Classic & Vintage - Skipping chain question....HELP!

I am getting my recently acqured Gitane Tour de France back on the road. I have purchased a Simplex Criterium to replace the incorrect Prestige that came on the bike. I am using a set of clincher wheels rather than the original tubular wheelset, at least for now.

Here is the problem! I temporarily set up a shift cable and went for a short ride. It shifts beautifully, much better than expected and I think I will really enjoy the bike. The only issue is that when in fourth gear the chain slips. First, second, third and fifth are just fine. I changed the freewheel and it still slips. The chain is brand new and not binding. It does not slip when on the large chainwheel, only when the front is on the smaller one. I am frustrated as I can see no visible wear on either of the freewheels, the chain seems tight when on that cog.

Am I missing something obvious? I would be grateful for any advice you can offer.

Thanks!

I guess I should also add that since this bike has Simplex dropouts, I can't throw a SunTour on to see what happens.

Fourth counting from which direction? The second largest cog, or the second smallest?

Unless the "fourth cog" is coincidentally worn on both freewheels, which is possible, that is weird. Shifting to the larger chainring increases chain tension and reorients the rear derailleur's jockey wheel, and, with Simplex, the rear derailleur body's position. Does the derailleur hang plumb and true? Are there any bends or other defects in the pulley cage?

I guess I should also add that since this bike has Simplex dropouts, I can't throw a SunTour on to see what happens.

Really? With very minor surgery, I put a SunTour Cyclone II on my 1980 Peugeot PKN-10 and later rehung the original Simplex.

Fourth being the second from the smallest.

The derailleur seems normal in all respects. The chain is feeding onto the freewheel with no obstructions and it is free in its movement. That is what puzzles me.

OK, I'll bite.....how minor was the surgery? I'd like to keep this one as original as possible, but maybe I'll try it.

I will also try yet another wheel and freewheel combination this weekend. One that is off of my Raleigh International that is known not to skip. I may even try that chain, too.

Keeping freewheels, chainrings, and chains together as you switch from bike to bike is a good idea as they all wear as one big family. That's why I've seen instances of a new chain causing slippage in a gear when the old chain didn't have that problem. That 4th cog on the freewheel is likely the one that gets the most use, so it's probably worn. I'd try swapping in a new freewheel or a new cog.

Neal

For some riders, I agree with you, nlerner, and if both freewheels were ridden by the same person, I might expect the same cog to wear out on both. With my half-step gearing, I am hardest on the second and third largest cogs.

In my case, one freewheel was an Ebay acquisition, while the other was pulled from a Nishiki abandoned in an alley. Both show little, if any, wear.

Update.....

This evening when the temperature got a bit more tolerable, I went out and switched wheels with another bike. No skipping of the chain in 4th. I put the Gitane wheel on the other bike-no skipping of the chain. I then switched freewheels between the two wheels, ending up with the freewheel from the non-Gitane bike on the Gitane. It skipped once with an extreme effort on the pedals, much improved from before.

My theory is that the new chain and the old freewheel would have worked just fine with a Campy or other derailleur, but with the Simplex they are a bit touchier. There is not as much chain wrap with the Simplex. I am going to try an older chain on the Gitane and I am hoping that will eliminate it completely.

The Gitane is not going to be a real high mileage bike, as my time is limited and divided among 4 other bikes. Hopefully this will eliminate the problem!

Interesting. So the Campy derailleur maintained more tension on the chain, you think? If so, how about using the Simplex but taking a link or two out of the chain.

Neal

Interesting. So the Campy derailleur maintained more tension on the chain, you think? If so, how about using the Simplex but taking a link or two out of the chain.

Neal

I tried that. I am running a 14-28 on the rear and it appeared to make the chain too tight when running 9th and 10th. Not that I would, but I don't want to put too much pressure on 30+ year old Delrin.