Very noisy clunk with lifted suspension, solid top mounts and konis

[afterburner]

So here's the deal. I'm preparing a B4 chassis with a somewhat lifted suspension setup for doing some sideways snow/gravel driving and messing around town without thinking a lot about potholes and speed bumps

My problem concerns the front suspension where I have stock springs, modified top spring perches (3 cm taller), solid offset spherical bearing top mounts (similar to Albert's) and Koni Sport shocks with external adjustments (that's in a 50mm strut).

I just got to putting the car on wheels and driving it for the first time. I like the firm ride, but here's the problem - when the wheel comes down from a speed bump or a kerb there's a very sharp clunk coming from the direction of that exact wheel. It only happens on rebound, not on compression. I can go over a smaller kerb with 20km/h and nothing happens, but going down from it is a completely different story... so it only happens on rebound, not on compression.

Is it possible that I'm fully extending my front shocks and when they hit their internal bump stop the sound gets transmitted to the chassis because of the solid top mounts?

I've driven those shocks before but only with +1 cm spring perches and OEM top mounts. I've even jumped the car on several occasions... this loud clunk never happened.

I rechecked the top mounts, all bolts. Everything. The inserts are very tight in the struts... Even with the lifted suspension, the shocks still have enough travel before extending all the way. I'd think that the rebound dampening wouldn't allow for such a strong clunk at the end of their travel, but maybe the greater preload that the spring has, because of the taller perches, forces the shock with enough force to make it clunk (in combination with the top mounts).

I'm now getting the idea of using the rebound adjustment on the shocks. They are currently on their softest setting, maybe hardening them will keep the shock from extending so fast (if this is the problem). But I won't be able to try this till the weekend, because the car has no headlights currently and it's dark after work

Anybody has any suggestions or has similar experience? Thanks!

[macspring]

Any photos of what your done / used / current set up as it is in place currently, may help others to be better able to assist you.

[afterburner]

Here are the pictures

I use a spherical bearing with a Golf Mk4/Audi A3 axial bearing underneath it so it takes all the rotation when steering. This way the steering is lighter, because you don't spin the spherical bearing. Also this means that the strut nut doesn't undo itself when driving.

Underneath it is a modified spring perch made of an OEM one + 20 mm spacer + Golf MK4 OEM perch (for the axial bearing to sit on) all welded together. Because the bearing is around 10 mm tall this gives ~30 mm of total lift.

On one of the pictures you can see a comparison between this setup and my previous +10 mm setup, that only used OEM parts with a +10 mm spring perch.

On another picture you can see the self vulcanizing tape I used to enclose the space between axial bearing and spring perch - that way no debris can get inside the bearing.

Using this setup also means that I can have a slim nut (that also acts as a spherical bearing sleeve) on top of the axial bearing, so I can remove the strut as one assembly and leave the top mounts on the car, without the need to compress the springs.

[macspring]

Hi Afterburner,

To be honest I wasn't expecting to be able to contribute anything further to this thread, but looking at the third photo, if I had to guess, I would suggest the top coil is too loose around the green collar.

But when I looked at the first two photos it appears tighter / tight enough ?

Others will certainly know more.

[afterburner]

It looks loose, because it has a transparent tube over the two ends. This limits the transmission of sound from the suspension to the body. Believe me, it's VERY well seated in there. I had to work my spring compressors a lot to assemble the unit. That's why I'm guessing the preload when the shock is extended may be too much.

[Rusty]

Spring is upside down. Seriously. BTDT.

They're different shapes at the ends. One end is flat and goes on the bottom, one is helical and goes on the top cup.

If it's not that, then check the subframe to driveshaft clearance.

[afterburner]

Spring is upside down. Seriously. BTDT.

Yep, me too, BTDT. No matter how many times I assemble springs, each time I get one mixed up. This time it also happened, but I corrected it, so the issue is somewhere else.

If it's not that, then check the subframe to driveshaft clearance.

I jacked the car to remove one of the struts on sunday... I got the strut out of the top mount (only just, to check the bearing for play) and I still had some clearence before the driveshaft was hitting the subframe. So this is also not the case.

[Lago Blue]

Clunk Cause

Afterburner, a question sir,

I think you are on exactly the right track WRT cause and possible cure. My experience is that some springs are quite nearly fully relaxed with damper at full extension, but your springs appear to have lots of pre-load. I have no experience w/Konis but if the damper was meant to be used with shortened lowering springs and your set-up makes it operate as though it has very long springs (stock length plus 30mm), would that help worsen the situation vs a damper for regular length springs?

[afterburner]

Well, the damper is for stock strings, it has a lot of travel, but I still think the preload is bugging it. I will drive the car tomorrow with a harder rebound setting and will see what happens. If it fixes it - I will know the problem. Next step will be trying some 5 cylinder NM springs. They are stiffer, but shorter. Maybe with them I will have less preload. If the front becomes to stiff and "understeery" I will try something that I wanted to for a long time - removing the front sway bar... otherwise - I will lower the car and try again

[afterburner]

OK, so some tests after the weekend. I have one shock that is shot... I tightened the rebound on both shocks and all clunking disappeared from the left side, but not from the right... When I rocked the car I noticed that the clunking side is far less restricted by the shock and I could get it to almost resonate with my bare hands... So I maxed out the rebound dampening and it was still softer than the other side on its softest setting... Those Konis were with less than 20000 kilometers on the clock... And nothing bad has ever happened to them... I bought them 3 years ago, so the warranty I had (2 years) is over... I will try to buy one replacement and start from there...

[Lago Blue]

Another option...

Although perhaps initially more expensive if you bought two brand new, with Bilstein, you could return the unit for re-build and the limited life-time warranty may apply.

see Bilstein B6/B8 warranty here

[afterburner]

Yep, but that's for Bilstein in North America Here in Europe they give you a 2 year warranty.