Suspension question

[mookster]

2003, 966, C2 Cab

The suspension is the M032 (standard suspension). The vehicle has 17” wheels. All four tires were replaced at 49,500 miles.

I have had this vehicle for 3 years.

The vehicle now has 56,000 miles on the odometer. I am preparing to take the vehicle in for an oil change and the 60k service.

While in for regular servicing I need to address the suspension. Let me explain.

The left rear of the vehicle is sagging (base on the fender/ quarter panel wheel arch measurements) and it appears the left rear shock is showing its life. I have completed the rebound test and it does appear the shock still has life. When I drive over 70mph the front ends does feel like it is floating more then normal.

1. I realize if I replace one shock I need to replace the other side. If I just replace the shocks will I need to realign the vehicle?

2. I have owned two 911s prior to owning this vehicle. Will I need to corner balance/reindex and realign the vehicle if I just replacing the shocks?

3. I have replaced the rear shocks and strut inserts on my previous 911s. Is this a DIY job on the 996? Easier/harder?

4. If this is not a DIY job what is the reasonable labor time to replace the shocks/struts? What is the labor time to align and corner balance the vehicle?

5. If I need to replace the suspension I will be lowering the vehicle to Euro height. I will replace the suspension with either the M030 (Euro suspension) or the PSS10 suspension. Both kits are about the same price but it appears the M030 kit is more complete. Any thoughts on either kit? Does the install time differ between the 2 kits?

6. I heard a bout a front bumper diffuser that can be bolted to the front cover to produce more downward force. Does anyone know the part number? Is it worth it? I did attempt a search and did not have any luck.

I will NOT be tracking this vehicle. This is my daily driver. In this economy I do not want to throw a suspension kit on the car if it is not needed. However, I do not want to be paying for overlapping labor for alignment and balancing due to other parts failing in the near future.

I appreciate your input and thoughts. Thanks in advance.

[Loren]

1. and 2. - yes and yes. Always replace shocks in pairs. To replace the shock the springs need to come out so a realignment will be needed.

3. Since you have done it before - yes. Check out the M030 suspension DIY in the 996 DIY section - it has all the tips you will need.

4. Most shops charge a flat rate for a corner balance - depending on where you live expect to pay $80 to $150.

5. Unless you will need to raise and lower the suspension for racing I would stick with the RoW M030. Pretty much fool proof.

6. I think the folks that have done that already added the Aerokit front bumper (from the GT3). In that case it is bolt on and combined with the RoW M030 suspension your car will be very stable to a much higher speed.

[jmj996]

I don't mean to hijack your thread, but I have exactly the same issue on my 1999 996 cab and perhaps we can both benefit from the same expert replies and discuss each of our solutions as they are implemented. First, some basics on the car: 52k miles. Standard suspension - standard everything (though I have already added the GT3 front bumper cover for more front downforce, GT3 side skirts, and a Strosek Level 1 rear wing). This car has been tracked three times, and one time I unfortunately caught a sharp inner curb at around 65 mph on a left-hander that jacked the driver's side wheels so hard it ruined them - the outer lip of the rims (OEM BBS lightweight 3-piece 18" wheels) were bent nearly 90 degrees on both the front and back where they impacted the front of the curb. This occurred back in the Spring of 2008 and I did not notice any other damage to the car - I put my street 17" wheels on and everything seemed fine. Also mentioned it to the dealer and had him check it out, and they didn't identify any problems (though they felt overly confident in the strength of the suspension and bearings to survive such an incident). I tracked the car again one more time after that and did not notice any obvious problems then either.

This week, the car started to drag in my driveway. I have a pretty steep driveway, backing down into a basement-level garage. Been using this driveway since June with no issues. Nothing has recently happened to the car, but now it drags - seems very bizarre and sudden, though it could have just been a gradual change that caused this. There is nothing hanging down underneath. I measured the fender heights in the front & back. Fronts are equal, but the rear left is a full 1/2 inch lower than the rear right. Rear tire pressures are equal and 34psi each (though I think they should be 36 psi each - anyway, not a huge deal), so something is very wrong. With a bounce test, the rear suspension seems fine - it settles immediately. Before I spend a load of cash on new shocks & struts all around, plus any dealer help I'll need for the alignment, I want to confirm:

1) Is there is any way to adjust the ride height at each wheel on a standard, stock suspension - or any other remedy you suggest?

2) If so, would it be appropriate to do this? If it means I could postpone any parts replacement and alignment a little bit, I'd like to do it because I won't have the cash to really do this right until early next year.

3) What are the possible causes of this one-sided sagging, and what could I do to confirm these?

As I mentioned in item 2, I need to wait to replace any major parts if possible. This will be a very expensive endeavor, not just because of the parts, but because any dealer assistance I require for a new alignment & such will be incredibly expensive. I have taken this car with me to Italy (my wife is in the Navy) and I would have to pay any dealer labor in Euros, which is 1.5 times the dollar right now. The problem is that this car is a daily driver for us, and we need to keep it on the road until I can afford to replace a load of major suspension parts.

Thanks in advance for your help!

John

Edited October 20, 2009 by John Jones

[PTEC]

Your struts have nothing to do with the your ride height. That's your springs. The springs hold up the weight of the car, the struts dampen the oscillations from the springs.

Removing the struts on a C2 is quite a bit easier than on C4 so both you guys are lucky on that front. You can remove the struts without any special tools really. Most of the nuts and bolts are either 13mm, 16mm or 18mm with the exception of the axle nuts on the rear, which is a 32mm. You'll also need a 10mm allen to loosen the brake calipers. A ball joint removal tool is handy for removing the control arms from the wheel carriers. Once you get the struts out of the car you will need a spring compressor tool to compress the spring for safe disassembly of the strut.

I'm not a race guy but I don't think its possible to corner balance a McPherson strut setup, only coil-over type suspensions. It is possible to replace a rear strut without loosening any alignment eccentrics but I would recommend any alignment anyways.

[jmj996]

Your struts have nothing to do with the your ride height. That's your springs. The springs hold up the weight of the car, the struts dampen the oscillations from the springs.

Removing the struts on a C2 is quite a bit easier than on C4 so both you guys are lucky on that front. You can remove the struts without any special tools really. Most of the nuts and bolts are either 13mm, 16mm or 18mm with the exception of the axle nuts on the rear, which is a 32mm. You'll also need a 10mm allen to loosen the brake calipers. A ball joint removal tool is handy for removing the control arms from the wheel carriers. Once you get the struts out of the car you will need a spring compressor tool to compress the spring for safe disassembly of the strut.

I'm not a race guy but I don't think its possible to corner balance a McPherson strut setup, only coil-over type suspensions. It is possible to replace a rear strut without loosening any alignment eccentrics but I would recommend any alignment anyways.

Is it really possible that one rear spring has degraded that much in ten years versus the other rear spring? Is this more common than just with the two cars being discussed here? Or is it possible that measuring the vehicle height at the top of the rear fender wells is not a valid measurement point?

[perryinva]

Yes, it is not that unusual for springs to sag at different times, and it is usually gradual and the drivers side first. However, 56k miles would be a pretty short life. Fender height, while a convenient and valid way to measure, and an easy 'check' (I use it all the time) is not the official Porsche way..they use the bottom of a nut on the control arm in the front, and the bottom of a bore on the rear suspension. I'd guess that there is a reason they say to do it that way, maybe for worn bushings, bent arms, etc. The numbers have been posted many times on this site. That said, however, anyone that states that a strut does not affect the height of a car, has never replaced them. Not trying to flame at all, but while that is true for shocks, and the springs certainly do support the weight of the car, most struts have a significant spring/gas pressure component that most certainly will affect height by easily 1/4 to 1/2". The bounce and settle test is worthless on these cars, as the spring rates prevent hand actuated bouncing. In all likelyhood, the strut is compomised/worn, so you've lost that extra push, and it has settled. You would never notice it on a highway commute, but a couple of switchback turns back to back, on a bumpy road, should reveal the strut issue. I agree with Loren, if you're going to replace a pair with stock, it's not that much more to go the M030 route (which includes sways, too) and see a siginicant improvement in handling and ride height.

[mookster]

Thank you for all the replies.

If you had the suspension/strut/shock replaced by a mechanic can you provide me the labor time for the operation.

I am aware the M030 suspension will be firmer then my current set up. This is not an issue.

I have located the spoiler/diffuser part number in the DIY forums. Thank you Loren for pointing me the right direction.

[jmj996]

I have to agree that struts affect ride height, which is why I was focusing on that. I also believe that shocks affect ride height. I have very little experience to back that up, but when I replaced a set of relatively new KYB's with a set of race-grade Koni's on the rear of my 86 951 last fall, the rear height went up almost 1/2"!! On this car, the ride-height effect of a rear shock is magnified because it's a torsion bar setup, not an a-arm setup, and the mounting point for the shock is between the suspension pivot point and the rear wheel, not AT the rear wheel. Fortunately I was able to install an aftermarket eccentric bolt that allowed me to drop lower than the stock eccentric allows, getting some of that undesired lift back down.

I'm sold on the fact that I'm buying new rear struts and springs for the 996, but I will not be going the M030 route. One, this is a cabriolet, it's more for joyriding and fun daily driving than really getting on it, plus small kids go for a ride on occasion, and they're stomachs don't always agree with the ride stiffness as it is now! Two, I believe the M030 kit lowers the ride height if I read correctly, and I definitely can't afford to do that with my driveway. :o

So, where is the best place to source OEM-spec strut and spring packages? I have used Sunset Imports on numerous occasions, these guys are great, and they make the extra effort to ship these to me with a nonstandard process (FPO military address). However, I'd like to get a set with the new springs and bump stops already mounted - I just want to pull the old struts and install the new ones in a single swap. Other than getting the caliper bolts, anything else I need to pick up?

I'm very interested by perryinva's comment regarding ride height measurements - I need to find the details and examine this closely after the struts are replaced to see if there's anything else awry. I've had a squeaky rear bushing on the driver's side for quite a long time now and am wondering if it's prematurely wearing out.

Thanks!

[jmj996]

Koni FSD's (just now available for the 996) from Paragon Products are on the way. I decided not to buy replacement springs yet, I'm going to install these and measure everything per the factory manual. I will probably also swap the LR and RR springs (assuming they are identical) to see if that has an impact. Really looking forward to driving the car with these. I have great highways for the daily commute, but the last five minutes to my house off the highway is just ridiculous (that's just Naples - it's like that here). Also, the salesperson said he had an opportunity to test drive cars with these at a Koni factory test center. One of the interesting aspects he mentioned is that cars fitted with FSD shocks/struts did not kick in the PASM as much as the cars that had factory struts & shocks, seeming to validate that these allow the car to keep a better handle on the road. Probably not a good solution for the track because you wouldn't always know exactly how the car is going to react at the limit, but they seem ideal for a daily driver.

From the web site:

-----------------------

Frequency Selective Damping

The first shock absorber offering superior road-holding without compromising comfort.

Koni introduces FSD, the first no-compromise shock absorber in the world. A revolutionary new technique which combines the benefits of firm and comfortable suspension in a single perfect shock absorber. Firm for sporty driving on even road surfaces. Comfortable for a smooth ride on uneven road surfaces.

Realizing the seemingly impossible! Two characteristics that seemed diametrically- opposed, proved to be a source of inspiration for specialists from KONI. Following lengthy development and testing, the ultimate solution was reached: KONI FSD - Frequency Selective Damping. A revolutionary new technique whereby the benefits of both types of ride characteristics are combined in one perfect shock absorber. Banishing the disadvantages of the past. FSD shock absorbers; a smart suspension system adjusting automatically to road conditions as well as driving style. And all of this in a fraction of a second. FSD guarantees greater stability, greater control and thus greater driving pleasure.

Edited February 1, 2010 by John Jones