We just got a partially assembled Mk3 delivered that my buddy Aaron44 and I will be building to completion for him. The previous owner/builder informed us that the brakes are installed and bled and indeed they are. Upon pulling the body this evening we could clearly see the master cylinder...full of purple fluid. Crap! Silicone DOT5! I'm hip to the whole DOT5 deal and want it out of there. I'm also well aware of it's incompatibility with 3, 4 and 5.1 fluid. My question is how to most effectively and fully evacuate it. Can it be done with a very thorough flushing using tons of glycol based fluid or are we looking at a teardown and cleaning of all components?
Has anyone been down this road before that can offer any thoughts or advice?
If you're going to flush with alcohol, don't use the drug store rubbing alcohol. It is typically 30% water. Go to a hardware store and get 100% isopropyl alcohol. Be aware, though, that all alcohol is hygroscopic and there will be water in it - even the stuff labeled 100%. Any residual alcohol left in the system must be cleared. Clean compressed air works well. If you leave any alcohol in the system, it will dramatically lower the boiling point of the new fluid.
Tim
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FFR 7681 Mk 4, IRS, 331 with Quad Weber IDAs. Check out my build site: http://www.timsroadster.com
I have been that route before of flushing DOT 5 from a system and replacing with DOT 4 glycol based brake fluid. Randy and the others are right about the denatured alcohol. It will dilute the DOT 5 and not hurt the seals and other brake components. DON'T use petroleum based solvents to flush it as it will kill the seals.
Open all the bleed screws and blow air through the system to help get the alcohol out. Get some cheap DOT 3 fluid to chase the alcohol out and then put in the good DOT 4 and thoroughly bleed. I would use a pressure bleeder if you have one to install the DOT 4 so it gets some velocity to help eliminate bubbles when you do the final bleed, otherwise do it with the pedal and a friend.
Ron
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Racing: "The world's most efficient way to turn money into noise and smoke"
"Think with your dipstick, Jimmy"
"Anybody can BUY a car, only a chosen few build their own"
FFR Challenge car #4182SP Carbed 302, Holley 600CFM, E303 cam, T5, 3 link rear-3:55, Levy wheels, Kumho tires, Fire Safe fuel cell, Griffin race radiator, ISIS wiring system, MSD 6ALN NASCAR ignition, 85 Mustang distributor,
I misguidedly installed silicone brake fluid in an SCCA EP MGB many years ago and couldn't ever get a firm pedal. Flushed it out with new non-silicone fluid (I can't remember which one) and never had a problem. Bad as it sounds, we could never completely get rid of an oily-looking silicone scum in the master cylinder but the brakes never seemed to notice.Raced the car for several seasons after this without any brake problems.
What is the downside of the DOT5?
I just completed my roadster, and put the purple in early on.
The only thing I notice so far is having to stand on the brakes (as compared to daily driver power brakes).
Will DOT4 improve the braking?
Thanks,
Rich
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Rich Townsend Catlett, VA
FFR 6343
Rich,
Plug "dot5" into the search function and get comfortable with a cold beverage 'cause it will turn up plenty of information
The Reader's Digest version:
---Silicone fluid traps air and in itself is compressable resulting in a soft pedal.
---Unlike glycol based fluids which are hygroscopic, meaning that they mix with the moisture which inevitably enters the system, DOT 5 silicone is not therefore water will remain seperated. Since water is heavier than the silocone fluid it will settle at the lowest point which are the calipers. When the brakes get hot the water becomes steam which is also compressable. The end result of this condition is that the calipers will not recieve fluid pressure for application and you'll have no brakes!
---It does not mix with glycol based fluids so once it has been introduced the system has to be totally evacuated, cleaned and flushed to use conventional DOT 3, 4, etc.
Thanks again to those who have offered advice. Lot's of denatured alcohol followed by lots of conventional fluid it is!
DAMN, SAM!
Is it possible that 5 years ago it was "the thing to do". I would guess that it's been around 4 years ago when I buttoned up the brakes.
Sheesh!
Rich
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Rich Townsend Catlett, VA
FFR 6343
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