Sachs Huret Front Mech?

[Markone]

I picked up a 1984 Raleigh Record Sprint with Sachs Huret front derailleur a couple of weeks ago.

I've overhauled all the bearings,touched up the paint on the frame had the wheels trued and installed new cables and bar tape.

Mechanically the bike is excellent and rides beautifully except for one niggle!

If I change from the front big ring down to the front small ring with the chain on any other cog than the biggest on the cassette the chain will often not drop down smoothly,but sit to one side slightly of the small chain ring and skips over it.Back peddling usually quickly drops the chain down on to the ring!

In all other regards the front mech works as it should and appears to be correctly set up, with the right amount of travel in both directions and with no chain rub.

Any suggestions as to what may be the cause of this problem will be most gratefully received.....

 

[Midlife]

How close is the front mech cage to the top of the big ring?

 

[Markone]

How close is the front mech cage to the top of the big ring?

It's pretty close,leading edge of the front mech is sitting about 4mm above the big ring and the trailing edge around 2mm-3mm above the big ring...

 

[Midlife]

OK, seems right, if the mech is too high then it can be a bit flakey changing. Is he outer plate of the mech straight or has it got a bow in it?

 

[Markone]

Re:

The outer edge is straight..

 

[Markone]

Does anyone have any ideas I've done much tinkering and head scratching,but the problem persists!

 

[Markone]

Re:

Finally,I have found that the problem was caused by the big ring being shimmed on each of the five arms of the crank.

Though I was aware of these shims they looked,(and may have been)factory fitted,but neither of my two other vintage bikes sported shimmed big rings.

I removed the ring,removed the shims,reattached the ring and with the two rings being fractionally closer together the chain drops down and meshes with the small ring from any rear cog!

Great,because I was starting to blame the front mech and was looking for an 'upgrade' replacement on ebay........