Should I switch to DOT4/5 brake fluid?

[DimitriT]

I'm going to overhaul my brakes with new piston/cup and a rebuilt master. I'm also going to switch to a new braided line. So it's an opportunity for me to switch brake fluids if I want to. Any reason I should switch from DOT3?

[Nessism]

Go with DOT 4, higher boiling point than 3 and fully compatable with system components. DOT 5 causes problems in some systems and requires a complete flush of the system before use.

Check the link below for more info.

http://www.xs11.com/tips/maintenance/maint1.shtml

[Steve]

DOT 5 will require more than just a complete flush of the system. Because it is so incompatible with 3 or 4, you will probably also need to disassemble master cylinder and brake pistons to dry them out first. Because it is a silicone-based fluid, it does not attract water like DOT 3 or 4, but the hassle of converting is usually not worth it. I have also heard that some components in older systems are just not compatible, either. Not sure what they are, so I just go with DOT 4 every couple of years and call it good.

A good indicator of when to change the fluid is looking at the color. New fluid is virtually clear. As it ages and absorbs water, it starts looking like ginger ale. It should be changed before it looks like root beer.


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[Grandpa]

No. I use DOT 4 and change it every year, both front and rear. Forget about DOT 5.

[bwringer]

But...but... 5 is, um, one better than 4, isnt' it? :roll:

The senseless DOT numbering system on brake fluid is a fine example of government work that makes no sense to anyone and can get people killed through confusion.

If you wanted to come up with a specification scheme that would suck in as many people as possible, you couldn't do much better than making a new, totally incompatible fluid type look like some sort up upgrade from the more common type.

DOT 5 is NOT an upgrade -- they are totally incompatible fluids. NEVER EVER use DOT 5 in a system that originally had DOT4, and vice-versa.

Use a good brand of DOT 4 fluid, flush every year or two, and ride happy.

[madjack57754]

Dot5 is out. even Harley uses Dot4 now. There is a newer version of a semi synthetic called Dot5.5 and it is compatible with both 3 & 4

[Big T]

I'm going to overhaul my brakes with new piston/cup and a rebuilt master. I'm also going to switch to a new braided line. So it's an opportunity for me to switch brake fluids if I want to. Any reason I should switch from DOT3?

Since you are replacing just about everything, flush the caliper body and hose junction with Brakekleen and use the DOT 5

Contrary to the above postings, I switched to DOT 5 over 20 years ago when I upgraded to braided steel lines. I've never had a problem and have only flushed the brakes twice in all that time. The nonwater absorbing issue was my main reason , being here in the rainy NW.

[mixongw]

The only difference between DOT-3 and DOT-4 is the boiling point. DOT-5 uses silicone chemistry and while it solves the water absorbsion problems of 3 & 4, it's totally non compatible. Don't mix 'em.

[salty_monk]

In England we have dot 5.1 & it seems to be what's called 5.5 above, fully compatible & higher boiling point.

Interesting point - 4 takes on moisture quiker than 3 & so up the scale.

5 is silicon. Non flammable, doesn't mess up paint but it's expensive & a bugger to bleed. I used it in a classic car but prob wouldn't use it again. It also gives a spongey pedal in a car so prob a spongey lever on the bike.

The two are completely incompatible, no chance if you aren't replacing all seals & cylinders as well as line. Makes the rubber swell & locks the brakes on in a car....

Also it has been reported that moisture can be trapped in the system as bubbles as it's not absorbed & if that bubble moves to a critical spot suddenly... boom, **** brakes.

It worked ok for me in a car (1967 Morris Minor, drums, no servo) but see above.

Was developed by US military to be used in all the tanks & equipment they had laid up to shorten "service to road" times. Even if laid up for 5 years allagedly with Silicon there is no need to flush.

Moisture in standard fluid lowers the boiling point & rots cylinders.

Dan

[Hap Call]

I used DOT 5 for a while on my 1100 and found no advantage at all. It is more expensive and is a booger to bleed the system (I don't know why). Also, the DOT 5 felt mushier under hard braking.

Hap

[KEITH KRAUSE]

The "new" 5.1 is supposed to be the best glycol based fluid.

[salty_monk]

Dot 5.1 has the higest boling point of the Glycol's but also takes on moisture the quickest meaning you should change it more regularly.
Likewise Dot 4 takes on moisture quicker than 3.

In your position I would just use a quality DOT 4. Don't use anything from an open container. Brake fluid is scrap soon after you break the seal (& some tests from some manufacturers have shown even before you break the seal....)

Dan

[DimitriT]

The procedure I'm using this time, since I have the whole thing apart, is to prime the system with some old DOT3 I have sitting around, to get all the bubbles out, and then flush it out with the new DOT4. I like to use up the whole container as part of the flush out.

BTW, I can't begin to describe the amount of crap in both the master and caliper. Everything from aluminum oxide, rust and even what looked like dried out old fluid. Fortunately there was no pitting and all the crap came off with a light rubbing using fine steel wool and cleaner.

[Boondocks]

Since you are replacing just about everything, flush the caliper body and hose junction with Brakekleen and use the DOT 5

Contrary to the above postings, I switched to DOT 5 over 20 years ago when I upgraded to braided steel lines. I've never had a problem and have only flushed the brakes twice in all that time. The nonwater absorbing issue was my main reason , being here in the rainy NW.

You're very lucky. Silicone based DOT 5 brake fluid has many disadvantages compared to the DOT 3, 4, and 5.1 glycol based fluids. One problem is that it doesn't absorb water. For this reason, it should be changed more frequently than glycol fluid. Contrary to the myth that water absorption is a glycol brake fluid shortcoming, it is exactly for this characteristic that it excels as a brake fluid. Moisture enters all brake systems, either through master cylinders, brake lines, or other parts. The master cylinder has to be vented to atmosphere in order to work. The question is - how to deal with the moisture. If not absorbed, it pools in areas like wheel cylinders and calipers and causes sludge and corrosion.

Glycol based fluids are hygroscopic, i.e., water absorbing. As long as moisture in a brake system is carried in suspension and dispersed in reasonably fresh glycol brake fluid, it will cause no harm.

If silicone fluids are not changed frequently, moisture in the brake system pools. This water can boil and create steam at only 212°, far lower than any glycol fluid. Silicone based brake systems are spongy to begin with due to the fluid's tendency to contain air. Running a silicone system with pooled water at over its boiling point will result in dangerous brake fade. It should never be used for racing or severe brake use. The inability to deal with moisture will seriously degrade braking performance. Silicone fluid also does not have the lubricity of glycol fluids, and will wear out brake parts faster.

I also live in the rainy NW, but would never use silicone based DOT5 in any vehicle.

See Brake Fluid Wears Out
and DOT 5 vs. DOT 3 Brake Fluid
and Understanding Brake Fluid