Mystery lock up?
 

I recently put a 11-32 sram cassette and chain with XT sgs rear der. and dura ace downtube shifter on a road bike. Up front = 53/39 rings….

I tuned it up, put it on the trainer and tested it under load. Worked fine…. Then took it on the road for a test ride on flats and hills. Worked fine…. I then delivered to the owner and all was good. He road it for two weeks….all good.

Then…we go for a good ride with some mix of flats, and hills. On the return trip the owner said that he was on the 53-11 and the rear der locked up or something and he couldn’t pedal. He said it did it twice. He said that he shifted to the 12t and it began to pedal again. I road behind him to see and asked him to shift gears and do the 53-11. Nothing… It worked fine…

Stumped!!! What could it be???? It sounds like bad new and it only happened on the 53-11 combination??

For an old, slow guy like myself, the answer is obvious: it's super-natural... at least mystical.

This situation is sort of like the old golf joke with the punch-line, "... even God can't hit a one-iron..." In this case, I wonder; "What mere mortal thinks they can ride a 53-11...?"

(I know... Iknow... a lot of you out there can handle it... but I sure can't.)

it's for the downhill!!! really...that is what he wanted it for.... other than that it is just along for the ride..

Could be a bunch of things, including the chain starting to pop a plate. Check it very carefully in the stand for any thing out of whack. Then go test it in the problem gear, when it does it, stop, no shifting or back pedaling, get off and look.

New chain and used chain ring? It might be an odd big ring suck problem, where the chainring is pulling the chain up, that would give you a lock up feel as well.

will do! .....let you know what happens.

it is a new chain with less than 200 miles on it now and used chain ring. In fact the crank is the only used part of the new drivetrain. I have a new chain ring in the same size that I could try out if it comes to that.

could it be a b-stop problem?....I think that it is what it is called....the screw on the rear dr. that pushes the rear dr. away from the frame....

thank you thank you thank you!!!

I don't think it would be the b screw causing a problem esp. in that combo.
Check the "H" limit screw, the chain may betrying to come off the small cog.

It sounds like chain suck. I had that happen once, but it was because of a worn cassette. When I was finnally able to see it happen, it was pretty scarey looking.

Could it be something strange like a 9sp (narrow) chain on an 8 speed cassette?

thank for the input, but it's all new stuff except for the crank. so all new nine speed stuff but an 8 speed used chain ring. I was told the 8 speed ring would work. I also called the owner and told him to run the 53-11 and see if it locks up and to take pics. He said he would and added that he was almost sure the lock up took place with the rear dr. :(

ok all found out what it was doing it. when he is in a cross chain gear combo and he pedals backwards the thing locks up.

tell him not to use the cross chain gear combos! :)

Seriously though, we all "know" that you aren't suppose to use the extremes of the gearing b/c of this type of event. There is just too much friction between the chain and gear/derailleurs (laterally) for it to ever work 100% *right*.

yup...told him...

Did it happen just after shifting to the "11"? Or was he reaching a downhill and quickly shifting from, say 20 to 11 ? If the clearance between right cog and seatstay is very tight, it is possible that when the chain is ok when it is moved by one gear, but that the chain doesn't clear the seatstay when it is moved across a few gears at once. Sometimes, adding a washer to the right of the cogset helps a bit.

I'd check the chain for a tight link. If a tight link hits the rear derailleur hard it can cause all sorts of damage, including serious frame damage. I've seen it done.

Al