[marshallf3]

I've seen it at the cycle shops and through reading have found there are quite a few advantages but some disadvantages to it, for instance if you system isn't really sealed well (or has old hoses & seals) it's more tendent to absorb moisture out of the air thus requires more frequent changing.



It also appears that if you see a DOT 4 that starts out with the word Super or ends with Plus it has the better boiling point features although I'm not sure about the viscosity part.



Some clips:

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In so many words, DOT 5.1 fluids are simply DOT 4-type fluids which meet DOT 5 performance requirements. Because of this, they typically can be mixed with DOT 3 or DOT 4 fluids without concern. In some circles, they are even referred to as ‘DOT 4 Plus’ or ‘Super DOT 4’ fluids because they are more similar to a conventional DOT 4 fluid by chemistry than they are to a conventional DOT 5 fluid. In fact, DOT 5.1 is essentially comprised of Borate Esters.



While it may not be obvious, the big advantage of the DOT 5.1 fluids is that they contain all of the nifty water-absorbing characteristics of the DOT 3 and DOT 4 fluids while simultaneously providing for very high boiling points and relatively stable viscosity over a wide range of temperatures. The best of all worlds, you could say.



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If you are simply topping off or bleeding fluid we recommend DOT 4, which is totally compatible with DOT 5.1. If you are refilling the entire system, call us and we will sell you DOT 5.1.



What's so good about 5.1?



DOT 5.1 has a wet boiling point of 365 degrees. Better yet, DOT 5.1 is half as viscous as DOT 4. This means a system filled with DOT 5.1 provides quicker lever response, better modulation and faster pad retraction When servicing, the lower viscosity facilitates bleeding and pad adjustment. DOT 5.1 also experiences less volume change as a result of temperature shift than DOT 4, allowing more consistent braking through a range of temperature. It may require a little more effort to purchase DOT 5.1, but we feel it is well worth it. In every case make sure any fluid used is labeled 'DOT 3', 'DOT 4', 'DOT 5.1' or 'Compatible with DOT 4'.



MOTUL DOT 5.1 BRAKE FLUID



Long life 100% synthetic fluid for hydraulic actuated-brake and clutch systems



TYPE OF USE



All types of hydraulic actuated-brake and clutch systems in accordance with DOT 5.1, DOT 4 and DOT 3 manufacturers’ recommendations. Fluidity specially designed for anti-locking brake system (ABS).



PERFORMANCE STANDARDS : FMVSS 116 DOT 5.1 NON SILICONE BASE & DOT 4 & DOT 3 (SAE J 1703)



Long life fluid : The high wet boiling point (185°C / 365°F), superior to DOT 4 (155°C / 311°F mini) and DOT 3 (140°C / 284°F mini) fluids enables to use this product longer. Indeed, DOT 3 / DOT 4 and DOT 5.1 brake fluids have the property to absorb humidity contained in the air, which reduces their boiling points and consequently security.



The wet boiling point is representative of the fluid after one year of use.



Specially designed to anti-locking brake systems (ABS) : The viscosity (820 centipoises at -40°C / -40°F) lower than DOT 4 (up to 1800 cp) and DOT 3 (up to 1500 cp) brake fluids, allows an easier fluid circulation in micro-valves of anti-locking systems. Perfectly neutral with seals used in braking systems. Anti-corrosion.



RECOMMENDATIONS



Mixable with DOT 3, DOT 4 and DOT 5.1 NON SILICONE BASE products.

 

[steve in reno]

Marshall

From reading your info it would outwardly appear that this brake fluid would be an improvement.

Increased ease of fluid movement under lower.

The higher boil point indicates that it absorbs an increased amount of humidity from surrounding.

Higher water content in the brake system leads to increased corrosion, and wear to seals.

"Perfectly neutral with seals used in braking systems. Anti-corrosion."

If both of these statements are correct it could be replacing DOT3 & 4.

It may need to be flushed more frequently.

A small trade-off for a better brake system!

my $.02

steve

 

[marshallf3]

One advaatage I can see is for us with the stock MC that has that tiny return hole in it, the far lower viscosity might help the brakes to release faster.



When reading some about it yesterday I also saw some comment that it does a better job at suspending any solids captured instead of letting them settle to the bottom of the system so you can better see when your fluid is dirty by looking in the reservoir.



It's being used on the high-end dirt bikes fas a racing fluid mainly due to its high boiling points however not all of the racing fluids meet the 5.1 specs. Some of them still have a rather low wet boiling point which they claim makes no difference as racers make it a habit of flushing their systems often. They certainly had a fair amount of it in two different container sizes at the dealer.



I'll be replacing my front hose with a braided one soon but don't have a clue how much I'll need for a complete refill, probably not much with the 1979 stock sertup.

 

[Panther]

There are some synthetic dot 3 and dot 4 fluids now that are very comparable to the 5.1 specs.

and they are available at most autoparts stores.

 

[DavidfromWisconsin]

My Honda dealer told me to definitely NOT TO USE DOT 5 on anything older. The older stuff wasn't designed for it and you are only asking for trouble.



He knows the old bikes as he is the original owner of the oldest Honda dealership in Wisconsin. He also knows that I will be all over him if he hands me any BS.



What is really interesting to me ... he asked me one day if I knew how to do a procedure on a GL that wasn't in any of his books ... and I knew the answer. Someone came in wanting him to do an engine in mechanical seal replacement. I told him how, but also that I am person who doesn't recommend it. He just smiled and said that was all he needed to hear and he wouldn't do it for the customer any way but by the book. I know I am lucky to have a good Honda dealer.

 

[marshallf3]

DOT 5 -- NO -- it's a silicone based fluid. Not many have heard of, nor have any knowledge of DOT 5.1



DOT 5.1 is just the next step up from 3 and 4 and they're all compatible. As a matter of fact if you look at some of the high-end motocross and other bikes from other manufacturers you may see the reservoir labeled as DOT 5.1 ONLY. Your mechanic will eventually be exposed to it over time.



Nobody can figure out why they didn't call it DOT 6 or 4.1 or something but it turns out it's because the boiling points are in the same range as the oddball DOT 5 silicone based fluid.



While there are superior DOT 4 products out there (as I've noted in the first post) they still don't have all the qualities that true DOT 5.1 have.



Interesting though, the true DOT 5 turned out to be a flop. Being silicone based, if any water got into the system it obviously wouldn't mix in and went straight to the bottom of the system which in most cases is the calipers. Heat from braking would cause these water "globules" to turn into steam at 212*F and cause all sorts of problems.



Although originally developed with military aircraft in mind (and their help) the military officially dropped DOT 5 as recommended not long ago.

 

[Billrod]

I read somewhere that silicone based brake fluids are difficult to get air out of and when the fluid gets hot the air expands and causes brakes to drag - especially in racing applications. I'm not sure if that is true.

 

[marshallf3]

I read somewhere that silicone based brake fluids are difficult to get air out of and when the fluid gets hot the air expands and causes brakes to drag - especially in racing applications. I'm not sure if that is true.

I REPEAT: DOT 5.1 IS NOT silicone based, it's just a step up from DOT 4 in boiling points that also comes with the advantage of reduced viscocity.



You don't want to use the actual DOT 5 (without the .1 after it) in anything uless it's specifically designed for it. It turned out to cause more problems than it ever solved



DOT 5.1 you can use as it's compatible with 3 and 4.