• Required reading for all forum users!!!

    Welcome!
    Register to access the full functionality of the GSResources forum. Until you register and activate your account you will not have full forum access, nor will you be able to post or reply to messages.

    A note to new registrants...
    All new forum registrations must be activated via email before you have full access to the forum.

    A Special Note about Email accounts!
    DO NOT SIGN UP USING hotmail, outlook, gmx, sbcglobal, att, bellsouth or email.com. They delete our forum signup emails.

    A note to old forum members...
    I receive numerous requests from people who can no longer log in because their accounts were deleted. As mentioned in the forum FAQ, user accounts are deleted if you haven't logged in for the past 6 months. If you can't log in, then create a new forum account. If you don't get an error message, then check your email account for an activation message. If you get a message stating that the email address is already in use, then your account still exists so follow the instructions in the forum FAQ for resetting your password.

    Have you forgotten your password or have a new email address? Then read the forum FAQ for details on how to reset it.

    Any email requests for "can't log in anymore" problems or "lost my password" problems will be deleted. Read the forum FAQ and follow the instructions there - that's what we have one for...

  • Returning Visitors

    If you are a returning visitor who never received your confirmation email, then odds are your email provider is blockinig emails from our server. The only thing that can be done to get around this is you will have to try creating another forum account using an email address from another domain.

    If you are a returning visitor to the forum and can't log in using your old forum name and password but used to be able to then chances are your account is deleted. Purges of the databases are done regularly. You will have to create a new forum account and you should be all set.

Should I switch to DOT4/5 brake fluid?

DimitriT

DimitriT

Forum Sage
Past Site Supporter
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?
 
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. :oops:


.
 
No. I use DOT 4 and change it every year, both front and rear. Forget about DOT 5.
 
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.
 
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
 
DimitriT said:
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?
Click to expand...

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.
 
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.
 
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 :)
 
Last edited:
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
 
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 :)
 
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.
 
Big T said:
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.
Click to expand...

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
 
You must log in or register to reply here.
Back
Top