Originally Posted by
trek830
I don't know that particular model trek, but I had an HG70 on my 93 Trek 830 before I upgraded it, as far as I was aware that was a mountain bike specific cassette, someone correct me if I'm wrong.
Also you will need a chain whip to remove the old cassette, and a freewheel tool to put the new cassette on. See the
Park Tools Repair section for more info, and also
Bicycle Tutor has some good videos on these repairs.
What is a mountain bike specific cassette? All cassettes are the same. Mountain/road is just marketing terms. Mountain cassettes usually have a wider and lower gear range. The Trek 420 is a touring bike, so it also has lower gearing.
The cassette you mentioned will be fine. You can actually use any of the 7-speed cassettes. Well, you might not be able to use the 11 tooth cassettes. It depends if you have the compact freehub body or not.
If your chain is skipping because of wear, you will most likely need a new chain also. A worn chain and new cassette will also skip.
Are you sure it is the cassette? Your derailer hanger might also be bent, this will cause skipping.