Rear Brakes issue

[Steve Kitchener]

G'day, I seem to have an with my rear brake system (disc). A few months back i was riding some primo off road trails in very wet and muddy conditions. I thought i'd take my bike in for a service and they changed my rear brake cable. Went out again and my brakes don't seem as responsive (no t slowing down as fast). Entered a 25km race and nearly killed myself as my brake didn't slow me down...dooh
I took the bike back to the shop and they replace the cable again (even though it was brand new) Again the same issue. The pads are fine with plenty of wear left on them. I thought bugger this and went to another shop and told them the issue. They told me they fixed the problem but low and behold ..no luck.
I've been thinking that i might change the pads but as i said they look fine. I've tried adjusting every way i can but with no luck..
Could it be the adapter that holds the pads or even the disc itself?
Please help!!!!!!!!!!!!!!!!

[JonB]

If the bike shop have said everything is OK then it probably hasn't been set up for you properly (i.e. the pads are too far away from the disc when the brakes are off, meaning that it takes too much of your brake lever's travel to make contact with the disc.
I don't know what model you have but this should be a standard fix anyway:
You should find that on the caliper are two sticks with bobbles on the end where the cable is attached. One the cable just moves through and should be fixed in place, the other will be attached to the cable and will move towards the fixed one when the lever is pulled. What you need to do is find the bolt that pinches the cable on this stalk and undo it enough to move the cable around. Move the stalk until the pads are a desirable distance away* (as close as you can get without rubbing is how I like them) and then tighten the pinch bolt (a 4th hand may be useful here but not essential). Test your brakes and move the pinch bolt along the cable again if they are too weak.
*(someone else may be able to suggest the optimal distance better than me)
If this doesn't work I have no idea, but check the disc anyway. If it's bent, bin it. Also, if you get oil on the pads, bin them as well.

[arcsat]

Did they replace the brake housing also? They should use heavy duty housing so there is no stretch. The disk brakes have a lot of mechanical advantage and can cause the cheap housing to compress and give a squishy feel.