decent brake fluid
21 November 2010, 07:43 PM
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decent brake fluid
hi all any one recomend a decent brake fluid i am putting brembo's on my 02 wrx ready for the track so after a decent fluid any one got a favourite
23 November 2010, 11:18 AM
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There's not much to choose between the top brands like Motul, Castrol, AP, Millers etc any of these will do the job no problem, if you absolutely have to choose a winner then look at the fluids boiling point, this indicates the temp at which the fluid starts to boil, so higher the better.
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24 November 2010, 11:04 AM
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Motul RBF600 has a DOT 4 rating and a very high boiling point. I use this in my track (kit) car. They also make a RBF660 if you really want to push the boat out.
I'd guess the DOT ratings are for application in road use where a 5.1 may have a longer service life and other properties but not necessarily a higher boiling point.
I'd guess the DOT ratings are for application in road use where a 5.1 may have a longer service life and other properties but not necessarily a higher boiling point.
24 November 2010, 10:14 PM
#10
Quick question as you guys seem to know your onions, I've bought a MY99 Sti and as it's 30k service was in Japan, service history is in Japanese. How do I know what brake fluid to add if I need to top up the system, i've heard you can't mix dot 3 or 4 or different fluid manufacturers. Is my only option therefore to drain and bleed the system with new oil? Guessing the answer will be the same for clutch fluid also?
24 November 2010, 10:57 PM
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cheers again guys got some great feed back sorry for the stupid questuon but whats dot system based on i get the boiling point and why just the dot rating
24 November 2010, 11:10 PM
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not all brake fluids mix,if you flush with a synthetic 5.1 fluid there is a risk of existing old brake fluid in the system being of the hygroscopic type which means it absorbs water,you wont realise so any moisture in the brake system will end up in that small amount of fluid left at risk of causing brake fluid to boil and excessive pedal travel,the safest option will be is to buy a quality branded dot4 or even 5 that will mix with older non synthetic b,fluid thus the fluid should be changed every two years.only 3% water will reduce the wet boiling point bu 100 degrees celsuis,dot 4 boils at approc 155 degrees and dot 5 at approx 180 degrees,i use castrol myself .if the systems completely dry then deffo use 5.1 synthetic imo
Last edited by classicgc8; 24 November 2010 at 11:12 PM.
25 November 2010, 10:39 AM
#13
Just finished putting an article together on brake fluids, hope this helps.
Brake fluid... Bit of a mystery topic!
Brake fluid... Bit of a mystery topic!
To help dispel some myths and for some good, solid general info on the mysterious world of brake fluids I decided to contact Millers Oils up in West Yorkshire.
Their Technical Director, Martyn Mann was on hand to give us some useful info… Below is Martyn's article on brake fluids.
There is a degree of confusion regarding the specification of brake fluid and this article sets out to clarify the situation.
The Department of Transportation (DOT) classifies brake fluids to defined specifications. These specifications relate to their boiling points and chemical composition, both of which are important. All currently available brake fluids are covered by one of the following specifications; DOT3, DOT4, DOT5 and DOT5.1.
The laws of thermo-dynamics dictate that the energy from motion is turned into heat through friction. A braking system only works efficiently if the fluid remains incompressible. If the brake fluid boils, it turns to gas, which is compressible and the braking system becomes “spongy” or in extreme cases fails completely.
A brake system is not perfectly sealed and moisture can get into the system and be absorbed by the fluid. The effect is to reduce the boiling point of the fluid, which reduces the efficiency of the braking system, as described above.
The DOT specifies two reference tests for brake fluids.
* Dry boiling point - the boiling point of fresh fluid
* Wet boiling point –the boiling point once the fluid has absorbed moisture (representing brake fluid after time spent in a real situation).
* Dry boiling point - the boiling point of fresh fluid
* Wet boiling point –the boiling point once the fluid has absorbed moisture (representing brake fluid after time spent in a real situation).
There are two main types of brake fluids:
* DOT 3, DOT 4, Super DOT4* and DOT 5.1 which are based on poly glycol compounds.
* DOT 5, which are based on Silicone.
Note the two types of fluid are not compatible and must not be mixed in a braking system.
SILICONE BRAKE FLUID (DOT 5)
Silicone based DOT 5 was originally introduced to give higher temperature performance over glycol DOT 4. Silicone fluid also has other advantages, it does not damage paintwork and it does not absorb water.
However, silicone fluid is a poor lubricant and does not lubricate ABS pumps as well as PAG fluids. It is also more compressible than PAG fluids, which can result in a sluggish or spongy pedal. It therefore requires special design considerations in braking systems. Further, because it does not absorb water, any water remains as globules, which can pool in low spots in the system and cause corrosion. This water can vaporise when heated under heavy braking giving a disastrous effect on braking efficiency.
DOT5 fluids are not recommended for motor sport applications.
POLY GLYCOL BRAKE FLUIDS (DOT 3, 4 AND 5.1)
Glycol based DOT 4 fluid is the current mainstream brake fluid, and you will see that the specification is considerably better than DOT 3 which it replaces.
DOT 5.1 has higher specification still and is for fast road and occasional track day use. It has a similar spec to DOT4 for the boiling point (>260) but is a lot lower viscosity @-40C typically 900 centistokes (compared to 1500 - 1800 centistokes for DOT 4 and super DOT 4).
Listed in the table below, are the minimum dry/wet boiling point specifications for each DOT level.
BOILING POINT:
DOT 3 - 205°C (dry) / 140°C (wet)
DOT 4 - 230°C (dry) / 155°C (wet)
DOT 5 (silicone) - 260°C (dry) / 185°C (wet)
DOT 5.1 (PAG) - 260°C (dry) / 185°C (wet)
Super Dot4 * - 300°C (dry) / 195°C (wet)
(racing brake fluid)
DOT 4 - 230°C (dry) / 155°C (wet)
DOT 5 (silicone) - 260°C (dry) / 185°C (wet)
DOT 5.1 (PAG) - 260°C (dry) / 185°C (wet)
Super Dot4 * - 300°C (dry) / 195°C (wet)
(racing brake fluid)
* Super DOT4: The main difference between DOT 4 and Super DOT 4 is the dry boiling point. Normal Dot4 is >260C whilst Super DOT 4 is more like>310C
With thanks to Martyn Mann - Technical Director Millers Oils.
Cheers
Guy.
Opie Oils
Opie Oils
25 November 2010, 04:52 PM
#14
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classicGC8 your getting your dot5 and dot5.1 mixed up.........
easiest is to forget all about dot5 which is suspect at best in most modern systems, and definately a no-no in a track/competing car
alyn
easiest is to forget all about dot5 which is suspect at best in most modern systems, and definately a no-no in a track/competing car
alyn
26 November 2010, 10:35 AM
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Buried in Oilman's info is the key difference between DOT 4 and DOT 5.1. 5.1 has a low viscosity to enable modern ABS systems to work better when rapid fluid motion is required. To get a very high boiling point race fluids have to use higher molecular weight glycols and these will be slightly more viscous and hence cannot meet the DOT5.1 viscosity spec. Not a problem if you don't have ABS or a DOT 5.1 specified system.
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