How to reduce corrosion on the inside of the seat tube?

jairaj

I have a problem where my seat tube keeps getting rust on the inside of the tube which makes it hard for me to put my seat post up and down.

I got the inside of the tube faced (sorry I don't know the correct word, it was lightly sanded down using a special tool and drill) this got rid of the surface rust and made the seat tube nice and smooth on the inside. This was fine for a few months but now the tube has become rusty again and it has become very hard to adjust the height of the seat post.

I have a 631 steel frame and carbon fibre seat post and an anodised shim which I think is made from steel too. I used to use carbon assembly paste on all the interfaces but now only use silicon grease.

So any advise on how to stop or reduce the corrosion?

Do I just need to use more grease? is there any other things I can do to reduce this from happening or is this simply what happens with steel frames?

nicklouse

if you are using a shim then there should be no issues as the seat post does not touch the seat tube.

shims tend to be plastic or aluminium.

jairaj

I may have the shim material incorrect.

But regardless, both the shim and the seat post are stuck pretty tight in their positions. I have to give it a real good tug to make it it move.

My theory is that the corrosion is decreasing the inner diameter of the seat tube causing the the shim to still clamp onto the seat post even when the seat post clamp is fully slackened off?

From what you are saying Im lead to believe that should not be happening? Should I try a different shim?

Anonymous

Sounds like bi-metallic corrosion. The aluminium shim binding to the metal seat tube. Stick some grease, anti fretting paste, or copperslip on it, and re-assemble.

jairaj

I already use grease or carbon assembly paste on it.

Sounds like Im just unlucky?

I'll clean everything out again, try a new plastic shim and LOTS of grease? and try to clean and re-grease more often ... ?