How To Stop Seat Post Sliding

[Scott Ehardt]

This is my school campus bike (for getting to class), a somewhat old Motiv
from Sam's Club. I fully realize the shortcomings of such cheap bikes, but
this one serves its purpose except for the current seat post problem.

So on to the problem: I am at a loss as to why this seat post won't stop
sliding down! As you can see in the photos (below), I have a bolt holding
in the seat post since the original fastener broke a long time ago. The
current bolt is replacing another one almost like it that was allowing the
seat post to slip. The new one has a finer thread and higher strength, but
it still allows the post to slip down. With this bolt I was able to tighten
it until the gap closed (was never closed before), which I thought would
surely be enough, but it isn't.

Is it possible that I stretched something? Any thoughts about how to stop
the slip?

Left Side:
http://img4.exs.cx/img4/1673/DSCF0218.jpg

Back:
http://img4.exs.cx/img4/6505/DSCF0219.jpg

Right Side:
http://img4.exs.cx/img4/24/DSCF0220.jpg

Thanks!
-Scott

--
Scott Ehardt
http://www.scehardt.com

 

[Mike Jacoubowsky]

> Is it possible that I stretched something? Any thoughts about how to stop
> the slip?

One of the photos makes it appear that the upper part of the seat tube
(where the seatpost emerges) is flanged out a bit, as would happen if the
seatpost weren't far enough into the frame. If that did happen, it can
deform & stretch things enough that you won't be able to tighten it enough.

Is it the original seatpost? Could be that it's just slightly undersized,
and buying a higher-quality aluminum seatpost might be just the ticket. Best
bet is to bring the bike into your LBS and see what they have to say about
it.

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com


"Scott Ehardt" <[email protected]> wrote in message
news:[email protected]...
> This is my school campus bike (for getting to class), a somewhat old Motiv
> from Sam's Club. I fully realize the shortcomings of such cheap bikes,
> but this one serves its purpose except for the current seat post problem.
>
> So on to the problem: I am at a loss as to why this seat post won't stop
> sliding down! As you can see in the photos (below), I have a bolt holding
> in the seat post since the original fastener broke a long time ago. The
> current bolt is replacing another one almost like it that was allowing the
> seat post to slip. The new one has a finer thread and higher strength,
> but it still allows the post to slip down. With this bolt I was able to
> tighten it until the gap closed (was never closed before), which I thought
> would surely be enough, but it isn't.
>
> Is it possible that I stretched something? Any thoughts about how to stop
> the slip?
>
> Left Side:
> http://img4.exs.cx/img4/1673/DSCF0218.jpg
>
> Back:
> http://img4.exs.cx/img4/6505/DSCF0219.jpg
>
> Right Side:
> http://img4.exs.cx/img4/24/DSCF0220.jpg
>
> Thanks!
> -Scott
>
> --
> Scott Ehardt
> http://www.scehardt.com
>

 

[[email protected]]

On Tue, 02 Nov 2004 05:08:40 GMT, "Scott Ehardt"
<[email protected]> wrote:

>This is my school campus bike (for getting to class), a somewhat old Motiv
>from Sam's Club. I fully realize the shortcomings of such cheap bikes, but
>this one serves its purpose except for the current seat post problem.
>
>So on to the problem: I am at a loss as to why this seat post won't stop
>sliding down! As you can see in the photos (below), I have a bolt holding
>in the seat post since the original fastener broke a long time ago. The
>current bolt is replacing another one almost like it that was allowing the
>seat post to slip. The new one has a finer thread and higher strength, but
>it still allows the post to slip down. With this bolt I was able to tighten
>it until the gap closed (was never closed before), which I thought would
>surely be enough, but it isn't.
>
>Is it possible that I stretched something? Any thoughts about how to stop
>the slip?
>
>Left Side:
>http://img4.exs.cx/img4/1673/DSCF0218.jpg
>
>Back:
>http://img4.exs.cx/img4/6505/DSCF0219.jpg
>
>Right Side:
>http://img4.exs.cx/img4/24/DSCF0220.jpg
>
>Thanks!
>-Scott

Dear Scott,

The problem is that the gap is not closing--at least not
where it matters.

The two flanges through which the bolt goes are, as you
note, now touching, presumably by bending inward.

The gap or notch in the seat tube that you see below the
failed flanges isn't doing much of anything to clamp the
seat post any more.

When you can tighten the two flanges together until they
touch, they've failed. One solution is a slip-on seat post
clamp of the right size:

http://www.biketoolsetc.com/index.cgi?id=203831268027&c=Components&sc=Seatpost Clamps

The clamps are just collars that slip onto a naked seat
post. Their ends clamp together just like your failed
flanges. They're fairly cheap, but you have to get the right
size.

If there's not enough room for a slip-on to fit, then you
have to saw off the failed flanges and grind or sand the
surface smooth.

Good luck,

Carl Fogel

 

[Werehatrack]

On Tue, 02 Nov 2004 05:08:40 GMT, "Scott Ehardt"
<[email protected]> wrote:

>Is it possible that I stretched something? Any thoughts about how to stop
>the slip?

I will assume that you have not swapped seat posts, and that the one
installed is, in fact, the correct diameter.

The welded-on clamp ears are not doing the job; when the ears meet, as
is shown in the "rear" pic, either the ears or the tube to which
they're welded is distorted to the point that the clamp isn't going to
get enough of a grip. The solution is going to depend on the tools
and equipment that you have available.

My solution would be to take an angle grinder, shave those ears off,
and use a proper seatpost tube clamp instead.

Of course, there is a chance that the ears may work satisfactorily for
a while if simply bent back out; insert a long bolt into one ear at a
time, and pry it forward so that the gap opens up. Reassemble and
ride; it will soon be obvious whether it worked. If it doesn't, you
still have options.

It might appear tempting to simply spread the ears apart and file
their surfaces so that the clamp can close up farther, but in my
estimation, the most likely result that this will have is either the
removal of the ears or the distortion of the top of the seat tube to a
point at which it becomes useless, or both. Should you try that, and
should my prediction turn out to be accurate, then if there's enough
protrusion, the tube could still be shortened and equipped with a
regular clamp. If there's not much protrusion above the top tube (and
from the side views, it looks like there isn't), this option would not
be available.

You might try inserting a short strip of beer can shim between the
post and the seat tube to see if that will get you enough of a grip
with the existing clamp.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

 

[Peter Cole]

"Scott Ehardt" <[email protected]> wrote in message
news:[email protected]...
> This is my school campus bike (for getting to class), a somewhat old
Motiv
> from Sam's Club. I fully realize the shortcomings of such cheap bikes,
but
> this one serves its purpose except for the current seat post problem.
>
> So on to the problem: I am at a loss as to why this seat post won't stop
> sliding down! As you can see in the photos (below), I have a bolt
holding
> in the seat post since the original fastener broke a long time ago. The
> current bolt is replacing another one almost like it that was allowing
the
> seat post to slip. The new one has a finer thread and higher strength,
but
> it still allows the post to slip down. With this bolt I was able to
tighten
> it until the gap closed (was never closed before), which I thought would
> surely be enough, but it isn't.
>
> Is it possible that I stretched something? Any thoughts about how to
stop
> the slip?

Looks like the "ears" have bent slightly. Try sticking a coin or washer in
the gap. It may be that the washers you put on are too big, causing only
pressure on the rear part of the ears.

 

[[email protected]]

On Tue, 02 Nov 2004 20:29:42 GMT, "Peter Cole"
<[email protected]> wrote:

[snip tale of woe]

>Looks like the "ears" have bent slightly. Try sticking a coin or washer in
>the gap. It may be that the washers you put on are too big, causing only
>pressure on the rear part of the ears.

Dear Peter,

When I look again at the pictures, your too-big washer
explanation of the failure sounds good--the washers stick
out past the red metal of the frame.

Carl Fogel

 

[Mike Jacoubowsky]

>>Looks like the "ears" have bent slightly. Try sticking a coin or washer in
>>the gap. It may be that the washers you put on are too big, causing only
>>pressure on the rear part of the ears.
>
> Dear Peter,
>
> When I look again at the pictures, your too-big washer
> explanation of the failure sounds good--the washers stick
> out past the red metal of the frame.

Funny how some things bring back old memories. I recall very specifically
having to use oversized washers for "repairs" to messed-up seatlugs, and
having to file down one side so it could properly fit against the frame.
Way, way, way back in the day.

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com

 

[Qui si parla Campagnolo]

SCE-<< Is it possible that I stretched something? Any thoughts about how to
stop
the slip? >><BR><BR>

Go to a bike shop that has a knurling tool, a nifty tool that will make ridges
in the seatpost making it 'larger'..

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"

 

[Scott Ehardt]

<[email protected]> wrote in message
news:[email protected]...
>
> Dear Scott,
>
> The problem is that the gap is not closing--at least not
> where it matters.
>
> The two flanges through which the bolt goes are, as you
> note, now touching, presumably by bending inward.
>
> The gap or notch in the seat tube that you see below the
> failed flanges isn't doing much of anything to clamp the
> seat post any more.
>
> When you can tighten the two flanges together until they
> touch, they've failed. One solution is a slip-on seat post
> clamp of the right size:

When you put it that way, it makes perfect sense!

> http://www.biketoolsetc.com/index.cgi?id=203831268027&c=Components&sc=Seatpost Clamps
>
> The clamps are just collars that slip onto a naked seat
> post. Their ends clamp together just like your failed
> flanges. They're fairly cheap, but you have to get the right
> size.
>
> If there's not enough room for a slip-on to fit, then you
> have to saw off the failed flanges and grind or sand the
> surface smooth.
>
> Good luck,
>
> Carl Fogel

I don't have the tools to cut off and grind smooth the flanges right now, so
I'll have to do that later around Christmas when I have the right tools.

Thanks for your help with this!
-Scott

--
Scott Ehardt
http://www.scehardt.com

 

[Scott Ehardt]

"Werehatrack" <[email protected]> wrote in message
news:[email protected]...
> On Tue, 02 Nov 2004 05:08:40 GMT, "Scott Ehardt"
> <[email protected]> wrote:
>
>>Is it possible that I stretched something? Any thoughts about how to stop
>>the slip?
>
> I will assume that you have not swapped seat posts, and that the one
> installed is, in fact, the correct diameter.

I have not swapped seat posts, so I'd say that's safe to assume.

> The welded-on clamp ears are not doing the job; when the ears meet, as
> is shown in the "rear" pic, either the ears or the tube to which
> they're welded is distorted to the point that the clamp isn't going to
> get enough of a grip. The solution is going to depend on the tools
> and equipment that you have available.
>
> My solution would be to take an angle grinder, shave those ears off,
> and use a proper seatpost tube clamp instead.
>
> Of course, there is a chance that the ears may work satisfactorily for
> a while if simply bent back out; insert a long bolt into one ear at a
> time, and pry it forward so that the gap opens up. Reassemble and
> ride; it will soon be obvious whether it worked. If it doesn't, you
> still have options.
>
> It might appear tempting to simply spread the ears apart and file
> their surfaces so that the clamp can close up farther, but in my
> estimation, the most likely result that this will have is either the
> removal of the ears or the distortion of the top of the seat tube to a
> point at which it becomes useless, or both. Should you try that, and
> should my prediction turn out to be accurate, then if there's enough
> protrusion, the tube could still be shortened and equipped with a
> regular clamp. If there's not much protrusion above the top tube (and
> from the side views, it looks like there isn't), this option would not
> be available.
>
> You might try inserting a short strip of beer can shim between the
> post and the seat tube to see if that will get you enough of a grip
> with the existing clamp.

There is not space to add a shim around the post, but I will be grinding off
the flanges and purchasing a new clamp when I have access to the necessary
tools in about a month.

Thanks for your help!

--
Scott Ehardt
http://www.scehardt.com

 

[Scott Ehardt]

<[email protected]> wrote in message
news:[email protected]...
> On Tue, 02 Nov 2004 20:29:42 GMT, "Peter Cole"
> <[email protected]> wrote:
>
> [snip tale of woe]
>
>>Looks like the "ears" have bent slightly. Try sticking a coin or washer in
>>the gap. It may be that the washers you put on are too big, causing only
>>pressure on the rear part of the ears.
>
> Dear Peter,
>
> When I look again at the pictures, your too-big washer
> explanation of the failure sounds good--the washers stick
> out past the red metal of the frame.
>
> Carl Fogel

I checked that and the washers only contact the flanges so I don't think
they are the problem.

--
Scott Ehardt
http://www.scehardt.com

 

[Scott Ehardt]

"Qui si parla Campagnolo " <[email protected]> wrote in message
news:[email protected]...
> SCE-<< Is it possible that I stretched something? Any thoughts about how
> to
> stop
> the slip? >><BR><BR>
>
> Go to a bike shop that has a knurling tool, a nifty tool that will make
> ridges
> in the seatpost making it 'larger'..
>

Interesting idea, but the seatpost fits in just right as it is; I don't
think there is any extra space. However, roughing it up in some other way
that doesn't increase diameter might help the problem.

Thanks for the suggestion!
-Scott

--
Scott Ehardt
http://www.scehardt.com

 

[A Muzi]

>>>SCE-<< Is it possible that I stretched something? Any thoughts about how
>>to stop the slip?

> "Qui si parla Campagnolo " <[email protected]> wrote
>>Go to a bike shop that has a knurling tool, a nifty tool that will make
>>ridges in the seatpost making it 'larger'.

Scott Ehardt wrote:
> Interesting idea, but the seatpost fits in just right as it is; I don't
> think there is any extra space. However, roughing it up in some other way
> that doesn't increase diameter might help the problem.

A knurl will raise the surface a couple thousandths of an
inch. Not a different size, just a closer class of fit.

Try measuring a selection of seatposts at an LBS sometime
with a micrometer. There are definitely larger and smaller
versions of each size.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

 

[Werehatrack]

On Wed, 03 Nov 2004 14:46:26 -0600, A Muzi <[email protected]>
wrote:

>Try measuring a selection of seatposts at an LBS sometime
>with a micrometer. There are definitely larger and smaller
>versions of each size.

There are also variations in how well they'll clamp in place depending
on the surface finish present if there is one. I had a post that just
wouldn't stop slipping until I took it over to a machine shop nearby
and used the bead blaster to remove whatever it was coated with.
After that, any reasonable amount of grab locked it in place nicely.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

 

[Ed]

The seatpost is too small. No matter how much more you tighten the
bolt, no more holding force will be applied to the seatpost. Notice
how the two "ears" are up against each other. They started out as
wide as the gap you see below them.

Easy solution: find a Bud beer can, cut a small rectangular piece of
this very thin aluminum, about 1 inch top-to-bottom and long enough to
wrap almost completely around the seatpost (you've made a shim!). The
metal is so thin you can just use scissors for this. Wrap the shim
around the seatpost and reinsert. Depending on how much too small the
seatpost is (hard to tell from pix) you may need two pieces of shim
material. You'll be able to tell it's right when you get the bolt
real tight and there is still a gap between the two "ears."

--Ed G--


On Tue, 02 Nov 2004 05:08:40 GMT, "Scott Ehardt"
<[email protected]> wrote:

>This is my school campus bike (for getting to class), a somewhat old Motiv
>from Sam's Club. I fully realize the shortcomings of such cheap bikes, but
>this one serves its purpose except for the current seat post problem.
>
>So on to the problem: I am at a loss as to why this seat post won't stop
>sliding down! As you can see in the photos (below), I have a bolt holding
>in the seat post since the original fastener broke a long time ago. The
>current bolt is replacing another one almost like it that was allowing the
>seat post to slip. The new one has a finer thread and higher strength, but
>it still allows the post to slip down. With this bolt I was able to tighten
>it until the gap closed (was never closed before), which I thought would
>surely be enough, but it isn't.
>
>Is it possible that I stretched something? Any thoughts about how to stop
>the slip?
>
>Left Side:
>http://img4.exs.cx/img4/1673/DSCF0218.jpg
>
>Back:
>http://img4.exs.cx/img4/6505/DSCF0219.jpg
>
>Right Side:
>http://img4.exs.cx/img4/24/DSCF0220.jpg
>
>Thanks!
>-Scott

 

[Thomas Cuny]

Scott Ehardt wrote:

> This is my school campus bike (for getting to class), a somewhat old
> Motiv
> from Sam's Club. I fully realize the shortcomings of such cheap
> bikes, but this one serves its purpose except for the current seat
> post problem.
>
> So on to the problem: I am at a loss as to why this seat post won't
> stop
> sliding down! As you can see in the photos (below), I have a bolt
> holding
> in the seat post since the original fastener broke a long time ago.
Drill a hole through the seat post and stick a nail through it.

 

[[email protected]]

On Wed, 03 Nov 2004 19:52:46 -0500, Ed
<[email protected]> wrote:

>The seatpost is too small. No matter how much more you tighten the
>bolt, no more holding force will be applied to the seatpost. Notice
>how the two "ears" are up against each other. They started out as
>wide as the gap you see below them.
>
>Easy solution: find a Bud beer can, cut a small rectangular piece of
>this very thin aluminum, about 1 inch top-to-bottom and long enough to
>wrap almost completely around the seatpost (you've made a shim!). The
>metal is so thin you can just use scissors for this. Wrap the shim
>around the seatpost and reinsert. Depending on how much too small the
>seatpost is (hard to tell from pix) you may need two pieces of shim
>material. You'll be able to tell it's right when you get the bolt
>real tight and there is still a gap between the two "ears."
>
>--Ed G--

Dear Ed,

I think that the rear view shows that the seat-post fits
snugly into the frame and that the sides of the slit down
the seat-tube are not compressed:

http://img4.exs.cx/img4/6505/DSCF0219.jpg

The seat post diameter is fine. The problem is that the ears
have failed--instead of tightening the seat-tube, they've
bent to the point that they touch each other and can no
longer tighten things.

Look how badly the ears are bent. You'd have to expand the
seat-tube quite a bit for any shimming to spread them far
enough apart to begin working again.

Or so it looks to me.

Carl Fogel

 

[Ed]

You're missing a couple valuable clues here;

1. Bike came from Sam's Club. What are the odds that some junior
high summer employee stuck the nearest wrong size seatpost in this
frame during assembly?

2. Original bolt broke. Wonder why? Perhaps because someone cranked
down on that one so many times trying to keep the seatpost from
slipping that the bolt stripped.

I would highly recommend you don't cut or modify the frame. Frame is
probably thicker CrMo and there's a chance that if you cut off the
ears you wouldn't get a more modern seatpost collar to tighten
properly either.

Make and install a shim, or take the frame and/or post to a shop and
get then to measure the inside tube diameter and recommend the correct
size seatpost. It may be one that's essentially unavailable unless
the shop has a nice supply of old posts. Or it's almost a sure bet
you could find it on Ebay.

--Ed G--


On Wed, 03 Nov 2004 17:03:52 GMT, "Scott Ehardt"
<[email protected]> wrote:

>"Werehatrack" <[email protected]> wrote in message
>news:[email protected]...
>> On Tue, 02 Nov 2004 05:08:40 GMT, "Scott Ehardt"
>> <[email protected]> wrote:
>>
>>>Is it possible that I stretched something? Any thoughts about how to stop
>>>the slip?
>>
>> I will assume that you have not swapped seat posts, and that the one
>> installed is, in fact, the correct diameter.
>
>I have not swapped seat posts, so I'd say that's safe to assume.
>
>> The welded-on clamp ears are not doing the job; when the ears meet, as
>> is shown in the "rear" pic, either the ears or the tube to which
>> they're welded is distorted to the point that the clamp isn't going to
>> get enough of a grip. The solution is going to depend on the tools
>> and equipment that you have available.
>>
>> My solution would be to take an angle grinder, shave those ears off,
>> and use a proper seatpost tube clamp instead.
>>
>> Of course, there is a chance that the ears may work satisfactorily for
>> a while if simply bent back out; insert a long bolt into one ear at a
>> time, and pry it forward so that the gap opens up. Reassemble and
>> ride; it will soon be obvious whether it worked. If it doesn't, you
>> still have options.
>>
>> It might appear tempting to simply spread the ears apart and file
>> their surfaces so that the clamp can close up farther, but in my
>> estimation, the most likely result that this will have is either the
>> removal of the ears or the distortion of the top of the seat tube to a
>> point at which it becomes useless, or both. Should you try that, and
>> should my prediction turn out to be accurate, then if there's enough
>> protrusion, the tube could still be shortened and equipped with a
>> regular clamp. If there's not much protrusion above the top tube (and
>> from the side views, it looks like there isn't), this option would not
>> be available.
>>
>> You might try inserting a short strip of beer can shim between the
>> post and the seat tube to see if that will get you enough of a grip
>> with the existing clamp.
>
>There is not space to add a shim around the post, but I will be grinding off
>the flanges and purchasing a new clamp when I have access to the necessary
>tools in about a month.
>
>Thanks for your help!

 

[Blair P. Houghton]

Ed <[email protected]> wrote:
>Easy solution: find a Bud beer can, cut a small rectangular piece of
>this very thin aluminum, about 1 inch top-to-bottom and long enough to
>wrap almost completely around the seatpost (you've made a shim!). The
>metal is so thin you can just use scissors for this.

Running kind of off-topic just to brain dump on this meme:

They used to be thicker. But of course lighter is
cheaper in aluminum cans, so two things have changed:
1. the sidewall material has been thinned to some sort of
theoretical limit; 2. the top has been reduced in diameter
because it still needs to be thicker than the sidewalls
and the only way to make it lighter is to make it smaller.
I bet you thought they were just providing a "lip groove"
or a way to stack the cans. They couldn't care less
about a functional requirement if they could save an extra
milligram per can.

Oh, and do you know why there are six circular dots in
the base of the can? That's where they suck the air out
of the mold when they suck in the flat, round blank to
make it a tube with one closed end.

It's amazing that aluminum can take that kind of stretching
and squeezing, but that's how they do it.

--Blair
"Ever watched a beer can evaporate
in a campfire?"

 

[Qui si parla Campagnolo]

Scott->Interesting idea, but the seatpost fits in just right as it is; I don't
>
>think there is any extra space.

But if it slips, it is too small...

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"