I got new calipers,master cylinders and brake lines..can I switch to DOT 5 brake fluid now?? all parts are new from HD and the master cylinders are marked for dot 4..but I want to use dot 5, but need to know if it is OK...also what are the benifits of dot 5?

Thanks

 

DOT 5 is not water soluble like DOT 4. Make sure all the old fluid is completely out of the caliper and all as if the two mix it can get messy and the fluid can gum up.

 

Your reasoning could help zero in on the best answer for you.

Why do you want to switch to DOT 5? You say you want to run DOT 5 but then ask what the benefits are over DOT 4. The former implies you have done some research and have reasons for the switch. But the latter implies you don't know why DOT 5 is or might be a good choice. How can you be sure you want DOT 5 if you aren't sure if its better?

Regardless of why you want to switch, you asked the question so here are the main points:

Mechanically, there is no difference in your braking hardware designed for either fluid.

DOT 4 is a polyglycol based fluid (amber color) and DOT 5 is a silicone based fluid (purple).

DOT 4 is hygroscopic (it attracts and absorbs moisture). Ever wonder why your brake fluid changes from amber to brown over time? That's the moisture content in there. DOT 5 is not. DOT 5 and moisture is like oil and water except that water is heavier in this case. So if you end up with water in your DOT 5 system it will settle at the bottom of the system (in the calipers) and heat as the brakes heat and degrade braking performance since water is more compressible than brake fluid. That means you have to compress the water fully before you start pushing pads to rotors. That's oversimplified slightly but you get the general idea.

Because all your parts are new, no need to worry about flushing the system so I won't cover that.

I suppose the biggest advantage DOT 5 has over the polyglycol alternatives (DOT 3, 4, 5.1) is the boiling point being higher. A higher boiling point means it will retain a more uniform compressibility as the fluid heats with hard brake use. This is why you see DOT 5 used in race applications. You get more uniform braking performance over varying brake temps.

DOT 5 is a bit less compressible. That means it takes less lever pressure to translate to stopping. From a rider experience perspective this feels like a little more responsive braking system. This is one of the reasons DOT 5 is generally not suggested for use in ABS systems. The grab can occur before the ABS systems can compensate. The two are at odds. The ABS wants to stop the brakes from grabbing real hard and fast but that's exactly what DOT 5 can give you.

Finally, DOT 5 is said to be less caustic than the alternatives. So spilling some on your paint is not necessarily as bad as with DOT 4.

So the short answer to your question is yes, you can switch to DOT 5 now if you want.

 

Excellent presentation bensonjv !!!

 

I would make the switch to dot 5, just to prevent paint damage. If you don't do all your own work, I would get a cover that says dot 5, to prevent someone from addi g the wrong fluid.

 

bensonjv, excellent post. Just to clarify one point you made though...
DOT 4 is not necessarily amber colored. In my Corvette racing group. many guys alternate between ATE Blue and ATE Gold brake fluid (both DOT 4). When racing, you need to flush and bleed brakes often. Switching between the two colors makes it easy to tell when you've flushed the old stuff out.

 

just be sure if you do use 5 that you let any service person know so they dont add 4 to it.