Front mech bolt - daft question

W1368

I have bought a new front mech after the last one seized (and wasn't very good anyway!).

For now I've used a spare bottle cage bolt that fits just right for mounting Not sure if its steel or aluminium. Would this be ok as a perminant fixture? Not knowing the exact bolt size.

The bolt on the new one (M5 x 17.5) is too short and doesn't reach the other side. But swaping with the bolt on the old mech (M5 x 21.3) is too long, causing it to push against the mech when tightened.

Old: Shimano FD-370
New: Shimano FD-M770

Both 34.9 band type.

muddytreker

It'll get you by for now maybe last for as long as you need it to,
time will tell, though it won't have torsional strength of a
steel bolt.
If your needing a suitable bolt in steel and struggling to size it, drop us
a pm and we can sort something out, if it helps

cooldad

A bolt is a bolt. If it fits...

But can't see how the right one won't fit if it's the right size mech. Are you sure it's not a multiple size with a shim?

muddytreker

" A bolt is a bolt. If it fits..."

Well sort of but the material can be relevant, ie alloy bottle cage bolts wouldn't
be advised for securing a brake rotor for long term.

A front mech band can vary from model to model, year to year, where the bolt head sits
in its tightened position, this part of the band can vary in shape and thickness, despite the mech being
suited the same seat tube diameter.
A pressed steel band can be different to that of an Aluminium band in its shape and form, as an example.
This may or may not be the OPs issue, but it does happen, a bolt can fit one and not the other.

cooldad

34.9 is 34.9. In my universe anyway.

The Rookie

Indeed, I've never come across a Shimano mech with a bolt that is too short....

An aluminium bolt would be fine for that anyway, its under minimal stress.