Bicycle Mechanics - Rear derailleur get jammed in the big cogs of the cassette

I have this problem and I can't shift to low gears in the back when I have low gear in front (first sprocket). It seems like the hanger is too short for this cassette or something (although is not).

Here's the pic with the der stuck in the big cog.

http://i43.tinypic.com/6h56jk.jpg


Any ideas?

You've tried to adjust the B-screw? Which RD. Look up RD adjustment on the Park Tools website.

B-bolt? That's the one that hits the fin on the hangar.

Another possibility is you have a freewheel/cassette with a large cog that is beyond the derailleur's capacity. Most derailleurs are rated for a maximum possible cog size and, while that can be stretched a bit, there are limits.

I can't find the damn screw on that derailleur. Even the old ones has this?

I screw the hanger of the derailleur on an angle so the spring gets more pressure. So for now it seems to work ok. Thanks for your help.

I can't find the damn screw on that derailleur. Even the old ones has this?

The cheaper ones may not have a B screw.
If you can change the "angle" of the DER, it sounds like you have one of the cheap ones that clamps on with the axle nut.

Another possibility is the chain is too short???

Did this problem just occur out of the blue?

Also the cheaper clamp on type DER's usually are only good for a 28T max cog.

I have seen this issue when cheap people will use a cheap crappy derailleur on a bike with a derailleur hanger. The cheap derailleur has no stop or b-screw and then as time goes on, the derailleur will then slowly rotate until it finally hits the cassette/freewheel cogs.

Can you show us a bigger picture of the whole area including the derailleur and how its mounted to the frame? And what kind of bike is it/

The cheaper ones may not have a B screw.
If you can change the "angle" of the DER, it sounds like you have one of the cheap ones that clamps on with the axle nut.

Another possibility is the chain is too short???

Did this problem just occur out of the blue?

Also the cheaper clamp on type DER's usually are only good for a 28T max cog.

No, it appeared when I change the cassette with a new one but with the same number of cogs. And the biggest one has 28. Yes it's a very old and cheap one. RD-YT20 is the model. No the chain is ok I think.


I have seen this issue when cheap people will use a cheap crappy derailleur on a bike with a derailleur hanger.

Cheap people??
It's an old Mercier - Special Tour De France
I don't think it's the problem you describe.

Two more photos
http://i43.tinypic.com/24cgkgn.jpg

http://i39.tinypic.com/246t7nr.jpg

Cheap people??
It's an old Mercier - Special Tour De France
I don't think it's the problem you describe.

Two more photos
http://i43.tinypic.com/24cgkgn.jpg

http://i39.tinypic.com/246t7nr.jpg
Bingo!

that is EXACTLY the problem I was referring to. That is a cheap low-end 80's era Shimano early sort of indexing rear derailleur. Cheap and made for Huffys and Murrays.

See how there is an extra hole in the hanger? That is for a bolt that goes into a cheap Huffy frame that keeps the derailleur clocked right. Without that bolt, the derailleur will eventually rotate and get tangled up again in the cogs.

Your mercer probably has a real derailleur hanger which is used with a mid range or higher derailleur that has a B screw. there is no b screw on that cheap SIS derailleur.

The problem is that the real hanger is broken for some reason. :(
Also, the derailleur hits the cogs without any rotation!

I 've managed to screw the hanger (the one with the hole) with an angle on the derailleur so the spring puts more pressure on it. So the problem solved for now atleast!

Ouch. Well then that is not a problem I am unsure of solving. I'm pretty sure you can get claw adapter so you can use a better derailleur (your bike deserves a better derailleur) but I'm not sure how it would work.

I wonder if you can get a new hanger welded back on but would that be too expensive?

I'm considering buying something like this: http://www.cambriabike.com/shopexd.asp?ID=133416
It has already a hanger.

It's a rare thing to see, a broken hanger. Especially on a road bike. I can imagine the tortures this bike went through from the previous owner.

I don't think a welded hanger would be expensive, but more of a hassle I'm not very prepared to go through. And this bike is a tough oldman, wouldn't mind rolling with some modifications on its frame :)))

I have seen this issue when cheap people...

Jeez, the guy is just trying to get his bike working. No need to run the guy down...

-Tom in SoCal

Jeez, the guy is just trying to get his bike working. No need to run the guy down...

-Tom in SoCal
That was not my intention. I had the same issue on my bike. Someone wanted to get the Univega I bought working as cheap as possible to flip on CL. So they stuck the same derailleur as the OP's (SIS Shimano that is found on lots of Huffys) onto my Univega bypassing the factory derailleur hanger. When i posted about "cheap", i was still annoyed with the guy who was trying to flip a bike for as cheap as possible hence my cheap comment.