Bicycle Mechanics - Trek 4500 chain keeps slipping

Hi im new to this forum and i am also a complete noob when it comes to bikes.

So heres my question, whenever i go to peddle hard my chain constantly slips, im thinking i might need a new chain or the gears are worn out? But im not sure and also ive had the bike for about 5 years now and i always run in dirt trails what parts should i replace on the bike?

And also if someone can give me the link to a website where i can purchases part that would be a big help.

Thanks
(sorry for being a noob)

Initally, would try adjusting the rear derailleur, see Park Tools website for how too's http://www.parktool.com/blog/repair-help/categories/derailleur-systems

If you have been using the bike for 5 years off road, would expect the the whole drive train is probably worn out by now, would check the derailleur hanger for alignment, then look at replacing the chain & cassette (if replacing the cassette, the chain should be changed at the same time), and then possibly the crank / chainrings.

For where to buy, you don't say what country you are in, wherever you are, what are yor LBS's like? for on-line in the US, there's Nasbar, Jenson, REI. depending on the exchange rate, have a look at places like CRC (Chain Reaction Cycles), if you are in Europe, look for German suppliers like Rose or Bike24

search on utube on how to set up your deraileurs. your cables and chain will stretch over time so dialing them in will probably fix your issue. if you still cant get everything working correctly then it may be time to look into replacing hardware.

Having the chain skip under hard pedal pressure is the classic symptom of a worn drivetrain.

You could test different cogs in the back to see whether the chain skips on all of them, or whether the skipping is limited to just one or two. (Not that it really matters).

You very likely need to replace cassette and chain. You may also need to replace chain rings.

Unless you have a strong desire to learn bike mechanics, I would take the bike to a shop.

To better determine if chain wear is the culprit, I suggest starting by measuring it. Directions can be found at the bottom of this page: http://sheldonbrown.com/chains.html. Use a good ruler and wipe off the crud from your chain beforehand. Measuring will allow you to see if your drivetrain is significantly worn, then you can take it from there.

I wouldn't recommend fiddling with your derailleur adjustments just yet, as you may create a problem where none presently exists.

I wouldn't recommend fiddling with your derailleur adjustments just yet, as you may create a problem where none presently exists.

adjusting his deraileurs is free, easy, and if done correctly (as instructed via utube or sheldon brown or whomever) cant introduce a problem. yes he may need to replace his drivetrain but he may also be able to fix his issue. You cant narrow down your diagnosis to one issue until you make sure everything else is working perfectly. I think that is trouble shooting 101 and a great place to start.

adjusting his deraileurs is free, easy, and if done correctly (as instructed via utube or sheldon brown or whomever) cant introduce a problem. yes he may need to replace his drivetrain but he may also be able to fix his issue. You cant narrow down your diagnosis to one issue until you make sure everything else is working perfectly. I think that is trouble shooting 101 and a great place to start.
...and measuring a chain is also free and can be accomplished in a two minutes, including the time to read the directions.

You recommend your starting point, and I'll recommend mine.

Ahh ok... Yea it looks like i have to replace the drive train. I have about 300 bucks to spend would that be enough to buy all the drive train parts? And i am located in the u.s

It can be done for about 90 + labor, if ya buy the parts online.