SRAM NX: lagging only to shift into smallest cog + jumping off into frame

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SRAM NX: lagging only to shift into smallest cog + jumping off into frame
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Posted: Nov 24, 2022 at 12:25 Quote
I recently replaced my SRAM NX's shifter cable and housing pieces (there are two housing pieces on an internally routed 2019 Kona Hei Hei AL). Upon indexing and resetting the limits, there were shifting issues.

I then did the following:
- Confirmed the springs and wires inside the shifter were in the correct positions
- The hanger was re-aligned (it was bent horizontally and vertically when checked with a DAG-2.2, but not to an amount you could discern with the naked eye)
- B-screw was adjusted to manufacturer's recommendation, 14 mm at sag (it was set at 6 mm before adjustment)

These changes improved the shifting dramatically for all cogs except the smallest cog. The shift was lagging more than the others but would make the shift after about two seconds, so I decided to test ride it on the trails. On ride the chain jumped into the frame from the smallest cog when pedaling under load. This has happened to me about three times total over the life of the bike. AL frame, so no cracks or catastrophic damage yet.

Other than the shift cable, the housing, cassette, and chain, all other drivetrain and derailleur parts are the originals. I'm wondering what to try next. Is it possible the 3-year old derailleur spring is worn and can't get tight enough anymore to reach the smallest cog? Anyone tried sticking a washer between the derailleur and the hanger to increase spring tension as per that video?

I may also try looking at the hanger alignment again, or just replacing it. I'm a novice 'home mechanic', so it's possible I didn't do a perfect job on the hanger or it was beyond adjustment with the tool. There is also an awkward bend in the cable's path to the rear derailleur in the Hei Hei's rear triangle that eventually caused the failure to the housing that initiated all this.

Thanks for reading!

Posted: Nov 24, 2022 at 13:01 Quote
My first guess would be weakness in the derailleur spring.

Have you tried unclamping the cable? Do that then pedal the bike in a workstand while you push the derailleur sideways (to downshift it), then ease off the pressure to let it upshift. Find out if there's resistance or lack of pressure to make that final upshift.

As far as the chain jumping into the frame--did you over-loosen the high limit screw to encourage that last shift to work?

O+
Posted: Nov 24, 2022 at 18:56 Quote
If the chain is hitting the frame the limit screw is not set right. Or the hanger is bent.
But if it’s shifting good in the other gears the hanger isn’t the problem.

As far as it not shifting into the smallest cog.
I agree with barp. Unclamp the cable and see if the derailleur will drop down. If it does then something is up with the cable.

O+
Posted: Nov 24, 2022 at 19:00 Quote
BTW. Always check for hanger alignment at the valve stem. Rotate the wheel to check in as many spots/positions as you can.
A bent rim can really mess you up.
Ask me how I know. Ha. Ha.

Posted: Nov 25, 2022 at 11:49 Quote
Drop the bottom jockey wheel and loosen the top one so you can get the chain clear of the mech. Put a drop of WD40 on each of the 8 parallelogram pivots and push the mech in and out to work the lube into the pivots. Then set the limit screws with a slack cable and to manufacturers spec. Then adjust cable tension followed by B screw. Had a few mechs over the years that get lazy at the high-end of travel where the return spring has the least effect- bit of lube works wonders

Posted: Nov 25, 2022 at 20:23 Quote
Dillsue wrote:
Drop the bottom jockey wheel and loosen the top one so you can get the chain clear of the mech. Put a drop of WD40 on each of the 8 parallelogram pivots and push the mech in and out to work the lube into the pivots. Then set the limit screws with a slack cable and to manufacturers spec. Then adjust cable tension followed by B screw. Had a few mechs over the years that get lazy at the high-end of travel where the return spring has the least effect- bit of lube works wonders

Great advice but for one big caveat: WD-40 isn't lube. It's a water displacer and a degreaser, but it's not a lubricant. It dries up in a few days and leaves less lubricity than when you started.

Posted: Nov 27, 2022 at 9:22 Quote
barp wrote:
Great advice but for one big caveat: WD-40 isn't lube. It's a water displacer and a degreaser, but it's not a lubricant. It dries up in a few days and leaves less lubricity than when you started.

The manufacturer thinks somewhat differently and says its a lube. I've used it on my chain, cables etc for decades and its definitely kept those lubed

Posted: Nov 27, 2022 at 9:37 Quote
Tell a bike mechanic you use WD-40 for everything and you just might get laughed out of the room. I've seen the damage it can do, as have most other mechanics.

I'm not saying it doesn't lubricate, just that it washes away any better, more durable lubricants.

It's right there in the name: It was developed as a Water Displacer. Not as a lubricant.

O+
Posted: Nov 27, 2022 at 9:57 Quote
Dillsue wrote:
barp wrote:
Great advice but for one big caveat: WD-40 isn't lube. It's a water displacer and a degreaser, but it's not a lubricant. It dries up in a few days and leaves less lubricity than when you started.

The manufacturer thinks somewhat differently and says its a lube. I've used it on my chain, cables etc for decades and its definitely kept those lubed

WD40 is good stuff but it doesn’t belong anywhere on a bike.

Posted: Nov 28, 2022 at 9:01 Quote
From the manufacturers web site-

"Myth: WD-40 Multi-Use Product is not really a lubricant.

Fact: While the “W-D” in WD-40 stands for Water Displacement, WD-40 Multi-Use Product is a unique, special blend of lubricants. The product’s formulation also contains anti-corrosion agents and ingredients for penetration, water displacement and soil removal."

As I said Ive used it for decades without problem and my drive trains last at least as long as mates who use a variety of bespoke bike chain lubes. Each to their own.

Posted: Nov 28, 2022 at 13:49 Quote

WD-40 has evolved into a brand that provides multiple products some of which are actually lubricants.

You can still get the original formula WD-40 stuff that is not a good lubricant if you want it.

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