Posts
91
Joined
5/10/2011
Location
whistler, BC
CA
Been battling this for awhile now, my fox 40 sounds like a creaking, popping single crown CSU. The headset is greased, upper and lower crown interface cleaned with isopropyl and torqued to spec, after a couple of laps it's sounds like a dying CSU again. Sitting on the bike I can push the front wheel into a brick wall and feel the noises coming out of the lower crown. If I undo the bolts and slide the stanchions down and clean the clamping area it's fine for another run or two and it's back to loud noises. It's driving me nuts! Anyone have any ideas before I buy a new lower crown or sell it altogether?
Try some wet sand paper, super fine, almost micro polishing paper. On the clamping area. Scotch brite the inner clamp.
What torque spec are you using? do you think the torque wrench is correct?
Anodized aluminum reacting with non anodized aluminum. I typically use a light layer of grease on both the lower crown/stanchion interfaces, the same for the upper damper drive side interface, and a light amount of carbon assembly paste on the air spring drive side interface. Torque spec is 7.34 nm. You also need to grease the head of the crown bolts/crowns.
If you grease the bolts the torque spec will need to be reduced, unless in the torque spec it specifies to grease threads or bolts. A greased 8nm bolt will be as tight as a 12nm dry.
Here’s some great info on bolt torque:
https://www.luxonmx.com/blog-luxon-bolt-torque-tension.html?srsltid=Afm…
I don't know if Fox puts pre-applied thread lock on the crown bolts, but if they do it might be worth removing. It can have a big impact on how tight the crown gets on the stanchions. Ohlins had so much pre-applied thread lock on DH38 crown bolts I had a stanchion slip after torquing to spec on a new fork. Ended up removing as much of the thread locker as possible, then torque spec held.
I have never seen a MTB fork crown bolt torque spec that specified dry, greased, or thread lock applied. But it would be quite helpful. This is interesting:
Currently having similar issues with a 35mm Boxxer, but it appears the creak is coming from the axle.
Exactly the same with me. 6 month old 40 Grip X2 factory. Crazy cracking from the lower triple clamp. After cleaning it goes away for one or two rides, then it starts again, and quite loudly...
Thanks for the pointers, I'll try the Scotch Brite and grease idea. As far as I know my torque wrench is ok but it's nothing fancy, so who knows. Had boxxers, 888s, 380s and other sets of 40s over the years and never had this happen before, driving me nuts! I'll report back, might help someone else out down the road
If you say so🤙
I’m glad I asked about this before I sold the fork, so far so good after lots of Whistler laps with a quiet bike. First try with motorex 2000 didn’t last long before a slight creak came back, switched to a bit of Mobil xhp222 and has been solid since.
Thanks for the suggestions, that was frustrating!
Thanks for following up. Just out of curiosity, did you try grease on the clamp bolts, scotchbrite on the inner clamp surface, or both?
I’d previously greased the clamp bolts with no luck, this time I scuffed up the inner crown surface a bit with scotchbrite and applied a very thin coat of grease to the clamping areas.
Nice, I didn't realize you were applying the grease to the clamping surface itself. That's wild. Clamping forces are crazy, yo.
He's not just saying so. It's an established fact in the engineering world for bolted joints. Every single torque spec should always include whether that spec is for lubed or non-lubed threads. The fact that the bike industry doesn't do this is mind boggling.
Ok
A small update on my part. Fox has fitted new stanchions and bridges under warranty. No more cracking.
What a pain in the ass that was...
Glad to hear you got it fixed. Just out of curiosity, what's a bridge? Are you referring to the fork's crowns?
Yes crowns off course..Sorry, bridge is the german word for it
That’s cool, didn’t know that the word differed in German or English. As an American I have a lot of respect for all the people who don’t speak English as their native language in these forums. Respect.
in my industry a deal with a pretty good amount of german manufacturing equipment. i have a special appreciation for the sheer length of some of their technical terminology.
In the moto world they are upper and lower triple clamps
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