I know that in the past couple of years, HD has gone from calling for DOT-5 fluid, (in my 2004),to calling for DOT-4 fluid in the newer models. Does anyone know the reason for this? Have the hydrolic components been changed? I know the 2 types of fluid should not be mixed but if I flush the system on my 04, can I use DOT-4?

 

I have no clue the difference. Hell, I didn't even know there was different kinds of brake fluid until I bought my sporty. But my 06 883 manual stills calls for DOT-5.

 

DOT 5 is silicon. DO NOT put DOT 4 in a system designed for DOT 5. A big plus is that DOT 5 will not harm your paint if accidently spilled. DOT 4 will. Using a fluid not recommended could (will) eat seals, hosesand other vital components. It's a matter of boiling point, the propensity to collect moisture, compressabilityand probably some other properties that instigated the change. Years ago (pre 2000 I think), DOT 4 was standard in Harley brakes. Unless you change your entire brake system, let it be.

 

Yea, it's really not a big deal, but having a can of DOT-4 for the cages and a can of DOT-5 for the bike makes me double & triple check the cans before I use it. I know sure as he!!, one of these days I'm going to have a brain fart and pick up the wrong can. [:@]

 

I do understand the differences, but why then did HD go back to DOT-4 on the current year bikes?

 

I asked the same question about the difference between the two at a dealer. I got a very technical, detailed answer. Here's similar information from a quick web search...(see below). Here's the highlights:
[ul][*]DOT 3, 4, and 5.1 are glycol based[*]DOT 5 is silicone based[*]You can't mix DOT 5 with 3, 4, or 5.1.[*]DOT 3, 4, 5.1 fluids are "hygroscopic"....They absorb moisture from the air. That's what causes the fluid to turn dark over time, letting you know its time to change[*]DOT 5 won't damage paint, the others will.[*]DOT 5 is more compressible (2x compared to DOT 3, 4, 5.1). This leads to spongy feel.[*]DOT 3, 4, 5.1 are less compressible. This leads to more feel when braking.[/ul]
The one question I never got sucessfully answered was why they were/are using different brake fluids for different models. I think up until a few years ago, the big twins were DOT 5. My 06 and 07's Softails are both DOT 4. Yest my 06 Sportys were DOT 5.

WEB info:

The two most common brake fluids used in the automotive industry are fluids that contain Polyalkylene Glycol Ether and fluid that contains Silicone or Silicium-based Polymer. Both Fluids are common but very different in regards to the manner in which they perform. Fluids containing Polyalklene Glycol Ether are more widely used and are the only fluids that should be used in racing brake systems. Because brake systems may reach extreme temperatures brake fluid must have the ability to withstand these temperatures and not degrade rapidly. SILICONE BASED FLUID
Fluids containing Silicone are generally used in military type vehicles and because Silicone based fluids will not damage painted surfaces they are also somewhat common in show cars. Silicone-based fluids are regarded as DOT 5 fluids. They are highly compressible and can give the driver a feeling of a spongy pedal. The higher the brake system temperature the more the compressibility of the fluid and this increases the feeling of a spongy pedal. Silicone based fluids are non-hydroscopic meaning that they will not absorb or mix with water. When water is present in the brake system it will create a water/fluid/water/fluid situation. Because water boils at approximately 212º F, the ability of the brake system to operate correctly decreases, and the steam created from boiling water adds air to the system. It is important to remember that water may be present in any brake system. Therefore silicone brake fluid lacks the ability to deal with moisture and will dramatically decrease a brake systems performance. POLYGLYCOL ETHER BASED FLUIDS
Fluids containing Poly glycol ethers are regarded as DOT 3, 4, and DOT 5.1. These type fluids are hydroscopic meaning they have an ability to mix with water and still perform adequately. However, water will drastically reduce the boiling point of fluid. In a passenger car this is not an issue. In a racecar it is a major issue because as the boiling point decreases the performance ability of the fluid also decreases. Poly glycol type fluids are 2 times less compressible than silicone type fluids, even when heated. Less compressibility of brake fluid will increase pedal feel. Changing fluid on a regular basis will greatly increase the performance of the brake system. [font="helvetica, arial"][size="2"]FLUID SPECIFICATIONS All brake fluids must meet federal standard #116. Und

 

Why do they still use push rods? How come no one has seen a Softail Rocker in person? Why did the Twin Cam come back after more than 50 years? Why do they bother putting a fuel gauge on big twins? Why do they make an 883 withessentially the same components as a 1200 except pistons, cylinders and heads? What the heck were they smokin' when they put fly-by-wire throttles on '08 dressers? Who the heck needs/wants an ambient airtemp. gauge in the fairing? And what's the deal with chrome derby covers on the Nightster? Shouldn't all Harley-Davidsons come with a warning label "Will increase credit card debt"? Can't they make the negitive battery terminal easier to get to? How come they act like every five years is a milestone? Why don't I have more than two Harleys? Why did the chicken...

 

I put a masking tape label on the DOT-5...Harley Only. It's also a different color that the DOT-4. DOT-5 is purple. I wish they would stick to a standard for fluids, nut and bolts, etc., but...

 

No the braking components did not change. In theory, you can switch from dot-5 to dot-4, but YOU MUST FLUSH THE SYSTEM COMPLETELY. If you do not, then you will have to rebuild your brakes. In practice, dot-5 is some tenacious stuff and it's very very difficult to flush it completely. Really, it's not worth changing it.

As for why the change? I can't tell you for sure, but it may be that they started to offer ABS and for consistency changed all the brake fluid to Dot 4. Dot 5 does not work with ABS.

As for differences:

Dot5:
Synthetic
Does not attract water
Will not ruin paint when spilled.
Higher boiling point than dot 4

Dot 4:
Mineral
Attracks water
Time to call your painter when you spill it on the paint
Lower boiling point than dot 5

People get in all sorts of arguments saying that Dot 4 makes your brakes feel better and that's why they use it, but I have test ridden both bikes and I can't really tell any difference. Either way, using braided steel lines with Dot 5 brake fluid should resolve most if not all the feel issues (I'm sure somebody will disagree). I'm sure people will debate which is better (it's kind of like arguing about oil). Honestly, I would just stick with Dot 5. There are were two people that used to use Dot 5. The US Military and Harley-Davidson.

By the way, Dot 5.1 is different from Dot 5. Basically it's a Dot 3/4 brake fluid with a higher boiling point and does not mix with Dot 5.

 

I can atell ya that dot 5 cost about twice as much!... Just changed my brake pads and had to buy a bottle of dot 5!.. It's purple in color and doesn't feel as slick and oiley as dot 4. Easier clean up also..