Chris Chicago

I have an 82 trek 610 I've been riding since spring. recently noticed the seat was lower than I'd like so I loosened the bolt, raised it and tightened. but I couldnt get it tight enough to hold the seat in place. then I noticed the collar was touching in back, ie it appears it can not tighten further. I also noticed a crack next to on side of the bolt. pictures are below, any advice on my next step much appreciated.

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wrk101

Get to a bike shop now. Your seat post appears to be TOO small. Overtightening is the result. Find a good one, and they will get you squared away.

Seat posts come in 0.2mm increments. Getting the right size is critical. There are 25.4mm in one inch, so 0.2mm difference in diameter is tiny (approximately 1/100th of an inch), but it matters on bicycle seatposts!

Chris Chicago

hmm. thanks wrk101.

by the way, you know who I bought this from....? that dude who was selling the big lot of bikes you were going to drive up to chicago and buy for 5k or whatever last winter. he built it up. carelessly apparently. or is this an easy mistake to make?

Chris Chicago

oh also, what will they do to fix it? figure out the right size or is there more to it with that issue around the bolt?

FBinNY 

This is fixable, but not cheaply or easily because the ears are buckled. Step one is to spread the lug so the tube is back to the original size and shape, ream it, and fit the correct post. Now cross your fingers.

You might get away with painting the post with the carbon seatpost stuff which will improve the hold and lower the clamping force needed. Or by using coarse lapping compound which will tremendously improve clamping force.

More likely you won't be so lucky and the ears are so weakened that they'll buckle more when you tighten the bolt.

The standard fix is to reshape them, clean them up and fill them with braze for strength, then drill the bolt hole. This is a bit of a skill job, and will result in burnt paint for a few inches down the tubes and stays. A plastic steel type material may work, though it won't be as strong. the good thing is that it'll be simpler and not damage the paint.

It looks like a fairly generic frame and may not be worth putting much dough into, so fixing it may only make sense if you can do your own work, though nothing stops you from at least getting an estimate.

FastJake

I've bought at least 3 bikes now with wrong-sized posts. Never seen anything this happen though, it's a shame. I have a 610 and really like it.

BTW - your bike takes a 27.2mm post, as do (almost) all vintage Treks. The lesson here is that seatpost diameter matters. I hope you are able to fix it.

Chris Chicago

it kind of boggles my mind that the post pretty much held all these months being small and now this. maybe the crack happened recently and the caused the post to slip? then when i tightened it the buckling occurred?

FastJake

Probably. Too-small seatposts can be held in place with enough clamping force and frame distortion. But eventually, something has to give (as you've seen.)

How big is the current post in that frame?

Chris Chicago

that I do not know and I suspect my gerry rigged method of measuring...ie tighten an adjustable wrench around the post then measure might not capture the size accurately to .2mm. need to find out though just to understand if damage was caused by human error or perhaps just wear and tear on 30yr old frame

FBinNY 

It's hard to tell from the photo, but the post may be the right size, and the damage and crack caused by over tightening. Here's the gauge I use to confirm seatpost size correctness.

If the top of the slot of the tube itself touches or is much narrower than the bottom of the slot than the post is too small. If the slot doesn't seem pinched together, but the ears touch than it's collapsed ears caused by over tightening.

Either way it's human error, either in post selection, or excess clamping force.

Chris Chicago

I guess then I could be culpable as I set the seat height back in the spring and do not recall how forcefully I tightened it. though given my smallish hex wrenches, and overall laziness, I cant imagine I would have pushed that hard, or past the point where the post stayed firmly in place.

it blows though if this frame is ruined or is going to cost a hundred bones to repair. a lot of money and effort sunk into this bike already.

FBinNY 

Yes it might have been you, but looking at the amount of distortion, I think you were more than likely only the one who finished a process started by the prior owner. For future reference the condition of the seat lug, and the slot is the second place I check whenever considering a used frame. The first being under the down tube just behind the head lug and the third, sighting along the headtube to check for a bent fork.

BTW- if the lug or ears are cracked, braze is the only reliable fix, but otherwise you should be able to get by with DIY involving some careful forming, filing and a plastic steel product.

DCB0

Not necessarily a too-small seat post. My old steel road bike had the same problem and I know the 27.2 post I had in it was the right size. THe solution for me was to file away some metal from the place where the two sides were touching. THat was several years ago and I have not had any problems with it since.

Chris Chicago

interesting and thanks for the helpful comment. what happened to the LarDasse moniker? i remember getting good advice from you in the past under that username.

DCB0

I use several different computers in different locations and I still use both usernames depending on where I am. I'm not sure why I am doing it like that, but i am.

hkhailey

I have used this fix several times over the years with good results.

fietsbob

A less Dremel (tm) dominated fix..

if you stack up 2 maybe 3, blades on your hacksaw
that will cut a wider parallel slot.

if there is a crack, a tiny hole drilled in the end of the crack can stop it's continuation.
Note that is what they do at the bottom of the slot you are restoring..
all else a longer bolt, nut, and a couple flat washers will do
for the holding , clamping force.
get stainless steel parts for that. and it will still look shiny

ultraman6970

Dunno probably was said before, the seatpost clearly is the wrong diameter. People never pay attention to this, they just stick a seatpost in there or even the shops they just go and stick one in there, since the clamp closes it works but the problem is not solved because there is a big chance that the seatpost besides messing up the clamp it creates an indentation in the seat tube because is just floating inside and I dont know if you guys have seen this but sometimes the seat tube just give up by fatigue and just gets a straight cut out of the blue.

Im almost sure that bike uses a 27.2 seatpost and the one in place is a 26.8, to put a 27.0 seatpost is ok too but 26.8 is too much and will mess the clamp the way it did.

hkhailey thats a good call... always something new to learn

wrk101

First tool in a vintage bike mechanic's arsenal is a decent digital caliper. Measuring with crude tools just doesn't cut it. Harbor Freight had a decent one on sale via a coupon for $10. Been using my digital HF caliper for five years or more.

+1 That bike needed a 27.2mm seat post.

I've bought quite a few used bikes, and it is not unusual to see the wrong size post. I check very closely before I do any tightening.

I never could get a straight answer from that guy in Chicago, the deal was looking really sketchy. And since then, I have found quite a few nice vintage bikes in my area. So its one of those deals that I am not disappointed that it did not go through.

Chris Chicago

hkhailey, not sure I follow your first step. seems like cutting more slot would be necessary if i want to keep using the small seatpost. is that what you're proposing?

here are some more pics. does it look like jbweld and washers will work or should i keep looking for someone to braze it?

Chris Chicago

I just pulled the seatpost out and it is marked 27.2. so unless that is a mismark, maybe i tightened it too tight. though i dont remember putting a ton of effort into it or anything. and like I mentions, my hex wrenches are pretty small

hkhailey

The cuts in the first step are basically going to give you a little more room to tighten your existing seat post. Looking at the pics, it looks like the steel has stretched, that's why the left and right side are touching. It happens, and not just from the wrong size seat post. Improper set up for someone too big/tall for the frame can cause this too. (Check out some older, pre-quickrelease BMX frames ridden by full grown "kidz" sometime.) Also, frequent and excessive adjustments over time (like about 30 years and who knows how many riders) add up.


This time I noticed the slight crack at the very botom of the slot. You can either use the drill trick or just square it up with whatever you use to trim up the rest of the slot. Either way, you stop the crack and get the corrosion out.



The JB trick in the second step should work. Again, getting any corrosion and "rotten" metal out will help prevent it getting worse and also help the JB bond better.




If the seat post is snug, easy to adjust but tend to slip over time, I'd probably use sandpaper to rough up the inside of the tube and the seat post just below where you adjust it to. Then ride it for a while to see if it still works it's way down.

If the post is "really" loose, I'd take the bike to the LBS to make sure I got the proper fit. If you have calipers, take them with you. Not all bike mechs have them at work.