Disc rotor thickness

[Racey Rider]

Originally posted by Dave
Don't use racing brake fluid unless your racing-because it must be replaced after every meeting.

Dave, Dave, Dave,

You don't fall for the old, " This bottles got the word RACING on it so must be far better than that other stuff, (that everybody else uses, which works perfectly well), even though it cost three times more and last only ONE MEET!" line do you???

[Dave]

Sad but true!- We have brake fluid testors in our w/shop vans that check for water content in fluid and yes the fluid is rooted after one meeting.

[gpercivl]

Dave's right, true race grade brake fluid can withstand very high temperature extremes but is very hygroscopic and in NZ's high humidity conditions absorbs water quickly...when this happens its heat expansion characteristics change and instead of staying at the same volume at high temperature it expands and can potentially lock on your brakes. Luckily you probably won't need this higher rated brake fluid...go for the std road grade or medium for racing.

[wkid_one]

Yep - the higher the dot rating the more hydroscopic the fluid is (absorbs water).....if you change your fluid regularly this isn't an issue tho.

Best improvement - go to Greenlane Speed Shop and get some Braided Lines - should cost about $100 - then fluid isn't as important.  Rubber hoses flex under pressure and what you may have is a weak point in the hose which is reducing pressure on the callipers.  Run to sperate lines off a double banjo bolt from the master cylinder - one for each caliper....copy length of existing lines - you pay per metre at GSS - so it is very cost effective - they just made some for the R1 for me and couriered them down.

Just get the reco'ed Dot fluid (stamped on Master Cylinder) - nothing else is needed.

 

[Motu]

Dot 3 fluid has a higher boiling point than dot 4,but is more hydroscopic,so needs to be changed more - this piece of highly esoteric information was found in the Motomail cataloge.You don't need a fancy brake fluid tester,and you don't need to pay them to test it for you - you should have a brake fluid tester at home....a digital multi metre.Put the positive lead to earth and the negative lead in your resivour - if it reads over 300 milivolts replace it...do it with your coolant too - over 600 mv and toss it.The water turns into electrolite,thats what we are measuring here,good enough for me.

[Coldkiwi]

now thats some good practical advice motu! I kinda assumed Dot 4 was simply better in all depts. than a Dot 3. I really need to get a multimeter now too

*sigh* (looks longingly at empty account)

 

[wkid_one]

Just fill the reserviour with water - and watch the fun

[Redstar]

one way to determine disc reduction is to feel the ridge on the outside edge and the difference like a 5mm detented to 3.5mm
warping. I'ts highly unlikely that brake disks suddenly present an issue its usually progressive? but a leaking fork seal is a common cause of thrilling sudden failure as the oil creeps onto the disk knowing 91 TZR250'S there might be an issue here?

[Coldkiwi]

..assuming you had 5mm discs to start with... but it won't be thickness causing any problems as much as subsequent warping etc. using fingers to determine brake disc thickness is a pretty dodgy way to go if you ask me! get a micrometer and do it right

[wkid_one]

Just steal your kids 150mm plastic ruler from their pencil case and use the compass