Trek 3700 with 3 broken axles
 

Before I begin, this is the bike I'm talking about:
http://i1179.photobucket.com/albums/...s/IMAG0334.jpg

During this past week, I've broken(snapped) 1 axle, and bent 2 new ones.
The local bike shop has now refused to give me new ones, saying that I need a new type of wheel with a cassette axle. Runs about $50 - $85, not outrageous(?), but a lot for an unemployed student.
I should note that the first axle was the first axle the bikes seen, and lasted maybe 600 miles. The 2 bent axles lasted maybe 3 each. I'm not offroading, but each of the new axles I used for a pretty aggressive hill climb, and broke as soon as I got to the top.
History:
This bike has had a badly bent frame, the local shop fixed it a few years ago, and it's been fine since.
This bike spent the winter in the bike shop storage, because the chain broke 8 miles from my house. :crash: The bike shop said it was due to a bent hanger, which they fixed.
After the first new axle bent, they kept it overnight to look it over. They said the frame was still true and they didn't see any problems with it.
So, should I upgrade to the new axle, or is there a special type of axle that won't break when I use it? I should also mention that the new axle was a temporary fix. They recommended I get a dual suspension bike, to the tune of $1200 - 1500. I'd like to eventually do that, but being an unemployed student prevents it.

Also, before I posted I noticed VERY descriptive titles. I'm new to this website and to other people that care about bikes. If I made this in the wrong section, please let me know :o

Reading the stickies, I should also include:
This bike is fairly new, not more than 5 years old. I'd guess about 2007.
This is a 21 speed, with 3 on the front and 7 on the back. Not sure of a better way to say that :(
No BMX, mostly ride on sidewalks or packed gravel. Occasionally I'll ride on a rough path, but I get no air. I usually just get stuck :roflmao2:

Check the dropout alignments. Putting new axles and wheels in place of failed one that suffered bent or broken axles WITHOUT checking dropout alignment is the same as tossing good money after bad.

If it turns out the dropouts are out of alignment - and the LBS has been doing the replacement work for you - either light a fire under their ass or find another LBS!!!

=8-)

(Dropout alignment tools look like T-Handles with adjustable cups on the ends...)

=8-)

Drop out alignment info can be found in the stickies?

if they said dropout alignment is fine and you are still breaking axles then get something better than a freewheel hub. i bet you are overweight or thrash on the bike hard

I doubt that bike has a freewheel hub. You say it had a badly bent frame and they fixed it. Aluminum frames aren't generally the best candidates for frame straightening if badly bent. I'd try a different shop.

Dropout alignment is simply the process of making certain that the dropout faces are perfectly parallel with each other. This ensures that the load placed on the axle when installing the wheel is linear or in line with the axle - not at an angle.

Basically, you are making sure that the bicycle itself is not doing anything detrimental to the axles...so that the only detrimental loads placed on the bike and parts is that which YOU AS THE RIDER place on the bike when using it.

When the bike is aligned properly and parts continue to break - then you know that either you need better quality parts OR a bike built to handle someone like yourself.

=8-)

Not to get too personal, but how much do you weigh? Are they all rear axles? From your first post, you mention "cassette axle". Do you have a cassette rear hub? Threaded hubs don't have as much axle support. Cassette hubs have better axle support (the bearings are further to the outside).

I occasionally ride hard, but the 2 bent axles broke on a 3 mile all paved route. If that's hard, then I need a bike made out of titanium!

Not sure what a free wheel hub is, I haven't had a chance to read the guides the stickies are recommending. It wasn't mangled like a pretzel, but the back frames bars were touching the tire if I remember correctly.

I was hoping I'd need better quality parts, because the first axle had about 90 miles on it this season before it broke, and last season it was my daily rider. If the last axle could last that long, then the new axles that bend after 3 miles must be inferior parts, right?

240 lbs. All rear axles. Not sure if it matters, but if I'm in 6th or below and start off the front of the bike will do a wheelie. I think when I was doing those hill climbs and shifted into those lower gears it caused too much stress to the axle. All 3 broke when I was going up hills. The current axle/hub combo places stress right at the edge of the wheel. The new wheel/axle/hub the store recommended moved the stress out past the gears right next to the frame.

When the axles bent/broke, they all caused the tire to rub against the frame. Particularly when I peddled.
This is one of the trips that broke the axle.

It's definitely possible you have a freewheel, and not a cassette. I've seen some newer (post 2000) name brand MTBs with 7-speed freewheels. This is important in diagnosing your problem. Figure out which one you have, they are not the same: http://www.sheldonbrown.com/free-k7.html

If you have a freewheel then I strongly recommend switching to a rear wheel with a Freehub and cassette as your bike shop might have recommended. This should solve your broken axle problems. The 7 speed freewheel has a long section of unsupported axle causing it to fail with even lightweight riders.

Most 7-speed setups these days are freewheels. The 2009 specs mention Sunrace 13-34. As far as I know Sunrace only makes freewheels.

The bike is definitely a 2007 and I'm pretty sure it's a freewheel rear hub.

Ok, I currently have the one on the left, and the bike shop recommended the one on the right. I'll go with that, but it puzzles me that the first axle lasted so long, and the next 2 broke so fast.
http://bikeforums.net/attachment.php...hmentid=198358

I remember back in my freewheel MTB days that most replacement axles were pretty weak. The average replacement was $5, but you had to pay $10-15 for the strong stuff (1988-1991 prices.) The stock axle on the Trek was probably a good one but replacements were inferior.

I haven't taken my Trek 4000 with 7-sp freewheel out on the gnar trails yet. Knock on wood that the stocker axle holds up.

That would make sense, I was putting in $10 axles. They didn't give me an option of a more expensive axle, so I'm probably going to go with the cassette. This mountain bike is much easier to ride than my 30 year old mongoose with no suspension and a rock hard seat!

Low quality or high quality axles - dropout alignment should be checked. Period!

=8-)

+1.
Same goes for freehub, get that alignment checked before dropping a new wheel in there.

I doubt they have any 7 speed freehubs in stock which will be compatible with your shifters. I am not sure whether they'll work when using only 7 sprockets of an 8-speed cassette, but I think they may. Sheldonbrown.com may be able to tell you if you can make a cassette work with your shifters.

However, I would just try to get a chrome moly axle. A lot of axles for freewheel hubs are crap. I've seen poorer ones which are thinly plated and chrome moly ones which could put a dent in the poor ones, which were black oxided, but I don't know if that's always the case. Just ask for or order a chrome moly axle online.

It's my theory that you also have to be very good about how you adjust the hub bearings with a freewheel-type hub if you want the axle to last.

A 7 speed cassette will work no problem on an 8/9/10 speed Freehub with a spacer.

IMO based on the OP's rate of axle breakage a chromoly axle is just a band aid of the real problem which is the freewheel design itself, once the dropout squareness is checked. Every wheel I've torn apart with a 7-speed freewheel has a bent axle, but these were wheels with solid axles from crappy x-mart bikes. In addition, my friend (130lb) recently broke the axle on his Giant Yukon with a 7S freewheel, and he does not ride hard. I've never seen a broken axle from a Freehub, although I'm sure it's possible.

will the indexed shifter work? Are the sprockets the same distance apart? And what does all that stuff cost? Might be worth looking in to before choosing this route-an old 7 speed cassette might cost too much possibly.I have had trouble with freewheels too. I looked into it a bit. Jobst Brandt, an avid cyclist and mechanical engineer, author of The Bicycle Wheel, said freewheel axle bending or breakage was a metal fatigue issue. In my eyes that makes it rational to simply put in a new axle and then check the wheel for wobble, replacing the axle every year or so or as needed, because it's going to be OK to use until it fatigues, just like an airliner.

Yes, yes, and not much. A 7-speed cassette will have the same spacing no matter what hub you throw it on. The spacer goes behind the cassette to take up the extra space provided to run an 8/9/10 speed cassette. Brand new 7 speed cassettes can be had for much less than $20 on ebay. The spacer should be a buck or two at most. The wheel would be the largest expense.

Further reading: http://www.sheldonbrown.com/k7.html

I am heavier than the OP and, based on my experience road racing at 200 lbs, I would not trust a freewheel hub for serious riding - or any riding where I had to get myself home. Shimano's freehub design is one of the great improvements in bicycle component design from the last 50 years.

The problems with simply replacing axle after axle as needed are that (1) much more time in the shop, (2) might not be good quality axles available the next time the axle bends and has to be replaced with another 3 mile cheapo, and (3) bending the axle might also bend the frame, and that's bad.

Edit: One question for GeoffM - do you find you get a lot of pressure on your hands or wrists while riding?

Freewheels are evil. I can't replace them fast enough when they show up. I'm replacing one (crappy Joytech) right now (with FH-M430) , actually. . . getting an extra cog (7sp to 8sp), to boot.

I otherwise won't ride a multispeed bike with a freewheel. Not worth the risk.

You're 200, I'm 240. How are you heavier?

My hands go numb. Usually at about 15 - 20 miles.

Love the ASCII diagrams.