Richard Cranium

What is the latest and greatest method or product to stop a seat post from slipping downward? I have a Specialized aluminum frame e bike with a "normal looking" seat tube and binder collar and binder bolt that sits atop the seat tube. I rode the bike for about a year before having to raise the post again.
At that time - I removed the binder and binder bolt and cleaned and lubed the binder as well as greasing the binder bolt. I used a four inch Allen wrench to re tighten the bolt. I believe the binder bolt is already tightened to it's maximum. Although the seat tube /frame tube fit seems "normal" - seat tube has settled and fallen again - but it did take over six months for this to happen.

Is there a prep or anything i can add to the seat tube or seat post to created additional stability? I don't think the binder can collapse the seat tube anymore to stop future slipping.

mpetry912 

Suggest you abandon the hope that some kind of "prep" or miracle goop will solve this problem. Unless you're thinking JB Weld

first you want to confirm that the seatpost is the right size. Look for a small gap in the seat tube between the binder ears. Also the inner bore of the seat tube should be as nearly round as possible

and the binder bolt not stripped or bottoming out. Again look for that small gap.

assuming all the above is good.then you need to establish some interference between the seatpost and the inner bore of the seatpost. First, with the seat at your desired height, draw the outline of the seat lug with a sharpie so you know what's in the frame.and hidden from view. Then pull the seat post out.

I have the wonderful J.A Stein knurling tool which will let you put knurling marks on the seat post below the insertion line.

If you don't have a knurling tool, you can use your automatic center punch to put some "dimples" on the post, again below the insertion line, to establish some interference, so when you tighten the pinch bolt, it will "bite".

Last and least favorite option is a shim. It need not go all the way around the post - just a strip of beer can 1/2" wide might be enough if all the steps previously listed fail.

proper attention to the above should help with the slipping seat post problem.

/markp

bboy314

You could try the Surly Constrictor clamp, which uses an 8mm bolt that you can tighten a bit more without fear of stripping threads.

Definitely verify you have the correct size post first.

Andrew R Stewart 

Applying a carbon seat post assembly paste (basically grease like mixed with tiny bits of solids to better bite into the post and frame) instead of a lube grease on the post/seat tube interface is often the quick and first attempt to keep a post from migrating.

Another contributor to slipping posts is the length of the seat tube's binder slot. Too short a slot will have the bolt fighting the seat tube's walls stiffness even more so and will concentrate the clamp's contact area (with the post) to a small ring at the very top of the seat tube. A suitable length binder slot will allow the tube to close up around the post with a fairly large area of actual contact.

I otherwise agree with Mark's suggestions. Andy

redshift1

Could try a loctite anaerobic cure product - one of the bearing retainers. They resist rotational shear loads very well. No rotation here, but still shear forces. A small bottle is cheap enough. If you try this, be sure to degrease all parts in contact first. I would suggest trying a lower strength grade first and work up from there. Also do not use a high temperature grade. Loctite softens nicely upon heating if required but you don't want to damage that frame paint...

But a proper mechanical fit would be best. I suggest only trying the loctite if you have exhausted other options first.

icemilkcoffee 

Get a seatpost rack mount: https://www.campfirecycling.com/prod...nt-p-3192.html

Clamp this on your seatpost right where it meets the seat tube. Now your seatpost won't slip down any more.

Rick

The Phil Wood seat binder clamp worked for me when the Surly didn't.

Crankycrank

As mentioned already, you may be able to fix the problem with a better clamp. I just replaced a nice looking clamp that came with a steel frame but the clamp was not especially strong. The post was the correct size and snug fit but would slip a mm every 100 miles or so. Replaced the clamp with a beefier model. Theory Trusty Single Bolt Seat Clamp (Silver) (28.6mm) - Dan's Comp (danscomp.com) Supposedly made for BMX'er abuse, not expensive and no more slipping.

rm -rf

My custom titanium bike came with an extremely smooth milled interior seat tube. The seat tube would slowly creep down over a series of rides. I eventually roughed it just slightly with some 320 wet-and-dry sandpaper. That probably doesn't apply to your seat tube, though.

The other suggestions are all good:
check that the clamp isnt' bottoming out where the bolt squeezes it.
an extra freestanding clamp above the frame clamp.
Carbon assembly paste: I like using it on aluminum to aluminum surfaces, where it's also effective. Seatposts or handbar stem clamps.

Richard Cranium

Thanks for all the comments and ideas. At this point - I took the bike to a different dealer so get an another perspective.

They found that the post was nearly .03 - 05mm smaller in OD than the stated size. Something like 26.55 to 26.57 on a 26.6 post - we both admitted we didn't know if that was an acceptable fit.

The mechanic tightened the bolt using a a shop quality torque wrench - and I have put another several hours of use on the bike without the post slipping.
Here's the deal - I know I had already tightened that bolt to "very large" amount of resistance using a 4 inch allen wrench. That was in August of 23 - I've never heard of a binder bolt just "loosening" up due to time or miles.
I should have had that mechanic measure a couple of other posts just to see if the micrometer measurements vary much. In any case, the post height is marked - if it slips again within this season - I have things too try.

As I said - I appreciated all the ideas - I'll use this thread as a reference if I have trouble in the future - you're never too old to learn something new.
.

Andrew R Stewart 

Andy

soyabean

Not sure what the fuss was all about, when I see a seatpost appears "free" I'll use some SAC-2 because it lets the fastener do less work (Park Tool claims 30% less torque is needed), and acts as an anti-seize.

Especially on vintage bikes where the clamp is welded to the frame and folks always overtighten to the point the seatpost is being scored, hate that.

esasjl

"I know I had already tightened that bolt to "very large" amount of resistance using a 4 inch allen wrench. 4" of leverage is pretty small, no wonder the effort was so high but perhaps not quite tight enough."

My understanding is that the short end of a hex/allen key should provide enough torque if the seat post is the right size and the seat tube round, but this is aluminium in steel.