Strange sound from rear (suspension??)

[fka]

Sorry - yet another can you help me identify that sound thread!

Since I've had the new suspension put on I've had 3 or 4 instances of what sounds like something metallic dropping of the rear left side of the car. Isn't related to going over bumps and has happened whilst driving relatively slowly round the back streets and at the end of a long blast down the motorway whilst still at speed on a long slipway.
It literally sounds like a bolt has dropped off, bounced off a few things and hit the ground. Everything on the rear suspension seems to be in place so I'm assuming nothing has actually dropped off!

I've got two possible suspects - firstly I've noticed the CrossClimates pick up a lot of stones. Is it just a well wedged stone that's finally come lose and been flung around the rear arch? Although this doesn't quite fit the occurrence at the end of a long motorway blast.. And usually when I hear stones coming off the wheels, it's sound exactly like that, gravel being thrown at the arch liner.
Secondly, the rear silencer on the exhaust is in the process of losing it's outer skin and will need replacing imminently. Is it bits of silencer skin being blown off and hitting other parts on the way out? Its seems bits of silencer skin would be too small/light to make the sound..

I'm not fully convinced with either theory, is there anything else on the rear suspension that could make such a noise?

[sgould]

I had an awfully loud noise after doing the rear suspension.  But it was related to going over bumpy roads.  The solution belied the noise.

All it was was about 1/4mm movement in the rear roll bar bush clip.  The bush is held in by a U shaped clip which is hooked in at one end and bolted at the other.  The hook was moving a tiny amount and making a noise inside the car as if some serious was about to break.  I fixed it by squeezing the bush with a small G clamp so that the hook moved out a bit, then jammed a bit of nylon cord in the gap.  I tried grease, but it didn't work.

Picture needs a close look to see the bush under the grease!!

[fka]

Thanks Will, I'll take a look at that but did that give you more of a straight clunk as you hit a bump?

[sgould]

It was a rattle on uneven surfaces and OK on big bumps. Silent on main roads.  The clue when I got in close was a small bright orange stain of fresh rust by the hook.

The other thing I would look at are the heat shields over the exhaust. Joe reported that he had had to fix some loose ones with big “penny washers” as the original fixings had rusted and fallen off the screws.

[fka]

Well that does sound like a possible culprit. As soon as it brightens up a bit I'll get it up on the stands and have a poke around.
Cheers 

[fka]

I've had a poke around this morning. Heat shields are all ok and the exhaust doesn't seem to be catching on anything but is in very poor shape from the DP back.
I can't see any evidence of the ARB bush clamps moving or having moved but there's a lot of movement of the ARB in the bush so it would follow that the bush is also loose in the clamp. I'm now torn between just replacing the bushes with Powerflex or going the whole hog and ordering Abbott's 20mm ARB which comes with bushes and comes in around £200 once the VAT is added..

[sgould]

I did toy with adding a bigger ARB, but I was told that it could make the car a bit tail happy.  Probably not too much of a problem to someone of my generation, used to ancient rear wheel drive vehicles with leaf springs, but in the end I didn't bother.  The Hirsch suspension seems quite OK without.  I can travel at speed on an autobahn with a loaded car and it handles the same as it does when unloaded.

[fka]

I've just done a bit of reading and without replacing front and back to match, a stiffer rear arb and softer front will lead to oversteer. Whether that would actually equate to much of an issue since it understeers anyway, I don't know. But I'd hope the Saab engineers knew what they were doing when they originally specc'd them. Think I'll just order the bushes.

[carrera]

That should be fine, and yes, stiffer arb will increase the propensity to oversteer. About the only place you will find out is on a slippery roundabout in the wet. I have had that a couple of times in the 9-5:- quite controllable as the electronics were clearly confused much to my preference.

Which reminds me about getting the back end out on my mums 948cc mk1 Polo in my younger days..... in the dry 

[sgould]

Long before the M25, I worked in East Kent during the week and drove back to London on a Friday evening.  One Friday, it rained heavily as I got to Vauxhall.  I was driving a Hillman Minx.  The 1500cc base model of the Hunter range.  I accelerated onto Vauxhall Bridge and the back end stepped out, I went most of the way across the bridge in a sort of drift!!   Didn't hit anything, but it was a close run thing!!  Mind you we had been practising all sorts of sliding because we were working in fields laying pumping mains for miles between villages for a regional sewerage scheme.

[fka]

I learned to drive when I was about 13 in farm fields, in a combo of pickups, tractors and my dad's company cars. Handbrake turns on wet grass was always amusing until one of the farm boys went flying out the back of a pickup but thankfully didn't break anything 

17mm bushes ordered 

[fka]

That should be fine, and yes, stiffer arb will increase the propensity to oversteer. About the only place you will find out is on a slippery roundabout in the wet. I have had that a couple of times in the 9-5:- quite controllable as the electronics were clearly confused much to my preference.

Which reminds me about getting the back end out on my mums 948cc mk1 Polo in my younger days..... in the dry 

One of my test routes when I've been tinkering is a set of fast roundabouts and the 9-5 is very (almost too) well behaved in the wet.
The 9-3 with the SAS rear arb and standard Aero arb up front and no ESP, was quite a lot of fun but very predictable.
With the kids on board most of time these days, the number of opportunities to go sideways without the Mrs beating me about the head, are few and far between.
If you got the back end of the Polo out without the handbrake, I'm impressed 

[carrera]

No handbrake involved, 50 hp and enthusiastic cornering.  Getting the back end out on a fwd car does take a bit more effort.

My 9-5's tend to be quite sensible, in that after a few days with me in the drivers wheel the electronics stop applying a brake unneccesarily. When the 9-5 does break away, which is very rare it has pretty much always been a balanced 4 wheel slide.