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Bontrager Stem Adjustment

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Bontrager Stem Adjustment

Old 04-05-12, 07:37 AM
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Bontrager Stem Adjustment

My Trek 1.1 has a stem I'm not familiar with, and my new manual won't be here for a few more days.
It's a Bontrager sport stem, and it looks like it clamps to a large tube with 3 spacers below it, and a cap on top with a hex screw. It looks like I should take the cap off, loosen the clamps, then re-arrange the spacers to adjust height. If I do that, am I left with a big stub sticking up? Does the screw on the cap allow the stem tube to move up and down?

And finally, why did they do it this way? It looks a lot heavier than a regular type stem.
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Old 04-05-12, 07:43 AM
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ummm... that is the same threadless system that has been used on most production bikes for the past decade. The top cap sets the bearing preload and the pinch bolts on the stem hold it tight to the steerer. Yes, you can change the height of the stem by moving the spacers over the stem, but the only way to shorten the steerer would be to cut it. Actually, it is lighter and easier to maintain than a threaded headset with a quill stem.
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Old 04-05-12, 07:57 AM
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Originally Posted by demoncyclist
ummm... that is the same threadless system that has been used on most production bikes for the past decade. The top cap sets the bearing preload and the pinch bolts on the stem hold it tight to the steerer. Yes, you can change the height of the stem by moving the spacers over the stem, but the only way to shorten the steerer would be to cut it. Actually, it is lighter and easier to maintain than a threaded headset with a quill stem.
My newest bike, before this one, was a 1994 so I'm waaay behind the times. Does the cap need to be removed? Anything special I need to know about setting preload?
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Old 04-05-12, 08:32 AM
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Yes if you want to move the stem down you end up with the washers and steerer sticking up above the stem.

"Preload" is just a fancy way of saying adjusting. To adjust/preload the bearing on this type stem/headset you loosen the two bolts on the stem and use the bolt on the cap to loosen or tighten the HS adjustment, then tighten the stem clamp bolts.

I am sure there are dozens of videos on Ytube about this.
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Old 04-05-12, 08:51 AM
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If you want the bars significantly lower you can "flip" the stem over to reduce it's rise.

Also to lower the stem you can, and should, remove one spacer from under the stem and place it on top. Then install the top cap on top of that spacer, snug it's bolt to adjust the headset preload, center the stem over the front wheel and tighten the stem clamp bolts. More than one spacer's worth of change will probably require shortening the steerer tube

And, yes, current threadless stems are significantly lighter than their quill predecessors.
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Old 04-05-12, 12:09 PM
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I appreciate the replies. I hope that manual comes soon. My copy of Anybody's is almost 40 years old.
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Old 04-05-12, 05:02 PM
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Originally Posted by WickedThump
My newest bike, before this one, was a 1994 so I'm waaay behind the times. Does the cap need to be removed? Anything special I need to know about setting preload?
That kind of stem/headset design is called "threadless" and actually is the regular design nowadays.

Look on the Parktool website repair tips section under headset service for pretty easy to follow directions on how to put the parts together and adjust. There are several variations of threadless headsets, but the principles are the same. If you have any questions, repost, most people here are familiar with them. If you understand how they work, they really are very simple to deal with.
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Old 04-05-12, 05:12 PM
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https://www.parktool.com/blog/repair-...eadset-service
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Old 04-05-12, 05:24 PM
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Originally Posted by Camilo
That kind of stem/headset design is called "threadless" and actually is the regular design nowadays.

Look on the Parktool website repair tips section under headset service for pretty easy to follow directions on how to put the parts together and adjust. There are several variations of threadless headsets, but the principles are the same. If you have any questions, repost, most people here are familiar with them. If you understand how they work, they really are very simple to deal with.
Thanks!
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