Just received my Speed Bleeders and I am getting set to flush the brakes. I own a 2008 Fatboy which takes DOT 4 fluid. I am aware of the paint-stripping nature of this stuff and will take the appropriate precautions.

Something I did not think of was: which brake fluid should I use? I can go the Amsoil direction with their claimed higher dry and wet boiling points, or I could go with stock DOT 4 which all seem to be the same. What do you suggest?

It is my understanding that all DOT 4 fluid is synthetic? Is this true?

Lastly, several Brands say they are "DOT 3/DOT 4 compatible". In my limited googling, it appears that these are all DOT 4. Valvoline DOT3/4 is a good example.S Hould I stay away from these and only go with a fluid labels DOT 4 only?

Thanks for the input, Chris.

 

Check my research on this, but from what I've read, DOT 5.1 is fully compatible with all DOT 3/4 systems, and its lower viscosity and higher wet/dry boiling points makes it ideally suited for ABS brake modulation and reduced brake fade under hard braking. Just to add to the confusion.......

 

Yeah, that is an understatement. First came DOT 3. Then the chemists developed a newer compatible version with higher boiling points, and they called it DOT 4.

Now DOT 3 & 4 had some issues, most notably with paint, and they created an all new fluid and called it DOT 5. Now DOT 5 is NOT compatible in any way with DOT 3 or DOT 4, so you can't mix them else you will **** everything up.

Lately, a new brake fluid has come on the market, and even better version of DOT 3 and DOT 4. It is fully compatible with DOT 3 and DOT 4 but ABSOLUTELY INCOMPATIBLE with DOT 5. "What should we call it, thought the chemists", yes, they called it DOT 5.1.

 

My 07 caps say's - Dot 4 only...


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Any high quality DOT 4 brake fluid from you local parts store will be fine. It's more important to replace it at least every other year. It absorbs water over time which lowers the boiling point.

I remember the beginning of Hwy 1 in California full of 20MPH corners on my FJ, and the horror I felt as my brake lever went all the way to the grip when the brake fluid turned to a gas ... I changed it every year after that.

 

Is there a chart that show what fluids for what years ? My '97 cap, and manual, say DOT 5 only. Why the back and forth between specs?? Anybody know ?

 

My 05 is DOT 5 also. The switch to DOT 4 has something to do with the ABS systems on the newer scoots. The silicone based DOT 5 fluid is too viscous to work properly with the rapid pulsing of the ABS system.