Replacing old rear derailleur

[eab]

I bought a very old Mongoose mtn bike from Goodwill for commuting to/from the metro station, and would like to replace its very old Suntour 3000 alpha rear derailleur.  Is there a model of derailleur I'm likely to find that will allow me to keep the index shifting?  Or should I give up and buy any old other derailleur for continuous shifting?
Thanks!

[elmore leonard]

(05-13-2015, 03:36 AM)eab Wrote:  I bought a very old Mongoose mtn bike from Goodwill for commuting to/from the metro station, and would like to replace its very old Suntour 3000 alpha rear derailleur.  Is there a model of derailleur I'm likely to find that will allow me to keep the index shifting?  Or should I give up and buy any old other derailleur for continuous shifting?
Thanks!

Hi eab.
I cannot help you, as it's over my head, other then to suggest you phone a bike shop or message Shimano through their web site.

[nfmisso]

To have indexing, you are MOST likely going to have to replace the freewheel, RD and the shifter.  If 8 speed or less, a new freewheel, a Shimano TX35 (with or without hanger depending on what your bike needs) and SRAM MRX shifters will get you going.  Sunrace offers similar shifters, that I like better than the SRAM, a bit harder to find.

[DaveM]

(05-14-2015, 12:09 AM)nfmisso Wrote:  To have indexing, you are MOST likely going to have to replace the freewheel, RD and the shifter.  If 8 speed or less, a new freewheel, a Shimano TX35 (with or without hanger depending on what your bike needs) and SRAM MRX shifters will get you going.  Sunrace offers similar shifters, that I like better than the SRAM, a bit harder to find.

He says he wants to "keep" the index shifting, so maybe it is currently indexed? If so, I think a standard Shimano or Shimano compatible RD will probably work with old Suntour indexed stuff. But maybe someone know for sure.

To the OP, is it 6-speed indexed?