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Old 12-04-2007, 01:49 PM   #16
Nas3car
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Quote:
Originally Posted by stever975
First, DOT5 brake fluid doesn't attack the seals in any brake calipers currently being sold. This has been discussed several times on the forum. Max sent a letter to Brembo and the response he received was that Brembos should use DOT4 fluid only. This bothered me since I've used DOT5 fluid in several different brands of calipers and master cylinders, including Brembo, with no problems. I called Brembo North America (800-325-3994) and talked with Jason Hiliger on extension 238 (he handles motorsport applications including motorcycles) and he told me that he had also heard that DOT4 was recommended but was never told that DOT5 couldn't be used. He said that most Brembos are used in high performance applications and DOT4 is preferred because it provides a higher dry boiling point and has less affinity for air than DOT5 fluid. He was interested in hearing about my positive experience with DOT5 fluid in Brembos and said he would pass the information along. I didn't make a big issue of this since it wasn't really an endorsement but I would say that the answer you receive depends on who you talk to. I will say that I've never had a problem with degraded seals due to DOT5 fluids in any of several brands of brake components since the 1980's when I first started using it. I will also say you should never mix DOT3/4/5.1 with DOT5 and never use DOT5 in a system that previously used DOT4 without replacing all soft parts and completely cleaning all traces of DOT4 from wetted metal surfaces. Also, never use DOT5 in an ABS equipped brake system.

Second, your description of brake fluids is incorrect. The DOT 3/4/5.1 fluids are composed of various glycol esters and ethers that are hygroscopic by nature but they contain no "anti-corrosion additives". These types of fluid need to be replaced when the quantity of absorbed water degrades performance (at least every two years). I agree that DOT5 fluid doesn't absorb water and I agree that all DOT3/4/5.1 hydraulic systems absorb water but I don't agree that all brake systems absorb water. Water only enters a hydraulic system with DOT5 fluid when allowed to enter while servicing the fluid or in small amounts through the vent. This potential water contamination is why DOT5 fluid should be replaced at regular intervals just like DOT 3/4/5.1 fluid. It's also unlikely that the small amount of water that might enter DOT5 fluid would ever migrate to the region of the caliper where temperatures would cause it to boil.

I don't want to get into a big debate on which type of fluid is best, but if you're familiar with the difficulties of bleeding DOT5 and want to use it in a new, non-ABS brake system that hasn't been contaminated with DOT4, then there's no technical reason not to.
Very well put. I can say that I do not belive that a motorcycle driven on the street would ever boil water in the caliper. I can say that the water is heavier than DOT 5 and settles to the lowest point. I have had the water freeze and render my brakes useless. My bad for not changeing the fluid more often but a tore cover seal and on outside kept bike did me in. We went for a x-mas eve ride and it was 20 degrees F. The water in my lines froze and I had no rear brake. It would work but would not fully release. It got worse as the caliper and rotor got hot. Just like steeping on the brake. Our 2 hr ride turned into a 6 hour event. The amount of wather that did come out was less than a small eye dropper. I do not think that DOT 4 or 3 would do this even if negleted for a period of time. I am thinking old cars that never had a brake flush and seemed to work fine for many years.
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Old 12-05-2007, 01:48 AM   #17
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Water mixes with Dot 3/4 while water separates from Dot 5. Water in Dot 3/4 stays in solution. The boiling point of the fluid is degraded but at least there aren't small pockets of water in the fluid as you wold get with Dot 5 were you to get lazy about fluid changes.
I will challenge the notion that you will never boil your brake fluid on the street. Ride the twisty roads in the San Gabriel mountains on an August day fast and hard, something steep like Glendora Mountain Road and you will very definitely get the brakes over the boiling point of water. I have faded Brembo brakes on BMW's on these mountains to the point where brakes would not stop harder no matter how hard I pulled on the lever. The fluid and pads were that hot. The performance of Dot 5 at high temps when there could be water in the system is not just idle chatter for those of us who sport ride mountain roads. On my Audi I have even boiled the power steering fluid and smoked the brake pads from hard use. Canyon riding/driving is how we enjoy our rides.
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Old 12-05-2007, 07:00 AM   #18
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I can understand that. I am sure some guys at the Dragon Tail have superheated their stuff. I was in my own little world. the other thing about DOT 5 is I understand that you never get a firm feeling brake. The fluid has some give to it. At least that is what some of the Nascar guys have told us.
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Old 01-08-2020, 01:01 PM   #19
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I have wagner brake fluid 3&4 (pepboy) does not say hydraulic on bottle, can i use it?
For clutch & brake flush it with this..
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Old 01-08-2020, 01:33 PM   #20
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Quote:
Originally Posted by Chencho View Post
I have wagner brake fluid 3&4 (pepboy) does not say hydraulic on bottle, can i use it?
For clutch & brake flush it with this..
If you bike is spec'd for Dot 4 , Dot 3 and 4 are hydraulic since all brake systems are hydraulic in nature. Dot 3 doesn't have the corrosion inhibitors that Dot 4 has so I'd not bother with it. Otherwise they are the same. Dot 4 might have a slightly higher boiling point as well. If your bike calls for Dot5, don't use Dot 3 or 4 to flush with.
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Old 01-08-2020, 03:12 PM   #21
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Dot 4 it is then, Thank you.
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Old 01-08-2020, 11:10 PM   #22
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Also- 3 and 4 will mix with one another, while 5 will not. Although it is not recommended
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