I am going to change out my factory brake fluid on my '15 Z06/Z07 soon and got the "good stuff", the Castrol SRF React racing fluid. This will be my 1st time doing this.

My question is: When flushing the "old" stuff out, is it easy to see when the new stuff is flowing and that it's time to stop, close and move to the next wheel? The fluid in there now has only maybe 500 miles on it. Is the Castrol stuff a different color? That would make it easy, I guess. Otherwise, how would you know?

Thanks!

Ron

 

What is your reasoning to purge and reflush the brake fluid when the C7 only has 500 miles.

Are you planning on tracking this car?

 

Yes, and I don't want to waste any of this expensive good stuff.

 

If I remember other postings I have read on the C5 forum, you can buy brake fluid in different colors. Maybe someone on here knows where to get the different colors.

 

More Questions...

What is the impetus for this decision? Is the "track ready" Z06 stock not track ready when it comes to brake fluid? Do you think you will notice any difference at all? Do you know the composition of the GM brake fluid to be inferior?

Just asking since it seems like a lot effort for the gain. Unless you just feel better on the inside

 

The Z06 manual calls for switching to a HD brake fluid for the track with a dry boiling point of at least 279 deg Centigrade. This prevents boiling of the fluid during hi-perf driving which the factory fluid will do.

The HD fluids mostly work well on the track but absorb moisture more quickly than std fluid and therefore must be changed every month.

This Castrol stuff is different in that it has a very high boiling point AND will last 18 months. So I am changing to it so I can street and track the car as I wish for 18 months. But it is expensive.

 

As far as color difference why don't you use an eye dropper and remove some of the existing fluid from the master cylinder reservoir or just bleed a little from one of the calipers and compare the color with the Castrol?

From the C7 owners manual - " Replace existing brake fluid with a qualified high performance brake fluid from a sealed container. Brake fluid with a dry boiling point >279°C (534°F) is qualified. If high performance brake fluid is used, replace it with GM approved brake fluid before driving on public roads. If high performance brake fluid is in the vehicle and the age of the brake fluid is over a month old or unknown, replace the brake fluid before track events and competitive driving. Do not use silicone or DOT-5 brake fluids."

 

I will certainly compare the colors when the time comes. But I don't want to open the new stuff until it's time to change. It starts absorbing moisture as soon as it is opened. Just wondering if anyone has knowledge of a color difference (or other technique) so as to waste as little fluid as possible.

 

Another consideration comes to my mind and that concerns the fluid in the anti-lock brake system, ie the pump, lines and valves. I've never replaced the brake fluid in one of these systems and have wondered if there's a specific procedure to remove, or flush out, the old fluid. Be a shame if there's enough old fluid remaining in the system to contaminate the new fluid being added. Does that old fluid automatically get flushed with new fluid? Anyone know about this?

 

Great question!

 

With the key off, the ABS and stability control module is out of the loop and some of the original GM fluid will be trapped behind the isolation valves, especially in the ABS accumulator. But that's only a few cc and not worth worrying about. It's analogous to changing your oil and worrying about what stays behind in the nooks and crannies, as well as the film layer that adheres to engine internals. SRF is compatible with conventional DOT3, DOT4, and DOT 5.1 fluids, so you won't "contaminate" the new stuff with the old.

If you're still concerned about that first flush and getting rid of all the trapped fluid, bleed the brakes once, drive around a little while, do a couple of hard braking events where you can just feel the ABS start to engage. Then let the car cool down a bit and bleed the brakes a second time.

Castrol SRF comes in one liter bottles, which is several times more than the capacity of your entire system. Use a baster to suck out the fluid from your reservoir before starting the bleed. Then fill it up with SRF and start working the 4 corners. It should only take about a half dozen pumps to get all the old fluid out of the caliper and the line running to it from the ABS unit. So if you pace yourself, such that you use up most of the bottle, there are no worries about getting the old fluid out. Just leave a little extra if you plan to bleed a second time.

Dave Z.

 

My main concern is would that small amount of leftover conventional fluid be prone to cause problems by boiling off during track sessions. Wouldn't want to find out at 125mph.

 

It would not. And braking a Z06 from 125mph wouldn't put much stress on ordinary DOT4 fluid, let alone mostly SRF with a few cc of the old stuff in it. Plenty of thermal capacity there. It's when you're braking from higher speeds (140+) repeatedly that you would start to think about better than stock brake fluid.

The kinetic energy that gets converted to heat in the brakes goes up with the SQUARE of the velocity. So if you double the speed from which you're braking, you quadruple the energy going into the brakes.

 

I am not posting to criticize or in anyway inflame the topic. I am asking from a technical and informational standpoint.

I was under the impression that to do a really good job of bleeding the brakes you needed expensive shop equipment like a Tech series GM device? A GM service manager said that w/o it, getting a really good bleed would be very difficult.

I have no issue with being proven wrong. Don

 

Somebody please prove this wrong as I would really like to be able to do this myself.

Please?

 

He's correct if you're replacing an ABS module or master cylinder. But with the ignition off, and assuming no air trapped in the ABS, you can bleed a C7 Corvette the same way you would bleed a 20 year old car.

The best bleed is going to happen when you use two people, with one in the cockpit pushing the pedal and the other at the corner, barking out commands and cracking open the bleed screw at the right times. Also, little racer's tricks, like tapping the caliper with a dead-blow hammer (non-marring face, of course) to break loose any tiny bubbles, so they'll float to the top and be expelled with the next "push", "release", "push" cycle.

 

Speedbleeders make bleeding the brakes or changing brake fluid a fast, one man operation about $28 for 4. If you use a clear plastic tube on the bleeder you can usually see a color change when you start getting fresh fluid. If you are worried about the fluid in the ABS just do it twice, once after a ABS actuating stop.

 

I did the one man version from this video after having a very bad experience with a pressure bleeder. Honestly, after the simplicity of doing it this way, I'd never bother with a pressure bleeder. You may have trouble seeing when the new fluid comes in, so I recommend keeping a small amount in a clean plastic bottle (water bottle or Gatorade bottle works great) right next to your "old" fluid bottle, and compare the color in the lines. Hopefully, the first stuff out is slightly (or greatly, even better) off (probably darker), and once you match up colors, you know you're good. I didn't use as much fluid in the Z51 as I thought I would, less than a liter, closer to 1/2 a liter.

Oh, and do the inside bleeders first, then outside.

 

I am trying these. Bought 8x of them.

Speedbleeders

Dorman 12701
https://www.autozone.com/brakes-and-...94_27048_2805/

Initial screw on appears to have worked. Haven't had a chance to bleed yet as I have the incorrect brake hoses

 

SRF is fairly clear but you can do it yourself. When you think its cleared through just let it run a bit longer, you got a liter bottle to use. If there is some old fluid in the ABS module who cares? It doesn't get hot there. Most important is getting the calipers full of SRF which is where all the heat is generated. And yes it is a superior product, especially its wet boiling point, so it definitely justifies the cost to do it.