driviniTT

<center><img src="http://pictureposter.audiworld.com/14718/noclutchflatbed.jpg"></center><p>I've been running ATE Blue DOT5 brake fluid for about 3 years now, ever since my first track event. Last week, at 95K miles, the car needed and got a new clutch, flywheel and throwout bearing. During the work though, I got a call from the dealer saying there was "contamination" in the brake fluid. "No" say I, that blue stuff *is* the fluid. The tech then tells me that the DOT5 fluid has corroded the plastic parts of the throwout bearing assembly and the clutch slave cylinder supply line, which is now leaking and needs to be replaced. OK, I know the clutch slave shares the brake fluid reservoir, but I never heard of this. So I gave the OK and they went ahead and replaced the supply line . . . the throwout bearing was being done anyway. They said the bled the brakes 3 times. Now I get the car back, and the brake pedal is mushy, grabs only after about 1/3 travel, can be pumped up to bring the pedal up, and generally feels like crap. Brake performance and feel was excellent before. I called and complained, they offered to have me come back and take a ride with the tech. They said they test drove it about 10 miles. Dunno how they missed the crappy brake pedal feel. That dealer has a kind of bad cred, so I won't be going back there. Situation and location of clutch failure necessitated using them for this work, unfortunately. I'll go back to my regular, and trusted, dealer to assess and correct the brakes. But . . . what about this DOT5 corrosion claim ?? Bogus ? Thanks.

AxeYrCat

Silicone Brake Fluids
In years past, all brake fluids were glycol. Then D.O.T. 5, a silicone fluid having a higher temperature rating, emerged, initially to meet the higher boiling point requirements of racing use. (Race car brake systems include oil-cooler-like heat exchangers and ceramic pads.) Silicone fluid was able to withstand the most heat of any brake fluid, so it earned a reputation as a racing brake fluid. However, silicone brake fluid has properties very different from glycol fluid, and has its own pros and cons. On the advantage side, silicone fluid will not harm paint or plastic, and does not aggressively attract additional moisture as glycol fluid does. On the disadvantage side however, silicone fluid aerates easily. Harley-Davison, one of the sole current OEM users of silicone fluid, warns buyers to let the fluid sit at least an hour before using it. The trip home in the saddlebag is enough to aerate silicone brake fluid until it looks like a freshly poured soft drink. Silicone fluid is also slightly more compressible than glycol fluid, does not change color to tip the user to its moisture content, and worst of all, neither accepts or disperses moisture, making systems using it more corrosion prone, and requiring much more frequent fluid changes. Silicone brake fluid also lacks glycol fluid's naturally occuring lubricity, making it incompatible with the mechanical valving in some antilock braking systems.

AxeYrCat

Brake system contamination
The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.) due to the introduction of petroleum based products (motor oil, power steering fluid, mineral oil etc.) A small amount is enough to do major damage. Flushing with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some BMW owners changed to DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. BMW brake systems should be flushed only with DOT 3 or 4.

If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system. Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers.

SpecTTre

two years after I got the car. I have the systm flushed every two years with the same fluid, per the manual and have had no problems. (Knocks on wood.)

OldSchool AG

Not worth the hassle. Lots of DOT4 fluids out there perfectly good for track use.

TTinCT

but remember, if it is not dealer supplied or "authorized", they will always blame something that is not supported.

95k out of a clutch is not bad....personally i would call it BS, but if the part is bad the part is bad....subjective as to how it got that way IMO.

driviniTT

and some pitting could be seen on the plastic parts. So as you say, *something* happened, but what we can't be sure. Of course, non-Audi standard stuff will be the first thing they would blame. Now must get brake pedal feeling right.

driviniTT

since the flush was with DOT4, so that could mean silicone is still in the system, and getting the pedal feel right might take some doing. Maybe just flush a couple of times with DOT4, and go back to the ATE Blue. I'll let me trusted techs decide. Thanks for the input.

J. Patterson

DOT5 brake fluids are silicone based rather than glycol based. Less corrosion, Less moisture absorbancy, But MORE compressable. (softer pedal) I thought ATE blue was a DOT 4 fluid that was dyed to allow a reference poind when bleeding. (Use blue this time, amber next time and so on)
I have always heard not to use silicone for track use or on ABS cars.
Regardless I would expect that your slave cylindar - throw out just failed on it's own. They do that. Your brakes probably just need bleeding properly. Good luck!<ul><li><a href="http://www.dnd-automotive.com/chassis/brake-fluid.htm">http://www.dnd-automotive.com/chassis/brake-fluid.htm</a</li></ul>

J. Patterson

I use ATE 200 amber. Blue is supposed to be the same just dyed.<ul><li><a href="http://www.ate-na.com/generator/www/us/en/ate/ate/themes/20_ate_brake_products/50_brake_fluid/bf_info_us.html">http://www.ate-na.com/generator/www/us/en/ate/ate/themes/20_ate_brake_products/50_brake_fluid/bf_info_us.html</a</li></ul>