Author Topic: Derailleur helicoil help  (Read 830 times)

Derailleur helicoil help
« on: October 06, 2018, 08:28:18 pm »

I recently bought a second hand dura ace 9 speed derailleur (rd-7700). When I went to fasten the cable the bolt wouldn’t tighten and I realised the helicoil in the derailleur body had backed out. The threads on the bolt are not in great condition (which maybe caused the problem?). I have removed the helicoil now. I assumed the derailleur body would have good threads, but they don’t look good at all.

My dilemma is should I try to replace the helicoil?

Or should I tap the derailleur body for a larger size bolt, with no helicoil?

Is there anything else I could do?

Another second hand derailleur will be about £20. It seems a shame to junk such a nice derailleur - it obviously hasn’t done many miles, but I don’t want to spend much on tools (and I don’t have any taps or helicoil tools)

Any ideas? For those curious, the helicoil is meant to be there.


Re: Derailleur helicoil help
« Reply #1 on: October 06, 2018, 08:55:04 pm »
I'd try a bolt in good condition first; it may just wind the insert back in. IIRC the thread is M5 x 0.8; you can buy helicoil kits cheaply on e-bay, and you can sell the kit on (with one thread insert less) if you think you might never use it again, and maybe it will cost you £5 or so that way. Or maybe someone has a kit that you can use?

I'd expect the thread in the aluminium part (that accepts the insert) to just need cleaning up. You can do this using the tap that comes in the kit.


Re: Derailleur helicoil help
« Reply #2 on: October 07, 2018, 11:31:50 am »
Thanks very much Brucey - I will give that a go.


Re: Derailleur helicoil help
« Reply #3 on: October 07, 2018, 03:09:43 pm »
IIRC there is quite a good 'how to' on the park tool site, in reference to pedal thread helicoils. Smaller threads work in a fairly similar way, so it is mostly useful.


Re: Derailleur helicoil help
« Reply #4 on: October 07, 2018, 10:33:46 pm »
They sometimes do have a tendency to wind out, a little epoxy helps retention.

Re: Derailleur helicoil help
« Reply #5 on: December 30, 2018, 08:46:41 pm »
Very belated thanks to everyone for your help with this.

It took a while but kit ordered, and a pleasant half an hour spent installing the helicoil. First one went wrong somehow but second went in nicely and all well!