sunday morning. I would recommend a combination of the RBF (Pro-Am stocks it on the shelf, as well as SRF if you're feeling rich) and that brake duct routing we talked about yesterday. Those two combined should give you a pretty bullet-proof combo. Glad you were able to stay on track when yours boiled!! I can't remember, which turn did you boil it in? Did you see the patch of burned grass from where I came to a stop?? 1500 deg rotors + grass clippings = fun with a fire extinguisher (fortunately NOT with the car in the middle).
08-16-2010, 05:44 PM
#16
Burning Brakes
Thread Starter
i didn't realize the grass fire was from you!
i think it boiled at the end of my entry into the carousel, so the pedal dropped at the end of the front straight. i was in traffic though, and braking early, so i quickly multiple-pumped and got enough brakes back.
ya, i'll definitely work on those ducts, how i have them now obviously isn't doing the job.
i think it boiled at the end of my entry into the carousel, so the pedal dropped at the end of the front straight. i was in traffic though, and braking early, so i quickly multiple-pumped and got enough brakes back.
ya, i'll definitely work on those ducts, how i have them now obviously isn't doing the job.
08-16-2010, 08:34 PM
#17
Drifting
i didn't realize the grass fire was from you!
i think it boiled at the end of my entry into the carousel, so the pedal dropped at the end of the front straight. i was in traffic though, and braking early, so i quickly multiple-pumped and got enough brakes back.
ya, i'll definitely work on those ducts, how i have them now obviously isn't doing the job.
i think it boiled at the end of my entry into the carousel, so the pedal dropped at the end of the front straight. i was in traffic though, and braking early, so i quickly multiple-pumped and got enough brakes back.
ya, i'll definitely work on those ducts, how i have them now obviously isn't doing the job.
Soft pedal going into Sugar and Spice???? I think my butt would've sucked the cover right off the seat from the pucker factor!!
08-22-2010, 03:46 PM
#19
Drifting
Yes, I got some video footage, unfortunately only during the first session though (ie SLOW). I think I was only turning 1'54"s. That was my first session ever on this track, with old shot up V710s. Didn't get the video of my spin, or my fast session on Sunday with the fresh R6s. I'll post it later today.
