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Wheel dish? (xpost tool time)

544 views 3 replies 3 participants last post by  will8250 
#1 ·
So I bought a new rear rim brake wheel for my commuter today. The frame is steel Univega from the late 90's. The wheel is a deore hub laced to a Mavic rim. When I went to set up the brakes I noticed that the left brake arm (looking from the back of the bike forward) has to lean about 15 degrees past vertical to hit the rim while the right brake arm is still about 15 degrees before vertical. Both pads have about the same amount of life left (medium... not new, not shot). Is the wheel dish off? Why would this be? The bike was originally designed around a 7 speed rear cassette but the 9 speed hub seems to fit in there just fine. Not sure if it's the frame/wheel combination, the wheel, or what that is causing the "funk". Any ideas would be greatly appreciated. Thanks!

Additionally... are chainrings designed for a 27 speed system narrower/different than chainrings designed for a 21 speed system? I'm mixing and matching spare parts. Thanks again
 
#2 ·
Uhhh... that's quite a bit.

1. Check dish by reversing the wheel in the dropouts. If the rim walls land in the same relative position (relative to the brakes, or better yet, relative to the frame), then the wheel is dished correctly.

2. Sounds like a spring tension adjustment on the brake arms is called for. Are you familiar with this adjustment? (It's the small screws usually located behind the brake arms, near the pivot, which press against the springs).

3. A Univega frame from the late 90's should have 135mm dropout spacing, which is the current standard. If you didn't have to spread the stays to insert the wheel, no problem there.

4. You might run into some shifting issues with your current chainrings. Nine speed chains are narrower than 7-speed, so the shifting ramps may not be as effective, and there is the chance you may experience some chain suck. If that turns out to be a problem, just install a new big and middle ring. The crank itself will be ok (the spacing hasn't changed).
 
#3 ·
Check your brake arms; if they are the later version make sure you have an equal number of spacers between the arm and the caliper. If they are the older canti-style (without spacers) check that they are both sitting the same height and have the same amount of brake pad post showing outside the brake arm.

Tim
 
#4 ·
Great suggestions. Thanks.

I'll check the dish by reversing the wheel.

The spring tension is set evenly between the two brake arms. Would changing the tension in the return springs change where the brakes hit the rim?

I'll swap over my spare 9 speed crankset.

Wombat: the brakes are xt v brakes. I'll double check the spacers.

Thanks again
 
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