Brake Fluid Replacement? Brake Bleed?
Question from a novice. My brakes are Avid Juicy 7's. A few months ago I was on a very long and steep ride. The guy riding behind me said he smelled something burning on a downhill section and since then my brakes have never felt like they had the stopping power they used to. I have changed brake pads and cleaned the rotors, but it doesn't seem to have helped. It just seems to take a lot more squeezing of the lever and and lot longer to stop.
My question is, can I possibly have overheated the brake fluid? If so, do I need to completly drain this and put in new fluid? If so, what is the best way to go about this?
I purchased an Avid Bleed Kit, but that seems to be geared more towards a system that is already filled with fluid. That being said, should I simply keep the fluid that is in the system already and try to bleed off any air that may have crept in?
Like I said, this is my first attempt at working on hydraulic brakes, so any suggestions would be much appreciated.
I'm a bike-newb, and am extrapolating from my experience with cars, but I think it should apply here: If your brake fluid overheats and boils, air bubbles can form in it, preventing the hydraulic system from exerting sufficient pressure on the piston (because air bubbles are compressible, unlike brake fluid, so when you squeeze the lever you will simply compress the air bubbles rather than transfer power to the pistons).
I can't help you with the practicalities, but yes, you need to bleed your brakes. You can't fix the problem by replacing pads or cleaning the discs. Furthermore, perhaps you should replace the fluid with something of higher quality (i.e. higher boiling point), because it doesn't sound like what you had in there before was sufficient for your desired usage.
If your lever feels squishy, that's the tell tale sign of a much needed bleed.
New pads will need time to bed in.
If you rebleed, do it with glycol based DOT 5.1 (not silicone based DOT 5). Avid brakes ship with DOT 4, and IMO don't have the best factory bleeds.
Sounds like you cooked your brake pads. Try sanding them down or replacing them. Brake fluid would not be the issue unless the lever bottoms out or feels spongey.
Originally Posted by Jasonp
High performance DOT 4 works well, too. Use Valvoline Synthetic, which is inexpensive and performs very well. Lot easier to find and cheaper than 5. Another sub would be ATE Super Blue, but it's more expensive and really no better than the Valvoline Synthetic.
The burnt smell was likely the pads, and perhaps they're not right mechanically anymore. They could have worn down, warped the backing plates, and of course, gases building due to boiling.
Do a bleed, then go from there. Check out the pads while you're at it, make sure the backing plates are straight.