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Discussion Starter #1
Re: Front fork problems

Please help!

I having a big problem on my front suspension. I replaced the ohlins FG329 fornt forks on my CBR929RR, everything is fine for the first 500 km, afterthat it causing a unexpected vibration during braking sometime, but it is not always happen.....sometime happen braking during corner, sometime happen just stop front of the traffic light during braking, sometime during gentle braking around 60-120km, sometime happen in high speed around 220+ km.

The FG329 is design for 04-07 CBR1000RR, but it can direct fit on CBR929RR, only the caliper mounting bracket is different, so I put the 06 CBR1000RR radial calipers on.

The vibration very like a kind of bottom out and chattering, I tried to turn the compression all in and all out and/or turn the rebound all in and all out, the result are similiar. When the compression setup is harder, it happen less than b4, but not sure it really the sourse of the problem.

I sent the suspension back to local distributor, they also can't find out the problem, even dismantle the FG329 forks to check it. They say maybe the radial calipers causing the problem and they going to put a new pair of Brembo calipers to test it.

On the other hand, my original CBR929RR forks was modified with Racetech gold vale kit and springs, it running well for 800km but it did happen the same problem as Ohlins. So I dismantle the forks and check carefully, find out the one of the compression check valve is not operate smoothly, can it cause the unexpected vibration problem? or the braking frequency affecting the valving operations? or other problem?

Please help!
 

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Re: Front fork problems

If it only occurs during braking, I would look at the brakes before looking at the forks.
 

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Re: Front fork problems

On the other hand, my original CBR929RR forks was modified with Racetech gold vale kit and springs, it running well for 800km but it did happen the same problem as Ohlins.
You didn't mention if fixing the compression valve fixed the fork problem.
I assume you're running the same wheel and rotors as you used with the original forks?
I'd try borrowing another wheel and/or disc rotors and probably new pads if you have any and see if it makes a difference.
 

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Discussion Starter #4
Re: Front fork problems

I use some different brake disc to try, PFM 330mm Cast Iron brake disc, Galfer 330mm wave steel brake diss and all test with new Ferodo CP.211 brake pads. I also tried to use a Marchesini 5 spoke magneisum and original front wheel. All are not work, still having a very strange vibration during braking sometimes....It really drive me to crazy!
I re-valve the compression and put one more shim on it today, but it won't solve the vibration problem.
I planning to use the original brake disc for a try tomorrow, let see what happen then.
Suggestions are welcome! Please advice.
 

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Discussion Starter #7
Re: Front fork problems

The front wheel bearing and steering bearing are new, and in good condition. I going to install the old original brake disc now, if it won't solve the vibration problem. Next step, try the other brand brake pad, like EBC sintered pads.....Thanks for helping.
 

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Discussion Starter #8
Re: Front fork problems

I confirmed the problem is causing by the Ohlins FG329 forks with 2 non local Ohlins Distributor's mechanics yesterday. After inspected by me and my friend, we found out there are some serious free play between the fork tube and slider tube, take the fender and wheel off, it feels a "tick" "tick" when you move the fork leg forward and backward. So we both agreed that it is a factor defeat, because my forks only run for 500 km, even I'm an agressive rider, both forks should not have the unexpected vibration and worn out so fast.
Actuall I found out the "free play" problem 2 months ago, but when I take both forks to the distributor, the problem disappear suddenly when we inspect it on a vice. I really have no idea for the result, why the free play problem will be disappeared suddenly, but it still giving you a unexpected vibration when you roll out the bike to test it.
Do anyone have an advice?
 

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Re: Front fork problems

After watching your video elder it appears the chatter you speak of is a rapid side to side or back and forth as opposed to rapid up and down movement. Am I seeing correctly? Chatter is generally rapid up and down. Good video and you obviously spent a lot of time on this problem. I'll wait until you answer before I comment.
 

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Discussion Starter #12
Re: Front fork problems

Before the video, I have no idea what kind of vibration it is, just guessing it feel like a kind of bottoming, likes chatter. After the inspection and video by myself, I can see it is a forward and backward movement, should be caused by the free play (not confirmed it caused by bushing or slider tube or outter tube yet). But the local Ohlins distributor said, the free play should not causing that vibration, they said maybe it is a rebound valve problem, will tried the superbike valving for me. Because they said it doesn't always happen, if it has a serious free play, the vibration should alway happen.
I really dunno why it causing by the rebound valve, Do anyone know what's worng at the rebound valve?
In my point of view, it should be the free play problem.
All opinions and advices are welcome! Please help!
 

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Re: Front fork problems

You don't see side to side then? Just back and forth meaning flexing to the rear of the bike and back to the front?
 

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Discussion Starter #14 (Edited)
Re: Front fork problems

From the back angle video sample 1 to 4, I can't see it has a side to side vibration. Yes, it looks like a back and forth only. Please give me some opinions and advices. Thx!
Do I need to take more video sample by different view angles? I'm arranging a high speed camera for video recording, hope it can help us to analysis by the 300 frame per second speed.
 

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Discussion Starter #17
Re: Front fork problems

The problem is not solve yet, the Ohlins forks are sitting in my store room now. Actually, I think it is an Ohlins factory defeat issue, I will write to Ohlins about my case and ask for refund!
 

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Discussion Starter #18
Re: Front fork problems

Finally, I can't find out what problem casued the funny vibration, but I found out there are at least 3 Ohlins fork FG series have the same problem as me, GSXR1000 K6, 05 R1, 04 CBR1000RR, I think it is a factory defeat issues, Ohlins sucks! I wrote an email to OHlins, they said is my brake system causing this vibration, but I change back orginial fork then the problem disappear. So my conclusion is FG Series Ohlins have a factory defeat and all users are suffering on this issues.
 
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