I noticed while I was biking today that my cranks/bottom bracket are a bit loose, as in the whole assembly (cranks bb and maybe even the cups) seem to have a slight movement to them within the frame. If I grab one crank arm and shake it a bit the other one moves (just a slight slight bit, you have to look for it). Basically what I am asking is if anyone knows why this would be, and how to fix it.

I am switching to a new frame in a few weeks, but the current one is a rush hour frame with a truvativ power spline BB and truvativ cranks. Both were installed on the frame aftermarket by myself.

That's a vague description. What makes you think the cups are loose? Have you simply tried tightening the cup? Are you sure your BB is compatible with the width of your BB shell, since you purchased and installed it youself?

So tighten your BB-- its loose.

I am not sure if the cups are lose, but something clearly is. I thought everything checked out width wise but I am probably going to take it in this week to check it out.

I am ordering a new frame this week so hopefully the problem will work itself out when I transfer the parts.

No, I am quite certain it isnt, I tried and it is tight as can be, loosened it today and re-tighted it and its still doing it.

Although this is arguably something that i would say or do,
It also a completely terrible idea.

I will get to the bottom of the issue with the help of my lbs befor I make any stupid moves, I appreciate the reminder to not try and solve the problem hastefully though.

I am currently using a 68x113 mm bottom bracket in my bike which used to have a 68x108 mm bottom bracket. Forgive my lack of knowledge, but perhaps that information would help.

It would seem that using a wider width wouldnt cause this problem.

There are three dimensions measured for the spindle - non-drive side of the spindle, middle of the spindle between the cups, and the drive side of the spindle. The size might be fine for all I know, I was just speculating. Let the shop help you diagnose the problem.

bottom brackets are my least favorite part of a bike. such a pain sometimes

if the cups are tight & properly installed- your bearings are shot. Can happen really fast with lower end splined BBs, as they've got smaller bearings. If you spin the BB by hand, you should feel some grittyness/resistance as well as the wobble. I don't know if the bearings in your case are replaceable, or if you need a whole new BB.

Two nights ago when I first checked the problem the bb felt smooth as ever, but I will check it again when I get back from my office today. I am shot for cash so I hope this isnt the case, but I appreciate the info.


on second thought since its isis drive and all the reviews describe the same problem, I am sure its shot. Looks like I get to buy a whole new bottom bracket and crank set.

truvativ power spline BBs are not ISIS, they're a different type of splined BB (because the world is not confusing enough).

ISIS has 10 splines, Powersplines have 12? (Could be wrong - this out of my jumble of a memory)

Someone deserves to be poked in the eye for inventing yet another proprietary BB design. Theres only one Powerspline BB on the market, made by Truvativ of course and its cheap and seeminly unreliable.

**** this I am buying a new crankset and BB.

Not only is it proprietary w/r/t truvativ, it's also incompatable with every other model of truvativ BB.

I second the poke in the eye with a sharp stick for whichever dingleberry thought that was a good idea.

you are correct sir here is a cookie however truvativ also makes isis compatible cranks