DOT4 vs DOT5
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Ultimate HDF Member
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DOT4 vs DOT5
I understand that DOT5 brake fluid is supposed to be pure silicone and is supposed to be able to handle higher operating temps than DOT4 but I was recently told that one gives a softer feel at the lever that the other. Does anyone know which one it is? Also, why would one be better to use than the other?
Club Member
Joined: Aug 2008
Posts: 2,875
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From: Texas
I understand that DOT5 brake fluid is supposed to be pure silicone and is supposed to be able to handle higher operating temps than DOT4 but I was recently told that one gives a softer feel at the lever that the other. Does anyone know which one it is? Also, why would one be better to use than the other?
I believe the Dot 4 feels "softer" as it absorbs water.
Road Captain
Joined: Feb 2010
Posts: 541
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If your using dot4 make sure if you change over to get evry drop out as I remember they are not compatable. Back in the 80s lot of people changed over because dot 5 wouldn't harm paint and higher boil point. disadvantages include air bubbles and no lubricity needed in anti lock brakes
Road Warrior
Joined: Jun 2009
Posts: 1,347
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From: Michigan
dot 4 and 5 aren't compatible
dot 3/4 and 5.1 are
i know my '11 sg runs dot 4 and all my metrics always have since 93 at least.
Road Warrior
Joined: Nov 2008
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From: Cheltenham, UK
Whilst I haven't personally experienced this, I did do some research recently (for another purpose) and there very clear indications that the seals required for these fluids are chemically incompatible.
I specialise in hydraulics and we often get involved with specialist fluids for aerospace applications, and brake fluid is often used as an equivelant test medium. Believe me, get the wrong fluids in a system with the wrong fluid and you will have an almighty mess on your hands.
An o'ring in not an o'ring! The rubber compounds used are very special for brake systems. Naturally the same issue COULD apply to your hoses. I would very seriously discourage you from contemplating such a change.
I specialise in hydraulics and we often get involved with specialist fluids for aerospace applications, and brake fluid is often used as an equivelant test medium. Believe me, get the wrong fluids in a system with the wrong fluid and you will have an almighty mess on your hands.
An o'ring in not an o'ring! The rubber compounds used are very special for brake systems. Naturally the same issue COULD apply to your hoses. I would very seriously discourage you from contemplating such a change.
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I'm not contemplating a change. I ask because my fluid (supposed to DOT4) has leaked out all over my new bike 2 times now due to the failure of the piece under the triple trees. The line from the mastercylinder goes down under the triple trees then branches out into two lines that goes down to the dual disc calipers. At the junction under the triple trees where the split into two is, it has leaked twice. It's has gotten as I said (supposed to be DOT4) brake fluid everywhere. I thought DOT4 fluid would ruin paint almost instantly. The first time it happened while I was riding and I noticed almost immediately and got it all cleaned off pretty quickly. No damage. The second time it was on my bike lift and may have been leaking for several days. I went out to ride and I was going to get my bike of the lift and noticed brake fluid all over my front fender and all over my lift. I trailer the bike immediately to the dealership because it's under warranty and the wind while trailering blew brake fluid everywhere again. I cleaned it off the best I could and they washed the bike as soon as I arrived. They say they'll take care of any damage but I'm concerned about it screwing up the paint on the frame and engine. Replacing the fender would be easy enough bit the frame and engine would be a huge problem. Then I came home and cleaned my lift. So far it doesn't seem like it hurt the paint on my lift so it got me wondering if they could have used DOT5 after the first spill? I was so upset over it yesterday my stomach hurt. I talked to the general manager of the dealership and he said "they would make it right" but I'm wondering how far they will go to correct the problem if the worst comes to fruition.
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Big Kahuna HDF Member
Joined: Nov 2008
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From: Calgary eh
Personally I don't think it would make a GD bit of difference. Use what the manufacturer suggests and you can't go wrong. You know the saying - if it aint broke don't fix it.
Sure if you're running a stock car at 200+mph where the brakes glow a bright red from the heat in the corners then you have to figure out the best fluids to use.
We have over grown lawnmowers in comparison. Run them for several hours in a straight line then gently apply the brakes to slow down for a light. We're not talking perfomance here, we're talking harleys.
Sure if you're running a stock car at 200+mph where the brakes glow a bright red from the heat in the corners then you have to figure out the best fluids to use.
We have over grown lawnmowers in comparison. Run them for several hours in a straight line then gently apply the brakes to slow down for a light. We're not talking perfomance here, we're talking harleys.
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Road Warrior
Joined: Nov 2008
Posts: 1,296
Likes: 3
From: Cheltenham, UK
I'm not contemplating a change. I ask because my fluid (supposed to DOT4) has leaked out all over my new bike 2 times now due to the failure of the piece under the triple trees. The line from the mastercylinder goes down under the triple trees then branches out into two lines that goes down to the dual disc calipers. At the junction under the triple trees where the split into two is, it has leaked twice. It's has gotten as I said (supposed to be DOT4) brake fluid everywhere. I thought DOT4 fluid would ruin paint almost instantly. The first time it happened while I was riding and I noticed almost immediately and got it all cleaned off pretty quickly. No damage. The second time it was on my bike lift and may have been leaking for several days. I went out to ride and I was going to get my bike of the lift and noticed brake fluid all over my front fender and all over my lift. I trailer the bike immediately to the dealership because it's under warranty and the wind while trailering blew brake fluid everywhere again. I cleaned it off the best I could and they washed the bike as soon as I arrived. They say they'll take care of any damage but I'm concerned about it screwing up the paint on the frame and engine. Replacing the fender would be easy enough bit the frame and engine would be a huge problem. Then I came home and cleaned my lift. So far it doesn't seem like it hurt the paint on my lift so it got me wondering if they could have used DOT5 after the first spill? I was so upset over it yesterday my stomach hurt. I talked to the general manager of the dealership and he said "they would make it right" but I'm wondering how far they will go to correct the problem if the worst comes to fruition.
Whatever the brake fluid reservoir cap says, that is what you should use. If you do not know your bike from new, then could it be that someone put the wrong fluid in which has led to the degradation I describe above? I only ask this as an option and don't want to try alarming you, but it is worth asking the question.
I would be challanging the dealership to provide a detailed description of the work they intend doing to "make this right", and encourage the assumption that this fluid has worked its way deep in to the bike.
I feel for you and I too would feel sick in the gut.
Outstanding HDF Member
Joined: Jul 2007
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From: Daytona, Fla.
Dot 4 will ruin paint, but I wouldn't let it make me sick. You have a couple of reservoirs of brake fluid on the bike, & a leak will happen eventually. I'd be more concerned with that leaky splitter & your front brakes.
If your paint isn't damaged then the dot 4 was not on it long. If it is damaged, well, it's only paint. Your dealer has said he'll take care of it, so give him the chance. The brake fluid won't hurt anything other than paint. I know it's a hassle, but don't let it ruin your day. It can be fixed.
Dot 4 usually eats the paint on the reservoir. Any damaged paint will become soft & bubble. Feel any areas that you think were exposed to dot 4 with your finger. If they're soft, expect trouble.
If your paint isn't damaged then the dot 4 was not on it long. If it is damaged, well, it's only paint. Your dealer has said he'll take care of it, so give him the chance. The brake fluid won't hurt anything other than paint. I know it's a hassle, but don't let it ruin your day. It can be fixed.
Dot 4 usually eats the paint on the reservoir. Any damaged paint will become soft & bubble. Feel any areas that you think were exposed to dot 4 with your finger. If they're soft, expect trouble.