Jockey cage hitting 2 x sprockets?

Slightly perplexed by this one. Apart from this issue, I've just finished putting together a build consisting of Shimano 600 Tricolor group with the exception of the BB, which is a generic UN55 as I haven't been able to source a tricolor BB in decent condition. The cassette is also a modern offering being a HG-50. Teeth range is 11-28T (I think 12-28 would have been a better option is the 11T cog is a bit clunky).

Having looked at the max cog size & chain wrap and looked at other peoples builds on the www, most had suggested that it is possible to have a 28T rear sprocket without issue. I've played around with cable tension, chain length and the gearing is sweet with the exception of two rear sprockets. Oddly it isn't the 28T sprocket which if there was to be an issue I'd of thought it would have been this sprocket.

The rings up front are 52 - 42, it's a 6401 8 speed derailleur in conjunction with 600 STI's. It should work, but it doesn't.

The issue is the upper part of the jockey wheel cage is hitting the adjacent sprocket when on the 21T & 24T sprockets (which are 2nd & 3rd on the cassette if the 28T is the first sprocket). In the troublesome gears, the angle of the junction where the derailleur connects to the jockey cage is under more tension than in the other gears. Chainline is bang-on so this isn't an allignment issue.

All a bit odd, I wonder if I could tap the minds of those who may have some diagnosis or advice. I spent 4 hours yesterday tinkering with this, my patience has run out i'm afraid to say.

Cheers

Re:

Appols if this sounds a bit obvious/already tried, but have to tried adjusting the screw at the rear of the mech, that touches the stop on the frame?
IIRC, this is adjust the gap between the cage and the sprockets.

Mike

Hi Mike, yes - that has certainly been tried, possibly on every thread of the screw :facepalm: It marginally adjusts the cage to sprocket distance, it actually had more of an effect on the derailleur 'bouncing' when in gear. I had previously put that trait down to the cable adjuster on the back of the derailleur?

Re:

I think it tensions the chain a bit, as well as adjusting the distance, as you say . Can't think of anything else I'm afraid mate :?

Can you post pics maybe?

Mike

No it's an odd one. If there was an issue with the 28T sprocket I could surmise that the chain length was wrong etc, but I started with the jockey wheels at 90 degrees to each other vertically on the 52T front & 11T rear and worked from there. It took the usual fiddling with cable tension, adjusting the limit screws etc - all the usual. I got it dialed in, it's just this issue with the 21 & 24T sprockets. The real blame is in my aging legs and having to succumb to a 28T on the rear

I've got to pop out for a few hours, but yes I'll post some pics later and see if that helps with the diagnosis.

Many thanks.

Is yours the version with the solid jockey cage?



Shaun

Re:

Is the hanger aligned correctly?

Re:

Afternoon Shaun. Mine's the open cage version. I've attached some photos which (hopefully) show the issue.

Top picture - jockey wheels when on 52T - 11T.
2nd picture - on the 5th sprocket - no issue with hitting.
3rd picture - on the 7th sprocket - cage hitting 6th sprocket.
4th picture - on the 8th sprocket - no issue with hitting.

As you can see the proximity of cage to jockey wheels is fairly close on most sprockets, but as already described it's just the 2 sprockets where it is actually hitting. There is obviously some part of my set-up that isn't quite right, although what that may be is a mystery to me.

Gav - Hangar is straight, dropouts are straight, frame is NOS - the RD has very little mileage, cranks are NOS, BB is brand new out the box - I'm leaning towards this being a chain-wrap / chain length issue?

I never ride big to big but I've just tried it and it won't reach, the RD goes to it's maximum 'forward' travel and locks up before the chain has fully engaged - could this be the problem, i.e. not enough links in the chain?

Hmm........."Slant Pantograph" mechs should be a bit more parallel to the chainstay than that.

Shaun

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It has to be chain length, on 42T - 28T the bottom jockey wheel is pointing forward towards the front of the bike, which can't be right can it? If I add more links then the 90 degree vertical on the jockey wheels when in big to big won't be achievable though, which I've always used as a set-up starting point. Perhaps this requires a slightly different approach.