Re: [CR] Gipiemme/Simplex LJ4000 CP Ders- Any Good ?

I am sure Mr Broderick will come in here because he knows more about Simplex derailleurs than I.  In the meantime, here is my 2 cents' worth.  The LJ4000 is actually a "Super LJ" derailleur with similar arms to the alloy SLJs but with resin top and bottom housings.  It does not use the not-so-nice metal and plastic combination arms of the cheaper derailleurs and is lighter.  The top and bottom pivot spring arrangement is slightly different from the other Simplex plastic derailleurs, so the housings are not the same.  The SLJ4000 became the Peugeot team derailleur of choice sometime in the late 70s and was fitted to the carbon race bikes in the 80s.

The production PY10FC was fitted with the LJ4000 rear der mated with an alloy front der, which I think was the Peugeot team setup.

I have that combination on my own PY10FC and, as with most Simplex derailleurs of the era in good condition, the performance is better than Campagnolo SR.  Also of course there is a weight advantage, probably amounting to a bike/rider combination weight saving of about 0.0000000000001% in my case.  That may be a slight exaggeration, should you be tempted to calculate that I weigh about 100 tons or whatever; the point being that unless you save weight everywhere to get a respectable overall weight saving, it is not worth the trouble.

So, in answer to the question, this is a great set of derailleurs to fit to a high end racing bike.  The question that I cannot answer is that of durability.  I would expect the linkage durability to be almost as good as an all-aluminum alloy derailleur because three of the four pivots are fixed in the body, so that the bearing surface is between the pivot pins and the alloy arms.  With respect to top and bottom pivots, I would think there is sufficient bearing area for durability.

I would suggest to go ahead and fit them - you may be so pleased that you don't bother with alloy SLJs.

Hugh Thornton
Cheshire, England