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DOT 5.1 vs DOT 5 Brake Fluid Question

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DOT 5.1 vs DOT 5 Brake Fluid Question

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flag fritolowrider
O+
Posted: Sep 26, 2012 at 7:20 Quote
I want to bleed my brakes in my Avid Elixir carbons. They take DOT 5.1, but the Avid DOT 5.1 fluid is 3 times as much as car DOT 5 brake fluid. From what I see they are both silicone based, so there shouldn't be any corrosion given the different weights. I'm assuming the only difference between the DOT 5 and the DOT 5.1 is that they are slightly different weights. I was just curious to see if this is like suspension fluid were it is far cheaper to buy motorcycle suspension fluid than to buy fox fluid.

My questions are:
1. Is it safe to use the DOT 5 in my brakes?

2. Is there going to be any noticeable difference in the performance of the brakes?

Thanks!
flag forkbrayker
O+ FL
Posted: Sep 26, 2012 at 9:45 Quote
dude dont use dot 5.

dot 5 is silicone based and dot 5.1 is glycol based and mixing the 2 will fubar your seals. if you want to save money buy dot 4 or even dot 3 oil as they are all glycol based and can mix with dot 5.1.

regarding differences i am not sure about viscosities but i would imagine they are all much the same as they have to pass through standard size pipes and holes. the real difference is in boiling point temperature.

dot 3 = 401 f

dot 4 = 446 f

dot 5.1= 518 f

if its for xc stuff you will probably be fine with dot 3 but here in britain its not readily available might be the same in US. dot 4 is perfectly fine have used it many times and of course 5.1 is the best for coping with heat.

dot 5 doesnt damage paint but dot 3,4 and 5.1 all do so mind and protect/clean up very quickly.

you definitley do not need to get fancy brand name dot 5.1 oil , its a standard that has to be met by the department of transport (DOT) to sell under 3,4 or 5.1, so just get cheaper automotive brands its the same shit.

just remember NOT DOT 5
flag fritolowrider
O+
Posted: Sep 26, 2012 at 11:42 Quote
Thanks!

I got confused by other posts saying that the DOT 3 and 4 cause corrosion in the components and that 5.1 is silicone based so you want that as opposed to the other. Also I didn't know you could get DOT 5.1 automotive brake fluid I only saw DOT 3, 4, and 5.

The temperature thing makes sense too. I definitely want the DOT 5.1 temperature handling I hate it when my brakes over heat and my brakes go. Its never fun.

Thanks again for the education! I'll have to keep my eye out for DOT 5.1 automotive fluid then because the Avid stuff seems like a rip off for the similar price I could get triple the amount of generic automotive fluid.
flag forkbrayker
O+ FL
Posted: Sep 27, 2012 at 0:32 Quote
cool, just glad your systems was saved before it got infected with dot 5, LOL. any motor factors (like a bike spares shop but for cars) should have dot5.1 in large amounts. also try motor bike shops

i suppose the issue here is whether to buy a small amount at triple the rate (via an mtb company) or a large amount at much cheapness (through a motor factor )but end up spending more, due to the quantity.


depending on what you have read, rememeber that DOT 3,4,5.1 all absorb water so dont go leaving the lid off of your newly purchased 2 litre bottle, the evil dot 5 is hydrophobic and doesnt absorb water.......... makes you wonder why the bike industry doesn't use dot 5 instead.......hydrophobic, non corrosive, high boiling temperature, cheap
flag junq
Posted: Sep 28, 2015 at 20:50 Quote
okay sorry but dot 5 will not ruin any seals. That is a total myth. I have soaked seals removed from systems in it for months with no effects at all. Not "told this will happen" "heard" did it myself. The silicone fluids do not harm paint either. Only problem I see is the silicone fluids do trap bubbles easy and the more air bubbles the mushier the brakes can get. But if you let the fluid stand for a hour, don't shake it, fill with a steady slow pour. Once in place it works great. it does not mix with glycol based fluid but the two in contact with each other seems to have no effects. put both in a jar and shake. they will quickly separate when you set it down. the glycol based fluid will goto the bottom. That's all. Mixing type 4 with 3 and sometimes with 5.1 can cause real issues. Here seal damage is possible. This is suppose to be fixed now with newer fluids but old 4 does not work with type 3.
flag junq
Posted: Sep 28, 2015 at 20:55 Quote
DOT 5 is silicone based, DOT 5.1 Glycol based. Whether the fluid was packaged for bikes, cars, trucks, motorcycles. Isn't really relevant. The standard is DOT and doesn't say what to make it from just what it has to conform to. Glycol was the cheapest to make that met the standard but it absorbs water, silicone doesn't.
flag junq
Posted: Sep 28, 2015 at 20:58 Quote
Only Harley Davidson has a DOT 5 requirement right now.
flag JWadd
O+
Posted: Jul 30, 2025 at 6:50 Quote
junq wrote:
okay sorry but dot 5 will not ruin any seals. That is a total myth. ...

I'll vouch for that, why would silicone damage seals made for glycol?
I mistakenly bled my rear Guide with DOT 5 in 2017. After realizing my mistake a few months riding later, I said what the hell and completely flushed it out with DOT 5. Nothing of any consequence whatsoever in the past 8 years. The paint is peeling off the front (DOT 5.1) reservoir cap and it's covered in corrosion, the back (DOT 5) looks like new still.

I don't mean to try to use anecdote as fact, but wouldn't lose as much sleep over it as people would suggest.
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