This headache has been plaguing me for a couple weeks.

First, the components: this bike has a triple chainring and a 6-speed Maillard hub (pretty sure it has 28T down to like 11 or 12). It has a deore LX long cage derailleur.

When I try to shift lower than the 3rd or so lowest gear, the chain will ka-chunk-ka-chunk along almost indefinitely. It is tough to observe directly while riding but it looks like the chain is still engaged with the upper portion of the cog I am shifting from, and it runs diagonally along the top of the teeth on the lower portion of the cog, but does not actually engage. Sometimes I can get it to skip a couple gears and shift into the lowest gear, then shift back up to the gear I wanted.

At first, it looked like the derailleur was rotated too far forward, such that when it moved inward, it just pushed the chain into the side of the next cog.

Things that I have tried:

- Initially, it did not have a long-cage derailleur. I got one from a friend and put it on. The info I found said that the current derailleur is good for up to 34 teeth, if I recall correctly.

- For both derailleurs, I tried adjusting the b screw to several positions: max in, max out, in the middle. Very little difference between the positions.

- I checked the chain length. It seems to be the proper length, according to Sheldon Brown's method of running it over the big gears, not through the derailleur, and then letting it overlap by a link. It actually overlaps by about 1.5 links, but that seems OK.

I'm at a bit of a loss. Is it possible that the length of housing is too short/too long, restricting the action of the derailleur? Is the hanger sliiiightly bent?



Any help would be greatly appreciated. I can take a video of what is happening if the description isn't clear.

Thanks!

a rear DR shifts into smaller gears because it is springloaded, given any extra cable the spring is designed to be strong enough to collapse the cage and move the chain to the outside. most problems, IME, involving inability to shift to a lower gears is a result of too much friction somewhere in the system. could be lever, cable/housing or even the DR itself.

i might first disconnect the cable at the DR. and see if it will shift into the smallest cog. this test should show whether or not the RD cage spring is even strong enough to do the job. if not, the problem is probably in the RD. broken or bent or just gunked up.

then i'd remove the cable/housing completely and test it to see if the cable runs smoothly through the housing.

Thanks for the input.

It shifts into smaller cogs from large cogs with no problems, and it is pretty new so I think that the springs are good. I will try the test though just to check.

Also, the derailleur moves inward, such that it is below the gear that it SHOULD be switching into, without difficulty. So even if there was excess friction, it is still getting over there. if that makes sense..

I agree with all but that part.

That's what happened when I had my Maillard Helicomatic freewheel. I think it's just a problem with them- it won't shift just one gear- you need to shift two and back one. Helicomatic freewheels have little grooves at the top of the teeth, and these were supposed to act like the shaped teeth of modern cassettes and catch the chain. But it also required a chain with sideplates with sharp edges to shift properly, to catch in the grooves of the teeth. Those chains aren't made anymore. Plus it looks like the tops of the teeth are worn so the little grooves are nearly gone.

Dump the Maillard stuff. Get a new hub/wheel and put on a modern cassette/freewheel with ramps and cutouts. You'll be glad you did.

s/b "higher".

anyway, just reread original post and saw that it is happening in the middle. i had read it as happening in the lowest gear. so what i suggest probably won't help. my apologies.

Probably should have happened a while ago.. But your description of the problem makes sense. Thanks for the info, and thanks to all for weighing in!

Did it ever work well? If so, find what changed.

Why has no one suggested lubrication? Spray it down with a WD 40 type product and see if it improves.
Good luck

This is typical of the non-conversations on this forum. Loads of detail going back and forth but so much essential information missing.

Based on the first and third photos you provided, it looks like the cable housing is not properly seated in to the barrel adjuster at the back of the derailleur. This could be causing extra friction on the cable and/or not allowing the cable to move through the barrel adjuster (i.e. - pinching the cable between the ferrule and the barrel adjuster rim). I'm not saying that this is definitely the issue, but it should be checked and corrected if wrong.

Lubrication of the hinge points on the derailleur might help if it's binding up, but don't use WD40 as that is a solvent, not a lubricant. I use Boeshield T-9 mostly for these applications.

After correcting the cable routing and lubing the hinge points, you may have to go through a basic adjustment procedure to get everything working correctly.

Bike care 101... Here in Ohio we use solvent first, to clean and lube second.... Won't lube dirty bearings, nor lube a dirty chain without a little clean-up first... If you learned something new today, just celebrate!

It seems like the "b" tension screw might be out too far? It's located beside the rear dérailleur bolt and pushes on the dérailleur hanger. Essentially, in the bigger sprockets on the cassette/free-wheel the dérailleur needs to clear the sprockets with a few links to move. If you manually move the ratio to the biggest sprocket and the biggest chain-wheel then adjust the "b" tension screw in far enough (lift the dérailleur back off the hanger) so that it clears the sprocket and the chain links can turn freely. Also, is your low limit screw in too far? You should be able to manually pull tension through the cable while pedalling and move the dérailleur to the top, but not over the largest sprocket. - Cheers

Yes, that could be the problem. Check the rest of the cable such as the bottom bracket area for poor setup.
A little bit longer housing would probably reduce friction a bit too.

not added friction
but extra cable pulled out
holding mech in third

I agree with that, however, the OP said he could shift two or more gears and the rear would skip allowing him to shift back up to where he wanted to be, hence my suggestion that it could be catching the cable. I'm with you that there's probably 1/4" or so of extra cable used up to make that bend as well.