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[Texas 103]

Getting ready to install both  Chrome front  and rear calipers on both my '02 SERK and my '00 Triple  Red. Any reason not to go to Dot 5??? Not real wild about what Dot 4 does to paint. Feedback would be appreciated.... Thanks Greg

I ASSumed  because my '06 says Dot 4 only that both  both of these bikes used Dot 4 >> They Don't ....clearly marked on top of the M.C Cover it says Dot 5 only....When did they go back to Dot 4 in '05 or "06???  Guess....That's what I get for ASSuming>>>>Thanks Greg

[Chief]

Getting ready to install both  Chrome front  and rear calipers on both my '02 SERK and my '00 Triple  Red. Any reason not to go to Dot 5??? Not real wild about what Dot 4 does to paint. Feedback would be appreciated.... Thanks Greg

For me, the safety DOT 5 gives you for paint and powder coat and its lack of moisture absorbtion outweighs its drawbacks.

I successfully used DOT 5 for the whole time I had my FLHTC and loved it. I'll probably switch back to DOT 5 on this bike.

[hogasm]

Each time I have switched a bike from 4 to 5, I have rebuilt the master cylinder and calipers. Never had it happen, but was told that the o rings would disintegrate after switching. Did not want to take a chance....after going that far, what is another hour of labor.

[Twolanerider]

Greg, there are lots of rumors and stories similar to what Brian is concerned about.  Truth is the parts generally don't care.  In fact the only difference between a chrome HD master cylinder kit for 04 and prior models and 05 and newer is the reservoir lid with its different fluid message.

The DOT5 silicone based stuff is safer around paint.  Good synthetic DOT4s aren't too bad either actually.  At least if you don't just let the stuff set for a long time.

DOT5 fluid isn't hygroscopic.  It won't carry moisture in the fluid like DOT3 or 4 will.  So the break system won't rot from the inside out if you're using DOT5.  Or at least not as quickly.  Of course if you flush the fluid every couple of years like we're supposed to that's not much of a problem for the DOT3 or 4 either.

The kicker for me is you have to be so damned delicate working with DOT5.  Handle the bottle a bit too roughly or turn it over too quickly while pouring and it will entrain air in the liquid.  That is air that can't be bled out of the system because it is literally suspended in the liquid.  When that happens the stuff is a total pain in the ass to bleed.  In fact the only thing you can do sometimes is just let it set.  On old cars or bikes I've bled them in a normal amount of time.  Or I've taken an entire weekend to get the job finally done. 

That effect of agitation on the fluid causing it to entrain air is why DOT5 can't be used on anything with ABS.  The pump shakes the stuff up and you get a hydraulic system full of air.  Harley's change from DOT5 to DOT4 at least coincided with their then greater ABS efforts toward cop bikes.  Rather than mixed messages within the fleet they seemed to have foretold the writing on the wall and went to DOT4 for everything.

The other benefit to DOT5 is a higher boiling point.  Again, however, not that much greater than a good synthetic DOT4.

I personally don't mess with the DOT5 stuff anymore.  When it's not a hassle it's great.  When it is a hassle it is a MAJOR hassle though.  When I just rebuilt or replaced all the hydraulics on the SERG I went back in with a synthetic DOT4 in it.  Front and back all bled out in no time .

[DavidB]

 
That effect of agitation on the fluid causing it to entrain air is why DOT5 can't be used on anything with ABS.  .

This is very important. Like Twolane says . Dot five in an abs wont let it work when you need it.

Entrained air will also turn into big bubbles with altitude and make the brakes go soft. Very soft and spongy.
Pikes Peak taught me that lesson.

[ultrafxr]

This is very important. Like Twolane says . Dot five in an abs wont let it work when you need it.

Entrained air will also turn into big bubbles with altitude and make the brakes go soft. Very soft and spongy.
Pikes Peak taught me that lesson.

Amen.  Had problems with rear brake on my '99 ultra when riding in the mountains the entire 7 years I owned it.  No dealer was ever successful in bleeding it properly.  Only after I got on this web site did I fully understand the problems when using DOT 5.  I'm with twolane - too much hassle.

[blowncobra]

from dot 4 to 5 ok
from 5 to 4 asking for trouble
air entrapment typical on 5 vacuum bleed the system via the bleeder will be OK then
synthetic dot4 is a good choice for sure