7 speed indexing problems???

[chambo34]

I'm having issues getting into the largest sprocket(28t) on the rear whilst using the smallest front ring (triple). All the others are going in fine, it's a new cable, a new casette and chain. The rear derailleur is an old but virtually unused long cage Exage 500 LX. The shifters all work fine, basically it goes on the sprocket but keeps jumping. I should add its a 7 speed casette on an 8 speed hub with appropriate spacer. Any ideas?

 

[2manyoranges]

Right - firstly, spacing is NOT the same. 5mm for 7 speed and 4.8mm for 8 speed. So spacing is not the same and they are not strictly compatible.

BUT...

A lot of people say they are fully interchangeable and they presumably say that since they have done it and it works well enough.

Secondly, if it's only the largest sprocket it could be that the end stop screw (L) needs letting out a little. Although it could be that all the 0.2s in the spacing difference are showing themselves at the end of the sprocket...but just let the L end stop screw out a bit and see if that does it. But make sure that it's set correctly and doesn't allow the chain to drop between the cassette and spokes (bad idea).

Thirdly. Is the jumping caused by the chain trying to climb or drop onto the next gear cog? If it is, then it likely is the case that you won't get away with using the 8 speed mech. If not, then it's likely a stiff link in the chain. For that, check each link and if you find a stiff link, just use the easing plate on a good chain splitter to make it loose again. Then see if the jumping stops.

 

[legrandefromage]

Have you used the adjuster screw stops on the derailleur?

A few things:

Its a 7 speed cassette on an 8psd hub - sprocket spacing is irrelevant!

Every Shimano rear mech from the 1986 'SIS' model year until the last of the 9spd mountain and the last of the 10spd road is all just about interchangeable (ignoring Dura-Ace)

An old MT60 Deore rear mech will happily shift with 10spd road shifters , especially bar-end shifters

Flange!

Sooooo, as long as your shifters are 7spd and the mechs reach has been adjusted to suit it, you shouldnt have any problems.

To look for dodgy links, eye up the mech from the back of the bike and look along the chain, then you'll see bent links, squiffy shaped chain and so on

But it sounds like its simply not adjusted properly

so about 2 seconds work or a 18 thousand word essay on what to do

 

[2manyoranges]

Hang on LGF ... that's what I said....

 

[legrandefromage]

no it isnt, I said 'flange!'

see if you can spot it

 

[chambo34]

It's a 7 speed mech and shifter, I just used an 8 speed wheel as I got a really good pair for cheap.

 

[2manyoranges]

LGF...Yep...I can see it ... but there you have it....is it an 8 speed shifter?...I assume 'yes'. I know I said only 'mech' but I meant shifter too...apoliogies

So.... hang on a minute ... if you are using an 8 speed mech with an 8 speed shifter, then the mech will be moving 4.8mm.
The cassette spacing on 7 speed is 5mm.
Result = janky shifting.

Is this wrong?

If it's right, then this could be the case (although the mech could be adjusted badly and the chain could have stiff links too....)

 

[chambo34]

Oh yes I've let out the stop screw, and it goes onto the largest rear sprocket with no jumping when using the middle or largest front chainring.

 

[2manyoranges]

Sorry - cross posting.

Sooooo.....

If you have: 7spd shifter. 7 Speed mech. 7spd cassette on 8spd hub with correct spacer....

Then it's probably

1 end screw not adjusted correctly
and/or
2 stiff link(s) in the chain

 

[2manyoranges]

arg more cross posting

So probably stiff links.
I would also say possibly worn mech, but you say it's virtually unused...perhaps give it a blast with lube to make sure that it's not gummy with old lubricant.

And thinking a bit more...is the arc of the cable from the chain stay to the mech reasonably large and a smooth curve?

And finally, you might need to adjust the B tension screw to get the right chain wrap around - look up B screw on line. If I explain here LGF will just accuse me of going on...and on...and on....which I agree I do tend to do....and on....