Brake Fluid, DOT4, DOT5.1

[imdying]

So, in summary:

- DOT 4 or 5.1 for your bike is fine, mixing during the fluid change process is fine too
- DOT 5 is only in some Harleys and tractors (a little ironic)
- The ratings you've read about aren't worth much, the DOT standard is a minimum, and most brands exceed that, some by a large margin
- Castrol and Motul brakes fluids are both of good quality
- How hygroscopic a fluid is isn't particularly important, if you're smart you'll change it every time you register your bike (i.e. every year) and that is sufficient
- It's sufficient to bleed the fluid through till nice clean looking fluid is coming out the hose (i.e. the same colour as you're putting in the top)
- All factory master cylinder reservoirs have a full mark, don't exceed that
- Some systems will make the fluid drastically discolour in days, just change it every year, or after a visit to your favourite track (or a coro loop if you're one of those types)

[Max Preload]

A VERY good all round fluid is Castrol Response Super DOT4.
It's the stuff in the silver bottle. About $14.00 from SuperCheap.
The fluid is clear, and discolours as it goes off.
I don't use anything else

Seconded. Castrol's Super DOT4 is good stuff and has better lever feel than DOT5.1. The worst for lever feel are the silicone based DOT5.

IIRC there is an incompatibility between those three brake fluids, and there is one combination that should be avoided. I don't recall what that combination was though.

Just never mix DOT5 with anything else. The others are backward compatible.

[CookMySock]

Just never mix DOT5 with anything else. The others are backward compatible.

Thanks for clearing that up. So DOT5 can be used in only new-fill or total rebuild + new hoses?

Steve

[imdying]

Yes, total rebuild with new hoses. Soak your seals in the DOT 5 for a day before installing them, just to check they don't swell.