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Fathom

DOT 5

23 posts in this topic

Anyone using this fluid? I went to it when I put on new brake pads. Not much diffence in stopping. Probably going to get the White Bros CR routing for it.

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I thought Dot 5 was a no no because of the synth nature of it destroying seals?

I am using Dot 4 Belray

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its silicone based.you really shouldnt put it in a system thats had dot 3/4 in it.they dont mix at all,and when they come in contact to rubber together the expand the rubber.

theres really no reason to also.you can get super temp brake fluid in dot3/4.

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The other problem with DOT 5 is that it is synthetic. It traps air extremely easily! When you pour the fluid in it will aerate it to where you cannot get a good brake feel. You have to let the whole system settle. IT is hard to bleed to put simply.

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Ahhh crapolla then. Reckon I'll go get some 4 and do that tomorrow. Been in there a while.

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DOT 5 is just fine as long as it is placed into a completely dry system. I have been running 5 in my 02 426 for almost a year. I did however make the mistake of just adding it to my rear brake system mixing 4 and 5.... Hell I needed a new res and actuator anyway....

Bonzai :)

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FYI - here are the wet and dry boiling points of various brake fluids. Temperatures are in degrees F.

Almost all of these on the list are Dot 4 (except as noted). Also, regular brake fluids (i.e. Dot 3 and 4) are hydroscopic, meaning they absorb moisture out of the air. This is unavoidable and as such, the manufactures state their wet and dry boiling points. I'm not sure at what point the fluid is deemed "wet". It has to do with an industry standard test for anhydrous vs. XX percent saturated with water brake fluid. When you first put the fluid in, it is dry. After it has been in your system for a while, it becomes wet by grabbing every little molecule of water vapor it can, no matter how good the brake system is sealed up.

That's why you are supposed to change the fluid every once in a while. Actually, for two reasons: 1)when the fluid becomes wet, it will corrode the metal parts in the brake system, and 2)the wet boiling point is always lower than the dry boiling point.

Once you have boiled the fluid, it gets trapped bubbles all in it and the lever (or pedal) gets real spongy.

DOT 5 is synthetic and not hydroscopic, but it is not compatible with DOT 3 and DOT 4 and requires that the rubber seals are compatible with it. Plus, it's hard to find and more expensive.

Anyway, enjoy :)

ARRANGED BY DRY BOILING POINT

DRY WET Fluid Name

401 284 DOT3 MINIMUM

446 311 DOT4 MINIMUM

446 311 Castrol LMA DOT 3/4

500 356 DOT5 MINIMUM

502 343 VALVOLINE SYNPOWER

509 365 MOTUL 5.1

527 302 AP RACING 551

536 392 ATE SUPERBLUE/TYP200

550 290 Ford Heavy Duty DOT 3

590 410 AP RACING 600

590 518 CASTROL SRF

593 420 MOTUL RBF600

610 421 NEO SYNTHETIC SUPER DOT 610

620 425 COBALT SUPER XRF

ARRANGED BY WET BOILING POINT

DRY WET Fluid Name

401 284 DOT3 MINIMUM

550 290 Ford Heavy Duty DOT 3

527 302 AP RACING 551

446 311 DOT4 MINIMUM

446 311 Castrol LMA DOT 3/4

502 343 VALVOLINE SYNPOWER

500 356 DOT5 MINIMUM

509 365 MOTUL 5.1

536 392 ATE SUPERBLUE/TYP200

590 410 AP RACING 600

593 420 MOTUL RBF600

610 421 NEO SYNTHETIC SUPER DOT 610

620 425 COBALT SUPER XRF

590 518 CASTROL SRF

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One important point that has not been raised:

From AP racing: "Additionally, DOT 5 fluid is highly compressible due to aeration and foaming under normal braking conditions, providing a spongy brake feel. DOT 5 fluid is best suited for show car applications where its anti-corrosion and paint friendly characteristics are important." http://raceshopper.com/ap_brake_fluid.shtml

I have tried DOT5 and have personally noted the loss of lever firmness, which was restored upon going back to DOT4.

Many of us that have spent the bucks to install a stainless steel, CR-routed brakeline in the quest to firm up the lever feel. Adding DOT5 to will likely destroy the intended benefit of the new brake line.

The reason Harley specs DOT5 is the same reason that show car guys like it--DOT5 doesn't hurt the paint if spilled. This properly reflects Harley's emphasis on the cosmetic and styling aspects of their products. Nobody has ever accused Harley of having great performing brakes!!

Steve

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Untrue..... DOT 5 has not had any impact on my steel braided lines front and rear.

True: The lever firmness is a bit softer but snatch a handful of front brake on my 426 and you'll end up in the cheap seats with the spectators.

The absolute best benefit that I like is not having to change constantly in winter and humid conditions, because the Synthetic fluid does NOT soak up a boat load of water.

That's my story and I'm sticking to it....

Bonzai :)

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Well, I flushed it and put DOT 4 in. Brake does feel better than it did before. Have a White Bros CR line coming for it. Should be able to throw myself on the ground pretty easy now.

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I don't know who told me but if your brakes are mushy just take a tie wrap and put it around the handlebar and the brake lever. Leave it over night and the next mourning the lever is harder than chinese arithmetic.

I don't know why it works but it does.

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I remember running dot 5 in a street bike years ago. Moisture got in the system. The water collected in the very bottom of the brakes and really messed up the caliper. I would not use it again unless I had to. It had to be changed constantly to be any good.

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I don't know who told me but if your brakes are mushy just take a tie wrap and put it around the handlebar and the brake lever. Leave it over night and the next mourning the lever is harder than chinese arithmetic.

I don't know why it works but it does.

Is that like tying a thread around your finger to remember something :)

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I don't know who told me but if your brakes are mushy just take a tie wrap and put it around the handlebar and the brake lever. Leave it over night and the next mourning the lever is harder than chinese arithmetic.

I don't know why it works but it does.

It works because if you leave the system pressurized (i.e. keep the lever pulled for a long time) it quickens the process of all the little bubbles in the system finding their way up to the top of the line. Then when you release the lever the next morning, the air goes up into the master cyclinder and bubbles up to the top of the resevoir where it belongs. It's just a way of doing a fine tuning bleeding. Works good though. :)

As far as Chinese arithmetic, I never was very good at figuring that out.... :D

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No way!!! I didn't know about that! Im gonna try it tonight....If it firms up the first 1/4 of lever travel, Im going to be very happy.... i owe you a beer beezer!

Thanks

Mike

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