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Discussion Starter · #1 ·
I'm trying to rehab my nephew's 8-speed Mongoose & I think that the front derailleur is bent. I noticed that while shifting the front der moves up & over which didn't seem right. On my bikes it's moves left or right. The housing where the adjustment screws are located seems like the 2 halfs don't meet exactly. The componets are Mongoose TD-Pro so I imagine that their not the best quality. I'm wondering if the frt der is hosed, can I replace it with Shimano & leave the rear der & shifters alone (for now). Also, is a 9speed frt der an option?

With regard to upgrading to 9-speed, this bike has an 8-speed freewheel. Would a rear wheel rebuild/replacement be required?

The last item concerns replacing the rear der. Do you have to replace the shifters with the rear der? Thanks in advance & have fun riding!!
 

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Most likely a Shimano front derailleur would work. You didn't mention what shifters the bike uses but I seriously doubt there's anything proprietary going on there that a standard unit couldn't be swapped in.

Depending on who you ask, 9 speed front derailleurs are anywhere from 0 to .5 to 1mm narrower than 8 speed. I personally have mic'd them and didn't find the difference. Others say they have. Point being, expect the possibility of some chain rub at the extremes, and be precise in your derailleur adjustment and a 9 speed front mech will work fine. You won't be the first.

9 speed cassettes fit on 8 speed freewheels.

Not sure what you're asking in the last question. If it's in regard to 9 speed conversions, then yes, you'll need to install a new shifter.
 

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Discussion Starter · #3 ·
Can you clarify one thing..

You mentioned that the 9-speed cassette will fit on the 8-speed freewheel. Does this mean that you disassemble the 8-speed & rebuild with the 9-speed cogs?

Also, with grip shifters, can you upgrade to 9-speed rear der & cassette with out upgrading these or is the shifting that precise?

Otherwise, I think that I'm all set to just replace the front der & wait on the 9-speed upgrade for a later date (when more $$ is available). I appreciate the help!!
 

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Bent_Spoke said:
You mentioned that the 9-speed cassette will fit on the 8-speed freewheel. Does this mean that you disassemble the 8-speed & rebuild with the 9-speed cogs?

Also, with grip shifters, can you upgrade to 9-speed rear der & cassette with out upgrading these or is the shifting that precise?

Otherwise, I think that I'm all set to just replace the front der & wait on the 9-speed upgrade for a later date (when more $$ is available). I appreciate the help!!
Yes, remove the 8 speed cassette and the 9 speed will slide right on.

You'll need to upgrade the shifters. The difference in cog spacing is a fraction of a millimeter, and yes, technically you can run an 8 speed shifter on a 9 speed cassette (or vice-versa) and make it "workable", but the end cogs get a bit "skippy" and run noisey and it really isn't something you want to plan on doing, just something that works in a pinch if you find yourself in some wierd maintenance predicament.
 
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