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Hope this isn't too dumb of a question, but here goes. I have a 90 Sporty and changed the rear brakes recently. I bought DOT 4 while there and assumed there was DOT 3 or 4 was in there. You can mix Dot 3 and 4 from what I understand, but not DOT 5 (synthetic).

After I changed brakes, I blead. Refilled the master cylinder up and put the lid on. That is when I noticed the lid said use DOT 5 only. At that point I got some tubing and sucked out all the fluid and blead the rest. Refilled with DOT 5 like it said. The fluid that came out initially seemed to be brown, but the 5 is purpleish. Also when I blead the 5 it seemed to kind of bead on top on the 4 that was previously blead in the drain bucket, so I assume it was initially 3 or 4. The brakes do work just fine as is but am concerned with traces of 3/4. With the 5 I have had no problems for the last week and a half or so, and brakes work perfect now.

So now what??? Should I drain again, clean out the lines with something and refill with 4? Will this system gum up now that has traces of 3/4? The rear brakes work great currently but did I screw up big time?

I will replace the front as well soon. The fluid in the master is brownish so I assume 3 or 4, but need to make sure.
 

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I {Heart} Hookers.
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DOT 5 will not get "brownish". Someone put something else in your rear brake system, before you. It sounds as if there's already DOT 3-4 in there, and now it's full of moisture/rust/contaminants.

In order to clean it completely, the rear brake system should be taken apart, and flushed/cleaned with denatured alcohol, then put back together with DOT-5.

Considering it's the rear brake system and it's small, it's not that hard to do. It also sounds as if it's necessary anyway, if there's brownish colored gunk in there to begin with....
 

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DOT 5 will not get "brownish". Someone put something else in your rear brake system, before you. It sounds as if there's already DOT 3-4 in there, and now it's full of moisture/rust/contaminants.

In order to clean it completely, the rear brake system should be taken apart, and flushed/cleaned with denatured alcohol, then put back together with DOT-5.

Considering it's the rear brake system and it's small, it's not that hard to do. It also sounds as if it's necessary anyway, if there's brownish colored gunk in there to begin with....
Dave do you run DOT 5?

Could I flush out my DOT 4 system and use the less corrosive higher boiling point DOT 5?
 

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I {Heart} Hookers.
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Dave do you run DOT 5?

Could I flush out my DOT 4 system and use the less corrosive higher boiling point DOT 5?

Yes, I use DOT-5, but only because the system came with it. If your system has any natural rubber seals in it, they'll degrade with DOT-5.

HD used DOT-5 for about 8-10 years, and then went back to DOT-4 for various reasons. Despite the advantages of DOT-5, I'd stick with DOT-4 and just change it yearly, or every other year.

It's 4:14am.... what are YOU up? :D
 

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Yes, I use DOT-5, but only because the system came with it. If your system has any natural rubber seals in it, they'll degrade with DOT-5.

HD used DOT-5 for about 8-10 years, and then went back to DOT-4 for various reasons. Despite the advantages of DOT-5, I'd stick with DOT-4 and just change it yearly, or every other year.

It's 4:14am.... what are YOU up? :D
Is the question why am I up or what am I up to? It doesnt matter because I refuse to answer either one. :rofl: Thanks for the info.
 

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SILICONE BASED FLUID
Fluids containing Silicone are generally used in military type vehicles and because Silicone based fluids will not damage painted surfaces they are also somewhat common in show cars.

Silicone-based fluids are regarded as DOT 5 fluids. They are highly compressible and can give the driver a feeling of a spongy pedal. The higher the brake system temperature the more the compressibility of the fluid and this increases the feeling of a spongy pedal.

Silicone based fluids are non-hydroscopic meaning that they will not absorb or mix with water. When water is present in the brake system it will create a water/fluid/water/fluid situation. Because water boils at approximately 212º F, the ability of the brake system to operate correctly decreases, and the steam created from boiling water adds air to the system. It is important to remember that water may be present in any brake system. Therefore silicone brake fluid lacks the ability to deal with moisture and will dramatically decrease a brake systems performance.

POLYGLYCOL ETHER BASED FLUIDS
Fluids containing Poly glycol ethers are regarded as DOT 3, 4, and DOT 5.1. These type fluids are hydroscopic meaning they have an ability to mix with water and still perform adequately. However, water will drastically reduce the boiling point of fluid. In a passenger car this is not an issue. In a racecar it is a major issue because as the boiling point decreases the performance ability of the fluid also decreases.

Poly glycol type fluids are 2 times less compressible than silicone type fluids, even when heated. Less compressibility of brake fluid will increase pedal feel. Changing fluid on a regular basis will greatly increase the performance of the brake system.

FLUID SPECIFICATIONS All brake fluids must meet federal standard #116. Under this standard is three Department of Transportation (DOT) minimal specifications for brake fluid. They are DOT 3, DOT 4, and DOT 5.1 (for fluids based with Polyalkylene Glycol Ether) and DOT 5 (for Silicone based fluids).

MINIMAL boiling points for these specifications are as follows:

Dry/wet

DOT 3 401ºF 284º F
DOT 4 446º F 311º F
DOT 5 500º F 356º F
DOT 5.1 518º F 375º F

Racing brake fluids always exceeds the DOT specifications for dry boiling points. Wet boiling points generally remain the same.


http://www.afcoracing.com/tech_pages/fluid.shtml
 

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Discussion Starter #7
Dave, I think you may have missunderstood a bit. There was not brown gunk in my system, the fluid in the master cylinder has a slight bronwish tint to it, definitely not the purple synthetic. What was beading was the synthetic that was blead on top of the 3-4 in my bucket.

I guess I had two questions and the answer to the first question may still be that I need to flush my system.
1. am I ok with my system currently since I put in the 5 like it required when there was 3-4 in there previously?
2. what should I do about the front brakes? There is clearly either 3 or 4 in there now.

The matser cylinder lid was replaced with an after market Harley logo lid so it does not say what to use but would have to be the same as the rear.
 

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1. am I ok with my system currently since I put in the 5 like it required when there was 3-4 in there previously?
No. DOT 5 (silicone based) is not compatible with DOT 3, 4, 5.1 (polyglycol ether based). If left long enough, the mixture of the two different types will gel.

This should answer your 2nd question as well.
 

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If the fluid was brownish colored, like Coca-cola, but still see-through, that's what clear silicone, DOT-5 looks like after 1-2 years.

Honda DOT-5 is orange. HD's is purple. Someone just used a non-HD brand over the years.

Keep the DOT-5.

Bleed the rear brake until the new fluid shows up, out the caliper bleeder. Careful not to drain the reservoir during bleeding, or you'll introduce air into the system, and have to start over.
 

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Old conversation but what is the reaction of the rubber components with the 2 different fluids? I'll elaborate better. Master cylinder suggested fluid dot 5. Calipers dot 5.1. System flushed and washed with denaturated alcohol. Will the dot 5 harm any rubber component in the calipers and/or the dot 5.1 harm the master cylinder orings amd such? Thanks

Sent from my D5503 using Tapatalk
 

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Old conversation but what is the reaction of the rubber components with the 2 different fluids? I'll elaborate better. Master cylinder suggested fluid dot 5. Calipers dot 5.1. System flushed and washed with denaturated alcohol. Will the dot 5 harm any rubber component in the calipers and/or the dot 5.1 harm the master cylinder orings amd such? Thanks

Sent from my D5503 using Tapatalk
Using DOT 5 will be fine . :nerd
 

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Using DOT 5 will be fine . :nerd
Thanks. Would the same be for 5.1.
Im more keen on using a non silicon since i can guarantee that the master cylinder is flushed amd rebuilt with all new rubber and components while the calipers were just washed but not split amd rebuilt

Sent from my D5503 using Tapatalk
 

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Dot 5 will NOT harm any of the rubber compounds used in brake systems. It does not mix with regular glycol based fluids, and that is where the compatibility problem comes from. Other than absolutely not usable in any ABS system, it can be used in all other brake systems.
 

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So, I should use DOT 4 when I do my brakes? 05 FLH
 

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So, I should use DOT 4 when I do my brakes? 05 FLH
Read the master cylinder cap, Jim.

My 2005 uses DOT-4. HD went back to 4 in 2005 on touring, and eventually ALL bikes.

Brembo makes HD's brakes now, not Kelsey Hayes, and DOT-5 can NOT be used with natural rubber seals, which Brembo uses. Also causes issues with ABS, due to bubbles.

As stated in their literature.

As well..........4 is cheaper.

DOT 5.1 is compatible with 3 and 4. Not 5.
 

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I'm swapping out the covers because the paint all flaked off the original ones. Does it say it on the little ring around the sight glass?
 

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Yes
 

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k, thx. Thought it might. None of the pics I've taken happened to capture that, and the ones I found by searching aren't high res enough to read.

 

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Dot 5 is always silicon fluid. Will not harm any rubber, but will not mix with dot 3,4, or 5.1. 5.1 is glycol based! The numbering system the government used got confusing after DOT 5. Not sure why they would use 5.1, but that's what they did.

If you changed all the fluid out and Dot 3 or 4 wasn't in there long, ride for a week or so and bleed again, with new DOT 5 and you'll be OK. If the system has had 3 or 4 in it for a long time, then you need to flush with fresh 4 or 5 then alcohol and replace all rubber then install new DOT 5.
 
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