Sram X7 Front Mech Problems

[autolycus]

It's been a problem for a year now, including a trip to Evans. I thought i had it beaten recently with a new chain, shifter overhaul etc and it's been working beautifully for a week. Then out of the blue today a front change down and a horrible seizure that i could only undo by slamming the pedal down to free the chain from the mech. I then had all sorts of problems getting home and had to stick with the chain on the bigger chainwheel.

I looks to me as if this last jam has damaged the mech, which would explain why i couldn't adjust it to work on the way home. Any thoughts?

I have a 2x10 set up with X5 (i think) shifters and GX rear mech on a Specialized Sirrus Comp. The X7 is not easy to get hold of and seems to have mixed reviews, so i was wondering if there is a natural replacement/upgrade?

Thanks

 

[Yellow Saddle]

You asking a lot expecting a diagnosis from an inappropriate photo.

Take a side-on photo with the chain on the small chainring so we can see if the FD height is correct.
Take a another photo from the top down, absolutely in plane with the chainrings (chain dropped onto the BB) so we can see if the FD is parallel with the chainrings.

Otherwise, bike shop. No amount of speculation will give you an accurate answer. Nevertheless, speculation will now pour forth.

 

[autolycus]

I took that photo to show the type of fixing to the frame as i believe they vary. Anyway, here are another two, although i couldn't work out how to drop the chain onto the BB so i removed it.
The position of the FD should be correct. In any event it was fixed during the last visit to the bike shop!

 

[fossyant]

How many miles have those chain rings done ?

 

[raleighnut]

I took that photo to show the type of fixing to the frame as i believe they vary. Anyway, here are another two, although i couldn't work out how to drop the chain onto the BB so i removed it.
The position of the FD should be correct. In any event it was fixed during the last visit to the bike shop!

It looks to have shifted the mech out of parallel with the rings.

 

[autolycus]

How many miles have those chain rings done ?

I'm not too sure, at a very rough guess i'd say about 3-4000 miles.

It looks to have shifted the mech out of parallel with the rings.

Can't see any evidence of the clamp having shifted.

I think a new front mech would be a good idea, but i'm struggling to find a SRAM 2x10 bottom-pull high (31.8mm) clamp (50x34T chainset).

 

[Yellow Saddle]

I took that photo to show the type of fixing to the frame as i believe they vary. Anyway, here are another two, although i couldn't work out how to drop the chain onto the BB so i removed it.
The position of the FD should be correct. In any event it was fixed during the last visit to the bike shop!

The second photo isn't good. We need to be able to eyeball the FD rails wrt to the chainring to see if it is parallel. Get the camera perfectly in plane with the chainrings.

The first photo is fine and shows that the FD is a mm or so too high above the chainring.

You may have experienced chainsuck. Are there scratches on the chainstay just behind the small chainring? Also, lets see the small chainring without the chain on it (shift to the big blade) so we can see if the teeth are worn enough to cause chainsuck.

 

[Ajax Bay]

I was deterred from speculating, not wishing to satisfy earlier predictions of it spewing forth, but my guess was/is chain suck.
In which case it's not primarily the FD to blame. Since the chainring is 'young' in wear terms, especially the inner (guessing), I'd be surprised if it is worn, but that (and poorly maintained chain - not in this case; the chain is new) is the most likely cause of chainsuck.

a horrible seizure that i could only undo by slamming the pedal down to free the chain from the mech.

Can't quite visualise how "slamming a pedal down" would free the chain - which was presumably 'doubled up' in the FD cage.

 

[autolycus]

Here's another from above the FD, which i think shows it to be in line, and one of the small chain ring.

There are no sratches that i can see on the chainstay and i think the teeth are in pretty good nick. The chainset is 3.5 years old and i don't do any serious mileage.

 

[autolycus]

Can't quite visualise how "slamming a pedal down" would free the chain - which was presumably 'doubled up' in the FD cage.

Nope, and i can't even recreate in my mind exactly what happened. It was a horribly complicated snarl up. But it was kind of stuck in two places if that makes sense like it had followed itself up in to the FD cage. And using the pedal as leverage was the only way i could see to unjam it. Twice. I was/am worried that might have damaged the FD.

 

[Ajax Bay]

Your description matches chainsuck, even if I can't visualise your remedial action. When I've had chainsuck (last year for a short period - climbing Wrynose Pass in the Lakes was not as pleasant as it might be, fearing a(nother) chainsuck any moment on a 1:5, with Hardknott 1:4 to come) I step on the chain (return stretch) but sometimes a wiggly tool was required, merely as a lever to unjam. Solved by replacing chainring, btw (well oiled old chain, new chain: both 'sucked'). Edit to add: My sucking ring was a 28t (inner of triple) with ~2068km on it.
I'd try a new small chainring first, before considering changing the FD.
Shift the chain onto the large ring, drop the FD a couple of mm (probably) and align it to the chainring.

 

[autolycus]

Thanks. I googled chain suck and it does seem to fit the symptoms, although i'm pretty certain the jam happened when i changed down to the small ring rather than up to the large.

I've found what looks a new direct replacement FD on ebay for a tenner, so i think i'll get that anyway as my current cage looks positively bowed to my eye now that it's off the bike. And i think i've found a suitable replacement small chain ring for £16 so i'll get that too.

 

[fossyant]

Chain suck happens when you change down also.

 

[Yellow Saddle]

Chainsuck has three contributing factors:

1) Chainring size. The smaller, the suckier.
2) Hygiene. The dirtier, the suckier.
3) Wear. I don't think there is such a word as wearier, but anyway, the wearier, the suckier.

It can happen in the absence of any one of the above factors, but at least two are required.

You can temporarily cure chainsuck on the trail to get you home by using your Leatherman to file the little ridges off the tooth edges of your small chainring at the two major wear locations i.e. with the cranks horizontal, at the two o'clock and eight 'o clock positions.

 

[Yellow Saddle]

Here's another from above the FD, which i think shows it to be in line, and one of the small chain ring.

There are no sratches that i can see on the chainstay and i think the teeth are in pretty good nick. The chainset is 3.5 years old and i don't do any serious mileage.

Yup, parallel indeed.