Levo Gen 2 SRAM NX limit pin

[TonyBalony]

So my limit pin made a hole in the part where it meets the "other part", causing it to clamp and lock up the spring action, almost destroying my chain as it went in "double" in the front cog.

I do not really know the correct term for the pin, but to solve my issue, I think it needs to be longer to contact the whole "other part", so it has a limit again and does not destroy anything because the force is spread more evenly.

Has anyone had this happen before? How did you solve this? Does my solution work or sound good? See attached picture (driving conditions were wet, and chain was lubed before the short ride).

 

[TonyBalony]

I discussed this with my LBS, turns out this is caused by what is called chain suck. Very unfortunate.

But, this would have been prevented if the limit pin was not tapered. The tapered-ness caused it to destroy the housing, because only one part touched the housing instead of a bigger piece. Then, the tapered-ness caused it to push the bracket to the inside, because it generates force in the side-to-side direction, and then it caught after the just destroyed housing, making sure the spring of the derailleur did not pull the chain back anymore, and causing the chainsuck to cause some damage.

So, who here can make M4 pins with straight shafts, preventing me and others from damage?

This is very much a design fault with SRAM.

 

[Jamze]

I suspect the chainsuck caused the mech to pull too tight and caused whatever damage occurred, rather than the other way round. So best to sort what's causing the chainsuck. Stiff chainlinks, worn transmission, lube, front chainring that's too big etc.

 

[TonyBalony]

Chainsuck was caused by the super wet conditions. Chain has no wear, lubed before the 10 mile ride. Stock chainring, nothing worn, or stiff. Chainsuck just can occur.

But, the pin is there to make sure it does have a limit. Which in this design, causes for more issues.

 

[TonyBalony]

To add to this: heavy bumps in the track caused the chain to slap around and caused the chainsuck, which in turn caused the derailleur pin to damage my derailler and get itself stuck, which then made the front ring suck up the chain completely and lock up the front ring, almost damaging the chain (luckily I got off the power in that exact moment).

 

[Jamze]

The issue is if you improve this stop on the mech (can't get my head around your pic), it's likely that the next weakest bit of transmission will then take the hit. Snapped mech or chain, bigger gouge in your chainstay and so on. You'll just move the problem somewhere else.

 

[TonyBalony]

True. But that implicates they made the perfect design with the tapered pin, which they did not since it can get itself stuck.

So options are:
1. Ride with no pin, which is a good option making sure the spring in the derailler always keeps tension on the chain, so the chain can't bind on the front ring (if you're lucky).
2. Ride with a decent pin. This is the best option. It could destroy the whole bottom part of the housing though, if severe chainsuck occurs and you're on full power. The engineers at SRAM thought the bottom part was strong enough even with the small contact point to the tapered pin, which it clearly wasn't.

So who can chime in. Ride with no pin, allowing complete free movement of the derailler, is that the best option?

 

[Jamze]

Worked out your pic now. I don't think that pin is designed to stop the mech rotating forwards. If you pull a mech it will keep going until it fouls on itself, the frame or your rear wheel/cassette. That pin parks the mech when you take the chain off, stops it unwinding itself.

So IMO chainsuck is your issue unfortunately. Hopefully some Specialized riders have some ideas for that in addition to the standard stuff.

 

[TonyBalony]

I know and understand you. The problem started with chain suck. The wet conditions made it suck to the front ring: I could feel this when I started pulling the chain off of the front ring. You could feel the resistance. It was extremely mucky, I also did not avoid any mud pools

The chain suck pulled the derailler in too far, and either another pin is going to keep the derailler further back, or with no pin at all at least there will be tension from the derailler to pull the chain from the front ring.

Now, with the original pin in place getting caught IN/BEHIND the housing, making the derailler stuck in place, there was no tension at all making it a great opportunity for the front ring to suck up the chain even further, almost destroying the chain.

So my question resides: would no pin be better than a decent pin? Do other brands have pins/limit stops there?

 

[Mikerb]

I suspect you are referring to the "Cage Lock" pin. It has only one function which is to lock the cage in its forward position to make it easier to take the chain off the cassette when removing the back wheel.........or perhaps for cleaning the jockey wheels. It has no function in ordinary riding. It is spring loaded, so you push it in once you have pulled the cage forward and it locks against the cage. Push the cage a little further forward when the pin is engaged and it should get released and pulled back to its rest position by its spring. If the pin is is not free moving in and out it is either in need of a clean and lube or the internal spring is broken. A simple fix if it does not operate as I described is to twist a bit of thin wire around its head to stop it moving in towards the cage.
ps.. a way to prevent excessive chain slap is to avoid using the smallest ( highest) gear on bumpy descents.

 

[TonyBalony]

No we are not talking about the lock pin. Please see the pictures and check with your derailler to see what the tapered pin does

 

[Jamze]

I have both Shimano and SRAM mechs on my bikes. Just checked, and that pin on the cage doesn't prevent the mech rotating fully anti-clockwise, so won't stop the mech hitting your cassette/itself/frame - although what it does hit depends on what gear you're in. It's there to park the mech when it rotates fully clockwise, with the chain removed for example.

What happens with chainsuck - mech hits the cassette. You can see the pin you're referring to - does nothing. If I pushed it far enough it would hit the silver 'X' linkage of the mech and damage that.

Chain off, mech parks itself, that pin locates against a stop rotating the other way.

 

[TonyBalony]

Well, mine does prevent it from going too far anti-clockwise. But it got stuck in that motion because the tapered end destroyed a piece of the housing as seen in my pic. And because it got stuck, there was no more force on the chain in the clockwise direction, which could have (but may not) have prevented my chain from going to far up the front ring.

Only without that tapered pin in place, does my SRAM NX have full motion in the anti-clockwise direction.

 

[Jamze]

Well, mine does prevent it from going too far anti-clockwise. But it got stuck in that motion because the tapered end destroyed a piece of the housing as seen in my pic.

As would mine if it hit the knuckle - but that's not what it's designed for. You don't want your mech there at all, especially on an eMTB.

 

[TonyBalony]

Yes, you don't want your mech there at all... but it can happen, that is the point I am making. And if it does happen, due to chain suck, it would be best that it is NOT a tapered pin, because that can more easily destroy the housing and get it self stuck than a straight pin would, causing the already-underway-chain-sucked-chain to have no tension on it whatsoever and slurping it completely on the front ring

So beware of this...