rear brake fade
 

Hi everyone tried to do a search to see if anyoneelse has had rear brake fade but couldn't find owt specific. My xt660r suffers from rear brake fade only when doing runs over Hardknott pass or Wrynose pass in Cumbria. The rear pedal goes all the way down and no braking at all. front brake is ok (thank goodness). I'm assuming having a few yams in the past and never such an issue with them, that it's because the brake line runs behind the right hand side of the swing arm very near the right hand upswept part of the exhaust pipe?? Because these fell passes are ridden relatively slowly due to steep gradients I'm also assuming the brake line gets warm and the fluid just looses hydraulic viscosity but no visible loss of fluid? Then braking returns once the bike is. Parked for a while and everything cools down? Any advice before I pull my rear brake to bits and buy shiney new bits please? ��ta muchly.

http://i1379.photobucket.com/albums/...psxtnikzw9.jpg I agree, after several runs up and down the Healy Pass on my XR650R the brakes were cooked, lever back to the grip!. Tea, cake and half hour later all back to normal! Steve

http://i1379.photobucket.com/albums/...psjydqajdo.jpg The brake-cooking Healy Pass! Steve

:thumbsup: thanks for the feedback. Wondering if a braided hose will stop this?

How old is the brake fluid, more than a year or so?? Always good to start there and bleed it out with fresh fluid and I'd make sure it's DOT 5.1 to give it the best possible boil point.
Matt.

Brake fluid.

I had it in my rat-bike Triumph coming down the Stella Alpina - the fluid was old, contained too much water (brake fluid absorbs moisture over time), lowering the boiling point, and when it was worked hard enough and got hot enough the fluid boiled - hey presto, brake fade.

I changed it, problem solved. As a rule of thumb if the brake fluid looks the same colour as if you had pissed it you'd think about going to a Doctor then it's time to change it....

Any excuse for a gratuitous rat-bike Triumph pic!

http://www.sweller.co.uk/images/Triu...llaAlipina.jpg

Macca and Sweller are spot on - BRAKE FLUID!

When was your brake fluid last flushed/changed? If you can't answer that question, or it was more than two years ago, change it now! Even if it looks good and normal in colour, change it. You cannot visually tell the moisture content of brake fluid.

Brake fluid, as has been mentioned, is hygroscopic (water absorbing) which means that as time passes water diffuses through the hoses and seals and becomes trapped in the fluid lowering its overall boiling point. Although, strictly speaking, it is actually the trapped moisture that boils (at ~100C) then causes pockets of gas (water vapour) to appear in the system which are compressible, unlike the fluid itself.

4% moisture in DOT4 fluid will lower it's overall boiling point from 230C to 150C, which makes a BIG difference to brake fade. 4% water absorption can occur in as little as a year in damper climates.

Just as an aside, DO NOT use DOT 5 fluid as it is silicone based and does not mix with all the other glycol based ones. It can only be used from scratch in a new dry system. Confusingly, DOT 5.1 is glycol-based and fine. Also, never use fluid to top up or replace from an already open or old bottle.

Yes and no. The braided hose itself won't stop the brake fluid boiling up, but changing the hose requires fresh brake fluid which will...

...and rubber hoses become gas permeable over time. Replacing your hoses will reduce the chances of moisture getting into the hydraulic system from the atmosphere.

Saw these on fleabay :idea1:
http://m.ebay.co.uk/itm/281381775934?nav=SEARCH

thanks again everyone for comments / experience. Great photos guys!

My thoughts too Pleiades. It's an 07 XtR. Only had it a 15 months - was fairly rough when l bought it. Gave it some tlc HH Pads fluid fork n engine oil. Leo Vince cans. Loving it great round my twisty back/fell roads.