Posted on Road Bike but no answer. Have an old aluminum Schwinn Super Sport and a new carbon fiber seat post, what can I use to put between the two. Grease? I don't want a chemical reaction as some products ruin the resin on the carbon. Vasaline? Dry? I realy don't know about this new stuff, I've worked on bikes 25-30 years, don't know s*** about carbon.

Generally, people advise against greasing carbon fiber, though you will find disagreement on this. The fear is that the carbon composite will absorb the grease and swell, causing a stuck seatpost and damage. This is especially true on carbon frames, where the inside of the seat tube is bare carbon with no protective clear coat. In your case the frame is not carbon, so that's not an issue, and the seatpost itself probably does have clearcoat. But unless the seatpost manufacturer specifically says it's okay to use grease, I'd err on the safe side and use an assembly compound specifically designed to be safe for carbon. These include Finish Line Fiber Grip, Tacx Dynamic, and a few others. These are usually made of some kind of gel with a gritty substance added to prevent slippage. Hopefully, they're also effective at preventing oxidation at carbon/steel or carbon/Aluminum interfaces as well.

Also, grease can make carbon seatposts really slippery (from what I've read anyway...I've alway used Al seatposts). With carbon you have to be really careful not to over-tighten the seat clamp, so the combination of super-slippery post and limited clamping torque means in some cases it can be nearly impossible to keep a greased post from slipping.

Pipe thread compound, would that work. It gives grip but parts can still be removed. It doesn't contain solvents and keep the post from squeaking on hill climbs.

Toothpaste?

Here is a thread about carbon paste. Consensus seems to be carbon paste or nothing. Carbon paste helps increase friction and reduces amount of clamping force required.

https://www.bikeforums.net/showthread...t=carbon+paste

I dont think toothpaste would do anything to carbon but I don't know what it will do to aluminum.

I understand that the paste is used to prevent a reaction between the carbon post and the aluminum frame, which will cause a stuck seatpost.

So you should use carbon specific paste.

Read this and learn all you ever wanted to know about carbon assembly paste.

https://www.competitivecyclist.com/re...Paste.388.html

Jashrr THanks I didn't truly understand the reasons for the carbon paste, so a carbon frame use paste and aluminum dry. No chance of a seized post.

The article above says they are using it even with lightweight aluminum parts. It is just grease with plastic balls in it apparently, so it is not going to hurt anything.

Grease will not hurt the carbon. Many carbon parts are greased in the normal course of their use. Indeed greasing is essential in open press fit bottom brackets, headsets, bolts into carbon threading, etc.
Carbon paste is merely grease with a friction additive to prevent seizure, but at the same time to increase friction in areas that need it, such as seatposts, handlebars on stems, etc.

Carbon as a bike material is more stable and inert than probably any other material used on a bike today. It is probably the last material that will be effected by most any type of solvent or oxidizing agent (normally used or contacting a bike). Although I would defer to an expert on this last part. But safe to say that grease will not harm your carbon bike parts.

1) Get some carbon paste, but until you do,

2) just assemble the post in the tube clean and dry.

3) after assembly, brush on a fine layer of waterproof grease, or whatever grease you have around the seatpost/seattube/seatclamp junction to seal it up from water infiltration.

HTH
zac

do not assemble dry. you will regret it. grease is not advised because the post can slip. when it slips people want to tighten the collar more leading to crushing the post. use carbon paste.