Brake fluid... DOT 5 vs DOT 4

Brake fluid... DOT 5 vs DOT 4

Postby Rabbit Farmer » Sat Oct 30, 2010 11:11 am

Scirocco has DOT 5 (silicon) as opposed to DOT 4 (Glycol). It does not run a brake booster.

Any reason I cannot run DOT 4 instead of DOT 5 in the car?

Any special steps to follow to flush out the DOT 5 and use DOT 4?

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Re: Brake fluid... DOT 5 vs DOT 4

Postby BugEyeRex » Sat Oct 30, 2010 12:40 pm

I have read that DOT 5 use after DOT 4 can gum up the lines and calipers. I have seen flushing instructions with various solutions to convert from DOT 4 to DOT 5 with stories of issues, but not the other way around. I believe it would be almost impossible to remove all of the silicone from the lines and calipers.
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Re: Brake fluid... DOT 5 vs DOT 4

Postby walterclark » Sat Oct 30, 2010 3:44 pm

Is this a VW brake system? If so it was originally DOT4 so unless something like a seal was changed for DOT5 the system is DOT4 compatible.

DOT5 has a bad habit of not being hydroscopic which means water will collect in the system. DOT5 is also slightly lighter than water (specific gravity around .95) so any water will accumulate in low points like lines and wheel cylinders instead of being suspended in the fluid. I would take things apart to be sure corrosion isnt a problem and while it is apart flush it with brake cleaner. That would take care of the problem encountered when DOT4 and 5 are mixed (sludgy mess) as well as ensuring no standing water or rust are in the system.
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Re: Brake fluid... DOT 5 vs DOT 4

Postby Rabbit Farmer » Sat Oct 30, 2010 10:12 pm

I have also read that DOT 4 + DOT 5 = sludge

Walter.... brake cleaner... as in the spray can? Clean the brake lines with that? (I would hope it comes in a big can to flush it all out)
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Re: Brake fluid... DOT 5 vs DOT 4

Postby walterclark » Sun Oct 31, 2010 7:35 am

The only brake parts cleaner I have seen is in a spray can. I usually buy it by the case and get the large 19 oz CRC Brakleen aerosol cans since it is so handy for lots of things. I have seen it for around $2 per can online.
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Re: Brake fluid... DOT 5 vs DOT 4

Postby Rabbit Farmer » Sun Oct 31, 2010 12:42 pm

Thanks for the input. Forgot to answer your first question... yes, Volkswagen system. I think Bill put in the antique fluid (if you will) because that is prob what he ran on the original Tub.
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Re: Brake fluid... DOT 5 vs DOT 4

Postby sdwarf36 » Sun Oct 31, 2010 4:28 pm

You young kids + your fancy hydraulic brakes--the tub had CABLE brakes! :o
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Re: Brake fluid... DOT 5 vs DOT 4

Postby STI NICK » Sun Oct 31, 2010 8:49 pm

Rabbit Farmer wrote:I have also read that DOT 4 + DOT 5 = sludge

Walter.... brake cleaner... as in the spray can? Clean the brake lines with that? (I would hope it comes in a big can to flush it all out)


it does come in large containers. (5 Gallons) I know Joey has a 5 gallon thing of it, Twisted Wrench does as well. Might be able to purchase a gallon or so from one of those places.
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Re: Brake fluid... DOT 5 vs DOT 4

Postby Rabbit Farmer » Sun Oct 31, 2010 9:23 pm

Thanks Nick. I'll get with Charlie or Joey to see what they have.
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Re: Brake fluid... DOT 5 vs DOT 4

Postby jkale » Mon Nov 01, 2010 1:04 pm

You can buy brake clean in 5gal jugs from Autozone.
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