Brake Fluid DOT 3, 4, 5, 5.1. What does it all mean?

[mylife98]

I am on a (very enjoyable!) learning curve at the moment and these two posts reminded me I needed to read-up on brake fluid and what it all means. ( Best Brake Fluid and VAG Oils Listed By Specification).

Found two really excellent articles to get me started, attached below. As ever, any thoughts and opinions highly valued!






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With full credit to Carroll Smith and James Walker, Jr. of scR motorsports (sourced from http://www.stoptech.com/tech_info/wp_br ... d_1a.shtml)
Reproduced here in case the link ever goes down.



Brake Fluid 1A
by Carroll Smith and James Walker, Jr. of scR motorsports

Carroll Smith's Notes on Brake Fluid

Brake fluid is possibly the single most neglected component of the automobile. Most high performance drivers check their tire pressures and change their engine oil at frequent intervals. Virtually no one (including me) ever changes the brake fluid in their street car - or even bleeds the brakes. WRONG!

The function of brake fluid is to provide an incompressible medium to transmit the driver’s foot pressure on the brake pedal through the master cylinder(s) to the calipers in order to clamp the friction material against the discs. The foot pressure is multiplied by the mechanical pedal ratio and the hydraulic ratio of the master cylinders, booster (if used) and caliper piston(s).

This is a simple concept. When fresh, all brake fluids are virtually incompressible and the system works as well as its mechanical and hydraulic design allows. There are, however significant problems. Overheated brake fluid can (and will) boil in the caliper. Boiling produces gas bubbles within any boiling fluid. Gas is compressible so boiling brake fluid leads to a “softâ€

[ollys]

Wow!

srf for me for sure - now I know what's contributing to mushy pedal feel on the B7 set up

Olly

[mylife98]

Well the SRF specs do read very impressively. But god it's a massive % cost increase by comparison.

Considering you apparently should be changing brake fluid regularly, how many times a year do you really push your brakes that hard?

I enjoy some spirited driving on the country lanes every couple of weeks, but only do 1-2 track events a year, which is the only time I've found the brakes to be challanged. And even then, that'll take a couple of hard laps, by which time it's time to start cooling the car down anyway. So figure a improvement of DOT 5.1 over the currect DOT 4 should be a good cost effective upgrade for me.

Guess if you're doing track days every other week SRF could be worth the extra??

Mind, if you have the B7 brake setup (very nice!) then why compromise on one component in the system??!

[NeilMc]

I always use SRF and I recently installed the B7 front brake setup. The pedal isn't exactly firm on mine.
I thought it was something to do with the master cylinder being a bit inadequate for a large 8 piston setup.

[dace]

I use Motul as it lasts a wee bit longer than SRF and cheaper to boot. Very good IMO and I track the car quite a bit.

No issues withe pedal feel.