Diagnosing Suspension Knock.

[Pure_Sincerity]

Diagnosing front end suspension knock.

R34 GT sedan.

Since I put new coilovers in the front, I have been getting a knock when going over small bumps in the road, going up driveways etc. I can feel it coming through the floor In the car when I am driving and the front end gets "bouncy" at the same time. The coils are not bottoming out and the damper and rebound is generally fine. But the bouncy ness and knocking comes and goes and is really annoying. I can hit big bumps etc and it's perfectly fine and comfortable in a coilover friendly point of view.

These coils are far stiffer then the greddy type s coils I originally had, and to match I'm still using hard race adj control arms and tie rod ends with a 26mm 4 point adj swaybar as I was with the old coils. The swaybar is set on the second stiffest setting and the link is so tight that I don't see a way possible It can be set to the next setting point. Could all this combind be an issue? Being such stiff coils now that it's upsetting the link ?

On the other hand, the coils were a little iffy to be put in. They are non base adj HKS. When installing, if I put the coilover on the bottom mounting point it then would not line up with the 2 holes in the chassis up top, then of I mounted the coil in the 2 chassis holes, then it would not line up on the bottom. In the end, I had to put it 1/4 on bottom mounting bolt, then put top 2 bolts through the chassis and tap the bottom of the coilover with a rubber mallet to get it over the bottom mounting bolt.

They are labeled L AND R And I have out the R on the drivers side and L on passenger so they are not on the wrong sides.

Could it be a possibility that the control arms are set wrong making installation hard ? Before was easy as the greddy coils were base adjustable and could be rotated down low to match the mounting point. Where now I can't.

Should I remove the LCA from the hub, and see if the coils line up perfectly ? Then if they do, adjust the LCAS to match the hub location ?

[darksky34]

Just for a start: go over every nut and bolt you have that is aftermarket suspension gear and check to see if anything is loose - if you haven't already.

[Pure_Sincerity]

That was the first thing I had done.

[V28VX37]

Good thorough description, tough one that. It may be a case where the most obvious thing (coilovers) is not at fault but instead highlighting an issue somewhere else in the suspension.

Couple of things worth checking that came to mind:

• What suspension tops are you running with the new coilovers? Are they substantially different to the previous ones you had?
• Sway bar link pins can get noisy, have you checked these?
• When I was installing my aftermarket tension (caster) rods, they came very close to the aftermarket swaybar when the car is jacked up. Could these be touching?
• Are your swaybar bushes ok?
• Is the knock simultaneous on both sides?

The root cause for my suspension knock was incorrectly sized crush tubes in the aftermarket tension rods that were loose around the OEM bolts. Never crossed my mind to check for like this before installing.

With the coilover being iffy to put in, I've found that you may need to adjust the LCA height a bit to line it up correctly. I've used a scissor jack underneath to just lift it slightly.

Good luck.

[Pure_Sincerity]

Cheers fellas.

Swaybar bushes are fine, links are old and tight as f**k on the adjustable sway. I may take it to the next "softest" setting to reduce the tension onto the swaybar. It's abit hard seeing as it didn't do it before, or it just wasn't noticeable with the softer coilovers.

The new coils are pillowball where as the old ones were bush resulting in a softer more enjoyable ride.

As for the tension rod, I do not have one of those tension rods that sit behind the swaybar, I will be purchasing one soon tho. I'm going to look into the links first.

[Pure_Sincerity]

Knock does go from side to side, and it will pay to check the bolt sizes also for the crash tubes where the LCA bolts to the car and where the caster arm joins to the chassis also.

[Pure_Sincerity]

Between the 26mm 4pt adjustable swaybar and the hardrace adj control arms, I have less then a finger width clearance. So I would imagine when hitting bumps the control arm raises and is hitting my swaybar ? After I looked at that, I tested it and tightened up my damper abit more and the knocking is there less and less.

How would I got about this ?

[GTSBoy]

Drop the ARB off and take it for a drive. Noise gone, diagnosis proven. How to solve the problem though.....that's a whole 'nother thing.

[Pure_Sincerity]

I'd say its because my old coils were base adj and I had them threaded right down making the length from top to bottom taller then my current ones which have me more clearance.

[Pure_Sincerity]

Okay, this wasn't the issue. I've listens more and more into depth and the knocking isn't there when both sides of the car is under suspension travel, eg going over a speed bump head on. But then it knocks and bounces dramatically if you take the speed bump on an angle, eg 1 wheel at a time.

[GTSBoy]

1 wheel at a time is when the ARB actually does something.

[Pure_Sincerity]

ARB dropped, then test driven. Knocking is still there. So swaybar is out of the question.

Perhaps it actually is these coilovers ? They are not bottoming out at all. But I can feel the knock coming through the floor.