Sucking sound when hitting bumps on Fox 34 SC

That's normal. Its just the sound of the oil passing through the rebound circuit. However if it got significantly worse since you got the bike it may indicate that their is a small amount of air in the damper.

HuckingKiwi said:

That's normal. Its just the sound of the oil passing through the rebound circuit. However if it got significantly worse since you got the bike it may indicate that their is a small amount of air in the damper.

Click to expand...

Thanks. I'm new to this. Does it mean there's a defect in the fork if there's air in the damper? How do we get the air out? Is that something we can DIY or does it need to be sent to Fox?

mooncake2 said:

Thanks. I'm new to this. Does it mean there's a defect in the fork if there's air in the damper? How do we get the air out? Is that something we can DIY or does it need to be sent to Fox?

Click to expand...

Its very unlikely that its caused by a defect and its usually caused by worn seals in the damper seal head. Removing the air from the damper requires a few specialty tools so I don't recommend doing it yourself. I have rebuilt a few fox fork with the grip damper and they sound like that even after a rebuild. Basically I would not worry about it for now.

I'm on the fence. I only heard 2 real compressions in your video and couldn't really tell based on that. I have a 36 and it doesn't make that sound riding on the street and hitting a bump. Mine is quiet.

Is the air pressure / sag correct for your weight? He said the fork is new... so worn seals shouldn't be the cause.

Mine had always done this. My 32 doesn't. I don't know why it does, but it's like it's sucking air into the damper leg on each cycle. Maybe through the top cap?

shadowsports said:

I'm on the fence. I only heard 2 real compressions in your video and couldn't really tell based on that. I have a 36 and it doesn't make that sound riding on the street and hitting a bump. Mine is quiet.

Is the air pressure / sag correct for your weight? He said the fork is new... so worn seals shouldn't be the cause.

Click to expand...

It produces the noise when I hit the bump fast. Slow rollover is quiet. I set the sag at 15-25% based on Fox recommendation. Only needed about 95 psi to achieve that. As for rebound settings, I followed Fox recommendation based on my weight which is 9 clicks.

That actually explains it. Since you are running 95psi and 9 clicks of rebound (from closed I assume) the noise is going to be louder because the rebound circuit is more restricted. In theory a more restricted circuit mixed with high flow rate(due to the air spring pressure) will generate a turbulent flow. So what you are hearing is the turbulent flow of oil.

HuckingKiwi said:

That actually explains it. Since you are running 95psi and 9 clicks of rebound (from closed I assume) the noise is going to be louder because the rebound circuit is more restricted. In theory a more restricted circuit mixed with high flow rate(due to the air spring pressure) will generate a turbulent flow. So what you are hearing is the turbulent flow of oil.

Click to expand...

Yes, it's 9 clicks from closed. Can you share more details on why the rebound circuit is more restricted? Sorry I'm learning here. Does that mean I have to change my rebound settings?

mooncake2 said:

Yes, it's 9 clicks from closed. Can you share more details on why the rebound circuit is more restricted? Sorry I'm learning here. Does that mean I have to change my rebound settings?

Click to expand...

Basically a damper is a tube filled with oil and their is a piston in that tube that moves up and down. In order for the piston to move up or down the oil has to pass through a channel in the piston. When adjusting the rebound you are basically changing the size of that channel. When the channel is small (restricted) the oil will have a harder time to pass through so the rebound will be slow in that case.

No you do not need to change the rebound setting. If you are happy with the way that the fork feels at 9 clicks and 94psi leave it like that. It is normal to have more noise from the damper when running a higher air spring pressure and less clicks from close.

Rebound controls how fast the fork returns after an impact. A lower air spring pressure will need less rebound (more clicks from close) to achieve the ideal return speed. A higher pressure (around 90psi and above) will need more rebound (less clicks from close) to maintain the same return speed.