Synthetic Brake Fluid

[FJCamper]

I've used all kinds of brake fluid in my racers, Castrol LMA, Super Blue, even old reliable NAPA DOT4.

NAPA DOT4 has worked well for us on the track because we frequently bleed our brakes anyway, and our brake system is mechanically up to the job.

The only time I tried synthetic was Valvoline SynPower, and it killed the seals in the brand new German master cylinder we were installing on our '70 Ghia within hours. It had never had fluid in it before.

Does anyone use SynPower with no trouble?

[FJCamper]

I should expand the question.

What about silicone DOT 5 fluid as well?

Is anybody using this and being happy with it?

FJC

[Bruce2]

I switched over to DOT 5 silicone juice 15 years ago. There are no downsides, only benefits.

[raygreenwood]

I think we went round and round on this one a couple years back. In the performance respect...Bruce2 is 100%correct. There are no downsides.

Silicone based DOT 5 has (in general) a higher wet and dry boiling point. The dry boiling point is useless information. An experiement published years ago in European car magazine showed that ALL brake fluids...synthetic or not... tended to get significant moisture entrained in them in a matter of weeks. The wet boiling point (after the fluid has absorbed a normal/nominal amount of water vapor)...is all that counts.

That being said...the one extra fine point about DOT 5 silicone that is both a "plus" and a "minus"....is that unlike normal DOT 3/4 fluids it is NOT hygroscopic...meaning it does not absorb water.
On the + side...it helps the DOT 5 fluid have a better wet boiling point and keeps it dryer longer than Dot 3/4...all good things.

On the negative side...silicone DOT 5 simply "carries" and suspends water vapor which brings it into contact with metal. When it reaches a certain level of suspended water...it causes corrosion/rust...faster than Dot 3/4.

So teh real reason for using Dot %...is not longer life of synthetics. It needs tyo be changed periodically too. Its all around better performance.

Also...if you do NOT get your system totally squeeky freaky clean when installing Dot 5....or if its very very wet in your area...you can be screwed up (not permanently mind you). Dot 5 will not mix with resdiual dot 3/4. It gums up the compensation ports and flap valves and makes them sticky. You can find your self with locked brakes in hot weather when entrained moisture addd to this starts to boil off. Been there...done that. Ray

[Marc]

Don't use it myself. It's slightly compressible compared to DOT3/4 (spongy pedal) and can cause corrosion problems, particularly an issue on cars where the master cylinder is the low point of the system, like most ACVWs. It was developed for use in military and emergency fleet vehicles that sit for months at a time; IMO that's the only application where its benefits outweigh the potential liabilities - and even then not on a low-M/C vehicle.

From the Tilton Engineering Brake and Hydraulic catalog:
"WARNING:
Despite advertising claims, silicone brake fluid is unsuitable for
racing at high temperature because of its compressibility. This is why
many people who have tried silicone fluids have complained about the
brakes going away after 10 or 15 laps...Currently, no major
team that taxes its braking system to the limit is using silicone brake fluid."

From the JFZ Engineering Braking Products catalog:
"Note: We strongly recommend that you do not use silicone brake fluid with any of our products. We have tested extensively and found that silicone fluid has properties that may cause seal swelling and may not be appropriate for racing use."

From the Wilwood catalog:
"We do not recommend the use of silicone fluids... ...Silicone fluid is also a highly compressible fluid and will cause your pedal to feel spongy, and get progressively worse as it heats up."

All these companies recommend the use of DOT3/DOT4 fluids- and periodic flushing of the system.

http://www.shoptalkforums.com/viewtopic.php?t=64349

[FJCamper]

Hi Marc,

You talked me right out of silicone fluid. We run through so much NAPA DOT 4 that you'd think we kept our local store in business.

Even under full racing stress, meaning 100+ mph braking several times a lap, our NAPA DOT4 has not failed us. I tell myself we're light enough and have enough brake swept area surface that we don't overtax our brakes.

And we use a stock master cylinder, Varga calipers and cross-drilled rotors up front, and cross-drilled drums in the rear.

I appreciate the info.

FJC

[raygreenwood]

Marc...what you are noting about compresability...is exactly what experiements have shown is caused by the entrainment of water in DOT 5 silicone fluids.

See if you can wrap your head around this:...In dot 3/4...the hygroscopic nature of teh fluids causes free water and water vapor to be absorbed (like the co-solvent action of alcohol and water)...so they are "one" fluid at a molecular level....albeit now with a lower boiling point and modified viscosity. With me so far?

Tthe DOT 5 silicone on teh other hand.....captures water and supsends it...in micro droplets. These droplest are not as dense as the silicone. It is these microdroplets that are compressing.

I too have never again used DOT 5. I also found that your system must in effect be brand new to keep incomptability from causing locking issues. Ray

[Marc]

Even with zero moisture present DOT5 is more compressible.
It holds entrained air much more readily than conventional fluid - you must take great care not to whip it up while handling it or bleeding the system or there will be bubbles accumulating at every high loop. A straight gravity bleed (not feasible on our cars) or a suction bleed is best, If you pressure bleed DOT5 do it only with an accumulator "bomb" that has a diaphragm to separate the air from the fluid.

[mikemck]

This thread seems to have quickly shifted from a discussion of "synthetic" to "silicone" brake fluid.

How about the original question:

"The only time I tried synthetic was Valvoline SynPower, and it killed the seals in the brand new German master cylinder we were installing on our '70 Ghia within hours. It had never had fluid in it before.

Does anyone use SynPower with no trouble?"

I have a bottle of this stuff and am wondering if I should use it.

Thanks.

[FJCamper]

Hi Mike,

I told our experience with Synpower the way it happened.

Before I understood that the new master cylinder seals were failing and we were bleeding and rebeleeding (I actually went out and bought a big bottle of the stuff) I was down at the master cylinder and watched the (new) forward brake light sensor begin to drip fluid from out of the male push-on connector!

It was one with the translucent type milky plastic center, and I saw something moving inside, then fluid began to drip.

When I dismounted and disassembled the master cylinder, the seals were sticky, as if they had partially melted.

I searched the internet for anyone else with a similar experience and only found one guy who mentioned it, but it wasn't on a VW. And most people speak very highly of Synpower.

All I can tell you is what happened to us.

[Marc]

I heard that Valvoline quit making SynPower fluid - but not why.
You're correct that "synthetic" does not necessarily mean "silicon" (DOT5). "Synthetic" has become a marketing buzzword that some makers will use if they have any excuse. If you ask me, it's all synthetic (man-made) since polyglycol isn't something you just find in a puddle somewhere.

DOT5.1 is a standard for polyglycol fluids (compatible with DOT3 or 4) with boiling points even higher than DOT5. Logical if you expect the DOT number to go up hand-in-hand with the boiling point rating, but confusing as heck because DOT5.1 is incompatible with DOT5.
For racing purposes you want the highest dry boiling point possible and don't necessarily care about the wet boiling point; there are some fluids that are great dry but only meet DOT3 because their wet point isn't high too - you might want such a fluid for racing, but for street use DOT5.1 is the best "all-around" stuff on the market.

http://www.afcoracing.com/tech_pages/fluid.shtml


ARRANGED BY DRY BOILING POINT:
DRY: 401F -- WET: 284F --- DOT3
DRY: 446F -- WET: 311F --- DOT4
DRY: 502F -- WET: 343F --- VALVOLINE SYNPOWER
DRY: 509F -- WET: 365F --- MOTUL 5.1
DRY: 527F -- WET: 302F --- AP RACING 551
DRY: 536F -- WET: 392F --- ATE SUPERBLUE/TYP200
DRY: 550F -- WET: 290F --- FORD HD
DRY: 590F -- WET: 410F --- AP RACING 600
DRY: 590F -- WET: 518F --- CASTROL SRF
DRY: 593F -- WET: 420F --- MOTUL RBF600
DRY: 610F -- WET: 421F --- NEO-SYNTHETIC SUPER DOT 610

ARRANGED BY WET BOILING POINT:
DRY: 401F -- WET: 284F --- DOT3
DRY: 550F -- WET: 290F --- FORD HD
DRY: 527F -- WET: 302F --- AP RACING 551
DRY: 446F -- WET: 311F --- DOT4
DRY: 502F -- WET: 343F --- VALVOLINE SYNPOWER
DRY: 509F -- WET: 365F --- MOTUL 5.1
DRY: 536F -- WET: 392F --- ATE SUPERBLUE/TYP200
DRY: 590F -- WET: 410F --- AP RACING 600
DRY: 593F -- WET: 420F --- MOTUL RBF600
DRY: 610F -- WET: 421F --- NEO-SYNTHETIC SUPER DOT 610
DRY: 590F -- WET: 518F --- CASTROL SRF

[mikemck]

Well, I am still wondering if I should use the SynPower that I have.

Does anyone else have experience with it, good or bad?

Thanks.

[Marc]

I spent the better part of an hour poking about on web bulletin boards for tales of woe regarding SynPower and came up with nothing (discounting the stories from a couple of clueless people who didn't even know for sure what they had) so FJCamper's experience is apparently unique. Dot 4 and 5.1 contain borate esters not used in DOT3 fluid and those might be a factor, but the rubber compounded for DOT3 (like in VW hydraulic components) is supposed to be able to stand up to them.
Valvoline's web site still mentions SynPower brake fluid, but if you drill down to the product page you see only DOT3/4 fluid. Maybe they changed the formulation, but I'd be willing to bet they just changed the name due to the confusion it has caused.

Good read:
http://www.stoptech.com/tech_info/wp_br ... d_1a.shtml

Experiment showing results of oil contamination of fluid:
http://www.stoptech.com/whitepapers/brakefluid1a.htm

[Jim Ed]

This thread seems to have quickly shifted from a discussion of "synthetic" to "silicone" brake fluid.

How about the original question:

"The only time I tried synthetic was Valvoline SynPower, and it killed the seals in the brand new German master cylinder we were installing on our '70 Ghia within hours. It had never had fluid in it before.

Does anyone use SynPower with no trouble?"

I have a bottle of this stuff and am wondering if I should use it.

Thanks.

A long time ago I used this Valvoline SynPower brake fluid in my 1973 Beetle. It caused the hoses to swell and the hose on my Motive Power Bleeder to swell. I looked on the motiveproducts.com web site and now they sell a blue hose for their power bleeders. Possibly it does not swell with the synthetic brake fluid. I will have to ask them.
Today I went to a local O Reilly's Auto Parts store to buy some store brand conventional DOT 3 brake fluid. All they had in the small bottles was synthetic DOT 3. So, I bought a quart bottle of the old type of DOT 3 brake fluid.
What am I going to do when the quit selling non synthetic DOT 3 brake fluid? Check at samba.com, eBay.com, and Amazon.com I suppose.
Thanks In Advance! Any help is appreciated!
.. just another aircooled VW novice.

[Ol'fogasaurus]

The main thing I remember reading or hearing about DOT 5 is that if they system is not perfectly clean like I think it was Marc who said it, that there can be problems with injecting DOT 5 into an older system; i.e., one that has had either DOT3 or DOT 4 in it (notice that I did not say used). The rest of what has been said here I have only via heard here-say from others.

The seal problem I was also aware of.

Lee