Back Brake Problem

[toetoe]

yesterday i noticed my back break was doing very little, it will slow me down but i have to push hard on the peddle, i took the wheel off and me and a friend had a good look to see if anything was stoping the pads from closing and cleaned everything with break cleaner but they where no better, we did notice that their was quite a lot of oil/grease on the disk but we cleaned the disk with cleaner, then someone else suggested riding the bike fast with my foot on the break and then riding into the small river which did work for a short amount of time and was great fun to do but then they went back to how they where, although there is plenty on the pads can pads degrade with time, i think i will change them first but any other suggestions would be helpful.

Edited May 4, 2014 by toetoe

[cabby]

No suggestions from me, however, I also noticed this on my sherco today, plenty life in pads, but very weak, rear brake working, though plenty fluid.

[ryanbrown]

I have had the same trouble. I solved it by removing the disc and cutting a new cross hatch pattern into it with a scuff pad on my right angle die grinder (carefull not to cut grooves and cause a pulsation). This removes the surface glaze on the disc. I recommend new pads when doing this. The brake fluid could also contribute to the weak feel. old brake fluid can absorb condensation and lose the pressure required to squeeze. Good brake fluid is not milky at all. Brake fluid is hydrophilic (absorbs water easily). The other possibilities include a hose with internal damage, a leak, improper adjustment preventing full stroke of master cylinder or simply air in the system.

I hope this helps.

Edited May 4, 2014 by ryanbrown

[toetoe]

I have had the same trouble. I solved it by removing the disc and cutting a new cross hatch pattern into it with a scuff pad on my right angle grinder (carefull not to cut grooves and cause a pulsation). This removes the surface glaze on the disc. I recommend new pads when doing this. The brake fluid could also contribute to the weak feel. old brake fluid can absorb condensation and lose the pressure required to squeeze. Good brake fluid is not milky at all. Brake fluid is hydrophilic (absorbs water easily). The other possibilities include a hose with internal damage, a leak, improper adjustment preventing full stroke of master cylinder or simply air in the system.

I hope this helps.

this helps a lot, can you advise me on what brake fluid to use and the other thing is the brake doesn't have a week feel, it feels hard but their is a fare amount of play when i press down, before the brake starts to work. it's not so bad now after i adjusted the little bolt but their is still some play, thanks for a fast rely.

[ryanbrown]

Free play in the brake is required to keep the brake from dragging and over heating. Free play can be minimal but make sure you still have some slack after the fluid has heated up (fluid expands when warm). The fluid reservoir cap will tell you what fluid to use in the system (dot 3, dot 4, dot 5). Do not use anything but the recommended fluid (higher number is not an upgrade). Use a high temp powersports brake fluid and not an auto parts store brand. It does sound to me like your disc is glazed over though.

[dadof2]

Could brake fluid be getting onto your pads, or grease from rear wheel bearing. Once contaminated some brake materials are nigh on impossible to get working properly again.

Ryan, why do you not like standard autostore brake fluid, its good enough to slow a 2 tonne car from 150mph, far more stress than a trials bike system ever gets.

Edited May 4, 2014 by dadof2

[ryanbrown]

automotive fluid sometimes does not have the heat tolerance that a a powersports fluid does. I may be biased as well because I am the parts manager of a powersports dealership.

Good point about contamination!

[dadof2]

Thanks for reply.

I use Castrol high performance motorcycle brake fluid in my bikes, not because of the temperature but because I find it or Castrol Girling has better lubricity and feel compared to others I have tried. I tend to use standard halfords cheap stuff (on my trade card) in cars.

Back to something closer to the original post - why do so many trials bike have the rear brake bleed nipple lower than the highest point in the cylinder, resulting in a trapped air pocket. Several bikes I know have to have the front wheel on a chair or higher to get the back brake to bleed properly.

[copemech]

Sounds as though you found the main culprit with the oil/grease on the stuff. It will contaminate the pads and may/ not be recoverable.

Find your sourse of oil/ grease. Remove the pads and give them a good soaking with brake cleaner. Re-install and ride the bike to heat rear disk, douse with water to steam things off(a pop bottle will do)and re- do this about three times and let rest and dry. Ck your results.

Do not mess with the fluid if you do not have to.

If this does not work out, new pads may be needed.

Standard dot 4 fluid works fine. If you want a refresh without jacking up the system, just do a partial change by sucking the old out the reservoir and adding fresh to mid level. If you induce air into the system you are knackered!

Edited May 5, 2014 by copemech

[toetoe]

Sounds as though you found the main culprit with the oil/grease on the stuff. It will contaminate the pads and may/ not be recoverable.

Find your sourse of oil/ grease. Remove the pads and give them a good soaking with brake cleaner. Re-install and ride the bike to heat rear disk, douse with water to steam things off(a pop bottle will do)and re- do this about three times and let rest and dry. Ck your results.

Do not mess with the fluid if you do not have to.

If this does not work out, new pads may be needed.

Standard dot 4 fluid works fine. If you want a refresh without jacking up the system, just do a partial change by sucking the old out the reservoir and adding fresh to mid level. If you induce air into the system you are knackered!

thanks, i think the culprit is me, spraying oil my chain and then on other things i see that look like they could do with some oil but not being to carful about spraying things i shouldn't so lesson learned, i will take a bottle of water with me the next practise, some time this week and if that doesn't work then it's a set of new pads.