Mosquito84

Hi There,
I bought a cheap Diamondback APEX DX MTB from facebook for my teenage daughter. She took it for a quick test ride and we brought it home, where she promply got out her art supplies and started painting the spokes and frame in pastels.lol
Anyways, on the first proper ride she took, the rear derailleur lost a pulley sprocket and it jambed up. (SIS index 6 Speed)

I figured I'll just replace the derailleur, but the part number that's stamped on it RD-TZ30 is discontinued and am having trouble finding one. It also has seemingly large pulleys/sprockets with 'mega pulley' written on them, I don't know if that makes a difference or not either.
I'm unsure what to replace it with. Are they model specific? Will a TZ31 do the job? will any shimano SIS 6-7 speed derailleur work?
I havent really played with bikes since I was a kid, so it's all a little new to me.
Appreciate any advice.
Thanks.

Harold74

The TZ31 should be fine. Stuff to look for to make your decision:

1) All of the six, seven, and eight speed Shimano rear derailleurs use the same pull ratio so, as you suspected, all will work as far as the indexed shifting goes.

2) You want a derailleur capacity adequate for the bike. This is basically how much chain the derailleur can take up in moving from the gear combination that uses the most chain to the combination that uses the least.

3) You want a derailleur that can clear your largest cog at the rear wheel of your bike.

#2 and #3 will be listed in the product specifications for the rear derailleurs. As such, you can ensure that you choose an appropriate derailleur one of two ways:

a) Ensure that the specs of the replacement rear derailleur suit the gearing on your daughter's bike or;

b) Ensure that the specs of the new derailleur match or exceed those of the original derailleur.

dedhed

Factually almost "any" Shimano road 6-10 speed road or Mt. 6-9s rear derailleur with enough chain wrap capacity and cog size ability will index with the shifters. There are some anomalies in there that won't.
Reality is, given how much and how hard a teenage girl is going to ride that bike, level of existing RD and bike, and other real life things you're best bet is likely a Shimano Tourney as I'm guessing you need a claw hanger. Cheap, works, readily available and long cage will handle the gearing.

Another option is is if you have a local bike co-op to pick up a used compatible RD.

https://www.amazon.com/Shimano-Tourn...55443404&psc=1

grumpus

Shimano replacement pulley sets are cheap and easy to fit, as long as the derailleur didn't get mangled when the other one fell out and the thread in the cage isn't stripped. If it's feasible then replacing just the pulley would require fitting just one screw and minimal/no adjustment.

dedhed

I wouldn't bother on a TZ30. Absolutely the worst POS shimano makes.

grumpus

That does look pretty nasty.