I'm not a fan of DOT 5 fluid.  It never seems to produce a confidence inspiring pedal.  Regular DOT 3 or 4 produces a great pedal and so long as you bleed it through every 2 years I've yet to have a caliper or wheel cylinder on any of my vehicles go bad.

I run silicone fluid in hydraulic clutches and low performance applications. It is nice since it has a lower attraction to moisture. BUT it has a lower bulk modulus so it is more spongy than a good racing fluid. Any car I put on the track gets the Wilwood stuff.  If you have a dual master cylinder set-up that has the two masters beside each other with a balance bar it is especially noticeable and unnerving! Makes it real hard to get the front to rear balance consistent. 

Been using DOT 5 since I redid the engine bay before the 331 install. I did not want any brake fluid damage to the new paint.
 For my kind of driving it has performed very well, doubt if I could make out any difference between it or the corrosive and hygroscopic regular fluid.
 At the time I put in a new master cylinder, line lock and all stinless steel brake lines.

Last edited by Rudi (2/16/2018 10:17 AM)

I can tell you 2 major things to keep an eye on with dot 5 brake fluid. First, although the fluid is not hydroscopic (absorbs water from humidity in air like regular brake fluid), water will pool like air bubbles in the fluid, so it is really important to bleed very well initially and everyv6 mos or so.
Secondly, dot 5 has a bad flaw in that once it reaches its boiling point, it becomes compressible. I found this out in our Shelby clone during a race at Laguna seca....very unnerving in the middle of a turn.
But, for street cars that don't do crazy braking it is fine. My friend uses it in all his old cars that have 2 wheel cylinders per wheel, as it keeps them from braking down, as they are very expensive to rebuild or have sleeved. I do recommend Castro dot 3/4 brake fluid as it has a good boiling point and is lma rated so it is good with different types of rubber/seals. For racing, nothing beats the motul 600, but it costs a fortune.

I have a lot of experience with DOT 5 in my 2005 Harley.  It came from the factory with DOT 5.

DOT 5 will be rock solid just like DOT 3 if it is bled properly.  DOT 5 can hold micro bubbles when it is agitated.  This is why you don't find DOT 5 used in an anti-lock braking system.  This is also why the pedal feel is spongy when you try to bleed it right after filling an empty system.  This happened to me when I changed front calipers on my Harley.  To get back the rock solid brake lever feel, I did a touch up bleed to my front brakes each morning for a few days after the installation.  Over night, the micro bubbles had a chance to migrate to the bleed valve in the caliper and the touch up bleed released these.  Each time the lever became more solid.  After a few days it was rock solid.  I did this work back in 2007.  I still have the bike and still take it on trips.  I've never had any issues with the front brake system.  So if you use DOT 5, remember this procedure if you have trouble with a spongy pedal feel.

Rufus68 wrote:

I have a lot of experience with DOT 5 in my 2005 Harley.  It came from the factory with DOT 5.

DOT 5 will be rock solid just like DOT 3 if it is bled properly.  DOT 5 can hold micro bubbles when it is agitated.  This is why you don't find DOT 5 used in an anti-lock braking system.  This is also why the pedal feel is spongy when you try to bleed it right after filling an empty system.  This happened to me when I changed front calipers on my Harley.  To get back the rock solid brake lever feel, I did a touch up bleed to my front brakes each morning for a few days after the installation.  Over night, the micro bubbles had a chance to migrate to the bleed valve in the caliper and the touch up bleed released these.  Each time the lever became more solid.  After a few days it was rock solid.  I did this work back in 2007.  I still have the bike and still take it on trips.  I've never had any issues with the front brake system.  So if you use DOT 5, remember this procedure if you have trouble with a spongy pedal feel.

I still have a half full bottle of DOT 5 on the shelf from my Dad's old Harley.  He'll be gone 19 years in June.  Its funny, when this discussion first started I thought about that white pint bottle that's been on my shelf for 22 years.