Dot 5.1 brake fluid

Ish · 22 Sep 2012 at 22:53

Hi

Is it ok to use Dot 5.1 brake fluid in a motorbike?

The reason i ask is that I garage that I use sometimes refused to bleed my brakes using 5.1 as they said it wasn't suitable for my Thundercat.

I have a feeling they confused it with Dot 5 fluid.

Fireskull · 22 Sep 2012 at 22:57

Not worth going to them again if they dont know the difference...

Perfectly fine to use Dot 5.1, have done so again recently on mine.

Dogbreath · 23 Sep 2012 at 10:49

The main difference between DOT4 and DOT5.1 is the viscosity. 5.1 has about half the viscosity of 4, and was designed for use in ABS systems where there is very rapid fluid motion though small bore brake pipes when ABS activates.

Chemically they are compatible and 5.1 can normally be used where 4 is specified. However, if you have any seals in the system that are past their best, 5.1 will find a way out more easily than 4.

daisycutter · 25 Sep 2012 at 06:20

Ive used 5.1 in my Track bike for 2 seasons, but ill be going back to a good dot4 race fluid next year. So id say no real point in using 5.1, and it definetly needs replacing more frequently than dot4

edd1e · 25 Sep 2012 at 08:17

I've always stuck to the recommended manufacture spec on bikes... which is usually DOT4.

thumperslaw · 25 Sep 2012 at 15:37

I thought 5.1 had a higher boiling point then 4 dot?
This could be wrong and i really could be talking crap here

I've used both and been fine (96 gsxr,98 storm)

Fireskull · 25 Sep 2012 at 18:57

Yes dot 5.1 has I think about 40c higher boiling point compared to 4.

Souleh · 25 Sep 2012 at 19:06

Shouldnt be a problem. If youre racing, use race fluid. If youre still cooking brakes then your pad choice is probably wrong or you need to upgrade calipers/mc.

Just stick to 4 if thats the recommended.

Dogbreath · 25 Sep 2012 at 22:28

Fireskull said:
Yes dot 5.1 has I think about 40c higher boiling point compared to 4.

Depends entirely on the specific fluid; there are plenty of "Super" DOT4 fluids around with higher boiling points than 5.1.

Fireskull · 25 Sep 2012 at 22:35

So it does! Learn something new everyday...

Didn't know there was a super! Seems it takes the boiling point to around 5-10 degrees higher than bog standard 5.1, but lets be honest none of us are really going to see consistent brake fluid temperatures of over 250°c on the road are we...