SpeedofLite 

Inspecting and cleaning a recently acquired, lightly used 1987 Cannondale Black Lightning.
Original seatpost is an American Classic 27.2
There is a soft plastic red cap inside the post just underneath the seat clamp (see photo).
The nipple will deform and return to original position with a light press.
And because I wasn't slapped or kicked after the first time I touched it, I figured it was OK to repeat that action about 10 more times.

I've found a few things crammed into seatposts (e.g. spokes, paper currency) but haven't seen one of these before.
I found an image of it online and in a separate old BF thread to believe it's original equipment, but haven't found an explanation as to its function.
So, is it protecting something? If so, what?

Kuromori

I'm pretty sure it's just a plug to stop water from having a giant hole to enter the frame through.

SpeedofLite 

Thank you for your input.
I thought the same as you initially, but I discounted that because most seat posts don't have any cap (or even had flutes), even those made during the years when steel frames ruled.
And also, why would a water protecting cap not cover the entrance at the top of the seat tube. Because it sits below the entrance, it creates a space that can only serve as an open reservoir for water.
I want to believe there's more to it than simply water protection.

steelbikeguy

I've got a few of the American Classic posts. There are at least two versions of this general arrangement. The first is machined out of a single piece of material, hence the hole bored all of the way through.

My examples of the first generation style have a black plastic(?) plug in the same location, although the plug is more flush with the top, and probably less prone to collect water. There seems to be some sort of sealant around the plug too....




Later versions had the head machined out of a separate piece and then glued to the top of the shaft. This version doesn't use any plug....



edit/addendum: I first got one of these 1st gen A.C. seatposts in 1989. It's very possible that the earlier 1987 design did use that red cap, and that the manufacturer later changed to the plug shown in my first photo to correct for leakage issues.

Steve in Peoria

Kuromori

Most seat posts, sans cheap seat pillars with a separate clamp, don't have an exposed hole like that. Most posts have flutes above the clamping area, or at least have an end point. I only recall seeing BMX posts with full length fluting.

dedhed

Looks like a repurposed protective cap a previous owner stuffed in there.
They are used in their first purpose for things like protecting threads in shipping. I keep a coffee can full of thes, both internal and external for plugging holes, protection, making grommets, or whatever use I might find for them.

SpeedofLite 

@Kuromori, @steelbikeguy. and @dedhed,

You all make good points. Thanks.

Part of me wants to see what's underneath the red plug/cap. The other part says leave it alone and don't pick at it.

Here's a link to an old BF thread in which the OP was concerned about the quality of the AC seat post: https://www.bikeforums.net/classic-v...-use-lose.html
You can see the red plug in a post 1 photo and a comment in post 17 from another BFer having the same part. I also saw another image of the red plug/cap somewhere online, but can't find it now.
This would be a huge coincidence for it not to be original to that post.

You're all probably right about the water prevention thing. I'll let it go.

gearbasher

I had a first generation (purchased new) that came with the red plastic plug. Word of warning: The lower part of the saddle clamp on the first generation ones are known to crack. These are the ones that look like they're stamped steel. I cracked mine (after about 30,000 miles). Thankfully not while riding, but while torquing it down to A.C.'s spec.

The Golden Boy 

Like a zit.

Or a button that has a sign that says "do not push the button."

Or a package of Charmin.

SpeedofLite 

Thanks 'basher. I wanted to move the saddle back about a 1-2cm, but I was having difficult just sliding it back so thought I might as well take it completely apart and clean everything and do it right. What I found was the the saddle was already as far back in the clamp as it could go, but didn't look like it from the side. The rails moved inward before moving up to the nose and that inward angle didn't match the lower clamp curves very well.

By the way, did you ever remove the plug? If so, what's behind it?

The Golden Boy 

gearbasher

Never did, but you don't have to. I saved the shaft part of the post. I use it to test 27.2 frames before I put a new post in. Here's a picture of the plug from the top. I never messed with it. So, this is the original position.



It just covers a hollow shaft. Here's a shot from a proctologist's point of view.



One last recommendation. If you do use the post, they also tend to creak. If you wrap the threads on the set screw that adjusts tilt with Teflon tape it won't creak.

SpeedofLite 

Well yeah, I could have removed the seat post too, but where's the challenge in that?

Seriously thanks!

I can't believe how many times I've felt foolish in this thread....sigh.

I'll blame it on the earthquakes. Yeaaahh....it was the earthquakes....that's the ticket.

clubman 

Broke one on a new Cannondale T1000 inside of 2 weeks. Shop replaced it with an XT to match the bikes group, I refused another AC.