Saddle moving

[francovendee]

My saddle keeps moving backwards. I've tightened it twice now and it's moved again. Last time I tightened it up very tightly and was a bit afraid to go tighter in case I stripped the thread.
Are there any suggestions for a cure?
The saddle post is about 2 years old and for the first 18 months it was fine. It's a no brand bought locally.

[pwa]

The short answer is that in your position I would go shopping for a new seatpost, possibly from a good value brand such as Kalloy. It must be long enough and it must be the same diameter. The diameter should be marked on your existing post somewhere. You should not need to go blue in the face when tightening.

[Brucey]

You don't say what seat pin you have but this talk of a single bolt suggests that it is a single bolt seat pin (with serrations?). Possibly the clamp parts are hitting one another before the saddle rails are being clamped properly. You may be able to overcome this by relieving the clamp parts or by using some packing where the rails sit.

However if the clamp parts bent and this caused the problem in the first place, then it'll surely happen again, and a new seat pin is a better way forwards.

cheers

[rjb]

Mrs rjb has a single bolt hockey style seat pin on the tandem. This has no serrations and occasionally tilts rearwards. No amount of tightening seems to cure it. I roughened the surfaces with some emery which has sorted it at the moment but if it reoccurs I may resort to filing some serrated teeth on it.

[peetee]

I think that as you have done it up 'very tightly' it is time to get a new post. You really don't want the bolt to shear when you are riding.
Been there.
Not nice.

[reohn2]

I think that as you have done it up 'very tightly' it is time to get a new post. You really don't want the bolt to shear when you are riding.
Been there.
Not nice.

Agreed,the only time I had this happen when when stripped to it's compent parts I found a crack in the top saddle rail clamp part.

[Vorpal]

Have you tried wrapping something around the rails? I might try duct tape or emery cloth.

But I agree with the folks who think a new seat pin is in order.

[francovendee]

Yes it is a single bolt with serrations. I'll take it apart and take a good look for cracks and that the clamp parts aren't hitting each other. This one was inexpensive but why would a better one (Kalloy?) hold it better?

[PT1029]

If the parts that clamp the saddle rails are alloy, it might be smoothed off serrations.
If the clamp parts are pressed steel then probably the lower plate has bent down a bit (as alluded to up thread), so the bolt is no longer able to secure the rails securely. Straightening the affending part might work, but only as a short term solution as it will bend back down quite quickly.
When you gert a new seat post, get one with alloy clamp parts to prevent reoccurence.

[Brucey]

Mrs rjb has a single bolt hockey style seat pin on the tandem. This has no serrations and occasionally tilts rearwards. No amount of tightening seems to cure it. I roughened the surfaces with some emery which has sorted it at the moment but if it reoccurs I may resort to filing some serrated teeth on it.

when such seat pins are new, they often still have whatever coating was on the parts when they were made, e.g. a thin layer of anodising. Until the parts have worn against one another a little, they are that bit more likely to slip and move, because the coating is hard and slippy. Once the coating is gone, there is a lot more grip; even if they don't slip, well-used seat pins of this type normally have some dark marks (most easily seen on silver coloured seat pins), where the parts touch and no longer have their coating, and don't slide at all easily past one another; abrading those areas slightly greatly speeds up the rate at which the parts really grip one another. They grip one another not because they are roughened, but because there is no anodising there any more; excess roughening is, if anything, counterproductive; smooth surfaces that contact over a large area, grease free, gives the best grip.

Once the surfaces mate with one another, such seat pins are -in most usages- very reliable and less prone to slippage than many other types. I'd normally favour that clamp design over other single bolt varieties, and some twin-bolt ones too.

FWIW tandem rear seats are more likely to provoke slippage than normal; the saddle is often set well back, the rider often sits quite upright on it, and doesn't see the bumps coming; all these things make slippage more likely.

cheers

[rjb]

Yes that sums it up nicely. I wish I was as good with words as you clearly are. I prefer numbers.
Thanks Brucey.