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Message started by SimonTuffGuy on 05/15/12 at 18:40:04

Title: Brake fluid
Post by SimonTuffGuy on 05/15/12 at 18:40:04

Clymer manual says DOT 3 or 4. Is there any preference or reason to.go one or the other? Fluid has been.completely drained, so no mixing will occur if I go one or the other.

Thanks!

Title: Re: Brake fluid
Post by justin_o_guy2 on 05/15/12 at 18:43:17

I think the Dot this & DOT that is about how much heat the fluid can take w/o boiling. Go with the high number the system can accept,

Title: Re: Brake fluid
Post by Dave on 05/16/12 at 05:08:52

594640475A5D6C5C6C54464A01330 wrote:

I think the Dot this & DOT that is about how much heat the fluid can take w/o boiling. Go with the high number the system can accept,

That is correct.......The rating is based on dry and wet (3.7% water) boiling points. Dot 3 has a dry boiling point of 401 degrees and a wet boiling point of 284. Dot 4 has a dry boiling point of 446 degrees and a wet boiling point of 311. The reason you are supposed to change brake fluid is that it absorbs water from the atmosphere (like ethanol fuel) and the boiling point will be lowered over time - and the fluid can become corrosive once it absorbs enough water.

Dot 5 fluid is silicone based and is used in applications like antique cars and military equipment that may sit idle for a long time. It does not absorb water and will not hurt paint - but it is compressible and will make your brake system a bit more spongy - and it does not meet the higher boiling points.
Dot 5.1 is hard to find but is similar to silicone based fluids and will not hurt paint or absorb water - but is has better compressibility and boiling values. It is used in bicycle hydraulic disc brakes.

If you change from Dot 3 or 4 fluieds to Dot 5 or 5.1 - the system should be drained first then flushed, however there will always be a bit of the Dot 3 or 4 remaining that can cause corrosion. The best thing to do if switching to Dot 5 or 5.1 is take the system completey apart and clean everything.

You probably don't need to worry much about the boiling points for cruising or normal riding. If you are riding on a track or taming the Dragon and using your brakes with little cool down time - then the fluid will be put to the test as the LS650 brakes are small and have little reserve capacity.

Title: Re: Brake fluid
Post by justin_o_guy2 on 05/16/12 at 05:36:19

& I thot fluids simply didnt compress,, silicone plays some strange games,, & wears many disguises. Ive seen it look like a colander,that will flatten out & stash, or a spatula, but I sure had no idea it compressed as a fluid, pure silicone oil is what I rub on plastics to keep them alive, like the dash of a car. You can still get it from old copier repair places, l;ots cheaper than Armorall, & theres no VOCs to evaporate out, once a year & it stays happy,

Title: Re: Brake fluid
Post by lch2 on 05/16/12 at 10:51:46

From my experience with cars, I have seen that DOT 3 is recommended for disc / drums combinations, and DOT 4 is recommended for disc only brakes, as disc brakes caliper will absorb more heat from the friction, it is recommended a fluid that will boil at higher temps.

Long story short, did my brakes on a 300SDL MB, that came in with disc brakes all around, swap the old fluid, and replaced with DOT 3, first highway trip and my brakes felt spongy and did not brake any well, went back to the brake specialized store and commented on the issue, they illuminate me with the DOT 3 and 4 difference, swapped the fluid again, and the breaking was completely different.

I will be using DOT 4 on any disc brake system from now on, including the LS

Title: Re: Brake fluid
Post by justin_o_guy2 on 05/16/12 at 10:55:07

swapped the fluid again.

Talk about FUN!!,, Does it have antilock brakes? Those are a pain to bleed, arent they?

Title: Re: Brake fluid
Post by lch2 on 05/16/12 at 11:11:14

405F595E43447545754D5F53182A0 wrote:

swapped the fluid again.

Talk about FUN!!,, Does it have antilock brakes? Those are a pain to bleed, arent they?

yes they are, but I made a "red neck tool" a modified brake deposit cap, that allows me to put some air pressure on the system, I fill the deposit, put the cap in place and apply from 5 to 7 psi of air, then open the bleeder screw and the bubbles jump out very easy, just need to be careful that the fluid level don't go too low, or new air will get into the system.

Title: Re: Brake fluid
Post by SimonTuffGuy on 05/16/12 at 17:40:09

The cap on my S40 reservoir says DOT4, so I picked up a can from NAPA today. Bled it by hand with 3-4 pumps while open on the bleeder, then closed and repeated. It worked fine and the brake is solid!

Took it out for a spin and it ran great. Few kinks to work out, but they'll get there. I'm just glad it runs (and stops)!

Thanks all!