Brake fluids..Dot 5, & Dot 5.1

[DragonRider]

Thought this might be of interest to everyone here...........I found it very helpful.

 

DOT 5 Brake Fluids

After paying a small mint for the paint job on my restored Norton, I started considering ways

to preserve and protect it. Chief among my concerns was brake fluid. I had once spilled

regular brake fluid on my toolbox, and a week later it was sporting a huge corroded area with

blistered paint. So after hearing about DOT 5 Silicone brake fluid I investigated. If you have

similar concerns, DOT 5 Silicone might be of interest to you as well.

Silicone based DOT 5 brake fluid was originally developed for racing, but has several

attractive qualities for use on classic bikes with hydraulic brake systems. These are:

• DOT 5 Silicone does not attract water. Lack of moisture absorption minimizes corrosion of

internal components for better sealing, longer component life, and less maintenance. On the

other hand, regular brake fluids are hygroscopic, and readily absorb water from the air and

other sources. Therefore, motorcycle brake systems using DOT 3 and 4 ought to have their

fluids changed regularly to prevent problems. The maximum life of DOT 3 or 4 is 5 years.

• DOT 5 Silicone will not affect plastic or painted surfaces, and is non-toxic, non-corrosive

and nonirritating. With glycol based brake fluids, like DOT 3, DOT 4 and DOT 5.1, care

must be used to thoroughly wash it thoroughly from skin and all painted surfaces.

• DOT 5 Silicone offers superior lubrication of master cylinder and caliper pistons preventing

abrasion between the sealing cups and pistons that can take place under racing conditions. In

street use, this could result in nearly zero component wear.

• DOT 5 Silicone has a very high boiling point that eliminates brake fade. Although it is no

longer the preferred brake fluid for racing, it is more than adequate for street use.

Things You Should Know

As with any product there are several trade-offs to consider before rushing out and

converting every vehicle you own:

Silicone fluids are not miscible with water. It’s the classic oil and vinegar scenario. DOT 5

Silicone, being less dense, tends to float on water. Therefore, if water ever entered the system

it would collect at the lowest point, meaning the bottom of the caliper. Water in the bottom of

the caliper could be hard to get out without removing the caliper and rotating the caliper to

place the bleed nipple at the lowest point.

 

While it’s permissible to mix DOT 3, DOT 4 and DOT 5.1 brake fluids, DOT 5 Silicone fluid

cannot be mixed with any other type. If the system is not completely purged before

conversion, the mixture may gel and result in very poor braking. Therefore conversion

usually requires disassembly and a thorough cleaning, or at least numerous bleeding sessions

over several days. Obviously then, the best time to consider conversion to DOT 5 is before

rebuilding the master cylinder or caliper.

Copyright RF Whatley, Suwanee, GA 2 Written June 04, Revised June 08

 

Because DOT 5 Silicone cannot be mixed with any other brake fluid it has been given a

special purple color. Any owner or mechanic seeing the special purple color should instantly

recognize that the fluid in the reservoir is not normal brake fluid.

There are actually two types of DOT 5 fluids. There is a SBBF (Silicone Based Brake Fluid)

and a DOT 5.1 NSBF (Non-Silicone Based Fluid). For several years DOT 5.1 was not

available to the general public and there was a very low chance of getting the two confused

with each other. However, the latest generation of motorcycles is now using DOT 5.1 and it

is becoming more commonplace. Be aware that DOT 5.1 has the same base chemistry as

DOT 3 and DOT 4 and therefore does NOT offer the advantages of DOT 5 Silicone.

Another point of confusion is that most people assume that since DOT 5.1 has a higher

number it must therefore be better. This is simply not true. DOT 5.1 was formulated for use

in ABS systems that require a less viscous fluid. From the information I was able to gather it

seems that most road racers are now relying on the latest generation of DOT 4 brake fluid,

along with regular fluid replacement, for the ultimate in hydraulic brake system performance.

So we may conclude that DOT 5.1 is not an improvement, but a modification for ABS use.

DOT 5 Silicone brake fluids are not generally available in Europe. If your Italian or German

motorcycle brake reservoir is marked “Use DOT 5” they are generally talking about DOT

5.1, which is not a silicone brake fluid. They do this because your bike is probably equipped

with ABS and DOT 5.1 is the preferred brake fluid for ABS systems.

The easiest source for DOT 5 Silicone brake fluid in the USA is your nearest Harley-

Davidson shop. DOT 5 Silicone is specified as the brake fluid of choice for use in all HDs.

And of course when working with any brake fluid, proper personal protection should be

worn, don’t mix brake fluids from different containers, and be sure and follow the safety

precautions on the label.

 

Summation

 

Although your bike shop may try to talk you out of buying DOT 5 Silicone, realize that this

is because new bikes on their showroom probably specify something else. However, you

should buy and use the brake fluid that is best for YOUR motorcycle. If effective braking,

low maintenance and protecting your paint job are your priorities then DOT 5 Silicone

should be considered.

 

Thanks to Bel-Ray Lubricants for supplying the technical information used in this article.

More information is available on their web site at http://www.belray.com/

Richard Whatley

Rodi British Bikes

[SilvrT]

Very interesting...thanks for posting that.

 

One thing that is apparently confusing and one wonders why they did it that way .... if DOT 3 and DOT 4 are non-silicone ... then why would they not make DOT 5 non-silicone and DOT 5.1 silicone. It would surely avoid that confusion of "Use DOT 5 fluid only" on ABS systems (really meaning 5.1)

 

I did read that right, didn't I ?

[Guest seuadr]

couple silicone caveats, though.

it does aerate VERY easily and thus can be VERY hard to bleed, and some seals are intolerant of 5 which can cause premature failure.

[KiteSquid]

I use synthetic DOT 4 in all my vehicles.

 

None of them call for DOT 5.

 

I dont like DOT 5 as it is not miscable, so you have to change it often, probally twice a year if you live in a humid climate......

 

I change my brake fluid every one or two years.

Edited May 28, 2010 by KiteSquid

[Tartan Terror]

Finally you guys are listening. I have had Dot 5 in my RSV For 3 years already. Also in my Honda before that. It works great. Only thing you need to remember is that you cant mix so you must flush completely. I actually wrote about this and battled with a few others here over the years about this too.

[1BigDog]

The improvement with 5.1 is its higher boiling point, otherwise its just about the same as any other DOT fluid. 3 has a low boiling point, 4 has a higher point and 5.1 has an even higher boiling point. I chose Motul 5.1 when I replaced my front calipers and rebuilt my rear caliper along with adding SS lines all around. Clutch was flushed with 5.1 too. ON really hot days it seemed to cause harder shifting, especially when sitting in traffic. Seems to be better with the 5.1 but im also sure that the addition of the SS lines helped that along as well.