Trek Domane Front IsoSpeed knock?

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Tinker, Taylor, Tart
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by RichTheRoadie

I searched on this - a similar topic came up which I have responded to, but there’s been no comments on that since so I wanted to start a more specific thread.

In Trek’s instructions for the front IsoSpeed on the Domane they say to tighten to 10Nm (I presume to compress the headset components down correctly) then back off and re-tighten to 4Nm.

I have done this, but it results in a knocking noise when braking or hitting lumps in the road. Tightening beyond 4Nm lessens the noise, but you’d need to go pretty tight to eliminate it - which I don’t want to do in case of invalidating the warranty etc.

It’s definitely not the headset knocking, but it is a similar sensation and noise. Looking at the setup of the system, it looks like it could be the top headset bearing moving in the IsoSpeed cup.

Anyone know a fix?

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by Calnago

Hmmm.... I’m not sure there is a “fix”, but I would think you’re on the right track with just tightening it down more until the knocking subsides. The initial tightening to 10Nm is just to make sure you get all the slack completely out of the system to start with. If you’re using a torque wrench and the final tightening to 4Nm isn’t cutting it then I’d take it to 5Nm. And keep going till it stops. And I’d definitely call Trek for their thoughts in the meantime.
I looked at this system pretty closely when it came out and immediately imagined future scenarios like you describe. A whole lot of potential for creaks and knocks in there... for what... I just couldn’t imagine the benefit, if any, justifying the added complexity of it all. Still can’t.
You say it sounds like “knocking” but it’s not. I would say it probably is knocking, just not in the sense that you you’re used to... a simple loose headset. Same thing here, it’s loose, but not simple. There’s just so many more parts interfacing that if it’s at all loose there’s more places for knocking to occur. Good luck.
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by TheKaiser

Yeah, assuming it is practical in your location, I'd say take it to a Trek dealer. Hopefully they can resolve it, but, if not, then they'll be the ones to have messed it up rather than you, which is better from a warranty perspective.

The 2 possibilities that jump to my mind are opposite in cause but similar in effect:

1. Something might be too tight a fit and binding up in the overall stack of parts, which is preventing the 4nm preload from effectively compressing the entire stack. In other words, you apply 4nm at the top, but only (hypothetically) the equivalent of 2nm is trickling out at the lower parts of the assembly. This could be due to too tight a fit in something that needs to slide, like the stem on the steerer, or headset part on steerer.

2. Something might be too loose a fit. I have seen this with things like older Chris King threadless headsets, which didn't use a tapered wedge, but instead relied in the top race being a perfect fit on the steerer. With a slightly undersized steerer, the steerer would knock back and forth in the headset race when a normal amount of preload was applied. You could kind of alleviate the knock by overtightening the assembly, so that friction between the other parts would sort of stabilize the steerer, but it was imperfect for sure.

If you bought the bike used, and have no warranty, then I'd try taking the whole thing apart and checking the interface and fit of each component. If something is obviously too loose, then certainly order a replacement part, but if nothing is clearly wrong then I'd try reassembling it with a very thick and viscous lube which would help both scenario 1 and 2 as it will both ensure smooth movement of the parts against each other and take up a slight bit of space in parts that might be a hair too loose.

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by RichTheRoadie

Sorted it!

There’s a sleeve that goes into the assembly to fill the space where the IsoSpeed decouplers are and give the internal stack of the headset something to press against in the absence of bearing cups - it would appear that this has to be in *dead straight* to avoid interfering with the IsoSpeed elements. It was slightly skewed; and therefore probably causing the knock (I clearly didn’t pay enough attention to this when I disassembled the headset late last week).

Straightened that, reassembled to the recommended torques and the knock has gone.

Thanks for the replies folks!

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