ZR1 Track Day update (road course) - didn't go well :(

[cbaclawski]

My track day got rescheduled from Sat to Sun(yesterday) due to weather. That part worked out great as the weather was beautiful...


I had big plans of coming back here, sharing some video, data screen caps, etc., but alas, it's not to be.


Being my first time out in the car I was taking the first session easy at first, braking early and not pushing it in the corners. Around lap 4 as I was slowly picking up speed, I was heading in to a high speed corner (Turn 8 @CMP for those familiar), went to brake, and the pedal went straight to the floor. I tried to make the corner way too hot but couldn't hold it and spun right off the track.


Getting to the pits, it was suggested that by going so easy I'd been dragging the brakes and the pads (hawk HP+) had overheated. Sounded reasonable, but just in case I let it cool and bled all 4 corners. The fluid was clear, obviously not boiled, and no bubbling at all.


Thinking all was well I went back out, this time braking harder and shorter to avoid what I thought was the issue in session one, brakes seemed better but sill very inconsistent. Around Lap 4 again, in the same spot, I spun off track. Once I pulled back on track, the pedal was completely gone and I limped back to the pits. Consulting with some other drivers, they said it could be caliper piston lash and I should try to give it a pump before the braking zone. (apparently this happens a lot in spec miata racing)


After a brief time in the pits, and with no frame of reference on how the brakes were *supposed* to feel, I assumed the brakes on the z just sucked by design. I headed back out for the third and final time. This time I was going to keep it on the track for sure. Unfortunately, on lap 2, while I was really still warming up, I couldn't get slowed for turn 4, lifted and spun again, this time in to a tire wall, ending my day.(and the pristine condition of my front end)

With a day to replay the days events in my head, I'm 99% sure I have a failing master cylinder, which led to brakes that ranged from wildly inconsistent to non-existent. Thinking back to the bleed, the person I had pumping the pedal for me mentioned that the pedal was sometimes slowly going to the floor before I even opened the valve, and when I did crack the valve I didn't always get that much fluid, sometimes more than others. Shame on me for not recognizing the problem sooner and calling it a day before crashing out.


The good news is the damage is superficial and can/will be fixed, also when the brakes did work, the car was better than expected in the corners. virtually no body roll, good grip, and it was easy to hit my marks. I did have to be more careful with the throttle than I am used to in my lower hp cars, but overall very manageable and predictable.


Can't wait to get the repairs done and get back out there...


Curt

[ghlkal]

I imagine most of us have similar stories on our first times out (I was 360 several times at Autobahn in Illinois, but let's not talk about that )


I would think this is a mechanical issue as you surmise. I'm glad the damage isn't too great, and that you're ready to tackle it again.


Keep us posted on the progress.

[tnova]

This is why I’ve put the Wilwood brakes in and upgraded the master cylinder. I just didn’t have confidence in my brakes compared to other cars I’ve driven in the track. Agree on your master cylinder analysis.


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[cbaclawski]

Originally Posted by ghlkal

I imagine most of us have similar stories on our first times out (I was 360 several times at Autobahn in Illinois, but let's not talk about that )


I would think this is a mechanical issue as you surmise. I'm glad the damage isn't too great, and that you're ready to tackle it again.


Keep us posted on the progress.

1st time out *in this car* I have plenty of experience in other cars... enough that I should have known something wasn't right...

Originally Posted by tnova

This is why I’ve put the Wilwood brakes in and upgraded the master cylinder. I just didn’t have confidence in my brakes compared to other cars I’ve driven in the track. Agree on your master cylinder analysis.


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For now, just going to replace the cylinder and give it a good road test before taking it back to the track. If I still don't have confidence in it, a full upgrade is next. Definitely no more track until I'm 100% sure it's working as it should... brakes are kinda important...

[S.hafsmo]

Originally Posted by tnova

This is why I’ve put the Wilwood brakes in and upgraded the master cylinder. I just didn’t have confidence in my brakes compared to other cars I’ve driven in the track. Agree on your master cylinder analysis.

What master cylinder did you use to upgrade?

[RussMcB]

Been (near) there, done that (or similar). Glad the damage was minimal. Any pictures?

Two thoughts: 1) I do think near-stock brakes can be made to work fairly well. Mine do, but (caveat), I have never gone more than say 5-6 laps really hard. I'm sure Wildwood and other upgrades are superior, but maybe not required, depending on your needs. I'll list my brake mods below.

2) I'd try hard to see if you can replicate some symptoms before you start the work. Easier said than done, I'm sure, but *IF* you can replicate a problem before you make changes, there's a better chance you'll be able to confirm your repair without going back to the track (and maybe not having fun). Maybe there's a country road with some coast down area. Maybe your emergency brake isn't affected by whatever your root cause is.

My mods: I rebuilt the calipers. It was a challenge to find the seals, but I might not have asked the right people (like Jerry's, Marc, etc.). I installed the stainless steel pistons from DRM, along with their brake bias spring (link below). Also steel braided lines and (aluminum?) backing plates that are supposed to stop some of the heat from getting to the pistons and fluid. Lastly, new, good quality rotors and racing pads (I forget which brand/compound, Hawk or Carbotech, I believe - purchased from someone here a few years ago).

http://dougrippie.com/category/produ...4-1996/brakes/

[cbaclawski]

Originally Posted by RussMcB

Been (near) there, done that (or similar). Glad the damage was minimal. Any pictures?

Two thoughts: 1) I do think near-stock brakes can be made to work fairly well. Mine do, but (caveat), I have never gone more than say 5-6 laps really hard. I'm sure Wildwood and other upgrades are superior, but maybe not required, depending on your needs. I'll list my brake mods below.

2) I'd try hard to see if you can replicate some symptoms before you start the work. Easier said than done, I'm sure, but *IF* you can replicate a problem before you make changes, there's a better chance you'll be able to confirm your repair without going back to the track (and maybe not having fun). Maybe there's a country road with some coast down area. Maybe your emergency brake isn't affected by whatever your root cause is.

My mods: I rebuilt the calipers. It was a challenge to find the seals, but I might not have asked the right people (like Jerry's, Marc, etc.). I installed the stainless steel pistons from DRM, along with their brake bias spring (link below). Also steel braided lines and (aluminum?) backing plates that are supposed to stop some of the heat from getting to the pistons and fluid. Lastly, new, good quality rotors and racing pads (I forget which brand/compound, Hawk or Carbotech, I believe - purchased from someone here a few years ago).

http://dougrippie.com/category/produ...4-1996/brakes/

pic:
https://www.facebook.com/photo.php?f...mtMFqs5RgO0sL2

I have steel lines, new good rotors, and while not true race pads, pads that should hold up fine for 10 laps or so...

I'm pretty confident that it's the master. I think it's just hanging on well enough to sorta work sometimes, and not gone badly enough to show much on the street... I haven't rebuilt the calipers, but they seemed to function properly when changing pads, and not a drop of fluid anywhere...


I can't think of any other reason it would behave like it is...

[tnova]

First let me say I totally agree with Curt’s analysis and methodical approach. As for my approach it’s more based on my driving style as a very late braker when entering a turn, picked up as a driver of “momentum” cars that had to keep speed up since they had little torque. Late braking and early off. For me the ZR-1’s brakes didn’t address my “style”. That’s why I went to Wilwoods. May not be the right decision for others. Second, the master cylinder I went with was from a 4th generation Camarillo, an old school C-4 solution. You have to make a spacer to keep rod length correct and trim some clearance from the inner fender. Also the fittings are different so you have to remake the attaching line ends. I would suggest going to a somewhat larger ‘95 C-4 master cylinder to keep originality over the 1” 4th gen Camaro one if possible to meet your track needs.


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[cbaclawski]

Originally Posted by tnova

First let me say I totally agree with Curt’s analysis and methodical approach.


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I just wish I had at least ridden in another c4 so I had a baseline as to how it was supposed to feel. I might have realized something was wrong before this "incident"

Prior to this car, the only C4 I'd ever driven was when I was in high school. My buddy and I would trick dealerships into letting us take one out for a test drive on the premise that "My dad was going to buy me a sports car for graduation and I needed to decide what I wanted" Believe it or not, in the early 90's, every dealer we went to was happy to toss the keys to a couple 16 year old's and let us take our car of choice out unsupervised for a few hours...

[Vette Guy]

Here's my $.02.... Don't simply replace anything - you need to find the problem and then see what you need to replace. Not sure a faulty master cylinder is the problem, and simply replacing it may give you a false sense of security for next time.

I think our J55 calipers are fantastic. They are nicely matched with the rears, and as Russ indicated, with the DRM bias spring make for one heck of a balanced braking application. I do race (88 Corvette Challenge) with the exact calipers and master cylinder (different brake booster) and am a threshold braker - meaning I typically go full throttle to full brake every lap, and I've competed the car hard on race tracks for the past few years. https://www.youtube.com/watch?v=hy6DG7In0sc&t=671s
Each test/practice/qual/race is 25-30 min. While I don't make a whole lot of power, I consistently push and catch up with faster cars in the turns. If you'd ride with me, you'd be amazed at what your stock brake system can do - it surprises me too! I've never once boiled my brakes, and a well balanced bias will stop you in a very short distance.

You started off with a faulty system if the brake pedal was going to the floor before you began bleeding the system... also, not getting a good bleed is another indication there is a big problem. My guess is that you have junk in your calipers and or master that will only be removed with a good cleaning. During the rebuild process, you should find the "ah ha" problem.

Prior to racing, I rebuilt the system - HIGHLY RECOMMEND the DRM pistons - I attribute my ability to keep the brake fluid from boiling to these pistons - my more expensive calipers on another race car do not have aluminum pistons - they transfer heat from the pads to the fluid quickly; the DRM stainless pistons will withstand much more heat.

A great time to rebuild and not replace your master cylinder is during the installation of the DRM bias spring. I found junk in mine that was blocking a passage for the rear brakes, meaning that I would have had too much front brake, and likely spun the car under any sort of hard braking. (in my case, I found a cracked spring withing the master cylinder, which then required I replace the master). Also, if there is any junk in your calipers, you'll find out when you switch out pistons. The rebuild kit for our J55s can be found at any Autozone, O'Rileys, or NAPA. I burn my dust shields almost every race, and replace them at the end of the season.

Lastly, use at least Super Dot 4 fluid (500 dry boiling point minimum). I recommend Pentosin, but started using Amsoil Dominator Dot 4 in the race cars - 580 dry boiling point, and it's not super expensive as is Motul.

Your existing brake system is likely more than you will ever need for a track day - and what was used during the Corvette Challenge and in later pro-racing series. Switching up to Wilwoods, etc., will require some time to find the proper bias. Don't get back on track without finding the exact cause of your problem.

To give you an idea what I run.... DBA 4000 series rotors (Club Spec with temperature indicating paint), Carbotech XP-12/10s, DRM pistons and bias spring, and >500 dry boiling point fluid. I don't recommend the same Carbotech models for street tires, rather you may like the XP-8's - which are grippier than the HP plus, but still streetable.

Regards,
Mark