Brake Fluid Question

[Alan Schlosser]

Ok, just one more time....... I'm going to flush my system over the winter. I bought a vacuum pump to basically flush the system by adding to the master cylinders until it runs clean. So the question is, my bike says DOT 3,4. Should I stay with DOT4 as I've read that DOT 5 fluid is silicone based and they say it requires seal replacement and is not compatible with glycol based fluids.
Your thoughts would be appreciated. Thanks!

[Nessism]

Use either DOT 3 or 4, 4 boils at a slightly higher temp so it's a good choice. DOT 5 is not compatable with regular brake fluid so I'd steer clear.

[OldVet66]

DOT 3 and DOT 4 are compatible. Only use DOT 5 after a complete rebuild and new brake lines, so there are completely virgin surfaces, so no contamination can take place. I did it on my '78 and it works great.

[Steve]

You should have no problem with either DOT 3 or DOT 4. The main difference between the two is the boiling point.

Unless you are going to be using your bike for racing, your brakes should not be experiencing the temperatures that would require DOT 4, but it's just a little bit of insurance.

You are right, DOT 5 is a whole 'nother animal and is not compatible.

However, there is a DOT 5.1 that is compatible, but rather hard to find.
No idea why they didn't just call it DOT 6 to avoid confusion, but they didn't consult me when they named it.

If you can't remember when you last changed your brake fluid, it's probably past time.
Easy way to tell: look at the color.
New fluid is virtually clear.
Fluid that has been there for a while will be about the color of creme soda or ginger ale.
If it looks like root beer , change it NOW.

.
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[twr1776]

Alan, I am using the DOT 4 on mine. Have you cleaned/rebuilt your calipers yet? If not here is what they look like on the inside. BTW this is a one owner caliper and this bike has only spent a few nights outside in its lifetime. Moral of the story I would recommend replacing all the rubber bits and then do a full flush & fill.

[almarconi]

DOT 5.1 is available under the motul name. I purchased mine from kneedraggers.com

I use it in my truck and both bikes. It is compatible with dot 3 and dot 4. If you can't find the 5.1 then the dot 4 will work fine for the bike.

Like any other fluid in the bike the important thing is that you change it.

[Grandpa]

Being the cheap SOB that I am, and will continue to be, I use the house brand (such as Walmart) of DoT 3. I used DoT 4 once, maybe 20 years ago, and it made no difference at all, so why spend the extra cents? Makes no sense to me.

I do change the brake fluid once a year, front and rear.

Same on the Venture, which has linked rear/left front brakes -- DoT 3 exclusively. It works just fine.

Cheapskate Nick Diaz
Middletown, MD

[salty_monk]

A point of interest... the higher up the scale you go of DOT 3, 4, 5.1 the more Hydroscopic they become.
This means that it absorbs water more readily so in turn you should change it more frequently.

Dot 5 is silicon based. It is designed not to take on water & was developed by the US army for use in vehicles that were standing for long periods but needed to remain battle ready. It also is supposed to inhibit corrosion & in not flammable.
Some people say that water can still get in & forms in pockets causing more damage.

From my own experience in old cars I wouls sat Dot 5 is a bugger to bleed & gives ou a spongey pedal feel, prob not good on a bike... spongy lever. Also you really need to start off with all fresg seals and pipes as there is a chance the seals could swell if Dot 3,4,5.1 meets Dot 5 anywhere in the system causing brake lockup. Also not good on a bike.

Funny - in the UK Dot 5.1 is very common & Dot 5 is very hard to get. Dot 3 is almost obsolete there now so it's hard to get as well. Everyone uses 4 for general use.

I have used Dot 4 even on the race track in cars with no issues and put it in the bikes.

[OldVet66]

I couldn't answer for old cars and the spongy petal, but I can say that on my rebuilt brake system on my '78 GS1000E there is absolutely no spongy feeling to the brakes at all with DOT 5, EBC pads in front and slightly more aggressive Ferodo pads in the rear, Russel street legal SS lines all around. They are very easy to bleed.

[bwringer]

Your enemy on bike brakes is age and corrosion from water absorption, not heat. Motorcycles are too light to generate anywhere near the heat car brakes do.

DOT 3 or 4 (it doesn't make the slightest performance difference which, and as noted above, DOT3 may be best since it's less hygroscopic), and change it EVERY year.