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newbie so Hi first of all !! I commute to work 20 miles round trip each day on a Giant XTC 3.5 mtb.

I have a clunk which I think is coming from my bottom bracket. Only happens on the left pedal and only when I am going hard or standing up peddling.

I have a Giant XTC3.5 MTB and need to know if I need and special tools to change it if it is the problem??

Pretty sure my rear cassette is gone too and therefore chain !!

[Image: IMG_03311280x853.jpg]

[Image: IMG_03331280x853.jpg]

[Image: IMG_03321280x853.jpg]

Also what replacement parts do I need, cassette, front rings, chain and bottom bracket?? ie, what types??


You may want to check that the crank arms and pedals are on tight enough first. It could be one of these getting loose rather than the BB. Since this bike has clearly been out in the elements, I would remove the pedals, and grease the threads then reinstall. Don't need to pull off the crank arm, but I would pull out the bolt and grease.

To check the BB itself, you can move the chain off the chainrings to the inside so the cranks can spin freely. Check to see if they spin smoothly or if you can feel and "crunchiness". Also check if there is any side to side movement in the crank arms. If those two check out, BB should be fine.

Your cassette is way worn, especially in the 4th highest gear. New cassette and chain are in order.
Hi Graham, welcome to BT!
To expound a bit on Daves good advice - when checking your pedals, grab it in your fist and try to rock the pedal body on its spindle. Also check that the cage (the part with the teeth) isn't loose on the body. Pedal noises are common and easily amplified through frame tubes.

In addition to checking the BB for a rough feel, take one crank arm in one hand, reach through the frame and grab the other. Try to rock them. Can you feel any lateral movement? You have a cartridge BB and no adjustment is possible.

Next, make sure that all of your chainring bolts are tight. Sounds crazy since the sound occurs on the left pedal stroke but, I get paid big bucks (I wish) to chase errant noises and I have seen some crazy stuff! Smile

If all of these pass the test, check all of your frames welds on the main triangle for stress cracks. This is unlikely but needs to be ruled out.

Once you tighten everything up and inspect, test ride her and report back. If the problem persists, we could use details such as where in the left pedal stroke the noise occurs, if it is every revolution of the cranks or random, can you feel the clunk in the handlebar, etc.
Wheelies don't pop themselves. (from a QBP fortune cookie)
Great advice, thanks.

Am away for a few days now but will look at asap and report back. Lots to think about there, need to get a cassette tool as well to change that !! Sort of knew these were gone but it's the clunk that worries me.

Will let you know how I go on and get some more info on where the clunk is happening etc.


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