Fox 2.0 IFP clunk sound

[burnoil]

Hello everyone,

Just had some Fox 2.0 IFP non-res coil overs and rear shocks (no rear coil replacement) installed. This is for stock ride height with the front leveled. Alignment is done and perfect. Rides very nice. I do have KDSS.

Once thing of note...when rolling evenly over a speed bump, for example, enough to flex the rear suspension I get a soft "thud" sound that you can also feel in the pedals and steering wheel. This only happens when the rear suspension is in UP travel. So, it compresses a little and then when the upstroke is complete...the thud occurs. Everything is tight, nothing is rubbing. Front coils are adjusted to level. Shocks move freely and no leaks...they're new!

It is really hard to determine where the sound originates exactly. Any ideas?

 

[gm350reratliff]

Both upper rear shock bushings in place and tight? Lower shock bushings ok?

 

[burnoil]

Yep, everything is good. All bushings are snug (not over-tightened). Swaybar ends are not loose, either.

 

[burnoil]

I see nobody has ever seen or heard of this strange issue. I suspected the rear shocks topping out, but not the case. Pulled the shocks today and they have full range of motion and are smooth.

What an odd issue. Fox has been very responsive in trying to troubleshoot, but still can't isolate the source.

Pulled the spare out just to make sure rear sway isn't hitting. Not the cause. Could the front be adjusted too high and somehow when the rear of the chassis goes up it has an effect on it? These are my first adjustable coils so new territory...

 

[Jono.ful]

I've heard they don't like the cold (I mean, like northern canada cold), but you probably don't get a lot of that in CA.

 

[jrandom]

Total long shot but put some fresh grease on the front coil-over lower linkage spacer then drive around, try an get that same thunk, then check the grease on the spacer to see if the lower linkage shifted forward or back. It is not solid like the original lower linkage, it floats.

 

[burnoil]

Interesting...I will take a look a that lower linkage and see if it is moving around.

 

[iowanative2001]

Subscribed since I have the same shocks and are putting them on in 2 days. The 1 thing I noticed when ordering mine is that fox offers 2 different shocks for the rear a 0-1" lift and a 2-3" lift. Which ones did you get?

 

[burnoil]

I went with the 0-1" lift...wanted to keep stock height and level out the front.

 

[burnoil]

Still have not been able to ID this noise. It only happens when the rear moves over a significant bump to get the chassis moving. I feel it under my feet and seat area. A very pronounced thud. Getting ready to remove it all and go back to stock...ugh.

 

[THEROK]

Go with icons. Riverside. Talk to brad.

 

[Ducmonsta]

Still have not been able to ID this noise. It only happens when the rear moves over a significant bump to get the chassis moving. I feel it under my feet and seat area. A very pronounced thud. Getting ready to remove it all and go back to stock...ugh.

Have you brought it back to the original installer and asked for their opinion? Since the noise started after the install, I would think they would want to take a look at it.

 

[iowanative2001]

I have been able to put some miles on my fox 2.0s and thankfully have had no problems with them. One thing to possibly check is that all the hardware is on properly for the rear shock. It should go:

Starting from the top:
Nut
Washer
Bushing
Frame
Bushing
Washer
Shock

Hope this helps and for what its worth I ended up using the oem bushing/washers for the top as toytec didn't ship mounting hardware for one of the rears. The only inconvenience was a trip to the local hardware store was needed for one extra nut and some rubber washers for the bottom connection. Maybe someday I might call them but the only way I am taking those off is when they need to be rebuilt.

 

[burnoil]

I pulled the rear shocks and they are correct lengths and also function normally and smoothly. I don't think the rear shocks are the issue. They are mounted with all correct hardware.

I chased every single bolt I could find related to the front and/or rear suspension. All tight. Alignment is good.

I did take it back to the installer...4 Wheel Parts. They couldn't find anything. Unfortunately the speed bumps in their lot aren't large enough to get the sound to happen although I did get it to happen for them very slightly. I have used this particular shop for all kinds of things and never had any issues on previous trucks...so I trust them. I guess I will call them again to see what they say.

Also, I wonder if the KDSS system could make this sound? The truck doesn't have any lean...that seems to be an issue with suspension work on KDSS-equipped trucks.

 

[Intruder]

Also, I wonder if the KDSS system could make this sound? The truck doesn't have any lean...that seems to be an issue with suspension work on KDSS-equipped trucks.

I've never noticed a clunk from KDSS. The "lean" is not a 100% thing either - you'll notice some people have more lean than others but it's generally only an inch or so at the most. Maybe check all the sway bar bushings to make sure they were reconnected properly and none of them are slipping, but I doubt the bushings would be bad on such a new truck.

 

[Flahart]

Are your shocks charged with nitrogen? If not you can get a clunk or thud when the IPF hits either the piston or top cap of the shock.

I pulled the rear shocks and they are correct lengths and also function normally and smoothly. I don't think the rear shocks are the issue. They are mounted with all correct hardware.

I chased every single bolt I could find related to the front and/or rear suspension. All tight. Alignment is good.

I did take it back to the installer...4 Wheel Parts. They couldn't find anything. Unfortunately the speed bumps in their lot aren't large enough to get the sound to happen although I did get it to happen for them very slightly. I have used this particular shop for all kinds of things and never had any issues on previous trucks...so I trust them. I guess I will call them again to see what they say.

Also, I wonder if the KDSS system could make this sound? The truck doesn't have any lean...that seems to be an issue with suspension work on KDSS-equipped trucks.

 

[burnoil]

Yes, I followed instructions from a Fox technician and they slowly, with effort, actuated normally by hand and slowly pushed back under their own pressure. They seem to act fine.

Sway bar links didn't look sloppy or like they were slipping . All bolts tight, too.

 

[Flahart]

How slow? they will extend with a small amount of nitrogen (50 psi) but that is too low on a 4600 lb SUV to keep the IPF in place doing it's job. Charge them to 200 psi when they are fully extended and see if the clunk goes away. If you don't have Nitrogen on hand you can use shop air to get you by until you take it back to 4WP.

Yes, I followed instructions from a Fox technician and they slowly, with effort, actuated normally by hand and slowly pushed back under their own pressure. They seem to act fine.

Sway bar links didn't look sloppy or like they were slipping . All bolts tight, too.

 

[burnoil]

How slow? they will extend with a small amount of nitrogen (50 psi) but that is too low on a 4600 lb SUV to keep the IPF in place doing it's job. Charge them to 200 psi when they are fully extended and see if the clunk goes away. If you don't have Nitrogen on hand you can use shop air to get you by until you take it back to 4WP.

Didn't time it, but I can say with some accuracy that it fully extended back to full length in about 3 seconds...from fully compressed to fully extended.

 

[burnoil]

So, an update to this old thread of mine. Finally got my truck over to Toytota for them to look and see what 4 Wheel Parts did...wrong. The rear "thud" is still there. Toyota confirmed it and suspects that the rear KDSS piston is compressing and then sticking...and then suddenly letting go after the suspension settles.

I am not an expert on KDSS, but I didn't think the KDSS piston was engaged when the rear axle moves evenly over a speed bump, for example. I could be wrong. Anyhow, Toyota ultimately refused to do anything from an adjustment standpoint. I understand their position as the issue is due to aftermarket parts.

So, now I am in a sticky spot. I don't trust 4 Wheel Parts to remedy this issue. They've looked at the truck once since the initial install. They didn't try very hard to reproduce the issue and didn't seem interested to begin with. They already have my $$$. Does anybody have any idea how to fix this or know a shop that can??? Thanks.