I have several 27.2's, and all slip loosely. They do not all mike the
same, I've checked. The original post has always been a loose fit.
It would only tighten when the binder bolt tabs were touching. Sad to
say, I think this a design flaw in an otherwise great bike. One of
the binder bolt tabs broke off, and Trek repaired the frame on
warrantee. I have had one or two long-time Trek dealers tell me nasty
anecdotes about factory problems at Trek. Still, this is a great bike
now that I'm getting it sorted out. The 73 degree seat tube suits my
legs very well.
Tony Oliver says in "Touring bikes" that 531 has clearance for 27.4
posts when they are brazed at low temperature. Trek advertized
low-temp braze in its 1984 brochures, and in the earlier brochures
called out silver braze. Perhaps I shouldn't be surprised that 27.2's
are sorta loose.
My thickest 27.2 fits well with a .001 brass sheet wrapped around it.
I guess I'll have an LBS check the ID with a guage before pulling the
trigger on a 27.4 post. Knurling sounds like a good thing to try on
the Laprade.
Thanks for all your input!!
Ken
"A Muzi" <
[email protected]> wrote in message
news:
[email protected]...
> Road Man wrote:
>> For my Trek 610, I want to try a larger seat post. The original SR
>> Laprade is 27.2, but it feels loose, and the integral seatpost tabs
>> converge when I tighted the binder bolt. I tried an old 2-bolt
>> Campy 27.2, and it is a bit larger, but still loose. Adding .001
>> brass shim stock helps. I'd like to try a 27.4 mm post, but I
>> can't find any on websites or the big sellers. Anyone have one to
>> sell?
>>
>> I really like the old Campy 2-bolt, cosmetics are not important!
>
> That frame has a notoriously narrow slit in the seat lug. Cut it
> wider, lube the integrated allen bolt well and you should be OK.
>
> Going from a 27.2 post to a 27.4 post is a _huge_ difference.
> Contemplate the law of unintended consequences
>
> for a moment
> and then don't do that! A good test is to slip the post in all the
> way. It should have no side play at all yet still move in and out
> easily in a clean seat tube. Your Trek will likely pass that test at
> 27.2mm.
>
> You might also try a micrometer on a few posts. Some will be big and
> some small. Knurling a smallish post is a reasonable solution if it
> is still loose after you clean up the seat lug.
>
> --
> Andrew Muzi
> www.yellowjersey.org
> Open every day since 1 April, 1971