Hi all, I picked up an old early 90's trek 700 that i'm fixing up.

The rear derallieur does not have a b limit screw ( Shimano Atlus c20 ) and the jockey wheel keeps hitting the cassette teeth.

Is there any way I can adjust it so the jockey wheel raises up higher away from the cassette teeth?

Can you very slightly adjust the chain length?

not sure how that would help? problem still exist if its in the small or large ring in the front

Your bike sounds like it's a '93 with a stock 14-28 freewheel, and I'm assuming this is your current setup.

But if your Altus RD isn't able to keep the upper jockey wheel away from the freewheel, it could be that the springs are worn out, and won't work no matter what you do to it. I suppose you could try to put a shim or wedge in the space where the B screw would normally go, but if that doesn't work, I suggest replacing the RD. You could find a cheap Shimano, or even a SunRace, online for around $20 that would handle a 28t sprocket easily.

An overly long chain can cause the problem.
With the chain on the largest ring AND cog-
See how many links of slack you can generate.
Report back.

Obviously the Shimano Altus C20 jockey wheel did not hit originally the cassette teeth, you've not mentioned if it is doing it in the high gear or the lowest gear or both ? & assuming you've not put a massive low gear set up like 36+ one has to assume as mentioned its basically worn out spring gone, the only other thing to check is that the dolly wheel is the correct size, (number of teeth) maybe some has managed to install larger ones.

Be careful trying this, that you do not make the chain too short to shift into the big chainring and big cog without strain.

there are pieces made for the trendy 1 by 11, 10 - 42t cassettes, it physically lowers the derailleur hanger, to clear that chainring sized largest cog.

may be cheap enough to just get a different RD , with a B screw..

ah, yeah mabye thats my problem, the bike has one of those old school shimano super low 34t granny gears.

I guess for now I can just set the low gear screw so it won't shift into the granny gear and maybe shorten the chain as well to see if that helps anything

Shorten the cable housing?

For $20 you can probably pick up a new Tourney that will run a 34t. I don't know if your Altus derailleur has an integrated hanger or not. You can buy a separate hanger or, I think, you can get a Tourney with a hanger.

My route would be an older used Deore LX or XT, but that is just my preference and have done so in the past. If you did this you would have to get a separate hanger, if the bike frame doesn't have one.

John

If the bike has the original freewheel or cassette, then your crummy C20 derailleur is broken. No amount of futzing with the chain is going to make it not broken.

But, if you have the C20 type with its own hanger rather than one built into the frame, make sure it is in the correct location on the dropout.

How do you do this? By pinching the chain and seeing how many links you can make touch?

C20 derailleur? Say no more.

I NEVER liked those things even when they were brand new. I'd dump that turkey and replace it. If the hanger is integral with the derailleur, get a Tourney. If the hanger is part of your bike frame, get a Deore.

+100

I built a purposely rat bike and ran into this after not reading the derailleur spec of 26t max cog. I got, "creative", because the bike is a running joke.

Do you have a co-op nearby? This will make it cheaper.

Isn't it fun when a previous owner adds something that doesn't work? Liked I said, finding a co-op will help or even your LBS might have some stuff lying around. Do you need the 34t? Then swap back to the 14-28 or 13-24t.

The picture below may help. There is a spring (item 3) that holds the derailleur in place that may be broken. If so, buy a new RD - or get an old one, used.

If you have a replaceable hanger, you could upgrade that, too.