Invicta1

It says in my owners manual that they recommend changing the brake fluid for track events. I assume the stock fluid in my GS is DOT 3??? Is there a special procedure required to change the brake fluid? Or so we need to do a manual bleed on each caliper? I want to upgrade to DOT4 fluid for track days. Why would they not put in DOT 4 from the factory???

BEZ06

Yes - the stock fluid in the brake system is DOT 3.

They do put DOT 4+ in the clutch system at the factory due to the heat from the engine, but DOT 3 is perfectly satisfactory in the brakes for street driving.

DOT 4 is slightly more hygroscopic. Here's an excerpt from a StopTech Technical White Paper:

Read all about brake fluid here:

http://stoptech.com/tech_info/wp_brakefluid_1a.shtml


DOT 3 comes in the brake system from the factory mainly because there's just no reason to spend one extra penny to put something else in, and DOT 4 also would require more frequent servicing of the brake system and most owners probably don't even get their DOT 3 flushed as often as they should.

You can flush some DOT 4 into the system just like you would with any other car, except that without a Tech 2 you can't flush new fluid into the ABS circuits. You can flush, go out and do a couple ABS stops to get fresh fluid into the ABS lines, then come home and flush again if you really feel the need to try to get new fluid into the ABS before going to the track.

BTW, your GS has fixed calipers, so you'll need to bleed through both the inside and the outside bleed valve on each caliper when you flush the system with DOT 4.

Bob

Invicta1

Thanks for the info. So the real question is do people generally feel that upgrade to DOT 4 is really needed on these cars for light track duty? Or does the stock braking system work fine with the factory fluid. In other words I don't want to go through all the work of swapping out the fluid to DOT4 if it is not really needed, I used to subscribe to the overkill mentality and perhaps it is really one of those "it depends how hard you drive the car" issues. Thoughts?

BEZ06

Many DOT 3 fluids may actually meet DOT 4 specs, and for "light" track duty may work fine.

When you get tech inspected at the track they're mainly just looking for clean fluid and a good level in the master cylinder, and they can't tell what DOT spec is in there unless you tell them.

Many events probably don't specify what you use, but the Nat'l Corvette Museum does for their HPDE's.

Here's an excerpt from the "Getting your car ready for High Performance Driving Educations" document from the NCM about preparing your car for the VIR HPDE the end of June:
Read the whole document here:

http://www.corvettemuseum.com/regist...20a%20HPDE.doc


Here's the checklist for participants to prepare their cars for the HPDE:

You can see the one document says flush with DOT 4 within 60 days of the event, and the checklist says within 30 days.


So....If you're going to flush your system before a track event, you might as well put in a good DOT 4 fluid.

When I flush fresh fluid into the system, I think it usually takes about 1-1/2 qts. I use Motul RBF 600, which is a DOT 4 and comes in 500ml containers (about a pint). I'll use 2 to 3 bottles (1 liter to 1-1/2 liters)for a good flush.

It usually takes anywhere from about 8 to 12 ounces from each rear caliper to get fresh/clean fluid coming out, and because of the shorter lines up front it takes about 4 to 6 ounces from each front caliper - but I just bleed until I'm getting nice clear/fresh fluid coming out.


You're gonna have to decide for yourself how much effort you want to put into preparing your car for track events, and what the requirements of the sponsoring organization may be.

Have fun at the track!!! Are you going to the NCM VIR event? C'ya there if you're going!!

Bob

Gearhead Jim

Bob-

Do you have any info on how long it takes for DOT 4 to degrade below DOT 3 performance? I now have GM DOT 4 in my 2009 Coupe, and plan to flush once per year (no track use, but vigorous mountain driving).

The article also mentioned possible compatibility issues brtween DOT 3 brake systems and DOT 4 fluid, but then seems to say that's only a problem on older cars. The DOT 4 seems to be doing fine in my car, but it's been in there less than a year. Your thoughts?

Bill Dearborn

It all depends on how long it has been since the brake fluid was put in your car's brake system. As mentioned brake fluid is hyrgoscopic and absorbs moisture over a period of time. As it absorbs that moisture the boiling point reduces. Some DOT3 fluids like the Ford Super Duty fluid specify both a dry boiling point (500 degrees for it) and a wet boiling point. A lot of brake fluids including DOT4 fluids only state their wet boiling point. DOT4 fluids have a higher wet boiling point than DOT3 fluids. The fluid maintains its dry boiling point for a while after it is put in so I usually bleed my brakes a week or so before the event. If it is a month between events I bleed everything out to make sure I have a high boiling point. I use Wilwood 570 DOT 3 which has a 570 degree dry boiling point. Even if you don't get the old DOT3 out of the ABS unit there isn't that much in there that it will degrade the new fluid.

If you are using stock pads it is unlikely you will get the fluid hot enough to boil new GM DOT3 fluid since the pads don't operate at that high of a temp. However, I always used the Ford fluid until they dropped the dry boiling point spec from 550 to 500 degrees. It is still one of the best fluids on the market for the price. Hawk HP+ pads have good friction at 800 degrees F and a race pad like a Carbotech XP12 probably can generate 1400 degree temps if you are running race tires and can use all of the friction the pads provide.

If you are a novice or low level intermediate track driver the Ford fluid is a great choice due to the high dry boiling point and the fact you can get lots of it cheaply at the Ford dealership. I used to go and buy 8 to 10 cans at a time.

Bill

BEZ06

No, Jim - I really don't know.

Like the StopTech document says brake fluids....:

It also says to buy small containers of fluid, because once you open it atmospheric moisture can be absorbed, so you don't want to keep opened containers. The common forum wisdom is that after using fluid from a container, even if it's tightly sealed most people say it's no good after a couple weeks on the shelf.

Many people say that you shouldn't remove the cap from the brake or clutch reservoir or you're letting moist air contact the fluid and transfer moisture, but I think that's very ****.

Many people don't like using a Motive Power Bleeder to apply pressure to the fluid to push it through the system when bleeding. As mentioned in that StopTech article, they think it pushes moisture from the atmosphere into the fluid. I use a Motive at 10-12 psi, and I don't think it puts any appriciable amount of moisture into the fluid that it won't absorb through breathers, seals, etc.

There's another type of pressure bleeder that uses a diaphragm to apply mechanical pressure on the fluid rather than air pressure, and if I were a professional racer using Castrol SRF I'd probably do every anally obsessive little thing regarding every aspect of maintenance on my car, but as an HPDE guy that goes to the track for fun and doesn't push for every last 1/10th second every lap, I don't think I'm compromising at all by using my Motive Power Bleeder to flush the brake system a week or two before every event.

If you live in a real dry climate the fluid may not absorb as much water over time as it does where I live in damp/humid/muggy/boggy Florida!

I would think that whether you're running DOT 3 or 4, a flush every year is plenty good unless you're tracking the car. Probably every 2 years would be okay.

If you track the car, flush before every track event, unless maybe you're running Castrol SRF, which is in its own class!!! Even the racers that put in SRF will run it multiple events, maybe even a whole race season, without any problem.

Bob

Gearhead Jim

Thanks. I note that you are using (good) DOT 3 rather than DOT 4, are you aware of any problems or just being extra cautious to follow the exact GM recommendations?