R33 'bouncy' Rear End. Your Input Wanted!

[Reflector]

Hey all,

So I was driving home on friday afternoon in the rain when suddenly I started to feel my rear shocks oscilations much much more than usually. I thought I may have punctured a tire from a pot hole or some other debris so I pulled over. Inspected my tires, all seemed fine. Checked my tire pressures, were a bit low so today (after not driving since friday) pumped them up to 40psi (235/R18s all round) and took her for a test. Problem still persists. Once home I did a shock bounce test and found them to still feel solid. (I have BC BR coil overs only about a year old). I have mine set relatively firm because of how low the car is with no guards rolled, keeps me from scrubbing .

Anyhow, decided to jack the car up and down in the rear end to make sure the shockies were still expanding and retracting with and without load. All seemed normal. Now I'm a little stumped. I hadn't felt or heard anything break before I started feeling the excessive bounce. The BC BR Coilovers are less than a year (if not just comming up to a year) old so I wouldn't imagine they'd have seized or failed already.

I've got one theory (which I can't test until I get tools from the workshop tomorrow night) but perhaps if I back the firmness of the coils in the back off a little more, it may allow the shocks to absorb more of the shock rather than it being transfered to the wheels. I haven't seen any obvious bushes 'flogging' out when I had it last on the hoist either, that's not to say something hasn't happened spontaneously though.

So I am stumped for now. Any one else had this problem?

In Short:

Problem:

Boucy rear end

Fixes Tried:

- Tyre Pressures

- Inspectated Tyres (fronts are new and rears use to be the front so they still have tread)

- Suspension Bounce test

- Jacked up rear to inspect load and no load operation of coil overs

Yet to try:

- Softening up the rear coils via adjustable dampening dials.

Edited May 27, 2012 by Reflector

[GTSBoy]

Um, you do realise that adjusting the dampers (softer) is not adjusting the springs, and will in fact make the suspension more bouncy?

Excessively hard damping will make the rear jittery and jumpy, which you may feel as being bouncy (or mis-describe as being bouncy). But bouncy is really when the springs are stiff and the loads are high enough to compress the springs but the dampers are not strong enough to control the oscillations of the springs after they get compressed.

[Reflector]

To my knowledge the springs in the coils control/can be adjusted to vary the ride hieght which is adjust before being put into the car. I'm nearly certain that means that the actual spring itself does not vary in stiffness. The damping adjustment controls both rebound and compression - effectively what a shockie would do in a shock and spring style set up. I'm sure they'd have the information on the BC racing website.

[GTSBoy]

Yeah, but in your first post, you said "softening up the rear coils via adjustable dampening dials". You can't soften the "coils", being the springs. Only adjust the damping. Hence my comment.

[nos man]

yeah unless you have something with a progressive spring rate like greddy coil overs

[89CAL]

You said that it was raining. Are you sure you weren't getting wheel spin and axle tramping?

[R TUNE]

Also lower your tyer pressure 40psi high and very hard. Try 34 psi. You may notice a difference also try some 17" rims as you will have more side wall to absorb the shock from the road

[89CAL]

Also lower your tyer pressure 40psi high and very hard. Try 34 psi. You may notice a difference also try some 17" rims as you will have more side wall to absorb the shock from the road

I used to have 19's I ran at 38psi no problems. Think the problem lies elsewhere

[Reflector]

Also lower your tyer pressure 40psi high and very hard. Try 34 psi. You may notice a difference also try some 17" rims as you will have more side wall to absorb the shock from the road

34psi is too low for high profile tyres. Have always run 38-40psi in my 18" and never had a problem.

That being said, the problem seems to have gone away. After jacking the car up and releiving the coils of the load, my ride seems back to it's relatively firm state. Also was able to drive it through similar conditions (ie wet weather) and the same path on the weekend and there didn't seem to be a re-occurance of the problem. Perhaps the coils temporarily got stuck? Will be aware in any sudden change though if it happens again.