Greetings all. I'm having a problem that's new to me. I have a SRAM Rival (i.e. Truvativ) double road crank and Shimano 105 front derailleur (also SRAM 10 spd cassette with SRAM Rival RD and Rival shifters). I've been using them together for about 2500 miles without incident. This past Saturday, I broke a chain while on a ride a long way from home. I stopped into a bike shop in a town I'd never been to, and they put on a new chain (Dura Ace 10 sp). The mechanic told me that he'd also made some "minor" adjustments to the FD that would make the shifting smoother. While I'd always found the shifting fine, I've never been great at derailleur adjustments, and so I wasn't surprised that he saw room for improvement. I thanked him and went on my way.

After about 10 miles, I found I was having trouble shifting into the front ring. Then I found that, when I could shift into the front ring, the chain was slipping when I shifted into the small ring. I rode the rest of the way home without shifting in the front.

Today I put the bike in the stand and found that the problem shifting into the front ring was caused by the FD clamp having slipped down the seattube a couple of millimeters so that there wasn't enough room between the derailleur cage and the big ring - probably the mechanic didn't tighten the clamp sufficiently, and it slipped each time I shifted until it stopped working. I fixed that, but found that the second problem - the sliding chain during a downshift - was not so easy.

What is happening is that when the chain shifts onto the small ring, it doesn't shift all the way inward, and ends up riding the tops of the small ring's teeth. I.e. the outer plates of the chainlinks (on the inboard side of the chain) are not clearing the teeth, and are riding on top of them, so that the teeth do not fall into the spaces between the rollers. Putting it another way, it's as though the chain is falling in between the two rings (though there's not enough space for it to fall all the way in). If I give the chain a nudge, it falls into place, but the FD won't do it on its own.

I've never seen this before. I tried everything I could think of, and eventually removed the derailleur and chainrings entirely and reassembled them. I adjusted the L screw, adjusted the inner wire tension, adjusted the indexing, rotated the derailleur, and tried moving it higher and lower. I rotated the chainrings in relation to each other. I tightened the chainring bolts. I checked the chainrings for warping. I adjusted the rear derailleur indexing. Nothing fixed the problem. My FD is now about as well-adjusted as it's ever been, but the chain still will not properly seat on the inner chainring when I shift.

It occurred to me that this could be a result of the chainrings having 2500 miles of wear, contrasted with a new chain. But the chain that broke was relatively new also (manufacturing defect), and its wear was not synched with the teeth either.

The problem does not occur if the chain is on the innermost three rear cogs, because then the rear derailleur pulls the chain inboard enough to overcome the problem. But if the chain is in the middle or outer portion of the cassette, there's a problem.

Thanks for bearing with the long story. I wanted to make sure I gave all the details, since it was sort of a sequence of problems that came and went, leaving only this intractable one. The shop I went to is many miles away (train ride and then long bike ride), and there's no way I can go back there. I'm grateful for any ideas or suggestions.

Chains slipping between the rings, or hanging on the tips of the inner, while riding the face of the outer, exactly as you describe is common when the chain is narrower than the crankset was designed for. For example when Campagnolo introduced 10s in 2001, the only change to the crankset was moving the outer ring in slightly to narrow the gap, otherwise 9s and 10s cranks and chainrings were identical.

I don't know if you have 10s cranks or not, but it's possible that the new chain is narrower than the original by just enough to make the difference. (Unless the mechanic "helpfully" added spacers between the chainrings). If the chainring spacing is unchanged from standard 10s Sram check the outside width specs of the new chain compared to the original chain, and if possible buy a slightly wider 10s chain to solve the problem.

BTW- chainrings have different offsets, so if you've replaced either with a generic chainring that may be the culprit.

Thank you. I think that's exactly what's happening. The crank is 10sp, and I've always had 10sp chains on there, but this is the first time I've had a dura ace chain - I've always had ultegra or SRAM chains before. I see on the shimano website that the dura ace chain has some new engineering - asymmetrical inner/outer plate thicknesses. I suspect it's related to that.

I did replace the inner chainring with a generic a few months ago, but never had a problem with it until now. The problem came with the new chain. Likely the differences in either the generic ring or the special thin dura ace chains would be fine separately, but together they exceed tolerance.

It's just too bad I can't get back to that shop. $50 for an ill-fitting temporary spare chain and a lesson learned.

If I do have to replace the inner chainring, can you school me in how offset is measured/labeled so that I can find an appropriate one?

Chainring offset is the horizontal distance from the center of the teeth to the mounting face of the ring. Most, but not all chainrings are symmetrical and have the teeth centered in the blank so the offset is 1/2 the thickness (or sometimes expressed as zero offset) but many are offset to either side.

Manufacturers can use different chainring offsets the way Campagnolo did to control the chainring gap without changing the crank arm.

Check the specs, and see if they give it to you, or lay the chainring on a table, mounting face down and measure up to the tip of a tooth. BTW chainring offset can be expressed as the distance to the face, or the distance that the teeth are off center, so if using a published spec. check which they mean.

I also have a Truvativ road crankset rated as 10-speed. I put TA Specialites chainrings on it to customize the gearing, and then started having the same problem as you, with the chain occasionally slipping between chainrings. I haven't used a Dura Ace chain, I believe it is an Ultegra 6600 that I was having the problem with. Instead of going back to the stock chainrings, I actually resorted to filing down the faces that the outer chainring clamps to, which made the chainrings slightly closer together. The problem has now disappeared. When filing, I removed all of the black paint and then a tiny bit more, maybe 0.2 or 0.3 mm total, I don't remember exactly, but I was using some calipers to measure it to try to get the amount consistent on all five tabs on all parts of each tab, but that was not easy. It seems to have solved the problem.

I would therefore say that your problem is mainly caused by the non-stock chainring, but for some reason didn't show itself until you got the new chain that has a slightly different shape to it.

A slightly simpler solution to your problem would be that as you moved the derailleur up the seat tube you increased the cable tension; thereby not allowing enough travel for the chain to easily shift to the smaller chain ring. I would make absolutely certain this was not the problem before addressing anything else.

Four years late to the party. So I am tuning up a 90s Look mtb with a Campagnolo groupo. I took the chainrings off to clean them and noticed some dented teeth. I then unwisely filed the offending teeth to match the rest. I also removed and soaked the chain. Now the chain skates between the chainrings on downshifts. I've tightened the bolts down and the problem persists. I have also considered that it may be an issue with the BB. Oddly the stock Campagnolo BB axel has a shorter R side than L side. I tried installing the longer L side on the drive side but it looked weird in relation to the front derailleur and I flipped it the other way. I will try flipping the chain over and see if that helps. Otherwise I'll flip the BB axel and see what happens. The BCD is looks like 110/74 so it should be easy to swap in new rings if that is the problem, but it would be a shame to lose the full campy mtb group. Or maybe I need a new chain? Did someone switch chains with me in while it was soaking? Any ideas would be appreciated.
Thanks

Tom

Since the only change I read you made was filing the chaining teeth, I suspect that is the problem.

yeah,agree,Since the only change I read you made was filing the chaining teeth.thanks

They teeth are uniquely profiled and not meant to match each other. The only reason to file chainring teeth is if there's an obvious dag mashed off a corner, and even then you're probably better off using a snap-blade instead.

As for the BB, if there's writing on it, it should read left to right when installed in the bike. If in doubt, compare the gap between the end of the crank and the chainstay on each side.

I've repaired several similarly-afflicted inner chainrings by carefully bending all of the ring's teeth toward the big ring, just a half-millimeter.

I've fixed others by carefully positioning a long file so as to bevel the inner edge of the ring's teeth while turning the cranks backward.
This is tricky as the crankarms try to whack into the file and my arm/hand that's holding the file.
Dropping the chain to the bb shell and using a light touch keeps the file gliding over the moving teeth, giving good control to the rate and angle of cut. If you overdo it with the file, the chain may then overshift off of the small ring when downshifting.

I had the same problem with my wife's bike after installing TA chainrings havin thicker teeth than the original Shimano rings. I cured the problem by filing the backside of the teeth on the inside ring. And I also installed a 1.5 mm bottom bracket spacer to move the chrankset out slightly.

After trying almost everything, I put a new SRAM 8spd chain on and voila! Perfect shifting. The old chain was only 25% worn. I was ready to swap out the chai rings, but fortunately that wasn't necessary. I then returned the bb to the unusual L and R orientation, whereby the drive side is shorter than the left side. Who am I to doubt the campy mtb gods? It may also be of interest that the spacers between the middle and granny ring give a slightly larger space than middle and big. (I hadn't explicitly said it before but I'm talking about a mtb triple. I know, I should get my own thread... Sorry)

Long story short: got a new chain and riding happy.

Ciao tutti.