2slowwheels
Member
I couldn't find anything in the search so I'll ask. My 77 RS manual says DOT 4 brake fluid but the sticker on the frame says DOT 3. Is there any difference and can I use the new synthetic DOT 3/4 stuff? Thanks
-
Welcome, Guest! We hope you enjoy the excellent technical knowledge, event information and discussions that the BMW MOA forum provides. Some forum content will be hidden from you if you remain logged out. If you want to view all content, please click the 'Log in' button above and enter your BMW MOA username and password. If you are not an MOA member, why not take the time to join the club, so you can enjoy posting on the forum, the BMW Owners News magazine, and all of the discounts and benefits the BMW MOA offers?
Brake fluid
- Thread starter 2slowwheels
- Start date
-
- Tags
- brake fluid
DOT 4 is just a better version of 3. OK to use! 
Recent discussion on brakes here:
https://forums.bmwmoa.org/showthrea...-intermittent-brakes-and-other-strange-issues
Recent discussion on brakes here:
https://forums.bmwmoa.org/showthrea...-intermittent-brakes-and-other-strange-issues
2slowwheels
Member
thanks
PGlaves
#13338
All brake fluid is synthetic. Putting that term on the label is just marketing hype to make people think it is better and worth more money. I thus avoid brands that try to dupe people this way because I consider it inherently dishonest. I choose not to reward this kind of chicanery. Your choice of course.
2slowwheels
Member
good info, I agree
alancoles
Dress for fall & avoid it
My thinking is that BMW were in the process of changing their spec from DOT-3 to DOT-4 and that lead to the conflicting specs, however, they still have conflicting specs showing up in their newer manuals so, who knows. ;-)
Anyway, as Paul mentioned both DOT-3 and DOT-4 are synthetic, as is most all brake fluid today. The two non-synthetic one's that I'm aware of aren't used in vehicles now and not readily avaiable (DOT-2 and LMT or something like that, can't recall).
Anyway, while some will warn against it, it is my understanding that for BMW bkes there is no issue with replacing DOT-3 fluid with DOT-4 if you do a complete flush (no need to do an overall system clean as with some other switches).
As was mentioned, some companies promote the fact that their fluid is synthetic (personally that doesn't raise any red flags for me as it is true) while others don't so this unfortunately can cause some confusion. Another source of confusion is "silicone" based brake fluid such as DOT-5 (although not DOT-5.1).
I'd do a proper system flush and run DOT-4.
It's specs are higher than DOT-3, it is widely available, and it should be completely compatible. You can read of not mixing 3 and 4 but those are relating to older and/or more specific applications where the systems and components may run into a compatibility issue. Also, DOT-4 absorbs moisture quicker than DOT-3 (more hygroscopic) so some point to it requiring more frequent changing but if one is doing proper mainenance schedules, and changing it every 1-2-3 years DOT-4 is the way to go.
Anyway, as Paul mentioned both DOT-3 and DOT-4 are synthetic, as is most all brake fluid today. The two non-synthetic one's that I'm aware of aren't used in vehicles now and not readily avaiable (DOT-2 and LMT or something like that, can't recall).
Anyway, while some will warn against it, it is my understanding that for BMW bkes there is no issue with replacing DOT-3 fluid with DOT-4 if you do a complete flush (no need to do an overall system clean as with some other switches).
As was mentioned, some companies promote the fact that their fluid is synthetic (personally that doesn't raise any red flags for me as it is true) while others don't so this unfortunately can cause some confusion. Another source of confusion is "silicone" based brake fluid such as DOT-5 (although not DOT-5.1).
I'd do a proper system flush and run DOT-4.
It's specs are higher than DOT-3, it is widely available, and it should be completely compatible. You can read of not mixing 3 and 4 but those are relating to older and/or more specific applications where the systems and components may run into a compatibility issue. Also, DOT-4 absorbs moisture quicker than DOT-3 (more hygroscopic) so some point to it requiring more frequent changing but if one is doing proper mainenance schedules, and changing it every 1-2-3 years DOT-4 is the way to go.
jagarra
Gerard
Alan,
You may be thinking of Castrol LMA brake fluid. I use that on older Jaguars after having the standard brake fluid eat my master seal away after a few days, of course that was back in the 70's. The new stuff may be better. It is still available, you just have to order it, still use it out of habit just in case the seals are natural rubber.
alancoles
Dress for fall & avoid it
That is the "Minimum Spec" but many good quality brake fluids spec out well above that. I've used DOT-4 fluid with a dry boiling point of over 600°F in race cars in the past.
Both are glycol ether based, but DOT-4 has borate esters added that DOT-3 doesn't have and therefore, in some applications, care must be taken (not in an R100RS). Their addition improves the properties of DOT-4 vs DOT-3 for boiling points and other areas that are important.
alancoles
Dress for fall & avoid it
PGlaves
#13338
Difference between Dot 3 and Dot 4
The U.S. Department of Transportation (DOT) does not spec the chemical composition of brake fluid. Instead it grades fluids by the Dry and Wet boiling point. Brake fluide gets "wet" because it is hydroscopic. Dot 4 has higher temperature ratings than Dot 3. If you like somewhere with mountainous twistie roads you will want DOT 4. For the rest of us flatlanders it won't really matter. Unlike auto brakes, motorcycle front brakes get the full force of cooling air flow. Ironically while DOT 4 has higher boiling temperatures when new it is more hydroscopic than DOT3. So old DOT4 fluid may well have a lower wet boiling point. DOT4 racing fluid has the highest boiling point--over 600f--but outside of a road racer I cannot imagine needing it on the street.
DOT3 and DOT4 are both made of glycol; DOT 4 is a bit higher viscosity and contains borate esters. By law DOT 4 fluids must have a minimum dry boiling point of 446°F and a minimum wet boiling point of 311°F. There is some disagreement about flushing. My advice is to flush but don't let the master cyclinder run dry which necessitates careful breeding.
Oliver Moore
2004 R1150r
1993 Harley FLSTC
1961 Bultaco
The U.S. Department of Transportation (DOT) does not spec the chemical composition of brake fluid. Instead it grades fluids by the Dry and Wet boiling point. Brake fluide gets "wet" because it is hydroscopic. Dot 4 has higher temperature ratings than Dot 3. If you like somewhere with mountainous twistie roads you will want DOT 4. For the rest of us flatlanders it won't really matter. Unlike auto brakes, motorcycle front brakes get the full force of cooling air flow. Ironically while DOT 4 has higher boiling temperatures when new it is more hydroscopic than DOT3. So old DOT4 fluid may well have a lower wet boiling point. DOT4 racing fluid has the highest boiling point--over 600f--but outside of a road racer I cannot imagine needing it on the street.
DOT3 and DOT4 are both made of glycol; DOT 4 is a bit higher viscosity and contains borate esters. By law DOT 4 fluids must have a minimum dry boiling point of 446°F and a minimum wet boiling point of 311°F. There is some disagreement about flushing. My advice is to flush but don't let the master cyclinder run dry which necessitates careful breeding.
Oliver Moore
2004 R1150r
1993 Harley FLSTC
1961 Bultaco
