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Old 08-06-05, 01:13 PM   #1
Rusty_Chain
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which derailleur

I have a mongoose 21 speed that I bought at Walmart for $150 2 years ago. I rode trails a little for first year but i live in a city now and am doing all road and paved trail riding, it is hilly though. I know the rear derailleur has a couple problems and have been looking to replace it. Its beyond adjusting. I need reliable shifting and it will be under pressure sometimes when I'm going up hills. I've been researching and looks like SRAMs are highest rated now and the x-9 might be a little overkill for this bike, but its also for 8-9 speed, and i have a 7 speed cassette.
My questions are:
which models are even compatible?
What is what is a good, reliable derailluer that will give me accurate shifts?
I've been riding pretty steady lately so I don't mind spending an extra buck for good quality, but don't want to overdo it either. BTW the bike came equipped with Shimano grip shifters and derailluers.
The gears on back are 14.16.18.20.22.24.28
and biggest on front is 48t

Bike has been pretty good for the price and I'd like to keep it up.

Thanx
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Old 08-06-05, 02:20 PM   #2
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If your derailleur is indeed broken go get a 7 speed shimano tourney derailleur ($12). There's no point buying anything more expensive.

There's no sense really upgrading a dept store bike. Just replace the parts that go broke.
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Old 08-06-05, 04:06 PM   #3
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Quote:
Originally Posted by operator
If your derailleur is indeed broken go get a 7 speed shimano tourney derailleur ($12). There's no point buying anything more expensive.

There's no sense really upgrading a dept store bike. Just replace the parts that go broke.
Is this really good enough to give me accurate and reliable shifting?
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Old 08-06-05, 08:24 PM   #4
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Quote:
Originally Posted by Rusty_Chain
Is this really good enough to give me accurate and reliable shifting?
The tourney RD came stock on on a LBS purchased Raleigh M20 I had a while before it got stolen, and up until it got stolen, I thought it worked great.

Quote:
Originally Posted by operator
There's no sense really upgrading a dept store bike. Just replace the parts that go broke.
Hey! I took a banged up POS department store Huffy and put all XTR components on it! [Just Kidding]

I agree with operator. The tourney derailleur will do you just fine. In fact, the Tourney may well be the only Shimano rear derailleur you'll find compatible with your chain and cassette, although for a better RD Altus or Acera might also work.

To be certain, refer to Shimano's Rear drive compatibility chart, attached below. Figure out what chain and cassette you've got. For other drive-train compatibility charts, refer to Shimano's web site. If you would like SRAM after-all, they may have similar compatibility charts, but the Shimano shifter may not work with a SRAM RD, but I could very well be wrong here.

Last edited by anonymouse99; 08-06-05 at 08:40 PM.
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Old 08-06-05, 10:33 PM   #5
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Any derailleur will shift fine, it just needs to be adjusted properly. There's nothing inherently wrong with cheaper components that don't make them shift properly.
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Old 08-06-05, 10:46 PM   #6
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Great! Thanx for all the help. I just ordered a Shimano Tourney RD-TX70 for $14 (plus $10 shipping, sigh) but actually I'm real happy with that. The chart was what I really needed Tgarcia, along with the good advice from the rest of you. I might get me a really good bike one day, so far I'm still riding this one. I hadn't rode a bike in over 25 years until a couple years ago.

Just in case your curious, on my old derrailluer, there was a worn out spring, so that sometimes I had to push the pulley by hand back over to the low gears. The spring was too weak to do this.
Also, the bottom pulley had a stop that kept it from swinging frontwards at a certain point, but that corner got rounded so the stop didn't stop and then the chain would be loose and start flying off on me. Don't know if that made sense but I tried. I've been trying to educate myself a little.
And when shifting, sometimes it works perfect, and sometimes I have to move shifter 3 gears before I get a response.

I downloaded adjustment instructions and did it repeatedly. Sometimes it would work perfectly for a couple miles and then go to hell. So I'm sure I need at least this much.

Thanx again for the help.
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