Brompton saddle height adjustment tube

[Mike1962]

Hi,
We've just bought my wife a used Brompton. I want to fit a new saddle height adjustment tube to the bike, but there's already a plastic insert in there. It looks different to the one that I've bought so I'm wary of taking it out. The new one won't go in with the old one in. If I take the old one out I can't set the seat height.

Any advice?

Mike

[drossall]

I'm slightly confused. The tubes are an optional fitting - without them, you can set the saddle height across the full range, but it's a pain getting the height right every time (remembering that I fold my Brompton four times a day, and there's nothing unusual about that). You wouldn't want two in there; for one thing, there's a catch/hook that stops the tube falling out all the time, and that can obviously only be in place for one tube at a time. For another, you'd have to be really short to need two one above the other, as they are long enough uncut to give a fair range of adjustment. Or do you mean one inside the other, in which case the seat post wouldn't fit because the diameter of the inner tube would be compressed?

There shouldn't be any harm in removing the existing one, and it would be easy to put back anyway. Just remove the saddle, drop the seat post out of the bottom of the bike, and unclip the tube.

If I'm not understanding, a photo always helps.

[Mike1962]

The tube that was in was actually glued in. there is a rim in the plastic that locates in the groove round the clamp.
The seat tube won't go in with the original in and the new one inside. If I take the old one out the new one just falls through and doesn't locate.
I'm wondering if, because ours is older, the design has changed?
https://photos.app.goo.gl/jS91ywXbcKGGJvjcA
https://photos.app.goo.gl/uuC7H9Sm6SUnPFcKA
https://photos.app.goo.gl/VqSd4X6AjBzjXDbW8
https://photos.app.goo.gl/T6h7JHh84gTS8Qrc7

[Pneumant]

What you have actually removed is the brompton seatpost shim, this is bonded into the frame and your seatpost won't stay in position without it! You will need to bond this essential part back in place. Don't even think of clamping up the seatpost without this part fitted!!
The height insert can only be fitted by removing the seatpost from the frame assembly, undo the saddle pentaclip and then pull <down> out of the frame bottom bracket end first. Once the seatpost is removed measure and cut the insert to size. The insert actually buts up against the part you have removed and determines max seatpost extension.

[drossall]

Should have spotted that was what you meant. There's advice on replacing it from Brompton - it is a part that can wear and need renewal. Officially I think you're supposed to have a dealer do it, though I've certainly seen instructions around about how to clean up the seat tube before fitting a new insert.

May be better to fit a replacement than to try to refit the old one.

[Mike1962]

What you have actually removed is the brompton seatpost shim, this is bonded into the frame and your seatpost won't stay in position without it! You will need to bond this essential part back in place. Don't even think of clamping up the seatpost without this part fitted!!
The height insert can only be fitted by removing the seatpost from the frame assembly, undo the saddle pentaclip and then pull <down> out of the frame bottom bracket end first. Once the seatpost is removed measure and cut the insert to size. The insert actually buts up against the part you have removed and determines max seatpost extension.

Ah, OK
On Youtube it looked like it fits inside the shim.

[Pneumant]

Might be for the best to fit a new shim. Part detailed below, solitary review of this part recommends an 'alternative' to the factory adhesive, Brompton also recommend reaming of the seat-tube by a dealer prior to fitting. The review says that this was not necessary.
https://brilliantbikes.co.uk/brompton-h ... sleve.html
No criticism implied but I think that youtube videos are good at 'showing' but maybe less good for encouraging independent thought about the task in hand. Having said that I do agree that Bromptons are unlike other bikes and have many unique components which are assembled contrary to expectation - the plastic shimmed seat post being a case in point.