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Front derailleur shifts when pedalling out of saddle

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Front derailleur shifts when pedalling out of saddle

Old 10-25-18, 03:10 PM
  #1  
TomJD
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Front derailleur shifts when pedalling out of saddle

I'm posting this in C&V instead of the mechanics/repair as my bike is a Holdsworth Special from ~1982. I weigh about 200 lb. The frame is a 56cm 531db throughout. Crank and derailleurs is early Shimano Deore, complete with with DynaDrive pedals. The crank is a 50-45-30 triple that uses a bolt pattern similar to the TA Cyclotourist. The derailleurs are friction shifting and the levers are down-tube mounted. The front DR shifts using a bare cable that runs through a brazed on guide over the top of the bottom bracket; increased cable pull causes front DR to shift to larger chainwheel. Love the bike. It has a nice light and resilient ride.

But should I decide to pedal out of the saddle to climb or accelerate, especially when on the large chainwheel, the front derailleur pretty quickly moves and the chain begins to rub on the derailleur cage and soon will shift to the next smaller chainwheel (downshifts). Is this due to flex of the frame? Crankset? How can I decide which? Any ideas for fixing or improving this situation? I'm reluctant to increase the friction on the shift lever as that will make normal shifting more difficult. Should the cable be lubricated where it passes through the bottom bracket guide? New cable?

Thanks for your ideas and suggestions.
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Old 10-25-18, 07:41 PM
  #2  
canklecat
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Front derailleur ghost shifting. Fairly common problem. May be due to frame flex around the bottom bracket, cable tension or both. With friction shifters sometimes the shift lever tension needs to be tightened.

Happened to me a few times on the Ironman when standing to climb and sprinting pretty hard up short, steep hills. This can be disastrous when skipping from the big to small chainring while standing, especially if the chain skips completely off and flops onto the bottom bracket. Fortunately that's pretty uncommon as the FD tends to keep the chain on the smaller ring. But as soon as I'd hear the chain rub warning sound I'd sit and ease up, shift into an easier gear and avoid standing to climb until I got the bike home to make adjustments.

I have to tweak the adjustments occasionally. The front derailleur cable is under more tension in the big ring and sometimes wants to creep toward the small ring when sprinting or standing to climb.

As with many shifting problems, this flaw can be hard to replicate on a shop stand. I usually make my adjustments with the bike on the trainer with the rear wheel under load to simulate riding conditions. I'll apply more resistance (Cycleops trainer), put the bike into the big chainring and smallest rear cog and stand to mash, then tweak until I'm satisfied it won't shift under load on the road. It still wants to creep under load when sprinting or standing to climb.

I suspect part of the problem with my bike is excessive spring tension in my Ironman's Suntour GPX group. Spring tension was definitely excessive in the GPX rear derailleur and swapping to an old Shimano 600 RD solved that particular problem. I still have the Shimano 600 FD but haven't installed it yet to test my theory.

I didn't realize how much difference a really stiff frame and BB makes until I test rode a Specialized Tarmac this summer. Wow. No flex in the bottom bracket. More pedaling energy goes into forward motion.

Rear derailleur ghost shifting can be annoying but less likely to result in losing balance and crashing. It'll try to skip from an easier to harder gear. Annoying but less dangerous.
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Old 10-25-18, 08:25 PM
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Get some ratcheting or retrofriction shifters, the pull will be easy but they hold on against spikes in cable tension as the frame flexes.
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Old 10-25-18, 08:29 PM
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Tighten the lever. You can also disassemble lever and degrease it so it's not so slippery.
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Old 10-25-18, 09:47 PM
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As an experiment, please consider:

a) tighten the front derailleur shift lever, as others have advised - see if it helps, then you can decide if "too tight" in normal circumstances is worth the result

and

b) double-check the crank arm fixing bolts on both crank arms, also the chainring bolts, for proper torque. Perhaps a small part of the flex under heavy load when on the large chainring is due to loose bolts?
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Old 10-25-18, 10:32 PM
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Ghost Shifting - ZEBRA

When you hear hoofbeats think horses not zebras!

ZEBRA = Medical terminology... Look for the simplest, most obvious answer to the question first!

@Classtime BINGO! 10 points... @cyclophilia 1/2 bingo! 5 points...

Disassemble both levers, thoroughly clean everything including the threaded holes for the adjusting screws. I use a Q-tip with alcohol or solvent to clean out the gunk.

Reassemble and apply a drop blue Loctite to the lever adjusting screws before you put them in. Re-tighten the screws to the point where they can still move but not too easily. Let the bike sit overnight so the Loctite will fully harden then take the bike out for a test ride.

If the problem still exists, call Dr. House.... Kidding aside, after you've done the easiest thing with the levers then it's time to explore other possibilities.

Did this problem just start? Are the cables in good condition?

Grab one crank arm at the bottom of the stroke and see if the BB is loose by trying to move it in and out.

Next do a careful visual inspection of the BB shell and seat tube. Clean the area completely so the you can see any crack in the tube. You can check the down tube too but if there is a crack, the seat tube is the most likely suspect.

If everything checks out OK then it's time to hunt zebras.

If this has been going on for a long time, there's a possibility that the seat tube is in upside down with the butted end at the top.

What size seatpost do you have? It should be 27.2mm or 27.0mm, maybe 26.8mm. If it's smaller, say 26.4mm or 26,6mm that may be the reason. I've seen it in even some of the top name sacred Italian bikes. It can happen.

BTW. Holdsworths are no slouches, have 3 of them myself.

My first "pro" bike was an all Campy (except for the brakes) 60cm 1971 Gitane Super Corsa. It was extremely light for a Reynolds 531 frame with an extremely comfortable ride. But it would ghost shift at the slightest sprint, sometimes both sides. Climbing was almost impossible. I was a masher back then.

I suspected 2 possibilities: it was made of some special super light thin wall Reynolds main tubes or more likely the seat tube was brazed in upside down... also the possibly they used a seat tube for the down tube. I traded it for a NOS 57cm Super Corsa frame and the problem went away.

Possibility of a cracked BB spindle or crank arm? You're entering the realm of wild a** guessing now. Good luck.

Another point, have you recently gotten stronger? You're an animal!

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Old 10-26-18, 09:15 PM
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Originally Posted by verktyg View Post
If the problem still exists, call Dr. House....
It's not lupus.




Unless it's lupus.
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Commence to jigglin’ huh?!?!

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Old 10-27-18, 04:32 AM
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Originally Posted by The Golden Boy View Post
verktyg wrote: "If the problem still exists, call Dr. House...."

It's not lupus.

Unless it's lupus.
HAHAHAHAHA! Thanks, you made my day!

You're SICK!

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Old 10-27-18, 09:39 AM
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Originally Posted by verktyg View Post
HAHAHAHAHA! Thanks, you made my day!

You're SICK!

verktyg
I may be sick. But I don't have lupus.

It's never lupus.





Unless it's lupus.
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Old 10-27-18, 09:59 AM
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Also, check with a torque wrench, your crankarm fixing bolts. Do not trust pure feel. Agreed with levers, but most bikes that come in my shop are improperly torqued which will affect chainline and flex.
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Old 10-28-18, 07:09 AM
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"Front derailleur shifts when pedaling out of saddle"


My front derailleur does not pedal, in or out of saddle.

Sorry for the grammarian post. I just suffered through a local newspaper headline, "Man punches intruder after beating wife." I got the editor to fix that one in the online edition ... .
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Old 10-28-18, 07:38 AM
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What is happening is cable friction and FD spring tension are allowing the frame flex to move the shifter slightly each pedal cycle. The FD spring then takes up the excess cable between each flex cycle.

The two ways that it can be helped are to also have spring tension in the shifter itself, or to have some indexing in the shifter that doesn’t allow it to move. The tension option assumes the tension can be matched to the FD, which is possible but sometimes it doesn’t match. Indexing is the most sure solution in terms of not having to constantly tweak something.
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Old 11-11-18, 10:45 AM
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Thanks for all your suggestions. I'll investigate further this winter while getting the bike ready for riding this spring.
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