geezerwheels

my wife's knees seem to have launched a few of their own--

she's a gutsy gal but was struggling on some long hills, so I swapped the 8sp cassette on her Marin hybrid, from one with a 25 tooth low cog to one with a 28 tooth. but dangit, the upper jockey wheel of the Shimano 3400 RD was ever so slightly too close to the big cog.

so, back to ebay for a Shimano 3500 RD (medium cage). But now, dadgummit, the shifter (straight bar type) won't pull the RD into low. The cable is as tight as the drone string on a banjo. Low adjustment backed all the way out--I can push the RD into the low position, if I back off the cable. all the other gears shift perfectly--so it doesn't seem like the cassette has the wrong spacing. It's more like the shifter decided it was a seven speed.

Could something in the shifter have slipped when the cable was slacked off? I read somewhere on the interweb that the 3500 RD was compatible with the 3400 shifter, but now i'm beginning to wonder...

Please help...the little lady is getting antsy

FBinNY 

I suspect that you have the cable too loose by one gear position. The easiest way to check is to shift to the 2nd high gear position on the lever (shift to high, then back on click) and see if the chain is on the second sprocket. If not use the cable adjust to get that dialed in (you might have to reposition the wire under the pinch bolt).

Also check that the cable is routed to the pinch bolt correctly. It should be attached on the FAR SIDE of the pinchbolt, effectively making the arm as long as possible. If there are any guides , posts or whatever at the end of the arm, the wire is usually routed all th way around the far side of those, NOT between them and the pinch bolt.

There are other possibilities, but those are the most basic, and consistent with you attaching a new RD.

dynaryder

To clarify,don't you mean to the side of the bolt closest to the cassette? To my mind,'far side' would put the cable on the outer side.


geezerwheels: prolly a silly question,but on the original derailleur,you did try playing with the B screw first,before deciding it couldn't handle the 28 cassette?

Also,check the entire cable run,just in case something got wonky when you disconnected the cable to swap derailleurs.

FBinNY 

Terms like far side are relative, but usually reference the part they're on, we're talking about the RD, or more specifically the lever arm. The pinch bolt is on that arm, like your wrist. So far side would be farther from the body, as in your finger tips are the farthest side of your arm.

I used to use a more precise term "distal" but only folks in the medical trade got it, so now it's far or near side.

BTW- di you go back and double check the gear position, ie. 1=1, 2=2 etc, vs 1=2, 2=3, etc.?