Derailleur Question
 

Riding bike this am and my bike chain jumped off in high gear when I hit a pothole.
The other day it did the same twice when in the higher gears and heavy bumps.

I feel I need to tighten the whole works up somewhat. Where is a tightening screw or bolt located? It doesn't need much.
I don't see any way to do it by moving the axle back in the drop-outs.


http://forums.pelicanparts.com/uploa...1758582924.jpg

Steve, isn't that and no need to move axle back. Large gear meaning the largest cog, the one closest to the spokes?

^^^ No...the next to the smallest gear...which is 7
I hardly ever use 8

The bike is in 2 in the pic....I just parked it in the garage

Does it jump into the next larger or smaller gear? I think the cable stretched.

It always stays in the same gear but the chain comes off the front sprocket. It's easy to get it back on, but a greasy mess on the hands.

The bike is about a year old with 3200 miles on it.

At the crank? Two chain rings? It jumps off the small one?

The bike is an 8 speed...so a single sprocket on the front.

When it bounces off, it always ends up with the front end of the chain hanging from the crank.
The rear of the chain remains on the gear that it was in.

I feel that if the chain was shortened/tightened up just a wee bit....it wouldn't happen.

Is that chain a newer chain?
The derailleur doesn't seemed very tensioned and you are in the next to what should be the "most" stretched derailleur position.

Put the bike in what you call "8" and see if the chain is floppy b/c not enough derailleur tension.

I should also state that it shifts up and down perfectly as it should.

I have a bike stand...I'll have to use that...which means tomorrow.
It's buried in the tool shed.

But I do know that when it is the higher gears the chain there seems to be less tension on it.
(which I thought was somewhat normal)

Used to be a way (on the old, old Shimano derailleurs) to adjust the spring tension. IIRC, it was done at the pivot (just above/11 o'clock from the 'A' in Altus). Of course this was ~40 years ago; design -- and my recall -- might be just a little off.

Regardless, if that's the original chain it's likely stretched more than you'd like; if it's original I'd just replace it.

get us a pic of the bike from the side showing the chain. Put that on the smallest cog in the back. I like to see the tension of the rear mech like Leak said.

Going out for a ride now before the sun sets for a couple hours. get back to you

Original chain....3090 miles...I just checked.

There is a small set screw behind the pivot....I didn't dare turn it before asking.

Reason I ask- if it's a new chain, it might be a link or two too long.
edit- nevermind=you beat me to it

There is something called a "b" screw- it's in your pic, which can move the derailleur back, but if the chain is too long to begin with, might be better to remove a 2 links to get the tension.

What you want to see is
How stretched is the derailleur in the "8" position?
How stretched is the derailleur in the "1" position?

Post some pics if you get a chance.

plenty of YT videos on adjusting the derailleur b screw, but want to see the chain at the extremes.
Worst case scenario with B adjuster- turn it to pull the derailleur back, remember the # of turns you turned it, and turn it back if it doesn't work. Adjusting the b screw can affect shifting responsiveness because it essentially pulls the derailleur away from the cogs sometimes.

Seeing how stretched the derailleur is in the one and eight positions, and how loose the chain is in those positions (floppy, loose etc..) is a good place to start.

Also- longshot, make sure you don't have a bent tooth on the front chainring. A single bent tooth can throw the chain if tension is low.

Just started raining here...I managed to get it into 8 by holding the rear end up, shifting with another hand and turning the crank all at the same time.:)

The pic shows the bright screw that the pivot rests on. (I'm tempted to back it out a quarter turn to allow the pivot to rest further back.?)

http://forums.pelicanparts.com/uploa...1758585604.jpg

I'm gonna throw up this video- didn't even really watch it, but it looks good :)
Should talk about what the b screw does and does not do.

<iframe width="560" height="315" src="https://www.youtube.com/embed/UXnLJpTVFJ0?si=qsB3hvV83sO-YuAy" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>

Still want to see the chain tension. I've never had a chain stretch so much the derailleur can't keep it tight- not in 3000 miles. It might have been on the long end to start with.

Weird.

Dang, wish I was there. This is the kind of thing, if Look or one of us was there, it'd be fixed easy peasy. It's tough sometimes diagnosing over the interweb.

It never happens on normal pedaling...it's only happened when hitting extreme potholes or bumps.
And I'm usually out of the saddle when it does it.

Other easy thing to do while you are in that gear is slowly pedal the chain backwards- see if there is a stiff or bent link. Sometimes it won't feed correctly through the derailleur if you backpedal.

The above pic looks good adjustment in/out. The derailleur is right under the cog. Thats why it shifts fine.

So, Steve, if I understand you right, the chain is bouncing off the big chainring, hanging up in the crankarm, (outside the sprocket, so to speak) when you are in big ring front and 7 on the rear cassette; does that sound like I'm understanding the issue?

edit; and it's not going into 8?

post edit. you don't have 8 on the cassette. And that chain is really dry.

While youve got it in the 8 gear- take a pic from the side of the bike. It looks like the top of the chain is dangling somewhat.

Same with the bike in the 1 gear.

Yes, it's been a couple weeks, I'll lube it up tomorrow. The front sprocket is a single.
It shifts and hits all 7 gears perfect....it just bounces the chain off the front on big bumps.

I looked at the B screw and I'm thinking backing it out a small bit will give it more tension.

You are correct....I only have 7 gears....my bad. :eek:
So it happens mostly in 6 because I hardly ever use high (7) gear.
Same situ just one gear less.

.

7th gear...I read it on the side of the bike. :)

http://forums.pelicanparts.com/uploa...1758587134.jpg

1st gear

http://forums.pelicanparts.com/uploa...1758587485.jpg

Alright. Looking at that drivetrain, I wouldn't be surprised if it's a combination of 2 things. Chain stretch, front cog wear. And if it's not getting into your smaller gears (bigger cogs) than there is some chain stretch, too. So,for the chain jumping off, adjusting the B screw in a little bit (wind it in clockwise) will probably snug the chain up again. It looks like it's in good shape other than just getting used (good for you on that! Bikes should be used!).

If you're not getting into your smaller gears (big cogs) unwind the cable adjuster counteclockwise until it goes in easily. You might have to adjust the cable 1/4 turn one way or another after you pull the stretch out of it.

heck, maybe the chain is stretched:D

If no one has changed anything...

Here's a video of a really stretched chain. I would've sworn it had too many links, but it didn't I've never seen one stretch like this far-

<iframe width="560" height="315" src="https://www.youtube.com/embed/w5i-dB9_dC4?si=as9fK4ylTYibjg2L" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>

No...I've never had any problem getting it into any gear. The reason I hardly ever use 7 is because it's too tall. 6th gear works better for where I bike.

If I try that, I'll mark it and turn it clockwise....I was thinking clockwise would loosen it.

.

The area that I've circled is the critical one for adjusting your b screw. You don't want the jockey wheel to foul on the cog here. So by screwing the b in, you increase the distance from the jockey to the cog here. The optimal distance is about 1/4' or less, but I think with this drivetrain, there is more leeway than with say, DuraAce or Sram Red. (no disrespect intended - this is a good, serviceable groupset.

http://forums.pelicanparts.com/uploa...1758587847.jpg

Good video...I watched it. (the first one)
If the chain was stretched, wouldn't it cause shifting problems? I have none.

Not necessarily. Sometimes it doesn't take much for a little stretch to cause a small problem (like the one you're having) where it bounces off the sprocket.

(That video is really exaggerated!! )

Not necessarily. Everything sort of stretches at the same rate cogs, chain, etc, until the chain will jump (not jump off- like yours) but jump and skip a tooth or two when you put the hammer down. Usually it's in the gear ratio you use most.

Very annoying.

Yours isn't jumping with load though- yours is just jumping off when things get bumpy. It's loose.

One challenge is that if you buy a new (shorter) chain, sometimes the cogs are so stretched that the new chain will jump on the old cogs, and now nothing will work- necessitating a new rear cassette or even front rings- BUT- yours is a 7 speed.

Those things are tanks. The cogs may be fine. The skinnier 10-11-12 speed cassette teeth/chains are much more finicky and prone to getting trashed.

I'll have to look closer at it to check measurements. Looking at my pics..the chain seems to be taut. Maybe it's just something I'll need to keep aware of.
Maybe being out of the saddle and a sharp bump causes me to nudge the chain off with my shoe?

.

One other thing, give the front sprocket a good inspection. Look for bent teeth, or unusual wear on any teeth.

PS - if you're not having any shifting problems, than do NOT adjust the cables.

That was easy to check...all looked good, including the two small idler sprockets.

.

No...I don't want to mess with those. Brake cables are easy.

.

Tomorrow I'll lube the chain up and take it on the same road as today and see if I can tell what is actually happening on the same bumps. (chatter bumps on a gravel road.

I appreciate the help guys...the derailleur is something that always worked, so I paid little attention to it.

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Just as a comparison, here's a pic of my 7-speed.
I'd expect your derailleur to be a little more extended than what your picture shows.

http://forums.pelicanparts.com/uploa...1758589950.JPG

^^^ Yours is in low gear though....I've never had it happen in any of the low gears.

Is there something happening with the chain? Is this a frozen link?

http://forums.pelicanparts.com/uploa...1758590711.jpg

^^^ Just looked...master link.
The chain came painted white...they must have forgot to paint the master links.