Wurlitzer

Hi,

I have this old Motobecane road bike from the late 70's maybe: https://imgur.com/a/RhNfH

The rear derailleur is in bad shape - it clicks all the time and seems to be impossible to adjust correctly.



Can I change it to whatever derailleur I want? I can get a Shimano 105 derailleur for 15€ for example.

Thanks.

jdefran

This might assist you: https://www.bikeforums.net/archive/in.../t-853703.html

duffer1960

Have you identified a reason that it doesn't work well? Worn bushings, or bent, or inadequate spring...? Just from the photo, it looks to be in good condition.

Looks like the housing between the stay and the derailleur is too short. A binding cable could cause a problem like you describe.

oddjob2

An indexed shifter with a freewheel could be a nightmare. I'd stick to a friction shifter. Find a Suntour GT or VGT.

wrk101

+1 Housing grossly too short. Regardless of what you do, new cable and longer housing is a must.

+1 Stick with one of the myriad of good friction RDs. Around here, they can be found at the bicycle co-op for free, or almost free ($5). I have also found really good vintage RDs at the local bike shop for about $5. The trick is finding a shop that keeps a bin of take off parts.

Wurlitzer

Thanks.

- So it seems I could try and change the cable for a longer one, including its housing.
- Regarding the possibility of a new RD, I have to look for friction ones, that are compatible with the hanger bolt.

Wurlitzer

Wait wait wait, isn't the indexing in the shifters?
My shifters are downtube friction shifters.
I should be able to use whatever RD with my friction shifters, right?

Bandera

Yes & Yes.

rootboy 

Is that a Huret-specific hanger on the dropout though? I don't know.

rootboy 

It is the housing that is too short. Should be a wide, easy loop, with no tight corners, as shown now. Cable is long enough but change to a new one when installing a longer piece of housing.

Ex Pres 

I think the little piece that covers the cage pivot bolt often times gets lost on those. Yours still has it. You might be able to sell it and buy a new derailleur even up or better. Worth checking ebay in any case.

unworthy1

Most likely it is. The issue with that is not the mounting-bolt threading (ISO) but where the pivot-stop notch is on the hanger.
Huret hanger will probably be at 4 o'clock where all the other popular replacements will be at 7 o'clock.
There is a work-around involving a small tap and grub-screw...and another idea to cut-and-bend a brass washer to make an adapter (this one looks very crude but you get the idea: https://bronzegears.blogspot.com/2008...rivetrain.html)
some people opt for a Shimano Crane-type RD which supposedly can be used on the Huret hanger with no mods, but others say look for a Huret Challenger or Success RD replacement, which should require no mods to the hanger and both work well.

Grand Bois

The Crane just requires tapping the hole. It's the same for a 1st generation Campy Rally. Neither one shifts great. I'd look for a Huret.

JohnDThompson 

Yes, that could be a lot of the problem.

The only potential issue is that the bike may have a Huret dropout, which would preclude using the integral hanger with a non-Huret derailleur. Note the location of the stop tab on the Huret hanger:



Contrast with a more typical stop-tab position:

Grand Bois

I think I read that somewhere recently.

JohnDThompson 

A picture's worth a thousand words, dontcha know?

jeirvine 

From the pic, it may also be that your chain is too short. It looks like it's already a bit tight and it's only on the second smallest cog. That could cause shifting issues as well. More pics can help us diagnose better.