Brake Fluid Comparison - Stock Brakes

[unclebilly]

I want to precursor this by saying that I am reporting my findings...

I have been running DOT 5.1 fluid in my 77 track car for the past 2 years (literally - I never changed it all last season or this season until my last event). The only stock things about this car are the 915 transaxle and the brakes.

I am running Brake Horse Power pads from our host which were much better than the factory Porsche pads.

I never had any brake fade with the DOT 5.1 fluid coming off of the straights at Race City (3/4 mile long front straight and ~ 1/2 mile long back straight) with the DOT 5.1. On the front straight I would typically hit 120 - 125 MPH on my speedo.

I put in the ATE super blue at the last event after I had problems in the warmup session. The brakes felt spongy in comparison and I did get some fade after a few laps - not nearly as bad as it was before I switched to the DOT 5.1 a few years ago but still not as good as the DOT 5.1.

I am switching my brakes over to a Turbo setup from an 87 Turbo this winter.

I thought I would give you guys this info that maybe Super Blue isn't quite as super as DOT 5.1 fluids. I would say that my braking system was more prone to boiling than guys running big brakes. The point I am making is that if you aren't running big brakes, you need to run as high a boiling point brake fluid as you can get and it isn't Super Blue.

[jpnovak]

Interesting. I have been running ATE fluid for a number of years. NO issues with braking but the initial pedal bite is not has hard as I would like.

I guess it might be time to check out the DOT 5.1. Are these silicone based fluids?

[jpnovak]

I just looked this up. DOT5 is silicone. DOT5.1 is mineral oil based.

Copied from the Wiki page.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Not to be confused with DOT 5, a silicone based fluid.

DOT 5.1 is one of several designations of automotive brake fluid, denoting a particular mixture of chemicals imparting specified ranges of boiling point.

A brake fluid's dry boiling point is the temperature at which the pure fluid will boil. Wet boiling point concerns the boiling temperature when the fluid contains water.

In the United States, all brake fluids must meet Standard No. 116; Motor vehicle brake fluids[1]. Under this standard there are three Department of Transportation (DOT) minimal specifications for brake fluid. They are DOT 3, DOT 4 and DOT 5.1.

DOT 5.1, like DOT 3 and DOT 4, is a polyethylene glycol-based fluid (contrasted with DOT 5 which is silicone-based). Polyethylene glycol fluids are hygroscopic and will absorb water from the atmosphere, which is necessary to prevent sheer and undiluted water in the braking system, which is very corrosive.

As of 2006[update], most cars produced in the U.S. use DOT 3 brake fluid.
[edit] Boiling points

Minimal boiling points for these specifications are as follows:
Boiling point ranges Dry boiling point Wet boiling point
DOT 3 205°C (401°F) 140°C (284°F)
DOT 4 230°C (446°F) 155°C (311°F)
DOT 5 260°C (500°F) 180°C (356°F)
DOT 5.1 270°C (518°F) 191°C (375°F)
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

by comparison: ATE blue is a DOT4 and has the following numbers

# Boiling point minimum: 536 degrees F -> 280C
# Wet boiling point minimum: 388 degrees F=> 197

[911st]

I love Castor SPF. It's "wet boiling point" is way better than the others. A low wet point is why we are suposed to blead our brakes right before a track events. Prices are a bit dated.

Brake FluidDry Boiling Point Wet Boiling Point Suggested List Price
AP SUPER 600 590°F 410°F $18.00/16.9oz.
CASTROL SRF 590°F 518°F $69.99/33.8oz. <-------------
NEO SUPER DOT 610, 610°F 421°F $15.00/12oz.
MOTUL RACING 600 593°F 420°F $15.00/16.9oz.
MOTUL DOT 5.1 509°F 365°F $6.50/16.9oz.
ATE SUPER BLUE 536°F 392°F $11.99/33.8oz
VALVOLINE SYNPOWER 503°F 343°F $4.97/16.9oz.
ATE SL 500°F 329°F $7.95/16.9oz.
CASTROL LMA 450°F 311°F $3.50/16.9oz.
AP 551 528°F 288°F $12.50/16.9oz.

[KTL]

Wet boiling point is only for old fluid that's been in service for a long time. Otherwise dry boiling point is a better reference. Which DOT 5.1 are you using? Brand name? I'll wholeheartedly agree that w/stock brakes, one should be running super high temp fluid. Especially if efficient braking (short duration, heavy application events) is not one's specialty!

That's great that you get better peformance out of it the 5.1 but it's only masking the problem- excessive heat. How long do your dust boots and seals last? One season maybe? With better cooling via actual forced air cooling or more thermal mass from the brakes, you increase the life of your consumables- brake pads, rotors, caliper seals.

[GaryR]

Originally Posted by KTL

Wet boiling point is only for old fluid that's been in service for a long time. Otherwise dry boiling point is a better reference. Which DOT 5.1 are you using? Brand name? I'll wholeheartedly agree that w/stock brakes, one should be running super high temp fluid. Especially if efficient braking (short duration, heavy application events) is not one's specialty!

That's great that you get better peformance out of it the 5.1 but it's only masking the problem- excessive heat. How long do your dust boots and seals last? One season maybe? With better cooling via actual forced air cooling or more thermal mass from the brakes, you increase the life of your consumables- brake pads, rotors, caliper seals.

Correct, wet is for fluid that has been is service (or open storage) for a while and if you run a car on the track you should be flushing the fluid at least once per year depending on how often you bleed/renew. I run Motul 660 (600 is fine) and have 0 issues. Castrol SRF is top notch but a bit expensive. I hate ATE Blue, dyes everything. I would use the ATE Gold if anything ATE. As for dust boots, mine turn to potato chips after a couple race days so none of us bother with them. For road use/DE days I guess they are a good idea..

[RWebb]

the OP may have had 2 yr or older fluid in his system & not flushed it all out

that might explain his problem - it is hard to tell what is up from the post

[911pcars]

"I love Castor SPF."

That must be their suntan lotion.

Sherwood

[175K911]

In 20+ years of tracking 911's I've never had good luck with the Ate Superblue. Can boil it in 20 minutes on the track. But that's running Red run group with racing pads. Long ago I switeched to either Motul 600 or Brembo racing and have never had a problem again.

I then thought I'd give the Ate a second chance and tried it in my Audi when I went with a big brake conversion, again boiled it almost instantly. Came into the paddock and flushed with Motul and finished the weekend without incident.

The Ate Superblue is probably OK for street and an occasional track day for an intermediate driver, but nobody I know who's an instructor with a track car will run it.

[unclebilly]

Yup, I did run the 5.1 for 2 and a half seasons but got away with it because it is so dry in Alberta. The car rarely (if ever) gets driven in the winter.

I switched to Super Blue because it was what we had at the track.

The 5.1 was purchased at a motorbike shop and I don't think it was a motul product. I will have to look when I get home in a few days.

I will be running the 5.1 again in my turbo brake setup when I get it mounted up.

This car sees more than 50% track use.

I'm glad I am not the only one with these findings with Super Blue.

Scott.

[911st]

With freshly bled brake fluid dry boiling level is what is important.

With older fluid, wet boiling point is what becomes important.

That is why I went with the SPF. I do not have to bled my brakes before a DE.

When compairing prices, the SPF comes in a bottle that is about twice the size as others and it keeps when others may not once opened.

Not an expert on this. I stepped up from Supper Blue to SPF and it works on a stock full weight Carrera's brakes.

Then my problem became the pad.

[RWebb]

"freshly bled"???

you must mean freshly replaced with fluid from a freshly opened can

[911pcars]

So as not to confuse, I think he means Castrol SRF. It's usually considered the best BF, but some experiment to see if other fluids can do the job. There's a cost difference (SRF being the most expensive) which can be offset by eliminating the need for frequent system bleeding.

Sherwood

[175K911]

Here's a great list of high performance brake fluids, with their wet and dry specs.

Pegasus - Racing Brake Fluid

Keep in mind that the first time you boil your fluid (you can tell because your pedal will get spongy), you've introduced moisture into the system, and you're now approaching the wet spec. Think of a glass of water- boil it, then let it cool and note the condensation that forms. Brake fluid does the same thing.

Castrol SRF has the highest wet boiling point of all fluids out there, almost as high as the dry bp of the Ate Super blue. Then again, it's 3-4x the price of the others too. But can you ever have too much safety margin with brakes?