okay I'm getting back into shape again. I have been riding my giant sedona around town and trails for the past couple weeks religiously and keeping to a diet and all is going good. Only thing is that i am getting sick of the twist shifters on the bike. It is a 2005 model and in desperate need of some new shifters. I have a good knowledge of tuning and can fix just about anything but i have a question about shifters. I would like to replace them with a set of trigger shifters. I have come across a ton of different ones on the web. currently it has a 21 speed set up with the shimano megarange gear and altus deraileur on the rear. suntour cranks also. wondering what i can use to replace them. don't need high end stuff just stuff that won't break in a month. I plan on replacing all the cables also at the same time so any help with some part replacement numbers would be great. thanks.
Shimano SL-M310 or SRAM TRX are two trigger options that would match your rear cogs. The TRX is one of the few SRAM shifters that matches shimano derailleurs and is, to my knowledge, the only SRAM trigger option to do so. Either appear to run near $30.
Providing you don't ride a chain beyond reasonable wear (1%), rear cogs can last through two or more chains. But continuing to ride a worn chain will quickly wear the rear cogs. If in doubt, measure your chain with a ruler.
The chain used on your 7sp is the same size as all chains used on 6, 7 & 8 speed drivetrains. They're inexpensive and last a long time.
I suspect you actually have a cassette, not a freewheel. If you do have a cassette, there's a great chance that it's mounted on a 8/9/10 speed freehub body with a 4.5mm spacer behind the largest cog. Some people would use this as an opportunity to upgrade their drivetrain. An 8 sp cassette with narrower spacing (12-23, 12-25, 13-26) would allow much easier transitions between gear ratios and make better use of your triple crankset. Of course, you'd need 8sp shifters and cassette. The cassettes are less than $30, and you can pick up Shimano Alivio M410 rapid fire shifters for just over $30 online. And you'd need a new chain, since you always want to replace the chain when installing a new cassette.
Just food for thought. Not trying to encourage you to sspend money.
We have an identically equipped Sedona in our stable. I successfully used Sram X-3 trigger shifters with the Shimano derailleurs. They cost me about $20 shipped (new) on Ebay. They are a well suited match for your 21 speed drivetrain.
For what it's worth: Our Sedona came with a Megarange freewheel, which is an actual freewheel and not a cassette. A cassette would be better, but the freewheel is okay on a Sedona. I switched mine out from the original 14-34 to a 13-28. This gave me even spacing between the gears, instead of having the large jump between the 24t and 34t cogs on the 14-34t. The freewheel is pretty easy to replace, using a Park FR-1 freewheel removal tool and a large wrench. The freewheel cost me about $20 at Amazon.com, and you can also purchase the tool from Amazon.
You may have to spend more money to convert to an 8 speed cassette than what the bike is worth to you, as you would have to switch out your rear hub or your entire rear wheel so that a cassette can be installed. An 8 speed cassette does have advantages over a 7 speed freewheel, but my opinion is that the advantages are probably not worth the cost.
Another problem you may have to deal with would be your bike's rear spacing is probably 130mm, as that is the usual spacing for a 7 speed freewheel, and uses mountain bike components. An 8 speed mountain bike cassette usually needs 135mm spacing. Your Sedona, unless it is a Sedona ST, has an aluminum frame that won't tolerate being respaced to fit a 135mm rear hub.
I would recommend changing out the shifters, but keeping the bike's 7 speed freewheel as is. If the freewheel is worn, I would recommend replacing it with a new 7 speed freewheel.