Trouble shifting front after upgrade from 7 to 8spd
01-15-09, 06:13 PM
#1
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Trouble shifting front after upgrade from 7 to 8spd
Hey!
BACKGROUND: Here's my story. You can skip it and go to the problem below.
I made the mistake of trying to tune-up a co-worker's '94 Diamondback Ascent. Pat said his old MTB was collecting dust and dog hair, wasting space in his garage, and that Kris (another co-worker) wants to get her husband on a bike. Pat and Kris' husband are both around 6-2 so we figured it would be a perfect fit. And a nice charity project. I said, "Bring it in. I'll check it out and get it going."
In retrospect we should have just craigslisted them a newer beater for around $150.
The bike was in great shape with barely any rust and oxidation, so naturaly I was lured into the prospect of reviving this beast and sending it on its way to its second life. It looked like all it needed was a chain cleaning, some adjustment, new pads, and a wipe down.
Where this 'quicky charity project' started going south was at the front STX SIS shifter, which wasn't engaging when thumbed. I took it apart, cleaned what I could clean, and messed with trying to get that little pawl to engage. It started to work again but intermittently, so I figured I'd dissamble it even further for a deeper cleaning. Thats when that pot metal shaft the assembly rotates on snapped. Oh well...
OK. What to do? eBay some used 7spd SL/BL combos? Naw, I got a set of LX 8spd shifters lying around and I can get some cheapo canti BL's for $12. All we need is a wheel with an 8spd cassette. I see those being dumped on craig's all the time. So I source a nice clean $25 wheel and cassette and put it all together.
Rear shifts clean. Front doesn't.
It resists going from the middle to the big. When I adjust the FD to push it across it makes it, but sometimes it dumps the chain over the side. Fiddle as I might, no happiness.
OK. What to do now? How about swapping in a ramped and pinned 42t ring? That should get it to bite and make the hop without adjusting the FD out as to throw the chain. Ordered. Wait, wait, wait.
Darn. It's the right BCD but it won't fit the spider.
OK. Now that nice 8spd XT crankset I've been hoarding is looking good for this. Right. Need to be done with this. Let's pull that STX crank and do the swap, see what happens. Puller is popping out of the threads as it doesn't want to pull. OK, time for the gear puller and some WD40. No dice. Where's the hack saw?
Saw, saw, saw. Bang, bang, bang. Good ridance!
Mount the XT crank. Swap the chain with an 8spd chain in better shape, just for good measure.
OK.
PROBLEM: Shifting up front from the middle to the big sometimes throws the chain.
Any ideas?
Maybe I should turn in my tools and go back to twisting wire with pliers, taping things together with duct tape, and supergluing broken metal parts.
BACKGROUND: Here's my story. You can skip it and go to the problem below.
I made the mistake of trying to tune-up a co-worker's '94 Diamondback Ascent. Pat said his old MTB was collecting dust and dog hair, wasting space in his garage, and that Kris (another co-worker) wants to get her husband on a bike. Pat and Kris' husband are both around 6-2 so we figured it would be a perfect fit. And a nice charity project. I said, "Bring it in. I'll check it out and get it going."
In retrospect we should have just craigslisted them a newer beater for around $150.
The bike was in great shape with barely any rust and oxidation, so naturaly I was lured into the prospect of reviving this beast and sending it on its way to its second life. It looked like all it needed was a chain cleaning, some adjustment, new pads, and a wipe down.
Where this 'quicky charity project' started going south was at the front STX SIS shifter, which wasn't engaging when thumbed. I took it apart, cleaned what I could clean, and messed with trying to get that little pawl to engage. It started to work again but intermittently, so I figured I'd dissamble it even further for a deeper cleaning. Thats when that pot metal shaft the assembly rotates on snapped. Oh well...
OK. What to do? eBay some used 7spd SL/BL combos? Naw, I got a set of LX 8spd shifters lying around and I can get some cheapo canti BL's for $12. All we need is a wheel with an 8spd cassette. I see those being dumped on craig's all the time. So I source a nice clean $25 wheel and cassette and put it all together.
Rear shifts clean. Front doesn't.
It resists going from the middle to the big. When I adjust the FD to push it across it makes it, but sometimes it dumps the chain over the side. Fiddle as I might, no happiness.
OK. What to do now? How about swapping in a ramped and pinned 42t ring? That should get it to bite and make the hop without adjusting the FD out as to throw the chain. Ordered. Wait, wait, wait.
Darn. It's the right BCD but it won't fit the spider.
OK. Now that nice 8spd XT crankset I've been hoarding is looking good for this. Right. Need to be done with this. Let's pull that STX crank and do the swap, see what happens. Puller is popping out of the threads as it doesn't want to pull. OK, time for the gear puller and some WD40. No dice. Where's the hack saw?
Saw, saw, saw. Bang, bang, bang. Good ridance!
Mount the XT crank. Swap the chain with an 8spd chain in better shape, just for good measure.
OK.
PROBLEM: Shifting up front from the middle to the big sometimes throws the chain.
Any ideas?
Maybe I should turn in my tools and go back to twisting wire with pliers, taping things together with duct tape, and supergluing broken metal parts.
01-15-09, 08:00 PM
#2
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Bikes: '96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '20 Surly Midnight Special, All are 3x10. It is hilly around here!
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FD's high limit screw need adjustment? FD too high?
01-15-09, 11:00 PM
#4
Really Old Senior Member
Have you checked the chain for any stiff links?
Have you done the FD adjustment procedure from step 1 from the Park or Sheldon's website? (including the height)
Is the current BB spindle the correct length for the cranks?
This may give you the correct specs & instuctions??
https://techdocs.shimano.com/techdocs/index.jsp
Have you done the FD adjustment procedure from step 1 from the Park or Sheldon's website? (including the height)
Is the current BB spindle the correct length for the cranks?
This may give you the correct specs & instuctions??
https://techdocs.shimano.com/techdocs/index.jsp
01-15-09, 11:05 PM
#5
Senior Member
Are you doing all of this testing on a workstand? If so, how about trying it out on the road and seeing if it works better with a slight load on the chain? I've found when simulating gear changes on a stand, it's difficult to shift the front and hand crank at the same time (maybe I'm just uncoordinated, or just need to flip the bike around on the stand). Some derailler/chainring combinations need the shift lever held down for a split second longer for the shift to complete. If that is the case with your setup, you might be getting tricked into thinking that you need to back out the high limit screw when really it's set ok and the shift just needs more time to complete.
Also, make sure the front derailler is aligned properly and not set too high. Either could cause shifting issues with the latter very likely to cause the chain to fall off on the outside.
Also, make sure the front derailler is aligned properly and not set too high. Either could cause shifting issues with the latter very likely to cause the chain to fall off on the outside.
01-16-09, 12:18 PM
#6
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Have you checked the chain for any stiff links?
Have you done the FD adjustment procedure from step 1 from the Park or Sheldon's website? (including the height)
Is the current BB spindle the correct length for the cranks?
This may give you the correct specs & instuctions??
https://techdocs.shimano.com/techdocs/index.jsp
Have you done the FD adjustment procedure from step 1 from the Park or Sheldon's website? (including the height)
Is the current BB spindle the correct length for the cranks?
This may give you the correct specs & instuctions??
https://techdocs.shimano.com/techdocs/index.jsp
I've gone over both the Park and Sheldon's drivetrain how-to's in the past and am confident in my understanding of the FD setup (Well before this situation, I was...)
Both 8spd chains I tried are good. Height and angle are good. Stop screws are good.
Now about that spindle length. I'm afraid to find out this is a chain line issue which will mean another BB. I suspect this is where this is headed. I checked the Shimano link for specs, but they don't go back to the FC-M739. I now have my hands on a FC-M737 which I'm going to give a shot to see if that changes things.
01-16-09, 12:32 PM
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Are you doing all of this testing on a workstand? If so, how about trying it out on the road and seeing if it works better with a slight load on the chain? I've found when simulating gear changes on a stand, it's difficult to shift the front and hand crank at the same time (maybe I'm just uncoordinated, or just need to flip the bike around on the stand). Some derailler/chainring combinations need the shift lever held down for a split second longer for the shift to complete. If that is the case with your setup, you might be getting tricked into thinking that you need to back out the high limit screw when really it's set ok and the shift just needs more time to complete.
Also, make sure the front derailler is aligned properly and not set too high. Either could cause shifting issues with the latter very likely to cause the chain to fall off on the outside.
Also, make sure the front derailler is aligned properly and not set too high. Either could cause shifting issues with the latter very likely to cause the chain to fall off on the outside.
After getting it to behave somewhat reasonably well in the stand, I sent one of the taller guys out with it and the chain jumped several times on them.
I believe I have the FD height and alignment set correctly. I even lowered it to its minimum clearance and tried various deflections, but none gave me the happiness.
Thanks for your response.
I think my next step is to swap out the crank with another XT, this time the 737 and study the chain line issue.
I just re-read Sheldon's entry and also the Park chain line stuff. This looks like my problem.
01-17-09, 12:37 AM
#8
Really Old Senior Member
" I think my next step is to swap out the crank with another XT, this time the 737 and study the chain line issue."
IF this is a triple, put it in the middle ring.
Then put the rear in 4th and eyeball the chain angle from behind the bike.
Then put it in 5th and eyeball again.
The angle should be from the opposite side and the same amount from "center".
It's actually pretty easy to tell when you compare measurements.
IF this is a triple, put it in the middle ring.
Then put the rear in 4th and eyeball the chain angle from behind the bike.
Then put it in 5th and eyeball again.
The angle should be from the opposite side and the same amount from "center".
It's actually pretty easy to tell when you compare measurements.
01-23-09, 02:54 PM
#9
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OK. It's all good now.
Replacing the 739 with the 737 put the chainline at the crank a bit closer to the centerline. This cleaned up the chain throwing but it was sometimes resisting the shift from the middle to the big under load - good on the stand but not when riding.
For another $20 I bought a new Deore FD-M511 which comes with clamp adapters including 28.6.
The bike now shifts cleanly and all is happy.
Like I said in my first post: I shoulda bought another bike.
Thanks fellas for the advice.
Replacing the 739 with the 737 put the chainline at the crank a bit closer to the centerline. This cleaned up the chain throwing but it was sometimes resisting the shift from the middle to the big under load - good on the stand but not when riding.
For another $20 I bought a new Deore FD-M511 which comes with clamp adapters including 28.6.
The bike now shifts cleanly and all is happy.
Like I said in my first post: I shoulda bought another bike.
Thanks fellas for the advice.
