AHC Rattling (1 Viewer)

[DubR]

I’ve been trying to diagnose an undercarriage rattle for a bit. I’v suspected it’s related to the AHC system for a while. I just discovered what I think is crucial information: the rattling stops when I put the AHC in high mode.

When in neutral, I hear a hollow rattling/clanking when I drive over very modest bumps/cracks. It does not take much, and, I think the sound is far greater than a rattle should be for the amount of jostling created by the bump/crack.

When I shift into high and go over the same section of road, the rattle doesn’t occur. (I don’t know if the noise persists or goes away when the AHC is in low because it won’t stay in low, which may/may not be a related issue.)

Additional info: I recently flushed the AHC. When I did, no fluid drained from either of the front globes. I assumed that meant those globes need to be replaced (membrane). However, my garage checked the globe pressure and was confident that they weren’t blown.

Is anyone familiar with this type of issue? My suspicion is that fluid is not pressurizing in the piston when it’s in neutral and the rattling is from interior components in the piston (my knowledge of the piston mechanics is admittedly lacking). I’d love to know if anyone has had this kind of issue before. I’m stumped and want to avoid replacing pistons/height sensors/ globes if possible. (And, no, I don’t want to delete AHC. )

Thank you in advance.

 

[GTV]

I'd take a close look at your bushings. Maybe with AHC in high some slack is being taken up and that's why it goes away.

 

[DubR]

I'd take a close look at your bushings. Maybe with AHC in high some slack is being taken up and that's why it goes away.

Thanks

 

[Coin]

I'd take a close look at your bushings. Maybe with AHC in high some slack is being taken up and that's why it goes away.

This is what I was going to suggest, particularly your sway bar links.

 

[suprarx7nut]

However, my garage checked the globe pressure and was confident that they weren’t blown.

This statement makes me wonder if they actually did the gradation test (which is the proper way to test globes) or if they did something else.

You can check globe health on your own. From H to L, how many grads does the fluid move in the reservoir?

Check bushings, sway bars and tie rods. Nothing in the AHC system should make a rattle, unless it's obviously broken. It's likely you've got something suspension related going and putting it in H changes the geometry just enough to stop the rattle.

 

[DubR]

I replaced all sway bar links and bushings. Tie rods seem fine.

Is there any part/component that would be affected by engaging height lift other than the piston?

 

[Hokie LX]

If you didn't get any fluid out of the front globes during a bleed, I would try bleeding until you get fluid. I agree the clunk may be a bushing for shocks, suspension arms, etc.