I just purchased a 2005 Deluxe and in the owner's manual and in the service manual it says I am supposed to use Dot 5 brake fluid. However, on the master cylinder for the front brake it says Dot 4 fluid only. Is it possible that the cover on that front master cylinder is wrong? I don't know how it would have got there-maybe at some point when it was getting serviced the guys at the shop put the wrong master cylinder lid back on. Anyway, should I use Dot 5 for both master cylinders? Is there a way to tell if Dot 4 is actually in the one cylinder housing-different color, etc.? Thanks in advance for any info.

 

No way to tell visually... I would go with what the master cylinder cap says. Do NOT mix Dot 4 / Dot 5 as they are not compatable! If unsure you can use (either) fluid after (completly) draining the system. Dot 5 is a fully synthetic fluid with a much higher boiling point. Tripple check with your dealer to see what they recomend.

 

I spoke with them today and they said no way should there be Dot 4 in there and they have no idea why the lid says Dot 4 on it.

 

Dot 5 is usually purple but can change over time. Dot 5 is a silicone base and Dot 3,4 and 5.5 are a glycol base. They do not mix. You can test what you have in it by mixing it with fresh fluid, if it mixes it is the same. If it doesn't and it will be pretty obvious they do not match. Dot 3,4 and 5.5 mix unless otherwise stated on the label.

Later

 

Hmmm...
My 08 FLSTSB master cylinder cap says to use Dot 4. If you are unsure your best bet is to drain the system...$15 @ your local auto parts store will buy you a 12oz bottle which is more than enough to flush the old fluid out.
Ultimatly, Dot 5 is better so if you ever have your brake system down then that would be a good time to change fluid...

 

That was what I was planning on doing most likely. Everything is fine at the moment, but I know eventually I will need to add fluid, so at that time I will just drain the system and use Dot 5 I suppose.

 

Use Dot 5 fluid, if it says to use it in the manual. The owner probably just threw a dot 4 cover on it. No one would convert from dot 5 to dot 4 (a notorious paint remover).

 

If you switch to dot 5 from dot 4, you have to rebuild your master cylinder and calipers as well as replace brake lines. Dot 4 and Dot 5 do not mix, your o rings will turn to jelly causing brake failure.

 

mine is the same way, books says one thing lid said another. when I changed fluid I flushed and filled with DOT 5. I wanted DOT 5 for the same reason stated above about DOT 4 eating paint. You don't need to rebuild anything just completely flush the system fill and bleed. If you had ABS brakes you would need DOT 4.

 

Don't need to rebuild anything? Have you ever seen a brake system when dot 4 and 5 is mixed?