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Maark

Original Poster:

83 posts

55 months

[news] 
Saturday 6th October 2012 quote quote all
Hi all,

I bought a 2005 Marin bobcat from a friend for using over the winter and to start to get into MTBing. Second ride out I managed to break the rear hanger and bend the rear mech, after replacing hanger I straightened the mech as best I could but although it works it doesn't seem to shift as well and is noisy most of the time so I am looking to replace it. The bike cost me next to nothing and is not special enough that I am going to throw a load of money at it replacing the whole gear set up but wondered if there is a rear mech of better quality than the current 8-speed shimano acera that will bolt straight on? The shifter on the bars is an 8 speed shimano v-brake? and the front mech is a 3 speed shimano nexave.

On another point, I seem to have the chain rubbing slightly on the front mech if I am on the large or small gear at the front and the opposite on the rear cassette (does that make sense?) I have tried adjusting the front mech but there just doesn't seem to be enough room between the cage on the front mech, is this normal?

Many Thanks
Mark

jrb43

444 posts

143 months

[news] 
Saturday 6th October 2012 quote quote all
Not special enough?! It's an old-school Marin: these need to be preserved at all costs! Well done on finding a replacement hanger. Frankly any rear mech you find will be better than what you've got. I would probably try and find an old 8-speed though because if you use 9-speed you'll have to replace the chain and I'll bet you'll find it's worn and stretched with the cassette and chainwheels, meaning that a new rear mech will quickly become a new drive train. With a new mech, you MAY need to transfer the old jockey wheels across to stop the chain skipping round.

Whatever you do, don't bin it!!

yellowjack

5,073 posts

54 months

[news] 
Saturday 6th October 2012 quote quote all
Maark said:
Hi all,



On another point, I seem to have the chain rubbing slightly on the front mech if I am on the large or small gear at the front and the opposite on the rear cassette (does that make sense?) I have tried adjusting the front mech but there just doesn't seem to be enough room between the cage on the front mech, is this normal?
Don't ride with these gear choices. If you are at one extreme or the other at the back, you will almost always find that there is a gear ratio using the middle ring at the front that will give you the same output for your effort. Riding with the chain at these extremes will damage the chain (premature wear) and you run a greater risk of dumping the chain off the chainrings with it running like that. Ultimately a roller chain is at it's most efficient when it is running in a straight line. Try to keep it that way, and you shouldn't go far wrong. Certainly with a triple at the front and an eight speed at the back, I would try to stay well away from using the inner 3 rear gears with the front big ring, and vice versa. If you feel that you need to use those ratios, select the middle ring at the front, and look for a rear gear toward the middle of the cassette. It's a little like driving your car in the correct gear, you just need to learn your way around the gears on the bike, and develop your inner sense of mechanical sympathy. It'll soon come.

Quite a few modern MTBs with ten speed rear cassettes are now running doubles at the front, because it reduces the amount that the chain needs to 'twist' between the extremes of gears, and although you think that there are fewer gears (20, as opposed to 24,27, or even 30), there are just as many 'usable' ratios, it's just that on an 8 speed triple (24), some of the ratios are duplicated on an adjacent chainring.

Hope that helps.


ETA:


jrb43 said:
Whatever you do, don't bin it!!
^^^What he said^^^

Quality piece of iron, well worth some TLC.

Edited by yellowjack on Saturday 6th October 12:02

Maark

Original Poster:

83 posts

55 months

[news] 
Saturday 6th October 2012 quote quote all
Thanks for the advice on the gear shifting, that makes sense.

Didn't realise the bike was maybe worth spending a few quid on, so on a different tack what would be the worthwhile upgrades I can do to the shifters,mechs, cassettes etc?

pablo

12,379 posts

161 months

[news] 
Saturday 6th October 2012 quote quote all
quality "iron" isnt far from the mark, apologies to bust the marin love-in but its really not worth spending that much on. the bobcat was closer to the bottom of the range than the top and as standard, wasnt spec'd that well at all. in all honesty, upgrading the drivetrain is are throwing good money at a resolutely average frame, forks and wheelset.

as for the rear mech, there are a few 8 speed mechs on ebay, xt etc but in terms of a new one, oyu are really looking at alivio or acera. both are ok but a bit heavy and clunky. whilst chains do stretch, you have to put a fair few miles (1500+) on the lower end stuff before wear becomes an issue. chains on lower end bikes tend to be stronger and a bit thicker than the high end stuff where weight is a premium. hunt on ebay or the usual classifieds for an old one, strip and rebuild it and it will be fine.
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.Adam.

1,571 posts

151 months

[news] 
Monday 8th October 2012 quote quote all
Mark, if you need a hand setting it up, I'm more than happy to help, as I am sure Kev or Keith are.
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