Brompton Seat Post sleeve

[Fastpedaller]

LW &B and Berlin summarise the situation very succinctly. It would seem important to identify and fix any issue with seat pin dropping early on. Tightening the clamp may only make the situation worse in the long run. The seat tube can be 'off round' either from the outset (heat distortion from brazing) or by being over-clamped. I concede my idea (bodge) of trimming the outside of the sleeve (if necessary to make it fit around the seat pin) could work, but will never be the same as reaming the hole. When I measured the seat tube length I was astonished to find how short it is (shows how well I know my bike) I estimate an adjustable reamer of total length 285mm would just be able to do the job, given it would have adjustment facility on the end, and a square on the other end to fit the wrench. A fixed reamed of less length (270?) could also be used. Anything shorter would be a struggle - I wouldn't relish using a socket poked into the seat tube to rotate the reamer, but it could be done.

 

[ExBrit]

The Ti-post may be one factor, the other may be the condition of the saddle tube and the seat post. If they are round and have not been overtightened pre reamed may work - that's probably why Brompton offered it in the first place: To make in time maintenance less stressful, cheap and easy.
On the other hand: If you are late to the party your seat post may even wobble in the frame with the clamp open. A pretty sure sign that something is seriously wrong.

I would pay close attention to what Berlinonaut says. I suspect he is actually Will Butler-Adams with a fake German accent.

 

[ukoldschool]

Lets all face facts, the sleeve is a poor way to try and stop the seat post slipping. It would probably work better if the seat post itself was knurled instead of polished chrome... but the reality is you can install a new sleeve, ream it to factory spec, scrupulously clean your post and ensure your seat post clamp is operating exactly at Brompton specification and the seat post will still slip, because its a terrible design, necessitated by the design of the bike. Some blame for slipping is obviously dictated by the weight of the rider, and the conditions they ride in and on (bumps, hopping of curbs, rain, sleet, snow etc...)

The second seat post clamp is the cheapest way to try and eliminate slippage, but yes it does chip your paint around the top of the seat post.

 

[T4tomo]

@Fastpedaller FFS I got my sleeve fitted and reamed for £15 (he was replacing a spoke and truing a wheel at same visit) but its not an expensive job as its quick to to do if you have the right tools. Take it to someone who knows what they are doing, not only will it be done correctly, it will be cheaper than your DIY bodge.

 

[Fastpedaller]

@Fastpedaller FFS I got my sleeve fitted and reamed for £15 (he was replacing a spoke and truing a wheel at same visit) but its not an expensive job as its quick to to do if you have the right tools. Take it to someone who knows what they are doing, not only will it be done correctly, it will be cheaper than your DIY bodge.

I don't disagree with your logic. If I can get a reamer for £30 or similar, (which appears to be the case) I'll be doing it myself when the need arises. I'm afraid I wouldn't trust anyone locally to us (Norfolk U.K) to work on any of my bikes (or cars for that matter).

 

[berlinonaut]

Lets all face facts, the sleeve is a poor way to try and stop the seat post slipping.

The intention of the sleeve is not to stop the seat post slipping. How should that work?

its a terrible design, necessitated by the design of the bike.

So basically the whole Brompton is a terrible design in your eyes?
I am curious: Why do you think it has a sleeve at all?

 

[brommieinkorea]

The seatpost sleeve and the seatpost slipping problem is one of the few flaws with the design of the Brompton. I own 4 Bromptons and they have all had a slipping seatpost from the start, all purchased new, I weigh 70-90 kg. The only thing that helps is a 31.8mm seatpost quick release clamp ,with the lip filed off ,stuck on the seatpost. Really there should never be wear on the sleave due to the loose fit, but it is a bad design because it is plastic.

 

[berlinonaut]

I own 4 Bromptons and they have all had a slipping seatpost from the start, all purchased new,

Sounds rather like a not so competent dealer or mechanic... There are 100.000s of Bromptons out there that don't have a slipping seat post...

Really there should never be wear on the sleave due to the loose fit, but it is a bad design because it is plastic.

Possibly you should rethink again why they may have went for that solution.

 

[brommieinkorea]

Sounds rather like a not so competent dealer or mechanic... There are 100.000s of Bromptons out there that don't have a slipping seat post...

Possibly you should rethink again why they may have went for that solution.

Cheap. The design also bends the steel in the rear of the seat tube(this causes unnessesary fatigue). But, a proper locking mechanism would require considerable more machining and mill work to execute i.e. more cutting welding (i know they're brased) etc... My collection of Bromptons don't come from the same shop, nor are they even the same year or model.

 

[Tenkaykev]

We have five Bromptons, 2x 2015, 1x 2019, 1x 2020, 1x 2022.
I’ve only ever experienced seat post slippage on the 2019 Brommie, and that was after fitting a Titanium seatpost. I gave the clamp screw a 1/4 turn and it’s never slipped since. Perhaps I’m lucky🤔

 

[ukoldschool]

The intention of the sleeve is not to stop the seat post slipping. How should that work?

So basically the whole Brompton is a terrible design in your eyes?
I am curious: Why do you think it has a sleeve at all?

Oh I just knew you would bite

Where exactly did I say the brompton is a terrible design? I said it was "necessitated by the design of the bike", ie its a folding bike, it has to have a seat post that slides up and down, hence the insert....

I honestly think you could start a fight in a paper bag

 

[rogerzilla]

I've only ever had a seatpost issue when I did a very wet BWC on a stripped-down bike without mudguards. Gritty mud on the seatpost does not make for easy folding. When I got home, I took the seatpost right out and cleaned it all.