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DOT 5 brake fluid


Hooplehead

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I was at my local parts store and he had some dot5 fluid on the shelf. I was a dot 3 user in cars forever, then went to dot4 in the bikes and newer stuff. I asked, and he said that it was for military use. What he described, was that it isnt hydroscopic (sp?) and the military has to use it, as their vehicles can sit for years before needing to go into immediate service. He also said it doesnt work on abs. It got me thinking... would moving to dot5 in a simple nonabs bike (like my drz), mean I wouldnt have the dreaded orange fluid from just sitting? Not a big deal, as I hope to ride, and flushing dot4 thru a system each year is no big deal at all. But, I could see it being handy for long term storage. I'll have to look into it some more, maybe it has a low boil point or some other drawback. Anyone here try the dot 5 with success?

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DOT 5 or 5.1?  Because seeing 5 on a store shelf seems very odd.  DOT 3, 4, and 5.1 are all glycol-based fluids that can intermix and work in the same systems.  DOT 5 is silicon-based and changing to it is a very involved process.  DOT 5 has a very high boiling point (close to the same as 5.1) and is not hygroscopic.  DOT 5 is semi-compressible and can cause a softer, less defined feel for the brakes.

 

Funny you call it orange fluid, because truly orange hydraulic fluid is LHS/LHM type, and used for some active suspensions as well as some unique brake applications.  It's totally hydrophobic, but has a lower boiling point.  There were also some other issues and I can't remember why it's no longer used.  A relative, straight mineral oil, is used on bicycles for brakes.

 

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As said, DOT5 is special stuff and you can't switch over easily.  I've also read that some seals are incompatible with it, but don't know if that's true.

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Thanks for the info. Its a local parts house, you know the type. They carry tractor parts, old stuff, you can still walk in smoking a cigarette. Such a random collection in there, mostly what the neighborhood (farms) use. He said it was silicone based and not compatible with 3 or 4 at all. I'll just keep using the standard dot 4 off the shelf (clear when new), and use the way it changes orange over time, as an indication to flush. Hell, its just a 10minute job solo, using a screwdriver and 8mm. Probably best to flush more often anyhow. As with engine oil, its usually the contamination that hits longs before the fluids break down.  Comforting to know that the guy where i buy my parts, looks redneck as hell, but also knows his shit. He mentioned its NOT compatible with abs. I dont know if thats because its 'semi' compressible, or perhaps some seals dont like it.

Edited by Hooplehead
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5 minutes ago, Hooplehead said:

He mentioned its NOT compatible with abs. I dont know if thats because its 'semi' compressible, or perhaps some seals dont like it.

I've heard the issue is that it's higher viscosity, but not sure.  Or maybe just that the ABS makers don't want to test/certify it for use.

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I also remember that while dot 5 is not hygroscopic, water can still exist in the lines.  Poor prep, high humidity when being filled, old open containers.

The difference with dot 5 is that the water does not disolve into the fluid. Instead, the water collects in pools.  The pooled water would promote rust in steel lines, and steam easier when heated.

I seem to remember some AD notices concerning its use in aircraft.

And people that I hung around refused to use it in race cars.

 

 

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14 minutes ago, redxxrdr said:

I also remember that while dot 5 is not hygroscopic, water can still exist in the lines.

Perhaps it's a double edged sword argument, but I prefer the ability to flush the fluid and it remove all the water that's in suspension rather than hope there aren't drops of water sitting around eating away at stuff.

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1 hour ago, superhawk996 said:

Perhaps it's a double edged sword argument, but I prefer the ability to flush the fluid and it remove all the water that's in suspension rather than hope there aren't drops of water sitting around eating away at stuff.

Very good point. I could see how 'pooling' of the water, would be worse than just suspension of water. Drain and fill would seem to be more effective on the later. Neither fluids make a difference (it sounds), with dirt being a culprit. SO odd that a brand new sealed system, gets moisture and dirt in it. Must be the slow wear of seals on both accounts.

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Even tho bike masters are better sealed than most cars, the rubber seal/bellows may be permeable so that some air is exchanging bringing in moisture.  It might also come in through caliper seals, maybe even the hoses.  The 'dirt' is more likely wear material, mostly the seals plus a little metal.  Ever notice that the clutch fluid gets darker quicker?

 

All this talk makes me wanna flush my systems.....but since they don't sell brake fluid in drums I'll just let it go.  The only brake systems I've had get really rusty is on boat trailers.  The master has no bellows, just an open breather, plus the brakes spend a fair bit of time under water, and in some cases the master gets plunged.

Edited by superhawk996
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DOT 5.1 seems ideal, if it's on the shelf and not a crazy price.  Otherwise, we've all done fine with DOT 4.  The BMW specifies a change every two years, and I have a shop do it since bleeding through the ABS and traction control system is reportedly a huge change.  $80 and they use DOT 4.

 

12 hours ago, redxxrdr said:

And people that I hung around refused to use it in race cars.

 

Being slightly compressible, they'd probably hate to lose the brake feel.

 

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10 hours ago, SwampNut said:

The BMW specifies a change every two years, and I have a shop do it since bleeding through the ABS and traction control system is reportedly a huge change.

Is that cars or bikes?  I changed my Explorer's a couple of weeks ago that has both (ABS & TC) and I had no issues.

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8 minutes ago, blackhawkxx said:

Is that cars or bikes?

 

The Z4.  I think it might be for the performance models, I know my friend with a sedan hasn't been doing that and I haven't heard of any warnings from the computer.  It's a 35 also, but not an M-sport.  Either way, for $80 every two years, that's an easy choice.  The Z4 may be a little harder to get under than an Explorer.

 

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Flushing with ABS isn't a big deal, bleeding air out of an ABS system appears to be hit & miss without the tool/computer needed to actuate the ABS system.  If one actuated the ABS while flushing it's probably better than flushing without actuation, some old fluid will stay in the accumulator/valves without actuating and actuating *should* purge that.

 

When I work on any brake system I don't let air into the ABS module if possible.  If I have to expose the ABS module to air I warn the customer that they may have to visit a dealer/specialist to get a proper bleed.  So far so good, but I've only done a couple.

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I have a "funny" clunk from the front calipers and the back takes two pumps to get brake.

 

Took the cap off the reservoir- almost out of fluid.

 

I got a can of DOT3 and filled it up. (Cover says DOT4) The clunk is still there. I think I'll ride as is because I've heard bad things about linked system bleeding going south. 

 

(Think this is a continuation of #3 dropping all three rideable bikes on each other two? years ago)

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