help needed gear problems again!

stevechambers34

got a real headscratcher! my '95' Edison TT bike's front mech rubs the inside of the cage whan at both extremes ie large front ring small rear and small front ring large rear!
I have tried everything to remedy this to no avail.
the front mech is a RSX100 'pull down'( FD-A550) I have tried it with a 105 mech(FD-1050) both are in good order, the frame is straight as are the crank rings/arms (shimano RSX 53/39) 68mm BB, rear casette is an 8speed Shimano Hyperglide again in vgc, chain is a Sachs PG
I am using Shimano105 8 speed gear/brake 'combo' units.
the whole machine is quite retro ,was built in 1995 and has had little use according to the previous owner ,and it does look that way, why should the chain rub...is there a specific 8speed chain needed?

portuguese mike

if i undestand correclty, what you are are experiencing is to be expected. when you have the chain on the either both the smallest cog at the back and at the front or vice- versa then the angle of the chain relative to the front mech will almost certainly cause it to rub.

in any case i've always thought that you shouldn't ever ride like this anyway as it's no good for the chain accelerates wear. Also, i tend to find that the gear ratios at these extremes are often, more or less, replicated with another combination of cogs and therefore it's not necessary. For example, 53x23 gives the same ratio as 39x17 - 62 inches

stevechambers34

perhaps I was a little unclear ...when the chain is on the outside (53) front ring and the smallest outside rear sprocket (12) it catches and also when on the inside front(39)ring and the largest (23) rear sprocket it catches NOT 'crossed' as it were. the front mech body will not go 'in' any further to the frame even when the setting screw is fully backed off.

portuguese mike

Apologies, in that case i've recently had a similar problem which i traced to the front mech being set too low so you could check that if you haven't already (it may also cause problems if it's set too high as well)