Rear Mech/Jockey/Chain skip

Bunneh

My Mrs bought me an old GT Timberline off a friend and suffice to say it's in a state. I've rebuilt everything from the ground up but the thing that's really lost me is why the rear mech refuses to work correctly. It's an ancient Acera piece of cr*p but will do the job until I get a few more upgrades.

When I spin the cranks to move the wheel the chain jumps to the 4th ring on the cassette, refusing to come off even with adjustment of the rear mech screws. The jockey closest to the cassette is skipping links and stops when I lift the rear mech up a little, the mech also shifts down to the gear it should be on. Soon as I let go of the mech it starts skipping again. I have messed about with the adjusters, swore at it, thought the mech was bent, thought the frame was bent, thought my head was bent... Still can't solve it. Before I go out and grab a new rear mech does anyone have any ideas?

I'll try and post a short video of what I mean later if my explaination isn't clear enough

Ta!

pilch

Bent hanger?

Bunneh

Cheers for the reply Doesn't seem to be bent, looks aligned okay.

I've uploaded a video which may explain better

http://www.youtube.com/watch?v=_7avm7mK ... e=youtu.be

Splodger

Is the mech adjusted so it is too close to the cassette? You say when you lift it away from the cassette the jockey wheel stops skipping. Could need the "B" screw adjusting? Is the cage clashing with the cassette too and causing it to move to 4th? Again could be the "B" screw.

Have you checked the cable isn't seized or somehow jammed?

If the mech isn't badly worn, it seems to be an adjustment problem

Splodger

Just looked at your vid. Looks like the jockey wheel cage is clashing with the cassette and preventing it moving properly.
There are three screws on the mech that adjust it - two side by side that adjust the limits on the highest and lowest gears, and the "B" screw which increases the clearance from the cassette - It's the one you "messed with that made no difference".

Have a go with that by winding it in. It should push against the mech hanger and move the whole mech away from the cassette.

Bunneh

Cheers for the replies; I'll have another go with the adjustment screws and get back to you. I did adjust 'B' screw moving it in and out but the screw just slides down the frame; however I may have missed something so I'll have another looksee Thanks again.

Splodger

It shouldn't slide along the frame, it should push against a "stop" on the hanger. That way, when you wind it in, it pushes the mech in the opposite direction, away from the axle. If you don't have the little projection on the hanger you will need to replace the hanger (assuming it is replaceable)

Bunneh

Aye there's a little stop on the hanger, it doesn't look too big really but I've pushed the mech onto it and it should, hopefully work now. i'm just currently swearing at jockey wheels and the chain

Bunneh

Problem fixed, thanks guys. Now it's just a matter of rebuilding it all back up, wiring and tyre pumping and it's going on it's first trip out since 1998!