1990 ZR1 Brakes

[Brian R.]

I finally purchased a "modern" Vette - '90 ZR1. Since I'd like to hit track days, I'm planning on installing ceramic brake pads, high temp brake fluid, etc. My questions: the caliper guide pins listed at Corvette America are standard and "HD" - I'm guessing heavy duty. How do I know which one I have? Also, I've never worked on a car w/ABS. When I flush the brake system, do I need to flush out the ABS "box" or will it flush out when I replace the fluid in the system? Thanks.

[Joe L.]

Re: 1990 ZR1 Brakes

I finally purchased a "modern" Vette - '90 ZR1. Since I'd like to hit track days, I'm planning on installing ceramic brake pads, high temp brake fluid, etc. My questions: the caliper guide pins listed at Corvette America are standard and "HD" - I'm guessing heavy duty. How do I know which one I have? Also, I've never worked on a car w/ABS. When I flush the brake system, do I need to flush out the ABS "box" or will it flush out when I replace the fluid in the system? Thanks.

Brian------


All ZR1 were equipped with J55 HD brakes, so you need the "HD" pins. You should find "J55" on your service parts identification label.

I can't help with the brake flushing procedure. My advice would be to use whatever procedure is specified in the 1990 Corvette factory service manual. If you don't have one, you need to get one.

[Brian R.]

Re: 1990 ZR1 Brakes

Thanks, Joe. I appreciate any and all help. Svc manual has been ordered.

[Joe L.]

Re: 1990 ZR1 Brakes

Thanks, Joe. I appreciate any and all help. Svc manual has been ordered.

Brian------


The pins you require were GM #10140666 but they are discontinued. Apparently, the Corvette vendors have an alternate source.

By the way, the rear brakes on your car are the same as standard brakes. Only the front brakes are different for J55.

[Edward J.]

Re: 1990 ZR1 Brakes

Brain, I think if you dot 5.1 brake fluid this will work with ABS systems and will raise the boil point of the fluid. but be warned that nothing will stop the brake fluid from boiling if you do to many hot laps, these systems were not made to handle to many hard high speed stops. These Corvette brake systems work fine in most conditions, track days??? I would always test my brakes before each turn, I had a cust. that had all the mods. he thought was necc. to take to the track in his 2010 ZO6, as you guessed he loss the brakes when going into a turn and crashed the car, and this was with a professional driver in the pass. seat with him.

[Rick A.]

Re: 1990 ZR1 Brakes

if you are serious about tracking - Castrol SRF

[Brian R.]

Re: 1990 ZR1 Brakes

Thanks for the advice, folks. Despite replacing calipers, lines, etc., on my modified '77, I lost my brakes while pulling into pit lane after approx. 15 hot laps. Thus, my desire to bulk this one up as much as possible without spending a fortune on Wilwood, etc. Again, all assistance is
appreciated.

[Duke W.]

Re: 1990 ZR1 Brakes

Depending on the OE pad material, they may be okay. You should probably talk to Porterfield and see if he has any customers who track ZR-1s and have a proven pad material.

I ran my Cosworth Vega in track events from the early eighties to late nineties, accumulating over 5000 miles and never had a problem with the car or me as a driver. I never spun, but nobody ever accused me of being slow. The scariest incident was when a Replicobra blew an oil line and spread 12 quarts of oil through Willow Springs' Turn 8 that I took flat in fifth at over 100 MPH, but I managed to keep it on the asphalt.

Knowing the limitations of production cars in sustained high speed hot lapping, I did a lot of prep before the first event. I knew the standard Vega solid front rotor brakes on the CV were totally inadequate, and the car suffered from premature rear lock-up, so I installed the vented rotors and larger piston calipers from the '76-up H-Specials, which was basically a bolt on mod by installing complete knuckle assembly. The larger front pistons rebiased brake effort to the front, and with the OE Vega proportioning valve rear lockup was tamed and nothing short of a car on slicks could outbrake me.

This was with the OE Delco semi-metallic pads, but one thing I did that I believe was very helpful was remove the dust shields from the knuckles, which allowed much better air flow to the rotors. There was some loss of pedal height during the day that I never really figured out, but it would usually recover by the time I got home. Over the years I went through about six sets of front pads, but never had to change the original rear shoes.

The front rotors are also original. I took the knuckle assemblies off a wrecked Monza that only had 5K miles, but to be sure I turned the .880" thick rotors down to .860" and rebuilt the calipers. The brakes were initially a little grabby, but by the end of the first track day, they had scored and were much more progressive. Over the years the rotors developed short radial cracks. Any brake shop would have looked at my scored, cracked rotors and said they were junk. I was concerned about the cracks and recalled a set of papers on the development of the GT 40 that I had in my library.

During dyno simulations or the LeMans brake schedule Ford noticed the same short radial cracks and developed a quick change rotor system, but later testing showed that these short radial cracks were not a problem, so I just did my normal pre-event inspection and as long as the cracks were short and didn't extend to the center or edge of the rotor, they were good to go. The only thing that would have killed them was wearing down to the .815" minimum thickness or warping, but neither ever happened.

One very important issue to understand is that new pads on gnarly rotors need a considered break-in in procedure, and you can't do it on the track. It takes about 300 miles of normal road driving to fully seat them. Initially, pedal effort will be high, but as they seat, pedal effort decreases and when it returns to normal, the pads are bedded-in and ready for the track.

If your brake system has a separate ABS reservoir it probably needs to be flushed independently. My two ABS cars don't, but I recall helping a friend flush a Honda Prelude, and it did have a separate ABS reservoir that we flushed. I used DOT 5 fluid (Castrol or Valvoline) and flushed the brakes every couple of events.

Another consideration is the oiling system. I don't know the specifics of the ZR-1 system, but most road cars have rather shallow sumps and dynamic forces can uncover the pickup. Back in the fifties and sixties before SCCA allowed dry sumps guys would run a quart or more over. The CV has a shallow sump - same as the basic Vega 140 engine that I ran a half to full quart overfull and never had a problem.

Probably the most important chore you have is selecting tires. Have you made that selection? Then you will want to experiment with different anti-roll bars, alignment settings, and shocks using the "scientific method" of making one change at a time. I started out with the OE bars, then increased the front bar 1/16" with a GM part, and, as expected, there was less roll, but more understeer. Prior to the next event I installed a 1/16" larger aftermarket bar, which limited roll to no more than about 3 degrees per g, and the car was dead neutral. I also dialed in front negative camber beginning with about negative one degree when I was running Phoenix Stahlflex 3011 tires, which were the hot setup for small sedans before DOT legal racing tires became generally available and increased it to minus two degrees when I installed Toyo Proxes RA-1s.

Increasing camber in the negative direction lost caster, and the most I could get at minus two camber was minus 3/4 caster when I wanted zero to plus one. So I tried a novel experiment. I swapped the upper control arms side to side and at minus two caster the least positive caster I could get was plus six. I took it for a ride and the steering response was utterly incredible, but it had enough kickback to damned near break my arms. Not all experiments are successful!

I started out with Bilstein Sport shocks, but was never fully satisfied with their damping rates - not enough rebound damping on the front and too much on the rear, so I replaced them with Spax rebound adjustable shocks, I had to crank the front adjustment to the limit, but only half-way on the rear, and it was near perfect!

Running four to five events a year - two at Riverside (Ferrari/Pantera Club and Porsche owners Club) and two at Willow, (Lynn Parks' Cobra Owners' Club of America) it took a couple of years to get the car fully dialed in. I would make notes on how the car performed and any issues, then figure out a solution, make the changes at home, and test at the next event. I got to the point where I was the first guy out in my sessions and the last guy in, and in the process I embarrassed a lot of name brand sports cars.

I sometimes bugged the event organizers into letting me run with the "race group" because the "street group" (Ferraris, Panteras, Porsches, Mustangs, etc.) was too slow and there was too much traffic, and the race group guys never complained about me being on the track with them. They could easily pass me on the straights, and I didn't really slow them down in the corners. I was always surprised how rare it was to see a road-going Corvette at these events, but there were a few vintage racers that ran with the race group.

I remember one guy coming up to me at Riverside and saying: "You're out there going 'round and around all day while most guys are in the pits working on their cars. What's your secret?"

My answer was "preparation".

It's always been my feeling that you're going to have more problems with a high powered car than a moderate powered car, but the high powered car may not turn much faster lap times and may even turn be slower. It's all about understanding basic vehicle dynamics so you can figure out how to tune the car and then driving skill and experience. Most novice drivers are tough on the car because they rocket down the straight, then stomp on the brakes way too early and tippy-toe though the corners. The secret to good lap times is to maintain as much speed as possible on every inch of the track.

Here's a link to an article in Hemmings Muscle Machines about my "track career" with the Cosworth Vega. Maybe it will help you understand what it takes to make a road car a competent track car.

http://www.hemmings.com/magazine/mus/2007/11/Pointless-racing---1976-Cosworth-Vega/1539002.html

Good luck and keep us informed on your progress.

Duke