i have a yamaha scooter that calls for dot4. when i look at the auto zone web page and search for dot4 it shows brake fluid that says dot3 dot4 on the can. are they the same?

 

1, no really, 4's better than 3. Cans marked DOT3/DOT4 can be mixed. Go with what's recommended in your manual. Use the search, there's alot of info there.

 

The DOT number i believe refers to the boiling point of the break fluid. If something is DOT 4 then it can also be used in a DOT 3 system, putting both DOT 3 and DOT 4 on the bottle makes it more marketble thats my guess. I wouldnt have a problem using the autozone stuff that says DOT3/DOT4 but thats just me.
My rear master cylinder on my Harley blew a seal and start pissing break fluid everywhere one day when i was out on a ride leaving me with no rear brake. all the gas station had was DOT3 (bike calls for DOT5 synthetic brake fluid) having no real other option i put in the DOT3, enjoyed the rest of the days ride and made it home safe without any issues until i was able to fix the seal and swap the fluid out.

hope this helps

 

If you put dot3 in a dot5 system your seals will swell and brakes will lock up. Did that on my 80' Sportster.

 

DOT3 is an earlier spec, replaced over time by DOT4, however as already stated, they are compatible, so can be mixed. Use DOT4 for preference, but if what you can easily get has both on the label, that will be fine.

 

Oh ****, i hope that doesnt happen to me. I mean after i got home i replaced it with DOT5 and then after bleeding the system i imagine most if not all of the DOT3 would have been pushed out.

 

Do not use DOT 5 in a DOT3 or DOT4 system, use the correct fluid. If you have the original master cylinder covers it will tell you on them.

DOT 5 is not compatible with any other type of fluid. If you have used DOT5, but your system should use DOT 3 or 4, I really recommend you strip and clean before using the correct stuff. At the very least flush out using a suitable brake flushing agent.