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Seatpost Diameter for 1984 Trek 400

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Seatpost Diameter for 1984 Trek 400

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Old 01-13-19, 11:02 PM
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amerikaner
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Seatpost Diameter for 1984 Trek 400

Have an '84 Trek 400 frame and cant figure out seatpost diameter...tried a 27.2 and would start to go in but was really tight. then I tried measuring with my digital calipers but measurements were between 26.6 to 27.1 (cheap Harborfrieght one). Also, checked Vintage-Trek, but could only find info for '89 and newer 400 series which varied between 26.6 and 27.2.

So is it a 26.6 or 26.8 or 27 ???

Thanks!
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Old 01-13-19, 11:16 PM
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My 87 should be 27.2 by all accounts. It is perfect at 27.0.
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Old 01-13-19, 11:59 PM
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Flex ball hone?
If it goes in part way and stops it sounds like it needs cleaning
https://www.rockymountainatvmc.com/p...nder-Ball-Hone
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Old 01-14-19, 12:36 AM
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That bike, that year: dunno.

But about 1/2 the vintage bikes I find in my shop were, at sometime, pinched down to fit a smaller seatpost and take some spreading and honing to make right again. It's absurd how common this is. I guess I get a lot of bikes that were stripped at some point? And then re-assembled by an indifferent builder?
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Old 01-14-19, 10:10 AM
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'87 used a 531 main triangle in its 400 model. My seatpost is 27.2.

But the '83 and '84 400 models used tange 2001 db mangalloy.
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Old 01-14-19, 12:51 PM
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an excerpt from the vintage trek site...

Seatpost Diameter - Nearly all road Treks prior to the mid 90s have the standard seatpost diameter of 27.2mm. Exceptions are Models TX200 and TX300, which have a diameter of 26.8mm, and the Model 170 at 27.4mm. Additionally, a 1985 Model 2000 (aluminum bonded frame) with a 27.4mm seatpost has been reported.
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Old 01-14-19, 03:38 PM
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IIRC, the 1984 model 400 was a Japan-brazed frame, and may have used a 26.8mm post. Most of the Waterloo production (except the off-road frames) used 27.2mm posts.
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Old 01-14-19, 08:44 PM
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I have an '84 400. 27.2 seat post and it's pretty snug. I honed mine. fit's fine.
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