Gear derailleur issue

[Mondo]

So it is part of an eBike, but I guess this is a more genral request for help on a rear deralleur system. I know a lot of folks here areactually good bike mechanics as well

I've "modifed" an old Altus derailleur of a Trek to fit my old steel framed bike. It shifts quite well on the stand but the chain "slips" on the smallest rear gears I'm sure the chain is tensioned correctly (if I take another link out it jams on the two largest cogs).

I'm wondering if the freewheel I have is not compaitble with the derailleur or whether it is my bodgy install or whether the freewhell is just worn (it doesn't look sharktoothed)

 

[Zoot Katz]

You need the steel derailleur hanger that bolts into the back portion of the horizontal drop outs.
If you score one off a dumped bike make sure it's not twisted before installing the derailleur.

The jockey wheels are too close to the cog.

Incompatibility issues are generally between the shifter and derailleur.

 

[Mondo]

Thanks Zoot

It does have a hanger, in fact it is nearly identical in construction to the orignal derailleur (itisn't a removable hanger). I guess on the bike it came off it attached to the frame lower than the axle.

The original derailleur did have a longer hanger and actually bolted into the dropouts behind the axle (ie hanger first then axle)

thanks Zoot - at least I can look at a solution now that I know what the problem is.

Mondo

 

[Gregte]

Another thing that will cause the smaller cogs to slip is if you put a new chain on a worn cog. It may work well (not slip) with the worn chain but will slip with a new chain.

The solution is to put on a new cog, or flip the cog over if possible, or file the teeth on the old cog to have a steeper edge if the first two options are not possible.

 

[dogman dan]

I had a worn freewheel on one of my bikes, and it was very hard to see anything wrong with the smallest cog on it. But under hard pedaling with the big chainring up front, it would skip some, and eventually got worse. You could have both problems, I have found with cars, it's never one single problem, but several, so as to empty your wallet better. We do tend to use that small rear cog a lot with an ebike.