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hi everyone, I’m about to put a new MC, never done it, so I’m wondering what liquid is in there? normal brake fuid?
 

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hi everyone, I’m about to put a new MC, never done it, so I’m wondering what liquid is in there? normal brake fuid?
yes,brake fluid.DOT4 seems to be the best
 

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I was waiting to see a what is this picture since most people seem to find a thick looking tomato paste in neglected mc's. But a new one. What fun is that.
 

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hi everyone, I’m about to put a new MC, never done it, so I’m wondering what liquid is in there? normal brake fuid?


DOT 4, like DOT 3 and DOT 5.1, is a polyethylene glycol-based fluid (contrasted with DOT 5 which is silicone-based). Fluids such as DOT 4 are hygroscopic and will absorb water from the atmosphere. This degrades the fluid's performance, and if allowed to accumulate over a period of time, can drastically reduce its boiling point.



Can you still get DOT 4?? I used DOT 5.1 on my rebuild. Do NOT use Dot 5 unless you have a completely rebuild system including hosing that is made for Silicon based fluid.
 

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I expect that Marshall will chime in when he gets back on his feet on this, but the 5.1 is the better choice if you can find it. Lower viscosity translates to less stress on hoses and mechanical items. Standard dot 3 is fine if bled through properly. But as said, stay clear of the silicon based type completely. Dire damage will ensue.
 

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Question--what are the views on synthenic fluid----overkill?? does it harm any internals books or lines.



Speaking of line--I would like to get SS line from JDA (still a good source???)--- what are the exact data points that I need to discuss-

Banjo fitting and the bolt-- size/pitch dia of SS line,etc
 

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Danny, do not use synthetic brake fluid in these systems. Unless you have fitted a complete new system that is rated for synthetics, it's just not good for them. As above, they absorb a lot more water, and the tight tolerances on our bikes are important. In an automobile system it is much less of an issue, but bike brakes are heavy use items for such a small system.



As for the lines, JD is still highly recommended, and basically just give them your bike model and year, as he already has templates for most, if not all of them.
 

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DO NOT use that crappy silicone based DOT5 fluid in anything unless it specifically calls for it.

DOT5.1 is a different story, it's not silicone, just glycol based like 3 or 4 and can be mixed with them.



The story I've heard about the development of the silicone brake fluid is somewhat believable. Supposedly the Army/Air Force etc wanted a brake fluid with a higher boiling point than DOT 3 or 4. Someone ended up developing the silicone fluid which indeed had a higher boiling point but was later found to have some serious drawbacks.



Water is heavier than silicone fluid and will not mix with it thus any condensation that got into the system would migrate to the lowest point of the system which was usually the calipers. If enough built up the boiling point went down to that of the water - 212*F - thus heavy braking would turn it to steam and you'd end up with virtually no brakes at all.



The Armed Forces quickly moved away from it due to this problem. Dot 5.1 was developed because it would mix with water so it didn't have that problem. It is also less hygroscopic, (absorbs less water from the air) is almost half the viscosity (faster brake apply and release) and has a higher boiling point that even the failed silicone fluid did. It should also work better on our stock MCs due to that tiny hole we have, it'll get through that far easier.



It's in my bike now exclusively and I'm looking forward to the performance. A dry (on a stand) test showed that the pads really do apply and release faster which will be an advantage. The only disadvantages are that very few places carry it, you pretty much need to go to a motorcycle shop to find it as it's being used in a lot of the new bikes and ATVs. It's also quite a bit more expensive but should last a lot longer since it doesn't absorb as much water vapor from the air over time. Also - Old Okie said it went in and bled a lot easier than normal fluid does which might help eliminate some of these bleeding nightmares.



In other words I'm sold and I hope others will change over to it to take advantage of its superior properties.
 

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I put a Valvoline SynPower ABS brake fluid in my system. It says that it exceeds dot 3 & 4 but does not have a numerical rating on it. The only clue is that it says that it contains glycol ethers, polyglycols and inhibitors. I assume this is 5.1. Replaced the brake line and rebuilr the master and the caliper. Hopefully, I am good to go.
 

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If you're not sure what it is:



DOT 4: Has a light blue or green color.



DOT 3: Clear or yellowish amber color.



DOT 5.1: Crystal clear.



THE IMPORTANT thing is that those three ARE compatible.



By nature fluids don't compress, so they all don't compress the same amount. The tame calipers on our decades old bikes will never reach temps, even in the twisties, that a DOT 3 can't handle. The primary difference between 3, 4, and 5.1 is higher boiling point.



It's rather illustrative of the how CLUELESS whoever stipulated the official designation for brake fluid is. They should have called it 4.1, since it's compatible with DOT 4 (and 3), but some genius decided to call it 5.1, which is NOT compatible with DOT 5. Leads to unnecessary confusion.
 

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It's rather illustrative of the how CLUELESS whoever stipulated the official designation for brake fluid is. They should have called it 4.1, since it's compatible with DOT 4 (and 3), but some genius decided to call it 5.1, which is NOT compatible with DOT 5. Leads to unnecessary confusion.



Shouldn't have been a .anything, some of th few that require true DOT5 silicone may think that 5.1 is just an upgrade and add it to their system. Since th two won't mix I can only imagine the mess it would end up causing.



It should have been called DOT6
 

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I put a Valvoline SynPower ABS brake fluid in my system. It says that it exceeds dot 3 & 4 but does not have a numerical rating on it. The only clue is that it says that it contains glycol ethers, polyglycols and inhibitors. I assume this is 5.1. Replaced the brake line and rebuilr the master and the caliper. Hopefully, I am good to go.


There are some "super" DOT4 fluids that exceed DOT4 in ratings but still aren't the same as 5.1



It's a confusing situation they've created.
 
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