rear end wiggle

[landlwilson]

I posted this over at Rennlist but I thought I would throw it out here to see if I get a different response.

I was getting on the freeway today and as I was accelerating the rear end started to wiggle or shimmy a little bit. I was doing about 80 and the on ramp has a sweeping right hand turn to it. I have felt this a little before but today it was more noticeable. A month ago I lowered the car with H&R's and put 19's on it. The wheels were balanced when I got them and the car has been realigned after the spring install. Any advice would be grateful

A further description would be it started to bounce and wiggle at the same time :drive: :drive: :drive:

[Loren]

Check for tire damage/proper inflation, loose wheel(s), loose sway bar, and perhaps even a spring that has shifted on it's mount.

[landlwilson]

Check for tire damage/proper inflation, loose wheel(s), loose sway bar, and  perhaps even a spring that has shifted on it's mount.

<{POST_SNAPBACK}>

I know this might sound a little off but should I check the front also? Could that have an effect on the rear?

[Loren]

Certainly if you had all four springs done - and chances are they loosened or removed the swaybars for the work. I would go through and make sure everything is where it should be and tight.

One other thing I guess could that happen is if one shock completely died - it might act pretty weird if that happened.

[landlwilson]

Certainly if you had all four springs done - and chances are they loosened or removed the swaybars for the work. I would go through and make sure everything is where it should be and tight.

One other thing I guess could that happen is if one shock completely died - it might act pretty weird if that happened.

<{POST_SNAPBACK}>

Thanks Loren! Outside of a shock leaking how can I tell it went bad?

P.S. I have been looking for an excuse to go to a PSS9 setup but I want to cure the problem first

[Loren]

Push up and down on a fender (not hard enough to dent it it) and if the car returns to normal after one cycle the shock is likely fine. Do this on each corner. A bad shock will not retard the bounce.

[JimB]

Landlwilson,

You received several good hints on Rennlist and Renntech. I'm curious what you've eliminated? Have you had the car in the air and checked your tie rods (my guess), wheel bearings, ball joints, swaybars, etc.?

The problem you describe could just be your springs, dampers, sways, tires, etc. not working well together of it could be something like tie rods or ball joints that should be fixed ASAP for safety.

Jim

[Coaster]

A further description would be it started to bounce and wiggle at the same time

I had exactly this same issue after lowering with PSS9s. While in a sweeper at high speed if I hit uneven pavement the car would start to bounce in response to the pavement and once unsettled would feel like it was wiggling in the rear. It was very scary and it felt like I was on the verge of being out of control.

My problem was corrected by changing the damping in the rear to make it stiffer and having the alignment checked and adjusted. There were no loose parts or leaking dampers. My car's ride height is set to X74 specs.

<opinion>

It is my impression is that the 996 ride-height, suspension, wheel, and tire setup from the factory is very well engineered and balanced if not as high performing as some would like. Once you alter that combo you throw things out of balance (and tolerance) to the point that it's noticeable. It's a fine line and don't think it takes much to get out of whack and it takes some work to get it back in line. It ain't a Chevy. Mind you, I'm not chastising -- I changed all of these things myself.

</opinion>

When I was going through this problem there was a guy on 6speedonline with a Turbo who was experiencing the same problem after lowering and he was convinced that the damper was hitting its bump stop and that was causing the wiggle. I called Bilstein and talked with a tech who didn't think this was the cause.

Lowering changes suspension geometry and I had a hard time getting the rear camber set within specs. And... the car is more prone to bump steer. Both the camber change and the tendency to bump steer can unsettle the car in a rough sweeper. The car is much more responsive to steering input but I'm paying a price for that. It requires more concentration and smoothness at speed.

I don't know if any of this helps. A Porsche racing shop near home helped me a lot in sorting out my problems.

[SPR]

I had a problem with this as well. The problem with my pss9's was that after my corner balance the idiot's lowered the front too much and the springs would fully compress during normal driving creating an under damped rebound problem. The car still is doing some of this albeit not nearly as much at the same settings I had it before the problem. I really wonder if the shocks were damaged/ worn out from the negligence??? I am really thinking about removing them sending them out to bilstein over the break as I am gone for a month snowboarding.