Seems like I remember reading a post that someone put dye in their brake fluid so that when they bleed their brakes they could see where the new brake fluid started coming out the bleeder. Does this work and are there any special dyes that are compatible with Castrol SRF or Motul fluid? Thanks!

 

That was actually ATE blue fluid which can no longer be sold in the USA as the FEDS decider all brake fluid must be amber

 

All (or most, as far as I know) brake fluids turn a darker shade of brown when they absorb water. If they haven't started to turn brown you should be fine. You'll be able to tell the difference as you bleed, as new fluid that supplant the OLD fluid will be clear and very light in color, while fluid that are OLD that have absorbed water and are no longer as efficient will be light to dark brown.

You don't need to "dye" your brake fluid.

 

It helps when you flush your brake fluid before every track event that is more than 1 month past the previous event. Castrol may have a high wet boiling point but if you want the best dry boiling point then you need to flush if the fluid has been in the system for a month. It doesn't change color in that time even though it has absorbed some moisture. For street cars that change once every two years a dark fluid will usually mark old Vs new clear fluid.

Bill

 

IMO that's a waste of money. I flush once a year on DOT 4 and have NEVER had brake fade issues. As long as the system is evacuating heat correctly, and the Corvette is exceedingly good at evacuating heat (only surpassed by Porsches, IMO), there's really no need to "flush" unless you start experiencing fluid fade.

And I don't even use the expensive stuff. I use Motul RBF600. On tracks that often see 100+ degrees heat (and two very brake intensive tracks no less), pushing a stock weight (3,500 lbs with driver) car with 13.5" rotors.

 

Thanks for everyone's input! I'll use the "color" method like I've used in the past.

 

anyone else find eyeballing the MC max line difficult?

 

It's definitely difficult, especially with new brake fluid.

 

I use a black felt tip marker pen to mark the print on the reservoir. It will eventually come off but it does help a lot.

Bill

 

Well I have had several brake systems that didn't hold up well to heavy track braking at tracks like the Glen and after boiling the fluid several times in my C6Z (in fact it boiled after I slowed down after the checker flag) as I drove from pit lane to the garages I was moving at about 5 mph when somebody walked in front of me and when I hit the brake pedal it went to the floor. That is when I decided I wanted the highest dry boiling point brake fluid I could get and I don't take chances on moisture build up which will lower the boiling point. Evacuating heat hasn't got anything to do with it but boiling point does. Once the fluid is over a month old it gets flushed a day or so before I take the car to the next track event. A lot of organizers tell participants right on the tech form if the brake fluid is a month old it has to be changed. A few of them spot check moisture level in the fluid during tech inspection and even though instructors self tech they will spot check instructor's brake fluid for moisture.

Bill

 

I agree, bleeding the system once a month is also a waste of time. unless your doing track events every other week at high speed tracks it seems excessive. I have Stop Tech calipers on the front, stock on the back and also use Motul 600. I only do 4-5 events/year, which includes Road America and Road Atlanta and have no issues with fade from a fluid issue. I'm known to break hard (my track buddies even gave me a shirt that says "don't break until you see God") and I have only had pedal issues when the pads are really low. Put new pads on, do a quick "caliper bleed" and pedal is solid again.

 

Actually evacuating heat has everything to do with boiling fluid. Fluid typically boil over time. You can put water in a pot over a 1,000ºC burner, but it won't immediately "flash." It takes time to transfer the heat from the burner through to the pot, and then the convection process of the water will result in the fluid circulating to a point where the bulk of the water will have to be at or near boiling point before it flashes.

I always make it a point to do a full cool-down lap after checker without using the brakes, because in that distance, a decent brake system SHOULD evacuate enough of the heat to prevent fluid from boiling. Because, like the water boiling in a pot analogy, brake fluid goes through the same process before it boils. It's the prolonged exposure to a heat source that boils the brake fluid, not the short term exposure it goes through on track, otherwise, most track pads capable of generating well in excess of ALL your racing brake fluid's flash or boiling point. A common entry level track pad like Hawk DTC-60 is expected, or capable of, a MOT of 871ºC (that means when you experience pad fade, as I have in a DTC-60. it's contact surface with the rotor is in excess of 871ºC).

But the fluid (RBF600) didn't boil. Why? It's insulated against pad, then on top of it the fluid inside the piston will have to be exposed to that level of heat for a while before it'll boil. So if the car kept moving, and the rotor turns, and if it can evacuate that amount of heat quickly, the fluid shouldn't boil. So after the checker, I take my cool down lap without using the brakes, but drive at normal, 7/10th speed (there will be spots on certain track where you HAVE to brake a little, but I use it as little as possible). That way, even if I'm out churning hot laps that can see in excess of 700ºC in temperature generated and then some through the brake system, I rarely if ever see fluid fade.

The majority of fluid related fade issues come from prolonged application of brakes (riding the brakes down a long hill), exposure to high brake temps while the vehicle is not moving at speed to evacuate (prolonged slow and go traffic conditions) or extended time sitting in the pit with hot rotors radiating heat into calipers, thus building up temp inside the pistons and slowly cooking the fluid like you're boiling a pot of water.

Changing brake fluids, especially racing brake fluids, ESPECIALLY Castrol FRS, on a monthly or by event basis, does not compute. Especially with Castrol FRS, which is designed to have a lower hygroscopicity (is that even a word?) than your run of the mill brake fluid, AND a higher wet boiling point. I know amateur level club racing TEAMS that would leave FRS in for a full season and only BLEED between events, rather than flush (they'll crack the bleeder, check for bubbles, if no bubbles on the fluid coming out, close it). I run with one of the most conservative and strict DE organizations on the planet, and even they only require the fluid be no more than 6 months old (and they certainly do not spot check).

In my opinion, if your pedals are going to the floor ON TRACK, you have two issues. 1. Your brake system isn't evacuating heat properly, allowing the rotors and pads to remain at high temp for a long time, and 2. You're braking well into turn-in and past the braking zone, thus not allowing the rotor to cool at its most efficient cooling zone (turn-in where the wheels are open to allow ambient air to flow through the hub of the wheel). If your pedals are going to the floor in the paddock, the issue may be that you're parking your car too early in previous sessions, allowing heat to remain trapped in the wheel well between runs and slowly raise the fluid temp past boiling point. At VERY brake intensive tracks on very hot days (which happens quite often in my neck of the woods), on top of my cool down lap I will drive the car around the paddocks or out onto surface streets right after my session, for an additional 5-8 minutes to evacuate heat from the system.

 

How about putting a large fan (or two) in front of the car to blow air thru the brake ducts? Wouldn't this accomplish the same thing? Between sessions I don't have time to drive around on surface streets because I also instruct and thus have to jump from my car into a students car. My brother (who also instructs) starting doing this with his Golf R and reported it worked well to help get heat out of the front brakes between sessions. Plus with the hood up the extra air flow helps some with engine temps too.

 

 

You didn't read my post thoroughly. My issue came after I slowed and entered pit lane. High speed kept sufficient cooling air coming through the ducts but once I slowed there wasn't enough air and the pedal went to the floor while driving 5 mph in the garage area. I almost ran over somebody who stepped in front of me. If I pulled into pit lane and stayed there for more than a few minutes the pedal was gone. One of the reasons I got rid of the C6Z Stock brakes the following season. Hot rotors could boil the fluid in both front calipers after slowing below a certain speed. I could lose the brakes on a cool down lap where I didn't use the brakes until slowing to turn into the garage area. I have been through the rodeo several times. I prefer to know I have a high boiling point in the brake system based on my experience with brakes failing more than once with that setup.

Bill

 

I disagree with needing an entire flush. I run sticky tires (Cup2, R888R, etc) on two tracks that are probably the hardest on brakes in the country (ECR and COTA). If you just bleed the brakes a bit, it will be fine. In the end, it's not like the fluid 2 ft down the line is going to boil. It's going to be the fluid int he caliper. It's not like coolant where it all flows through the whole system and will be similar temps. General rule of thumb is bleed every event and flush every 6-12 months. I just run SRF and flush every 6-12 months, depending on how many track days I do.
100% agree on clear vs dirty though. After one track day my fluid turns brown.

First, Dot4 isn't just Dot4. There is a huge range in boiling points. Second, You REALLY should bleed your brakes (I just do 1 bottle's worth from the combined 4 corners) before each event if you're using RBF600. Third, GM's brake cooling isn't particularly noteworthy, or even good. They don't even have directional vanes anymore.

Very important and should be re-read if you don't get it. Rotors have a ton of heat. Without airflow they'll transfer it to the pads and then the fluid. That is one of the many reasons cool down laps are important. Engines can do the same thing if they're turned off without a cool down lap. There is a lot heat in the block. When the engine is shut off, heat goes in the coolant in the block. It's not getting pumped around and boom, your coolant in the block (the only place you really care about) is super hot. And there goes a head gasket. Always do a good cool down lap, kids. And if you dont get a good one in, drive a round for another 30 seconds. It makes a huge difference. This is more prevalent in the old days of iron blocks and aluminum heads, but it shouldn't be ignored just because you have an aluminum block.

 

While on the subject... any thoughts on titanium shims? I ran some on my Nissan 350Z but in searching it appears they only make them for the Z06 or Z07 brake setups, nothing for the Z51.

 

That's interesting to read. For the record, I'm not as well versed in Corvette as y'all. I'm a life-long German performance car fan, but primarily BMWs because they fit my needs better compared to the Dark Side. From my perspective, the cooling brake cooling system on the C7 is phenomenal. There are multiple ducts that redirect air into the hub of the rotor, including a rear cooling duct on wide body cars. That's unheard of in the BMW realm, not even M3s come with such complicated cooling set-ups. All they give you is a hole in the front bumper that lets ambient air into the general area of the wheel well.

So when I picked up my C7 GS and took it to the track, I was simply AMAZED at the amount of brake, how LATE I can brake, and how consistent the brakes are. And looking at the general construct of the cooling ducts, the ONLY cars I've ever seen that has such an efficient setup are Porsches. So from my perspective, the Corvette, at least the C7, has fantastic cooling for brakes. And the brakes on the C7 GS with Z07 package is JAW DROPPINGLY GOOD.

But my main point of reference still goes back to my BMW, which has been my primary track car for about 12 years. In that span of time, all I ever did was drain and flush once a year, very occasionally bleed if necessary (which was rare, on occasion I'd have the "soft pedals" after a hot 100ºf day at Auto Club Speedway when you have to repeated slow down from about 120-150 down to about 35-40. Repeatedly. 3-4 times a lap depending on who you run with), all on stock BMW sliding calipers for the first ~5 years and last 7 on RacingBrake fixed 4 piston front, 2 piston rear calipers.

That's all belaboring the point, of course. Different drivers and different cars, your miles may vary and all that. The BMW certainly doesn't make the kind of power ANY Corvette makes in the last 20 years (330hp at the crank, on a cool day) nor does it weigh as much as the C7 (3,400lbs soaking wet, full tank with driver). I've only taken the GS through a shake-down and burnishing of the CCM rotors and brakes, so I don't know if it's got any potential fluid boiling issues, but judging by my experience with the steel rotors on the BMW vs the CCM rotors on the GS? I don't think I'll need to bleed the Motul either.

Fingers crossed.

 

I'm not exactly sure how BMW does it (maybe because they have smaller tires or less power or whatever it may be) but they do very well on the track in stock form. BMW, Lotus and Porsche all do just fine on the track right out of the box. I couldn't go 3 laps in my GS or Z51 without upgrading pads and fluid.

 

I think I have 6 or 7 hard track days (and 13k miles) on my OEM rotors running DTC70 pads and I probably have 2-3 days left in them. Just do a cool down lap and it's fine.