JoeBass

I've cranked the bolt to a tightness beyond reason, and still, over time, the seat will start tipping, nose up. The old post doesn't look like it has any type of grooves cut in the metal parts which make contact with each other such that a positive lock would occur to prevent this type of thing, so I'm at a loss. Is there some trick here, other than trying a different post?

FBinNY 

Without knowing the particulars of the post, it's hard to say anything specific.

However, one place to start is by looking at where you;re clamping the saddle and sitting on it. If you sit well back or on a saddle that's well back in the post, your weight is trying to tilt it back down/nose up. OTOH, if your weight is centered over the clamp area, or at least close, there won't be a net torque trying to tilt the saddle either way.

juvela

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Sounds like it could be stripped splines.

Open 'er up and have a look-see.

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Trevtassie

Yep, this^
I'm thinking you are referring to the old style band clamp style. Sometimes you can switch the clamp 180 on the post to get the pivot point under the maximum weight point. Can also help if the clamp is above the seat rails. Sometimes, however, the clamp faces are just worn out and you need a new one.

Rollfast

Is your bolt stripped?

juvela

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Joe,

We need to get everyone on the same page. You say your clamp is a single bolt. Is it a single transverse bolt or a single bolt from underneath?





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CroMo Mike 

On Campy single bolt (like Super Record) I've had good luck by taking the clamp off and lightly sanding the areas where the clamp meets the post. Don't wipe the sanding dust off. Reassemble. The left over sanding grit helps the parts get a grip. Works for me.

JoeBass

It's a single bolt from underneath. I just took the thing apart for close inspection, and it looks to me like it's just horribly designed. The top section of the post that contacts the clamp is a continuous curve that's dead smooth except for where it's rubbed through movement, and the clamp section looks to only contact the post in four tiny areas. Ugg...

juvela

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Thank you.

Appears to have been designed by someone who had absolutely no plans to use it themselves!

BTW - frame looks like an emigre from Neuchatel.

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Salamandrine 

Are the threads of the tightening bolt greased? If not, it may not be as tight as you think it is.

You may simply be one of those people that needs a two bolt post. Nitto S83 is the obvious recommendation, if it is budget appropriate for you and your bike. Or look for a vintage 2 bolt on ebay in the right size.
https://www.rivbike.com/collections/...t-26-8-or-27-2

BTW, that post looks like a copy of the nitto s65, which works fine for most people. It may be a matter of execution.

markk900

Awful design, but if it were mine and I *had* to keep it I would spend the time to sand down both the post curve and the clamp to get better contact, then I would cut some grooves in the contact area, to provide some friction.

FBinNY 

This design actually has a good history of working well, but as I pointed out early on, there may be a balance issue.

In any case, it's very easy to greatly improve the traction and prevent slippage. Visit your favorite car mechanic, or an engine rebuilder and beg a tiny bit of the coarsest lapping compound (grit in a grease base) they have. Apply it to the contact areas, making sure NOT to get any on the screw or nut. When the camp is tightened, the grit will bite into both mating parts, and effectively lock them together.

When using this method, it's important not to set the angle by tightening slightly and nudging the saddle. Doing so, will cause the grit to score grooves, defeating the purpose.

fietsbob

So? Pull it out and put something else in.. classic 2 bolt Campag?

their 1 bolt had full surface contact.. I have 2 , 25.0 from 2 Alan's I owed in the 80's

then bought shims from USE in 27 & 27.2 to use them in steel frames,

then got better fitting proper sized 27.2 posts

[machined out the 27.0 framec to 27.2]




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JoeBass

Good eye!

It's an early 1970's Allegro, which I'm guessing means I'm going to have a hard time finding an appropriate replacement seat post. Anyone know off hand what size post an Allegro would take? I measured this one, and it looks to measure right between 25.5 and 25.6. While it fits, I'm sure this isn't the original post.

FML123

I have exactly the same problem! Following this thread.

squirtdad

6 year old zombie thread. OP would be better served by starting a new thread with their issue details (and will help get post count up)

repechage

‘not really enough info- my hunch is one where the post is an outside radius, and the seat clamp is convex.

take it apart and really look for the clamp under magnification for cracks, review for distortion. Perhaps a friction paste such as valve grinding compound, be sure to lubricate the bolt, maybe antiseize- counter intuitive but you want the torque to not be wasted on the threads, you want clamping force.

Campagnolo single bolt posts have this problem - I have found small cracks in the clamp, they let the part expand under load. I have also gone to a bolt with ah higher profile, easier to tighten.

repechage

zombie jamboree

RCMoeur 

If you don't change seatposts, keep a close eye on the seatpost and bolt, especially if you hear clicking or creaking noises.
Don't ask me how I know these things...

nlerner

I think any subsequent advise in this thread should start with "First, get a time machine . . . "

RCMoeur 

"The shop called. It still isn't fixed, because the part manufactured in 2274 was mistakenly delivered to 1887."

Bad Lag

Zombie thread or not, the very first component I ever upgraded was to a Campagnolo two-bolt seat post from a transverse single bolt design.

norskagent

I had the same issue with a campagnolo super record one bolt seatpost, I swapped out the flat head bolt for a hex bolt (easier to tighten properly), + used carbon assembly paste, and that solved it. Kept the original bolt of course!

Ex Pres 

If carbon assy paste doesn't do it, a small piece of wet/dry sandpaper, like 600 grit, has been put to good use by me in the past on multiple slippage items.


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