Seat post bolt shears!

[Geofff]

My seat post bolt sheared of whilst I was riding in torrential rain on Tuesday, so a good day got even better! I had been aware that the saddle was making some squeaks but didn't get as far as checking anyhting out before it snapped. The bike is a Trek 7.5 FX. Doing a quick google last night I found another example of this problem, which apparently was due to Trek using an aluminium bolt.
(1) Anyone else aware of this problem
(2) My lbs who is also a Trek dealer was surprised to find that the bolt is 7mm - they have 6 & 8mm in the shop and now tells me that they can't source one. Anyone any suggestions?

[rualexander]

This happened to someone I was cycling with in New Zealand in 1993. It wasn't an aluminium bolt as far as I know, but he was able to make a temporary repair by cutting a section of wire from a roadside fence and threading it through the hole and twisting it tight enough to hold until we got to the next town with a garage workshop.

[Big T]

Just buy a new seatpin. £10-15 for an alloy one, unless it's a strange size. Sorted.

[Gearoidmuar]

It's happened to me twice or three times in the past but not for many years as I found out what causes it, in a magazine article..
It's caused by overtightening, weakening the bolt.
You should NOT put a lever on the allen key when tightening these.

[531colin]

I seem to remember reading CJ in the CTC mag. many years ago saying "The regular design(s) of micro-adjust seatposts with a single bolt put a bending stress on the bolt, which can result in the bolt breaking. Go to your local bolt stockist and buy a high tensile steel bolt (usually M6) and this won't happen." All my bikes now have high tensile seatpost bolts. For the tiny outlay its just not worth risking the thing breaking, that can be quite exciting.

Ps sorry if I'm mis-quoting!

I guess if you Google you will find an internet bolt stockist who keeps M7 high ten bolts...........