Both the 996 and 997-generation 911 can develop a knock over bumps, leading you to think antiroll bar rubbers have had their day. More often than not, the fault is caused by suspension tuning fork bushes letting you know they're ready to give up the ghost. We visited the workshop of Suffolkbased marque specialist, PIE Performance Porsche, to find out how to replace these vital parts...
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Owners of early water-cooled 911s will know only too well their cars are getting on a bit. Through wear and tear, but also age, comes the very real threat of tired suspension bushes. Control arms (also referred to as tuning forks) work hard to deliver a smooth ride, but when their rubber bushes fail, knocks and vibrations can be felt over bumps in the road.
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The problem also affects 986 and 987 Boxsters. Complete Oem-specification arm assemblies with pre-installed bushes are available from independent Porsche parts retailer, Design 911, along with adjustable control arms for motorsport applications. It's worth noting, the parts for each generation of cars differ (997 tuning forks feature bigger front bushes).
Our 2006 997 Carrera 4S's coffin arms, bushes, top mounts and anti-roll bar bushes were replaced a few months ago, leading us to conclude duff suspension tuning fork bushes are the cause of knocking.
Raise the rear of the car and remove the back wheels for access. You'll also need to remove the chassis protection panels, held in place by 10mm plastic nuts and a series of T25 torx screws.
You'll need 18mm and 21mm sockets to remove each tuning fork bolt. Be patient — there's a chance this is the first time they've been removed. When you've loosened the bolts, wiggle them free.
To further assist with access to the subframe end of the rear tuning forks, remove the T25 fasteners holding the tail end of the wheel arch liners in place, enabling you to gently pull them forward.
Underbody plastic panels ably protect the chassis, but over time, a layer of dirt can develop on the inside surface. Now is a good time to clean the grime away, should you be so inclined.
With both ends of the arm unfastened, use a pry bar to slide the part free. If it refuses to budge, you may wish to loosen the rear chassis brace (pictured bottom) by undoing its 15mm nuts, one at each end.
A removed rear tuning fork. You might find only one of the parts is at fault, but it's worth replacing them in pairs or, better still, all four items (two at the front of the car, two at the rear) at the same time.
Tighten all bolts, including those you may have loosened to allow easier fitting of the tuning forks e.g. the 15mm rear chassis brace bolts. Reinstall the underbody panels and wheels. Rear forks done!
Haynes made it sound easy, but old cars can be stubborn. If you're struggling to squeeze the subframe end of your new rear tuning fork into place, you may wish to loosen the subframe bolts.
Slide one of the new rear arm assemblies into place. As the late, great John Haynes famously wrote, refitting is the reverse of removal!
Use a long screwdriver and poke it through the bolt holes to help align each end of the new tuning forks before refitting the bolts.
Work your way around the protective underbody panels. When all fasteners are removed, carefully slide the trays away from the car.
We advise fitting new front suspension tuning forks when replacing those at the rear (and vice versa). Fortunately, the front forks can be installed without having to remove their neighbouring wheels.
Unlike the rear tuning forks, those at the front feature wraparound plastic ducts channelling cool air to the brakes. Using a large flathead screwdriver, carefully prize the plastic part's clips free.
As per the rear, 18mm and 21mm sockets are required to remove each front suspension tuning fork, which attaches to the subframe at one end and to the coffin arm at the other.
As was the case at the rear of the car, when you've removed the chassis protection panel covering the front end, you may wish to clean the part free of dirt before reinstallation.
You will also need to unfasten the locking clips wrapped around each tuning fork arm. Your flathead screwdriver is all that's required, but work with care, avoiding breaking either of the clips.
Having successfully removed the air duct from the suspension tuning fork, carefully prize it over your new replacement part, fitting it exactly as it was installed on the now dismissed component.
You may need to slide the duct along the new tuning fork arm for a comfortable fit. When you're satisfied the plastic part is correctly installed, fasten it in place with the two locking clips.
Once again, use a long screwdriver (or similar) to 'pull' the subframe end of the tuning fork into place, thereby ensuring the subframe and tuning fork bolt holes align.
This picture reinforces our earlier claim of being able to fit the front suspension tuning forks without having to remove the wheels, though you may wish to do so if access is difficult on your garage floor.
The complete suspension tuning fork assembly — now carrying the brake cooling duct — is ready to be installed. Repeat the process when working with the tuning fork on the other side of the car.
Remove the front underbody panels. Five 10mm plastic nuts and eleven T25 torx screws hold them in place. Be sure to put the removed fasteners somewhere safe to prevent them being misplaced.
When removing the front undertray, you'll need to slide it back before sliding it forward for removal. Be mindful of the grime and small stones which may have made their way onto the inside surface.
THANKS PIE Performance Porsche, 9 Hill Farm, Lavenham Road, Sudbury, CO10 9PB 01787 249924 www.pieperformance.co.uk
With the tuning fork in place, you can now refit the bolts holding the part to the subframe assembly. As you can see, we removed the neighbouring subframe bolt for additional manoeuvrability.
Grab your 10mm plastic nuts (ooer!) and T25 torx screws and securely fasten the plastic panel, safe in the knowledge you've drastically enhanced your 911's ability to beat back potholes.
Refit the underbody protection tray. You might find it useful to enlist the assistance of a friend to help slide the part into position and hold it in place while you refit the fasteners.
Worn suspension tuning fork bushes are a common failure on 996 and 997-generation 911s. The fix is simple and cost-effective, but if you want a specialist to carry out the work, speak to PIE Performance.
Repeat the process on the other side of the car. Even a 911 with moderately worn tuning fork bushes will be hugely improved by the appointment of new parts, so don't be tempted to replace only one side.
Refit the bolt holding the new suspension tuning fork to the coffin arm. You know what John Haynes would say at this point, right?!