I'm going to bleed my Juicy 7's,replacing the old fluid,wondering if anyone has tried using DOT 5,seems like it would be an improvement.
DOT 5 or DOT 4?
- Thread starter RepoDemoRider
- Start date
Well 5 is more than 4 so it has to be at leat a 20% improvement. Right?
(They are the same as far as bikes are concerned. Buy the cheaper dot4)
No do not use DOT5. Its totally different and NOT compatibly with DOT4 or DOT5.1 systems. DOT5 fluid is silicon and something very different to DOT4 and DOT5.1 fluids. DOT5.1 is backward compatible to any DOT4 system. Though you should not really mix brake fluids, so a full drain and top up with whatever your using is best. Don’t let the names confuse you, DOT5 is nothing like DOT4 or DOT5.1.
Dot 5 is 36% less dense which ultimately leads to a lighter oil mass, thus saving roughly 38grams per brake line.
Just to clarify what I said before DOT4 and DOT5.1 are glycol based fluids and are basically the same things. DOT5.1 is just a newer standard that refines the original DOT4 standard for use in modern brake systems. If brakes are specked to work with this fluid the seals, brake lines, unions and so on are made to work with this fluid. Introducing mineral or silicon oil can damage the brakes if not designed for it. One more common problems when you put the wrong fluid in is swelling of seals. If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. Silicone is very tenacious stuff and you will never get it all out of your system. DOT 5 fluid is not hygroscopic, so as moisture enters the system, it is not absorbed by the fluid, and results in beads of moisture moving through the brake line, collecting in the calipers. this collected moisture will boil causing vapor lock and system failure. Additionally, DOT 5 fluid is highly compressible due to aeration and foaming under normal braking conditions, providing a spongy brake feel. Most brake manufactures actually specify specifically not to use DOT5.
Bingo!!! I've mixed them before in the past, mainly because I didn't have the time to flush the system. Never saw a performance loss, but still feel it's better to keep one it one or the other.
i use dot 5.1 in my hopes oh do they feel great (running a 6 inch rotor mono mini on a sunday dh bike at diablo) never had problems bled them once a month
If you're using Dot 5 in a brake system that wsa designed for dot 3/4/5.1 you're most likely going to have problems with your seals/leaking as your system wasn't made for Dot 5. I don't know any MTB brakes that spec Dot 5.
Dot 5.1 has a higher wet boiling point over Dot 3/4, etc etc basically its a lot better.
Man I see this soo many times here, search please, search. To say it again, dot3/4 "5.1" are glycol based. Dot5 is oil based and they are NOT compatible with each other. As far as using 5.1. It works fine, you can get a quart at Autozone or kragen for about 6 bucks. Thats what i used for mine, cant really say it worked that much better, if your rally looking for better performance, get some goodridge lines. thats your best bet to change the feel of the bike.
DOT 5 will eat you seals
was making a weight joke....wasn't serious
Thanks for most of your replies.I'll forget the 5,and look for the 5.1.
In our MINI's, we run ATE Super Blue. In a bike application, no great performance gain (simply can not generate the kind of sustained heat that a car can), but the advantage is when changing fluid, the change in color makes it easy to tell when the fluid is all new (ATE also makes a gold version).
FWIW: Always ran Hope sourced Dot 5.1 in Hopes
, now Dot 4 in Hayes 
.
FWIW: Always ran Hope sourced Dot 5.1 in Hopes
, now Dot 4 in Hayes .
One thing well worth researching is the requirements list for a glycol fluid to be classed as either DOT3, DOT4, or DOT5.1.
In short, DOT3 tends to have lower boiling points with lower viscosities. DOT4 did not put restrictions on viscosity, only a requirement for an increased boiling point; so DOT4 (and higher boiling point "Super" DOT4) fluids tend to have higher viscosities than DOT3, decreasing lever response speeds and making it more difficult to get air out of the fluid and brake system.
DOT5.1 is a newer standard designed to cater for ABS brakes (which have very small orifices for fluid and require the fluid to be able to move quickly through these orifices with minimal restriction). This standard also requires a relatively high boiling point, but more importantly requires a lower fluid viscosity.
Therefore a DOT5.1 rated fluid is going to be the best choice for an MTB brake. The thinner fluid will give a faster lever response, easier bleeding, and an adequately high boiling point. As suggested already, MTB brakes don't get all that hot - and while boiling point should be considered, most DOT fluids are more than adequate in this regard.
After doing a bit of research I ended up deciding on Motul DOT5.1 fluid, I forget the numbers now but it had a very low viscosity compared to other fluids and a relatively high boiling point as well. Most other high end DOT5.1 fluids should do the trick too.
In short, DOT3 tends to have lower boiling points with lower viscosities. DOT4 did not put restrictions on viscosity, only a requirement for an increased boiling point; so DOT4 (and higher boiling point "Super" DOT4) fluids tend to have higher viscosities than DOT3, decreasing lever response speeds and making it more difficult to get air out of the fluid and brake system.
DOT5.1 is a newer standard designed to cater for ABS brakes (which have very small orifices for fluid and require the fluid to be able to move quickly through these orifices with minimal restriction). This standard also requires a relatively high boiling point, but more importantly requires a lower fluid viscosity.
Therefore a DOT5.1 rated fluid is going to be the best choice for an MTB brake. The thinner fluid will give a faster lever response, easier bleeding, and an adequately high boiling point. As suggested already, MTB brakes don't get all that hot - and while boiling point should be considered, most DOT fluids are more than adequate in this regard.
After doing a bit of research I ended up deciding on Motul DOT5.1 fluid, I forget the numbers now but it had a very low viscosity compared to other fluids and a relatively high boiling point as well. Most other high end DOT5.1 fluids should do the trick too.
Not to burst any bubbles or anything, but 95% of ABS systems use DOT3. Some vw's and other German makes come with a Dot4. dot5.1 has a higher viscosity that 4 or 3. but has a much higher boiling point. Like i said before i have run both the dot4 and dot5.1 in my juicy sevens, and CANNOT tell a difference, untill i got the goodridge steel braid lines.. By the way, I know about the fluids, i use them everyday when i work on Cars/Trucks, And i can back up teh knowledge with two degrees in teh feild, along with some Master certification.
Consider my bubble un-burst.
The reason a number of ABS systems may run DOT3 is because it does have a sufficiently low viscosity, as opposed to DOT4 which generally doesn't.
That's incorrect. Read my post for the correct information, I spent quite a while researching this and just thought I'd share for the sake of helping everyone else.
Your forgetting one thing, Dot3 4 and 5.1 are not tested at the same tempuratures, or pressures for there viscosity. 5.1 IS a slower moving fluid, that is why it is NOT a factory used fluid, and even though it is a glycol based fluid, it will void abs warranties. This is what i do everyday, well five days of the week, The ONLY advantage to 5.1 is boiling temp, which should be about 500 degrees.
And what do you make of their wet boiling points...
Eh? ASTM D-445 specifies measuring these fluids at 40ºC and 100º and both at atmospheric pressure. Their viscosity (cSt) is pretty much exactly as udi mention in his earlier post. Even if a kinematic viscosity bath isn't used, a slide press or ball displacement test will still use the same "standard" temperatures of 25ºC, 40ºC and 100ºC.
All these tests are conducted under the same temperature and atmospheric pressure conditions or else they'd be useless.
BTW, my personal opinion is that BP isn't as high a priority as visco and expansion coefficients in a MTB brake where temps in excess of 250ºC are much less likely than in automotive applications. The service and work load of the brake is however much higher than many other brake systems, with extended periods with a restricted or locked master cylinder affecting grab point as the fluid expands.
Actually you're wrong, they are.
Any reputable brake fluid manufacturer giving fluid viscosity specifications will give two figures, one is cSt@-40C and the other is cSt@100C.
Actually, 5.1 isn't a slower moving fluid as dictated by the actual viscosity numbers given by fluid manufacturers (which I'll take over your word thanks), and in fact manufacturers go as far as recommending the fluid for use in ABS brakes.
Direct from the Motul DOT5.1 data sheet:
"Especially designed for anti-lock brake systems (ABS), the viscosity (820cSt@-40C) is lower than DOT4 (up to 1800cSt@-40) and DOT3 (up to 1500cSt@-40c) brake fluids, allowing an easier fluid circulation in micro-valves of anti-lock systems."
Again, you're wrong. The advantage to the DOT5.1 standard is that not only does it require a high boiling point, it requires a lower viscosity; this is what sets it apart from the DOT4 standard which only requires a high boiling point. I have said this twice now, but it doesn't seem to be sinking in so it's time for the cold hard facts.
Before that though, I'll add that your degree/qualification/field of work adds nothing to your argument, in fact it usually just detracts from whatever point you are trying to make. Stick to facts and figures next time.
These are the specifications a fluid has to meet to be classified as either DOT3, DOT4, or DOT5.1. Clearly you can see that DOT5.1 requires the lowest viscosity by a large margin (900cSt@-40 max), while DOT3 and DOT4 follow with 1500cSt and 1800cSt respectively.
Grab a few data sheets from brake fluid manufacturers and this is confirmed. One great example is Motul RBF600, a high end, high boiling point fluid that most people in motorsport will be familiar with. Viscosity is 2.5cSt@100C, and 1525cSt@-40. Clearly this will only let it meet the DOT4 standard, which is quite loose on the low viscosity requirement.
Compare that to Motul DOT5.1 which has a viscosity of 2.1cSt@100C, and 820cSt@-40... that's a big difference, while still maintaining boiling points that aren't much lower than the RBF600.
Happy braking!
Udi
So can I use the bottle of Valvoline Synpower Synthetic Formula that I've seen at the auto parts store? I says it exceeds Dot 3 and Dot 4 but I don't bleed my brakes that much so I'm not sure. Says on the bottle, "high dry boiling point exceeds 500 deg F" and has a "minimum wet boiling point of 343 deg F". Thanks for any help
Cheers for the informative post Udi, though I'd have liked to see DirtyMike come back and either admit that you may be right, or explain what he knows from his work/qualifications that goes above and beyond a few numbers that you've read...
For example, I could see an argument that a fluid with a lower viscosity will need better seals, so DOT4 is actually a better choice as it won't wick past o-rings as much?
FWIW my new Formulas specify in the manual to ONLY use DOT4. Doesn't mention DOT5.1 at all.
For example, I could see an argument that a fluid with a lower viscosity will need better seals, so DOT4 is actually a better choice as it won't wick past o-rings as much?
FWIW my new Formulas specify in the manual to ONLY use DOT4. Doesn't mention DOT5.1 at all.
Me too, but admitting defeat isn't much fun.
I think your question about seals is legitimate, but in reality I'd say it's a non-issue. The fluids' viscosity difference within their operating temp range isn't going to be hugely different, and you'd find that if fluid was escaping past seals the issue would be the seals themselves and it would have happened with any fluid.
For the record, I've run (as well as Jonny5 on here) Redline LikeWater suspension fluid in Saint brakes, which is a noticeably thinner fluid than the genuine mineral oil - and had no issues whatsoever.
That'll work fine.