jackb

My adult son has a 2022 Trek Checkpoint SL5. On the last few rides the seat post slips down a bit. He brought it to a Trek dealer in Seattle, who put on some kind of gritty grease to keep it from slipping. that didn't work and he is now home in Missoula, where he brought it to another Trek dealer. This dealer greased the tightening screw in case the screw was binding before actually tightening sufficiently around the seat post. This did not work. So the dealer is contacting Trek to see what they have to say. Any ideas? I would think that the first thing ought to be changing in seat post, but the dealer has not tried that.

veganbikes

What I would recommend is measuring everything with a set of calipers and confirming everything is correct. Then if everything is correct I would clean everything throughly including inside the seat tube and using carbon paste (the gritty grease) and using a torque wrench to torque it down to spec and try that. If it isn't correct then I would figure out which part isn't correct and purchase that part in the correct size and then do the above.

I would see what Trek says as well. It is their bike and they might have found an issue and this could be covered and likely should be covered under warranty if new parts are needed assuming nothing is damaged or your son hasn't done anything out of spec to damage something (not saying he did).

soyabean

If that bike is going to be stored indoors, wipe down that seatpost and seattube with gasoline and get it bone dry.

A premium bike like Trek shouldn't need any lube at all on the seatpost

When there is a lube on any seatpost, the seatpost clamp has to fasten with more force. I've seen plenty of M6 bolts snap due to that.

maddog34

from the web... WARNING:

Does epoxy react with gasoline?

Epoxy is not resistant to gasoline, ethanol, kerosene, diesel fuel, and jet fuel. Epoxy is also not resistant to brake fluid.

If you are planning on using epoxy in a space that contains any of these chemicals it’s important that you take steps to ensure it won’t react with them and cause harm or damage to the object being coated with epoxy.

Carbon fiber parts are made with Carbon Fiber Material and EPOXY.

HillRider

After over 60,000 miles the Thomson seatpost in my Litespeed Tuscany began slipping. It had never done that before and I always kept it greased and torqued to spec. Removing, regreasing and re-torqing didn't help. Over-torquing didn't help. I replaced the factory seat tube clamp with a Wolf Tooth and that didn't cure the problem. The real solution was to install a stainless steel radiator clamp fastened very firmly on the seatpost as a travel stop and that cured it. Why a properly sized seatpost that held its position for 60,000 miles suddenly started to slip is still a mystery.

soyabean

Wouldn't that be the same as a double seatpost clamp?

An area of the clamp that clamps on the seattube, as with all bikes with seatpost clamps.

And an area of the clamp that clamps directly to the seatpost.

HillRider

Yes it would be but I didn't see one of those when I was looking to replace the OEM clamp. I thought the Wolf Tooth would hold better but it didn't and I went to plan B, the radiator clamp. The benefit of the separate clamp is that if I remove the seatpost it serves as a depth-stop/ height reference.

Polaris OBark

Here is a unique solution. (Link goes to RoadBikeReview, but this is worth it.)

maddog34

and.... it will keep the post's Finish Happy!

79pmooney

Something to look at - with the seat pin tight, does the gap at the back of the seat tube close completely? If it does, you can continue to tighten the seatpin until it breaks or something else bad happens ant you aren't getting any more pressure on the seatpost.

It was common in the years of metal bikes to simply saw down with double hacksaw blades or the like to restore that slot on older, tired seal lugs.

FBinNY 

The first rule of diagnosis, both mechanical and medical is to ask what changed?

If he's had this bike a year without the problem, and now does, is very different than "its always been this way".

So if something changed, then what? If it's always been a problem, then possibly an undersized post, or a frame reamed beyond spec.

If it's a new issue, and you haven't changed anything, I'd suspect a new, unknown crack in the clamp area.

FWIW- a correctly fitting post has near zero clearance. It will NOT slide in easily, and ideally need a bit of gentle twisting to work up or down.

jackb

Thanks for all the responses. I'll past them on to my son and post the solution after he finds it.

Kontact 

Bad idea. Always use something in there to prevent the post seizing in the frame.

squirtdad

gasoline should pretty much not be used ever on a bike, too flammable to start with, and there are better solvents to use

seat posts should not be dry, for steel and alloy grease or anti seize have been the standard.

I just got a custom steel bike. to my surprise the builder recommended seat post paste like this https://www.parktool.com/en-us/produ...compound-sac-2 as in his observations, seat posts are a bit smaller than they used to be because carbon bikes are not as precise as machined steel.

seat post paste has been the common recommendation for carbon bikes for years

easyupbug 

In difficult cases I have mixed valve grinding compound with grease or anti-seize depending on the application.

Pop N Wood

I vote get a new seat post.

cyccommute 

I’ll preface this by saying that using gasoline as a solvent is stupid! It’s more stupid than slathering yourself with honey and then finding a bear and poking it with a stick. Eating Tide pods is less stupid. Participating in just about any of the incredibly stupid hot ideas on Tiktok are less stupid than using gasoline as a solvent. Hell, walking into the Chernobyl reactor and picking up a fuel rod is probably less stupid.

That said, epoxy is an incredible stable material that stands up to most all chemicals. According to the Engineering Tool Box there are very few chemicals that epoxy can’t handle. Notably, ketones…of which acetone is one…are not recommended but all of the chemicals listed above, with the exception of brake fluid, have excellent resistance to epoxy.

I will reiterated again: DO NOT USE GASOLINE!!!! If you insist on doing so, make sure you have a will, make sure your house is paid for (insurance won’t cover stupidity), make sure you alert the fire department, and put up a giant sign saying “I’m stupid. I’m using gasoline in the garage” so that the fire department knows where to look for the body.

Better yet, just get out that tub of honey and find a bear.

icemilkcoffee 

Looks like this bike uses a 27.2mm carbon seatpost. Just replace the carbon seatpost with a generic 27.2 aluminum seatpost. Smaller diameter Carbon seatposts are notorious for slipping. Just like 26mm carbon handlebars- they will slip.

Iride01 

Let us know what Trek said or offered as a solution.

This is the original seat post that came with the bike when new isn't it?

jackb

The bike is a year old and is the original seat post. My son hasn't yet got back to me about what he has done since I passed on to him the info that all the responders to my post gave me. When he does I'll post his results. Thanks again.

Iride01 

I don't know if it got sufficiently answered, but the gritty grease they put on it is probably what we call carbon assemble paste. Carbon parts are a little more slippery than steel, aluminum and other stuff. Especially since we can't use the same amount of clamping force with out destroying the stuff. So the paste is gritty to give a bite for the things being clamped together.

You might check that someone didn't think the seat post didn't slide smoothly and easy enough in the seat tube and did something like sand their surfaces to make them feel smoother. Many people wanted they steel seat posts to operate like a precision piece of machinery and would ream and sand them. But steel bikes had the ability to deal with that, most carbon bikes are not built with that much ability to clamp anything that is no longer the correct size.

mpetry912 

golly you guys, don't set your garage on fire

and forget "gritty grease". it is worthless. Mouse milk.

jackb have you got a center punch ? just take your seatpost, mark where it goes into the seat tube / clamp area with a sharpie, and use your centerpunch to make some "dimples" so that the clamp has something to bite on. Set up some interference below the point of insertion

I have not tried this with a carbon post but I might be tempted to try it. works great on aluminum posts.

you could also try a shim, just a little one, to give it some more bite.

good luck and report back

/markp

Schweinhund

And since, from the recent news about a carbon fibber submersible collapse and delamination effects on carbon fibber and high pressure water should people be aware of any type of compromise on the surface epoxy and seal it?
\My water hose has surprising pressure, and with a fireman's nozzle on it it'll blast stuff pretty clean alone. I'd hate to delaminate something and cause a crash.

maddog34

I've had a Marin CF bike here that had extensive Water Damage.. it had a few scratches, then got left out in the weather... the Water seeped into the CF material, then it Froze... many large delaminations occurred... that frame went to the dump, in pieces.

maddog34

you would ruin a CF post by doing the dimples thing. the epoxy would micro-fracture, not deform. you wind up with dust instead of dimples.