# DOT 5.1 instead of DOT 4 for formulas?



## norbar (Jun 5, 2007)

Well formula fluid is very expensive around here and I can get high quality motul race dot 5.1 fluid on good price. It's definately better quality but will the brake work ok with it? No seal problems? Anyone tried? Any advantages? My friend shifted in his old car from dot 4 to this 5.1 I can get and his brakes are much harder (ie. less rubbery modulation that I dont like). It also has much higher boil temp which could be usefull on longer steeper trails.

What do you think about it?


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## XSL_WiLL (Nov 2, 2004)

A glycol based DOT fluid will work fine, just fine. DOT 5.1 is fine, I used to use the Motul DOT 5.1 in my Avids and Hayes. I've since moved on to Motul RBF600 - It's a DOT 4, but it's got a crazy high boiling point.

The change from DOT 3/4 (most likely 3 if it's an older car) to DOT 5.1 should not change the feel of the pedal - it probably had more to do with the fact that he had air in the system, and by bleeding, he got it all out.


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## Rover Nick (Jul 13, 2006)

If you can find it, I would use it. Around here, I had to go to 4 different auto parts store and a couple of motocross strores to find it.


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## XSL_WiLL (Nov 2, 2004)

Rover Nick said:


> If you can find it, I would use it. Around here, I had to go to 4 different auto parts store and a couple of motocross strores to find it.


I ordered mine out of a catalog.


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## norbar (Jun 5, 2007)

Well have a couple of friend that make it easy to get it.

But from what I know there is also a viscosity differance between dot 4 and 5.1. That is what affects the work of the brakes.


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## Ithnu (Feb 16, 2007)

XSL_Will is right, it shouldn't change the feel, the different brake fluid is DOT 5 with is silicone based, which is a big no for bike brakes. I thought the only real difference is the boiling point between the fluids. I went and got DOT 5.1 at a motorcycle store.


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## CrustyOne (Oct 29, 2007)

agreed, ...... 4 and 5.1 will feel same...........stay away from 5 on formulas or hope ........ probably others


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## chooofoojoo (Feb 22, 2007)

CrustyOne said:


> agreed, ...... 4 and 5.1 will feel same...........stay away from 5 on formulas or hope ........ probably others


ummm.. newer hopes are designed around use of Dot 5.1


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## 1000-oaks (Nov 15, 2006)

There is a TON of bad info about DOT 5 silicone fluid out there, especially in the automotive world.

- DOT 5 doesn't absorb water like DOT 3 and 4 do, which is intentional so that steel brake lines don't rust. DOT 5 is okay in race cars because they change fluid every race. Possibly not an issue in bike brakes, since there's no steel.

- New/clean DOT 5 may have a higher boiling point than DOT 4, but water droplets in the caliper still boil and turn to steam = spongy brakes.

- Clean DOT 5 is more compressable than clean DOT 4, which means brake feel will be LESS firm. (clean DOT 5 may feel the same as old/wet DOT 4 though, depending on how much water is in it)

- Prior to changing to DOT 5, the entire hydraulic system MUST be flushed with alcohol and all DOT 3/4 glycol-based fluid removed. If any DOT 3/4 remains, it will react with the DOT 5 and turn to gel. When this happens in cars they sometimes have to trash the whole brake system and start over. (may be possible to disassemble and clean the calipers, but the lines are junk)

Bottom line: unless DOT 5 is recommended by the brake manufacturer and comes with it new, just run the highest boiling point glycol-based fluid you can find. It's cheap and it'll perform better - and all you have to do is change it once a year or so.


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## CrustyOne (Oct 29, 2007)

chooofoojoo said:


> ummm.. newer hopes are designed around use of Dot 5.1


exactly..thats why I said stay away from 5


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## Jerk_Chicken (Oct 13, 2005)

Use high quality DOT 4 in place of 5.1 if you can't find it. Even the racers use these as well, including Ate Super Blue/Green (expensive), Castrol LMA, and Valvoline DOT4, which is what I use in my Hopes, and what they are shipped with for the US.


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## XSL_WiLL (Nov 2, 2004)

1000-oaks said:


> There is a TON of bad info about DOT 5 silicone fluid out there, especially in the automotive world.
> 
> - DOT 5 doesn't absorb water like DOT 3 and 4 do, which is intentional so that steel brake lines don't rust. DOT 5 is okay in race cars because they change fluid every race. Possibly not an issue in bike brakes, since there's no steel.
> 
> ...


I said DOT 5.1. I even said glycol based. DOT 5.1 is NOT DOT 5.

Supposedly DOT 5.1 is less viscous, but you probably won't feel a difference. Works nice for ABS systems where there are all those microvalves and what-not.

There are DOT 4s with higher boiling points than DOT 5.1.


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## norbar (Jun 5, 2007)

Well actualy I can get both Motul race dot 4 and 5.1 brake fluids at very good prices from 2 sources so I don't think availability is a problem  From what I read the viscosity shoulde change how the brake works. Also I asked a car mechanic and he said that it was the visco change that affected my friends car brake work (change from 4 to 5.1)


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## XSL_WiLL (Nov 2, 2004)

As I said, the change would be slight, and it would not make the brakes feel any firmer (assuming comparison between two properly bled systems). I work on cars and bikes. :thumbsup: I bled the daily driver with Motul DOT 5.1 (had a few bottle chillin). Brake pedal felt no firmer than before (had no air), but didn't experience as much fade as before.

Any difference in pedal feel is most likely the consequence of removing air from the system. Air does compress - that's why it would feel soft of spongy.


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## chooofoojoo (Feb 22, 2007)

EDIT : Redundant post. Please delete.


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## dhtahoe (Mar 18, 2004)

Just a note. If you use 5.0 in DOT 3,4,5.1 it will eat the seals. I didn't see that point covered.


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## norbar (Jun 5, 2007)

Actualy that was said like 10 times in this tread even though I never said I'm gonna use dot 5. I was going for 5.1 or 4 as 5.1 meets 4 standards. You just need to read the bottle - I'm not that dumb


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## rustyskills (Dec 23, 2007)

why do people keep talking about DOT 5 thats not what this thread is about..


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## Perigeum Development (Jul 18, 2005)

Hi Guys,
Just to clarify any confusion about our products:

Our brakes come with a high performance DOT 4 fluid. They are compatible with DOT 3, DOT 4 and DOT 5.1, or any glycol based fluid. Changing between different fluids will affect the boiling point of the fluid and the systems ability to resist fading but will not affect actual lever feel.


Cheers,

Chris Costello


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## Octane (Mar 16, 2004)

I've used dozens of brake fluids in my race cars. I've had best success with Castrol LMA for the past couple years, you can buy it at almost any autoparts store, ie Kragen, NAPA, Autozone, etc. It's relatively inexpensive at less than $10. 

Look for a brake fluid that has a high WET boiling point. This is a better number to judge a brake fluid than the DRY boiling point. 

I've noticed that the Valvoline Syntec (sp?) Dot4 fluid was harsh on the rubber seals and caused premature seal failure, especially if the seals were older. Castrol LMA has not had this issue. 

I buy small individual bottles and write the date I open it around the lid. This helps keep track of old fluid, which is a HUGE area of concern. A bottle of brake fluid, once opened, should not be used after 6 months. Especially if it's in a severe-duty application.

Remember, brake fluid wants to chemically absorb moisture. It will pull moisture past the lid of a bottle, the seals on your brake system, etc. The harder you use your brakes, the more heat you'll generate, and the more likely you'll boil the moisture in the braking system. The bubbles don't go away until you bleed the system, and they cause the spongey brake feeling.

-Brad


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## Jerk_Chicken (Oct 13, 2005)

Octane,

It's funny you mentioned that, as I've been using Valvoline for over seven years now, from my automotive applications, to my mtb brakes. I have found the opposite with the Valvoline, and this includes usage with my clutch master and slave cylinders. I have extended the life of clutch parts, have not had a caliper seal failure (and some of my calipers date back to 1983), and in fact, once I purchased a car with a failing slave cylinder. I flushed with the Valvoline, just in case there was air, but it did not help. I checked the car a couple days later, then the slave worked perfectly for several months, in fact, until the day I changed it. The Valvoline does likely condition seals, but in my experience, it likely helps to preserve them.


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## Octane (Mar 16, 2004)

I was using the Valvoline in a copper-colored bottle. I think it was SynPower or something, but it wasn't the normal white bottle from Valvoline. I don't see it on their web site anymore.

Maybe it was the conditions I was using it under. Not sure. Everyone's experience can be different.

-Brad


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## Jerk_Chicken (Oct 13, 2005)

Yup, that's what I use.


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