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Am I correct in thinking that it's ok to upgrade from DOT 4 to DOT 5.1 brake fluid by just bleeding the DOT 5.1 through on top of the DOT 4 that's already in my braking system?

I am going to start doing some track days this year and think that it's worth changing to DOT 5.1 fluid. How often should you bleed DOT 5.1 as I am aware that it takes on moisture alot quicker than DOT 4 does?

Cheers

Stefan.
 

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Yup, they are compatible, no problems. As an alternative, if you can get Motul RBF (racing brake fluid) Dot4, I'd highly recommend it. It has a higher boiling point than other Dot 4s. The brakes should be bled enough to refill with fresh fluid at a minimum of once a year.
 

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once a year?!?! I usually change my brake fluid once ever 2-3 years and ive never had a problem...if you only track your bike 5-10 times a year you will be fine changing it every 2-3 years...its important to make sure the reservoir is full and tightly sealed..air is the enemy even if its not in the lines...DONT SHAKE THE FLUID BEFORE YOU PUT IT IN...i know u pro bably know that but ive seen someone do that before..ha ha..5.1 is a good fluid to run...5.0 is the one thats not compatible with others...
 

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once a year?!?! I usually change my brake fluid once ever 2-3 years and ive never had a problem...if you only track your bike 5-10 times a year you will be fine changing it every 2-3 years...its important to make sure the reservoir is full and tightly sealed..air is the enemy even if its not in the lines...DONT SHAKE THE FLUID BEFORE YOU PUT IT IN...i know u pro bably know that but ive seen someone do that before..ha ha..5.1 is a good fluid to run...5.0 is the one thats not compatible with others...
Brake fluid has a maximum life of two years under the best conditions.
Change it yearly. Leaving it for three years is likely to start causing rust in the system from the amount of moisture in it. It's cheap and easy (easier than an oil change) so there's no reason to run it for three years.
The reservoir does not need to be full unless you've just put new pads in. If you fill it with worn pads it will be overfull when you replace the pads. There is a rubber diaphram that goes in before the cap that limits the amount of air in the system but you should never need to open the reservoir except when you're replacing the fluid.
The brakes are a sealed system. The fluid drops as pads wear and is pushed back up to full again when new pads are put in.
 

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Discussion Starter #5
So can I assume that its ok to leave DOT 5.1 in the system for 1 year before bleeding?

It wouldn't bother me if I had to do it every 6 months because fluid is relatively cheap and is a very simple task to bleed.
 

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So can I assume that its ok to leave DOT 5.1 in the system for 1 year before bleeding?
Of course.
5.1 and 4 are completely compatible.
Bleed the new fluid through until you see fluid coming out of the calipers that looks exactly like the stuff you're putting in the reservoir.
Use the whole bottle if you're unsure since it's not worth keeping it once it's been opened.
 

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Is it worth upgrading to 5.1 for street use ?
I use DOT4 for road and track.
If I were having problems with it then I'd definately look to DOT5.1.
 

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Not to be confused with DOT 5 which is silicone based and totally not compatible with DOT 3 or 4.

Personally, I'd stick with DOT 4 and change often unless you race.
 

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Not to be confused with DOT 5 which is silicone based and totally not compatible with DOT 3 or 4.
...or DOT5.1 :)
As far as I'm aware DOT5 is not compatible with anything else at all?
I have read that some European manufacturers use DOT5 as their OEM fluid in some vehicles.
 

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Yeah, change it annually. Brake fluid absorbs moisture. Easy to change, no need to leave it in there for 3 years. When it absorbs moisture, the boiling point decreases, and so does your stopping power.

Dot 3, 4, and 5.1 are compatible. DOT5 is silicone based and is NOT compatible with 3, 4, or 5.1. NEVER use DOT5 in a system that calls for DOT3 or 4.

Not all DOT4s are created equal. Some have higher boiling points, the Motul RBF I mentioned is one of them. If you ride on the track, I'd look into one with a higher boiling point. For street riding, any DOT4 will suffice, just change it annually.
 

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once a year?!?! I usually change my brake fluid once ever 2-3 years and ive never had a problem...if you only track your bike 5-10 times a year you will be fine changing it every 2-3 years...its important to make sure the reservoir is full and tightly sealed..air is the enemy even if its not in the lines...DONT SHAKE THE FLUID BEFORE YOU PUT IT IN...i know u pro bably know that but ive seen someone do that before..ha ha..5.1 is a good fluid to run...5.0 is the one thats not compatible with others...
I get noticeable fade on hard braking courses if I don't change it at least once a year.... of course it has to stop an RC and me (it's just wool, really)
 

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I have heard from a few of the shops not to use the DOT 5.1 because it has silicone in it. If not silicone, there is something that will absorb more water than the 4.0. Can anyone here shed any light?
 

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I have heard from a few of the shops not to use the DOT 5.1 because it has silicone in it. If not silicone, there is something that will absorb more water than the 4.0. Can anyone here shed any light?
Sounds like you're confusing it with DOT5.
 

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Discussion Starter #16
Looks as though I might aswell re-bleed some decent DOT 4 through my system in March then :)

Cheers for all of the feedback.
 
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