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What did I do wrong. adjusting deraileurs

1135 Views 4 Replies 4 Participants Last post by  05stumpy
I was so excited because I thought I had just figured out the rubix cube of shifter /deraileur adjusting. I built up and dialed in my wifes MTB with newer XTR shifters and derialeurs. When I got done it worked perfectly and I felt triumphant. I was so confident that I wanted to tackle putting new shift and brake cables on my old mountain bike.

First off the front deraileur I have adjusted so it shifts to the right points and won't throw the chain off the largest and smallest biopace rings (so I am pretty sure I have my high and low stops set correctly). However when on the largest ring shifting skips straight over the middle ring to the small ring. When Shifting up from smallest to largest it works perfectly and appears indexed correctly with no need for trimming regardless of the rear cog selected. I just can't figure out how to get it to stop on the middle ring when going from large down.

If that wasn't bad enough, when dialiing in the rear deraileur it works great on the rack. It shifts up and down thru the gears with no problems. It shifts clean and crisply...but when I got on the bike, under stress on the largest rear sprocket it will shift itself to the next smallest sprocket. It only does this when on the largest sprocket. Any other spocket indexes fine. I am probably due for a new chain, but it didn't have this problem before I fitted the new cables and housing....again it works find on the stand, but not in the field.

This is a early 90s shimano 7 speed SIS system. I believe LX series rapid fire shifters.

Any advice would be appreciated. I thought I had the limit screws set properly and cable tension set correctly..but appearently the setup of my wifes XTR components gave me a false sense of confidence in my abilities.:confused:

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Half an answer

I'm only going to try your rear derailleur issues. Biopace rings are notoriously difficult to keep shifting properly, so I am afraid I won't try to see what's going on there.

You don't say what kind of bike, though I will make an assumption by the mid 90's 7spd LX drivetrain that you're riding a steel hardtail. What's probably going on here is flex in the frame when you're on the bike, which is why it's ok in the stand but not when you ride it's problematic. This is where your barrel adjusters become your best friend. Start with like a quarter turn out, ride it, see how it feels, then another quarter turn, and so on. Hopefully that makes it better.

Otherwise you might want to revisit the limit screws, so that it rides a little closer to the spokes when you're in the largest cog. Once the shifters are indexed you won't have to worry about throwing the chain into the spokes, but take it easy in the beginning to make sure.

Sorry that I only half-answered half of your issue. Good luck.
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Thanks for the 1/2 answer. I undid the cable and re-did the rear from the beginning. It worked perfectly and shifts great now. New cables, adjustment, lube makes it ride like a new bike again.

The front is still a different issue. I even checked my sons Acera shifters and my wife's XTRs and they index correctly both up an down on the chainrings. Mine goes up fine, but on the way back down it skips the middle chainring...largest straight to smallest. I will tinker with it just a little more, but I am beginning to think the front shifter pod may just be worn out.


PS: it is a 1991 schwinn impact chromo frame/fork. fully rigid...and yeah it was made when splatter paint jobs were all the rage. I know it is probably time to upgrade to a more modern bike, but this one has been very good to me. I kinda look like Fred Flintstone when I take it out to the trail where nearly everyone has either FS or minimum front susp. I keep trying to break this Schwinn, but I can't.
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whether this helps or not...but I have an idea about the front der. When I first stated doing my own work on my bike, I had to replace some shifter cables that blew apart. When I did the front one....I would pull the tension real tight and then tighten down the cable clamp, and then proceed to adjust der. It did exactly what you are saying, worked fine going up, and shifting down would shoot over the middle ring. I just loosened the tension of the cable a bit, re-adjusted things, and it worked. I could tell something was a little when I shifted down I could def. feel it was under a lot of tension, It moved with a lot more authority...:D However, if you don't notice a lot of tension, and know you didn't have the cable under a lot of initial tension... it may not be the reason. Just thought I'd mention it as the issues seemed similar.

This was on an 8 sp. from the late 90's with a stx rc front der. for reference. I believe the shifters were also stx.

Good luck
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you need more cable tension in your front cable, try 1 turn out of the barrel adjuster.

might need to re-set the lower limit screw (turn it in a bit) spec is 0-0.5mm space between chain and FD when in the lowest ring. set the inner limit, then re-adjust the cable tension if needed.

also make sure the FD is lined up properly and is spaced correctly from the rings.
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