Another reason to avoid DOT5 brake fluid?

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Randakk
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Another reason to avoid DOT5 brake fluid?

Post by Randakk »

Setting aside word parsing and semantics - unless we are dealing with a 100% virgin, clean and dry system, DOT 5 brake fluid is absolutely incompatible with any rubber components that have ever been exposed to DOT3/4 brake fluid. I am personally familiar with many field failures caused by the ill-advised introduction of DOT5 brake fluid into vintage motorcycles. In my experience, most amateur and even pro bike mechanics are not able to clean a glycol DOT3/4 system sufficient to allow the safe introduction of silcon-based DOT5 without significant risk of seal failures.

I present this as incontrovertible and non-controversial information widely held by much greater experts on the subject than me.

Irrespective of the technical limitations of DOT5 vs. DOT3/4 brake fluid for most vintage Hondas (like the CBX), there is another compelling reason to avoid DOT5 brake fluid for serious riders.

I’ve come to learn that I am blessed (cursed?) with higher than average level of sensory perception compared to others. I state this not as bragging, but as a matter-of-fact realization in my experience.

To wit: I can synchronize multi-carb engines by “ear,” “touch” and “sight” better than many mechanics can do with elaborate diagnostic equipment. (I do use my gauges for the very best result).

On to the subject of braking, I can feel:

1. The difference observed by the inclusion or exclusion of hydraulic brake light switches. I dislike the noticeable feel of the extra “compression” a hydraulic brake light switch adds at the lever. On all my bikes so-equipped, I remove these hydraulic switches and substitute electric brake light switches for better "feel."

2. On a properly bled system, the “feel” of DOT5 brake fluid is inferior to that of DOT3/4.

3. There is greater compressibility to DOT5. In normal use, it foams and aerates more. This adds “sponginess” at the lever or pedal.

4. I can feel these differences. High-spec DOT 3/4 is much easier to ride skillfully at a high level.

I think the improved braking feel of DOT 3/4 is significant and a worthwhile consideration for serious riders.

Just my 2cents. YMMV.
Randall Washington (Randakk)
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Randakk's Cycle Shakk, LLC
Pinehurst, NC USA
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Don
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Re: Another reason to avoid DOT5 brake fluid?

Post by Don »

I read that same thing everywhere I look Randall - If you're going to convert, change everything . . . . there is no safe way to flush an old system and then switch to DOT 5

"Since DOT 4 fluids were developed, it was recognized that borate ester based fluids offered the potential for boiling points beyond the 446F requirement, thus came the Super DOT 4 fluids - some covered by the DOT 5.1 designation - which exhibit a minimum dry boiling point of 500F (same as silicone, but different chemistry).

You can go ahead and mix or flush (replace) any DOT 3, DOT 4, or DOT 5.1 brake fluids, no problem. So there are no special bleeding procedures and you don't need to run anything in the lines. The only one to watch out for is DOT 5 (silicone brake fluid).

DOT 5 does not damage paint like other brake fluids do, but is not recommended by AP Lockheed for use in their systems due to higher wear than with other type fluids.

Brake system contamination:

The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.) due to the introduction of petroleum based products (motor oil, power steering fluid, mineral oil, etc.) A small amount is enough to do major damage. Flushing with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some owners change to DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. Brake systems should be flushed only with DOT 3 or 4.

If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system. Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers.

British Cycle Supply Company does not recommend use of DOT 5 silicone brake fluid on British motorcycles equipped with any AP Lockeed disc brake components."


Don

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Re: Another reason to avoid DOT5 brake fluid?

Post by zxbob »

I had no idea that brake fluid threads were as good (or better) than oil threads !

Image

Bob
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Re: Another reason to avoid DOT5 brake fluid?

Post by ericfreeman »

I've been reading all these threads about Dot 5 with some interest since I own 6 vintage bikes. I do all my own paint work and originally went with Dot 5 about 5 years ago when I picked up my '78 Sportster and switched brake hoses (didn't want to risk paint damage from Dot 4 fluid). At the time, I only flushed the MC and calipers with new Dot 5 when I fitted the hoses. Subsequently used Dot 5 in both my '77 Sportster and '79 CBX, although I did rebuild the entire CBX brake system from MC down. To date, I've had absolutely no problems with seals leaking or any other sign of brake system damage from the Dot 5. Plus, all my paint work has remained unblemished. I'm not disputing what has been posted about the Dot 5 shortcomings, just that my personal experience has been perfectly fine. However, I don't race or do track days, just spirited mountain riding.

Eric

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Re: Another reason to avoid DOT5 brake fluid?

Post by Randakk »

zxbob wrote:I had no idea that brake fluid threads were as good (or better) than oil threads !

Bob
Actually, the brake fluid issue is fairly cut and dry. The issues on either path are pretty well documented.

For me, one additional characteristic of DOT3/4/5.1 that I like is that it is an excellent paint remover. This dictates careful, thoughtful and diligent planning whenever it is part of a maintenance operation. That's a useful mindset when working on brakes I think.

For real controversy, consider the issue of the best throttle cable lube. I've seen otherwise rational folks really "go to the mat" on that issue. I don't use it myself, but I've heard several eloquent soapbox orations on the virtues of peanut oil (of all things!) for that application. :)
Randall Washington (Randakk)
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Pinehurst, NC USA
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oilheadron

Re: Another reason to avoid DOT5 brake fluid?

Post by oilheadron »

"For me, one additional characteristic of DOT3/4/5.1 that I like is that it is an excellent paint remover."

Only when you don't want it to!! Seriously, I've tried it several times on tough overspray, whatever, and it didn't do **** dang it! :)

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Re: Another reason to avoid DOT5 brake fluid?

Post by Mike Cecchini »

Randakk wrote:Setting aside word parsing and semantics - unless we are dealing with a 100% virgin, clean and dry system, DOT 5 brake fluid is absolutely incompatible with any rubber components that have ever been exposed to DOT3/4 brake fluid. <snip>
Apologies Randall.......but this just isn't so. I've been working with DOT 5 brake fluid since Dow introduced it back in 1980. I've found that only natural rubber (as used by Brembo).....is the only rubber that when used with DOT 3/4 first......then switched to DOT 5...... is the only rubber that swells and deteriorates.

But like you say...... if the rubber has never been exposed to DOT 3/4, then DOT 5 can be used with zero issues. As a point of fact, I have 3 Brembo systems full of DOT 5 presently and have been for nearly 10 yrs now with zero problems or issues.

What I've also found is that DOT 5 can be installed in non-natural rubber brake systems like our CBX's without any pre-preparation or negative effects. I installed DOT 5 in my X brake system in 2005 after being disgusted how DOT 3/4 causes all sorts of problems with X's if they sit around for months like so many of them do. I had 4 X's and only one of them got used over a 5 yr period, so the other 3 developed such brake issues that I had to rebuild all three of them.......so when I rebuilt them I installed DOT 5 brake fluid and not a single problem or issue since.

Like many things in life and like you..... I read and can appreciate some of the information.....but there are times when I want to see for myself and you'd be amazed what I find out like this DOT 5 issue.

To me DOT 5 is a god-send and I put it in every bike I can simply because it doesn't cause brake cancer that causes all that white caustic mess that comes with DOT 3/4.

Btw...... I just rode my DOT 5 80X at the Clairsville Rally where we ran 50--100 mph through the twisties for hours where brake performance is essential. My DOT 5 converted system worked and performed flawlessly right behind the leader riding a 1200 ZRX at a very nice pace for 2 hrs at a time.

Hope this helps everyone realize that DOT 5 is a good thing and not to be feared.

My best.........Mike
It's not what you ride.....it's how you ride.

oilheadron

Re: Another reason to avoid DOT5 brake fluid?

Post by oilheadron »

Mike, if I wanted to convert the healthy brakes on my '79 X to DOT 5, what would the correct procedure be??

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Re: Another reason to avoid DOT5 brake fluid?

Post by EMS »

Nils: could you please get us a "Beating a Dead Horse" smiley?? If you can't, I have to come up with one myself.

And Ron and Mike : As you two guys seem to be so close and exchange phone calls all the time, why don't you discuss the advantages of DOT5 brake fluid in privacy among yourselves and spare the forum another lengthy fruitless attempt to "educate the masses" :teasing-poke: Or better yet: Take it to the Brewer list. Most guys there are still in the 70s and sure would appreciate that update to the latest technology :laughing-rolling:

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Re: Another reason to avoid DOT5 brake fluid?

Post by NobleHops »

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Re: Another reason to avoid DOT5 brake fluid?

Post by Mike Cecchini »

oilheadron wrote:Mike, if I wanted to convert the healthy brakes on my '79 X to DOT 5, what would the correct procedure be??
Hi Ron,

It's dead simple....... just pump in the DOT 5 as the DOT 4 leaves. No draining, flushing or anything else really needed.

I'm rather anal, so after a few weeks of riding my X......and all the fluid was mixed...... I did it again just to clean things out.....something line you'd do when going from dino oil to full syn oil.....if you wanted to make sure you got most of it out. I'm on my 5th year of DOT 5 and not a single issue. Brake lever is as firm as it's ever been and the brakes feel great. Like I mentioned in my earlier posts, the late model (4 piston) calipers are still on the shelf because I like the original brakes now that everything is working well.

Fwiw......sometimes DOT 5 is a little harder to bleed 100%......but if you've done brakes before it shouldn't be an issue..... my 80 wasn't.

Then sit back and enjoy the non-corrosive protective properties of DOT 5 for years and years. I love it. :dance:

My best........ Mike
It's not what you ride.....it's how you ride.

oilheadron

Re: Another reason to avoid DOT5 brake fluid?

Post by oilheadron »

EMS and others, seeing as how we work on vintage motorcycles of all types here practically every day, maybe a tiny bit of respect is due?? Or are we of the wrong "religion" to get along here??? You know what I'm talking about.

Mike, we have a ONE-OWNER 1970 Ducati RT450 in the shop right now. Original tires, chain, sprockets, paint, everything. NOT for sale though. :)

P.S. For the naysayers, we HAVE seen a late-model Busa that was converted to Dot 5 (I don't know what procedure the owner used, if any), and it did develop seal problems in the calipers (swelling resulting in dragging brakes).

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Re: Another reason to avoid DOT5 brake fluid?

Post by Mike Cecchini »

Hi Ron.......thanks for the religious words.

Re: Busa w/DOT 5....... tis the first Japanese bike I've heard with neg results. Neg happenings usually happen with Brembo systems.... not Japanese products.

No worries here though..... as we concentrate on our X's and how to keep them alive in their seditary lifestyles. With 5+ yrs of DOT 5 in several X's.....no problems..... quite the contrary......they don't sit there and puke their caustic white foam DOT 3/4 brake fluid.

Thanks for you thoughts and imputs.

My best........Mike

ps...... I'm a V-twin Duck man, so no thumpers allowed in the shed. ;))
It's not what you ride.....it's how you ride.

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Re: Another reason to avoid DOT5 brake fluid?

Post by steve murdoch icoa #5322 »

Keep it coming fellas.
I read all the threads, try and filter through the personal biases and them make my own decisions.

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Re: Another reason to avoid DOT5 brake fluid?

Post by Mike Cecchini »

steve murdoch icoa #5322 wrote:Keep it coming fellas.
I read all the threads, try and filter through the personal biases and them make my own decisions.
Amen Steve........and it you were closer you could drop over and see for yourself.
It's not what you ride.....it's how you ride.

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