allout1

Every day I put some medium thread locker on the bolt, tighten the seat post bolt back up, and then in hours it's all loose again. It's insane.

What am I doing wrong?

Last bike I was riding did this too. I don't remember ever having this problems with bikes in my life before.

JohnDThompson 

Hard to determine via remote viewing. Wrong size post? Insufficient torque?

freeranger

Is the bolt loosening also (you said it's ALL loose again)? If the bolt is loosening, is the bolt threaded all the way to the head of the bolt, or is there a non-threaded portion? If there is a non-threaded portion, maybe it's not threaded far enough up the bolt to allow it to sufficiently tighten. Do you have a collar for the post-if you do, make sure the tabs on the collar aren't touching when tightening. If none of that is the problem, and the post is the correct size, check for any cracks in the seat tube. As JohnD said-hard to tell w/o pics.

cb400bill

Thread moved from General Cycling to Bike Mechanics.

HillRider

You should never need thread locker on a seatpost clamp bolt. You have a fundamental problem with either the seatpost size, the condition of the bolt or how you are tightening the clamp bolt.

le mans

Yep, first thing you need to check is to see if the seat post is the correct size for your seat tube

le mans

what i do with troublesome bikes is, remove that seat post, panel beat to collar clamp if need be, then bring my box of seat posts out and check them by feel, it shouldn't too loose or too tight when slid in, even if there's a bit of play it's too small i found

once i've selected the right one, the clamp doesn't need to be tightened that much to get a good grip

fietsbob

In addition to John's, - Wrong size post? Insufficient torque?,- there is badly machined seat tube bores ....





Update, turns out it's the top end , the head of a $5 seat post...





....

_ForceD_

Rick

I have had seat post slippage but never had the the seat post collar bolt come loose. My current bicycle is the only one that had the slippage problem. A better collar and the assembly grease did not fix it. I purchased a Nitto seat post and a a seat post shim for the diameter difference. This solved the slippage.

cambiker71

A simple thought, where is the clamps open section in relation to the frame? The open or bolt side of the clamp should be on the same side as the slot cut into the seat tube to allow it to close up. if it's the other way round it won't grip properly and will keep appearing loose.

CliffordK

Post some photos to your Gallery/Album page. Direct rear shot?

https://www.bikeforums.net/g/user/497031

If the bolt is loosening, then it should be twisting. Determine this by marking the bolt and the frame with a sharpie (both ends?).

Stripped bolt? Stretching?

Lots of good ideas above to check post fitting,and an auxillary clamp to keep the post from sliding down. Also, if the clamp is a separate ring over the seat tube mast, then there are some two bolt rings that you can buy.

I know, playing with fire, but I'm not a big fan of lubing the posts, especially if using like materials together; aluminum (anodized) + aluminum, or Carbon + Carbon.

allout1

It's really as you would suspect for an older bike. Plain ole bolt with threads top to bottom and a regular nut.

But I thought of the solution while reading your reply. Just run to Home Depot, and grab that kind of nut with the plastic in it to keep it from spinning free. I forget what they are called now. Hehe. And probably put the ole one and the new on on there at the same time. The bolt is long enough. That'll probably do it.

I'll try to get pics on here to make the thread much more "moral to the story" for the next readers.

allout1

Just a simple ole seat bolt and post set up. Every day I have to tighten back down. I didn't get in Home Depot to grab the nut with plastic stop inside today.

freeranger

Looking at the pics, I think I may have misunderstood the problem. Is it the clamp that holds the seat that is coming loose. I'm guessing it is, from the pics. If that is the case, are the straight portion of the rails in the clamp--looks like the clamp might be too close to the nose of the saddle, and maybe partially on a bend in the seat rails?? The clamp doesn't seem to be sitting "flush" on the seat rails in the pics. If the clamp is spread where it won't tighten on the rails, even if on all straight portion of the rails, you may need another post, as if the clamp has spread, trying to bend it back to where it would tighten may weaken it to where it won't hold good when tightened. Make sure the clamp is on the straight portion of the seat rails only, and not partially on a bend in the rails.

Andrew R Stewart 

These types of post/seat clamps are known for their bending under clamping pressures, the lower half of the clamp is just simple stamped steel and it gives under the clamping pressure. Often when loose the seat's movement will cause the clamp's serrations to be worn smooth, further worsening the clamp plate's bending as then even more clamping pressure is needed to keep all stationary. I suspect a replacement clamp set of plates will be needed, but good luck finding any that are not take offs from another post of the same model.

For the cost of a replacement post the problem can be fixed. Hint for future- check the clamp bolt's tightness before it loosens and the clamp will last far longer. Andy

fietsbob

Its bottomed out and deformed, you should go shopping for a much nicer seat post , many out there

even a basic tubular one with a separate saddle clip will be better ..

le mans

reckon everybody did there Lol

allout1

Okay, so it's called a lock nut. It's got the nylon donut in it to grab on the bolt, so it don't slip up. I'll try that now. See how it goes.

Rick

The bolt loosening had me scratching my head. As with everyone else I did not know why a bolt would loosen like that. Having had no info worth sharing I did not post until now. When I put a Brooks seat on my Burly tandem the seat would slide back no mater how tight I made the bolt. I solved the problem by shimming the seat rails with cut up pieces of aluminum cans. I also used aluminum shims between the handlebar and stem clamp on my custom chromoly Salsa stem . Neither have slipped or moved in over 29 years.

fietsbob

It won't help your Deformed >saddle rail clamps< it's the deformation that is the issue ..

as finally shown in 14 post.. Pictures of removed post upside down,

apparently from the saddle rails moving , with the clamp bottomed out.

not a fan of those seat posts , but fitting an expensive, well mad e, one
is not in the parts pick until bottom line of bike is much higher..

As I mentioned above in all diameters those tubular seat posts are a Good basic component

Put another $35 out and the saddle clip from Brompton the British folding bike company..

called the Pentaclip (5 main parts) is Excellent..



...

allout1

Nope, locknut is not working. Going with the new post and clip this time.

Charliekeet

Ditto!