slimshaky

My son has a well used diamondback cobra 20 bike. He's having a problem whereby he can only shift from 6 down to 5 and back, but can not shift down to any of the other gears (like the grip was stuck). I have tried adjusting the tension on the cable. I can get to a point where the shifter will shift freely, but it seems that there is not enough tension on the cable at that point to move the derailleur. When I tighten it up again, I am once again in the same boat of not being able to shift through all the gears. Does anyone have any advice on how I might remedy this? This is a 6 gear bike with just a rear derailleur. Let me know what other information may be useful.

JoeTBM 

Does the cable move freely through all control points if you release it from the DER. If it does then check the limit screws for proper alignment. If not then possibly a new cable and/or housing is in order.

This Parktool video should give you some help

https://www.parktool.com/blog/repair...roubleshooting

dsbrantjr

Which gear are you calling 6, big cog or small? My suspicion is that the cable is frayed inside the shifter, or it may be time for a cable and housing replacement.. I would shift to the small cog, detach the cable from the derailleur, check the cable for fraying along its entire length and check the shifter/cable system for free movement. Then check the derailleur for free movement by pushing it by hand while turning the crank; watch your fingers. If all checks out OK, set the system up by following this procedure: https://www.parktool.com/blog/repair...eur-adjustment

Miele Man

Is t he derailleur hanger bent?

Cheers

McBTC

They're probably is a limit screw that you need to adjust.

andrewclaus

If it was working before and suddenly stopped working, the problem could be failed cable housing, broken shifter, or badly bent hanger.

You can easily disconnect the three major components from each other and test them individually. Does the shifter click five times each direction? Does the cable move freely through each piece of cable housing? Can you manually push the derailleur through all its gears (while pedaling in a stand or upside down on the ground) without hitting spokes?

slimshaky

Thanks for all of your responses. I'll tell you what I know so far.

The cable does seem to move freely along with shifter, if I unhook the cable from the derailleur. I can see the cable getting shorter as I shift from 6...5...4...etc...

I need to read up on how the limit screws work to check those.

I have a new shifter and cable. Even with these, I am seeing the same problem that I saw with the old shifter and cable.

I am calling the small cog gear 6. That's where the chain is currently positioned.

I can flip the bike over and push the derailleur in by hand to get the chain to go on each of the cogs as i move the pedals.

I just checked the hanger and it looks properly aligned to me.

slimshaky

I watched a video on the limit screws and those are in a good spot now. I did a very slight adjustment, so the alignment on the small cog and the large cog look good when adjusting the derailleur by hand.

It is working a little bit better now, but still problematic. i can shift all the way up into 2nd gear now. however, the derailleur doesnt move at all when i go to 5 and only a little when i go to 4. when i go to 3, the chain moves to the next cog. it takes a lot of pressure to get into 2nd gear, and i cant get shifted into 1st at all while attached to the derailleur currently.

AeroGut

One possibility (among many) is that the cable is not attached to the derailleur correctly so you don’t have good leverage and also the derailleur doesn’t move as much as it’s supposed to with each click. Can you take a picture of how the cable is attached to the derailleur?

slimshaky

I tried to post the image, but this forum will not let me post an image or a URL, so you've gotta love that. Hopefully words will be helpful enough. I ran the cable straight across. If there is any bending needed at the nut, then that could be my problem.

Moe Zhoost

Long shot: Check all of your cable housing, especially where it goes through a cable stop. It may be that under tension, the housing is pulling through the hole in the stop. New housing with proper ferrules should fix that.

slimshaky

I found a hi res pic of one of these bikes online and the cable routing matches mine, so i think i can rule out incorrect cable routing.

Since a couple of people have mentioned cable housing, I will likely look at that next. I have one of the sections, as it came with my shifter. The other section is perhaps a custom size, as it does not match the size of the second housing that came with my shifter. Do housings come in standard lengths or do you generally need to get those from the bike manufacturer?

subgrade

Cable housings usually are sold by meter (or whatever units you're using), and you then cut them to needed lengths - which varies from frame to frame and other factors like handlebar height, stem length etc.

slimshaky

Thanks again for all your feedback, folks. I replaced the cable housing and still no luck. At least I know how to replace cable housing now.

Miele Man

Whereabouts are you located?

Cheers

slimshaky

I'm near Cincinnati, OH. There are bike shops near me, and I could take the bike there, but it will cost more than the bike did. With that in mind, I may end up just giving up on it and leaving it as an essentially single gear bike.