v-brake rim rub, any advice ?

[rollinstok]

please help with a couple of tips if you can
was out today with my son to do a 32 mile local ride
last few miles I really struggled to keep up only to find when we got back that my rear brake was rubbing against the rim on one side, it was ok at the half way stop
I keep the cables lubed and they look in good condition
I've had a few problems with front brake needing regular adjustment but this is first time with rear
They are deore lx brakes and new cables fitted about 1200 miles ago
I'm at a loss why the front needs regular adjustment and hope the rear isnt going to start being temperamental

 

[simon.r]

IME V brakes do require fairly regular tweaking. It's a simple job to 'balance' them, just turn the small bolt* on the side - clockwise to increase tension / pull the block away from the rim. Squeeze the lever a couple of times after you've done it to check it's OK. I generally check that the brake blocks are equ-distant from the rim whenever I do a mini-service on the bike, hopefully to prevent situations like the one you had today!

Whenever I remove and refit a wheel it seems that the brakes need tweaking, despite the fact that it's gone back in exactly the same position as before!

*Normally a cross-head bolt, maybe a small allen bolt.

 

[rollinstok]

Yes, I'm forever at those screws in the front brake and had to adjust the rear when I got home
Its getting to the stage where I check my skewers regular to see if they have worked loose and the wheel has shifted, but the skewers are always ok
Do you know the optimum distance between pad and rim ? mine looks to be around 5 or 6 mm on either side when they are playing ball
I'm worried that if I gave a little too much clearance that it would affect the performance too much

 

[simon.r]

According to this Shimano document it should be 1mm either side, but I think that's a bit optimistic. Without measuring mine I'd say they're 2 or 3mm and they work

 

[HovR]

Regarding the rear wheel which suddenly started rubbing - Have you checked to make sure the rim is still running true?

Running rim brakes with badly tensioned spokes and/or untrue wheels will cause you to have to make adjustments far more regularly to prevent rubbing, in my experience.

 

[rollinstok]

Regarding the rear wheel which suddenly started rubbing - Have you checked to make sure the rim is still running true?

Yes, did that when I got home, turned bike upside down and adjusted brake, gave wheel a spin and looks good

 

[bananaboy]

Are the blocks worn? Know it sounds dumb but caused mine to rub on one side.

 

[snailracer]

Clean and regrease the mounting bosses?

 

[Moodyman]

Deore LX are pretty decent.

As Snailpacer says, try cleaning the calipers and spray a little GT85 into the spring (don't get any onto rim though). When you apply the brakes, there's a spring that pulls them away from the rim. If that spring is dirty, it might not be going back far enough. Cleaning and lubling will free it up.