New member, question about rear shocks and handling

Hi, I'm new here and just bought a 2001 996 C4 6MT with 100k miles for a very good price The Carrera 4 has been a dream car for me for a while and I'm extremely happy to finally get one! I love driving it but I noticed that it seems a bit unstable at high speeds (but not dangerous) especially when taking left hand corners. It tracks straight with no pulling, just the back end feels a bit loose. The car has been in an accident, it was hit in the back about 10yrs ago. I took it for a prepurchase inspection before buying and had the alignment checked and it checked out ok. I jacked up the car and took a look to see if there was any obvious problems, everything felt very tight, the bushing look ok and there is no play anywhere and there are no strange sounds when going over bumps. The suspension does feel a little softer than I would have expected from a porsche, but I don't have anything to compare it with. Now onto the one issue I was able to find, it seems that when they fixed the car they replaced the right rear strut with another Bilstein strut but a different type, the B6 version (PN: BE5-2993), and from what I can gather, they come stock with something closer to the B4 version. Would this account for some of the instability and poor left hand cornering (it feels like it floating or the tires are really low on air)? Currently the rear tires are on 18" rims, Continental ContoProContact 265/35 R18 at 40psi. The rear tires were at 36psi originally but then I added more air and it did improve the handling a bit. What else should I look for or check while the car is up on jack stands? Cheers, Dave I've included a gratuitous pic

Here is a pic of the alignment from the garage. I asked about the out of spec numbers and was told that they were so minimal that it shouldn't affect the handling. I'm going to replace the rear shocks and probably the front shocks as well. I'm just worried that, while having different struts is definitely a problem, there could be something else adding to the problems described in the above post and would like opinions as what they could be.

Congrats on your purchase! Unmatched units would definitely not be good for handling. I saw a set of pss10's in the classified with top mounts if you want to replace them all. i have a 996 too and in general the car is a little "squirrely" in the rear when compared to my previous boxster. Baby got back

Thanks! For sure a fun car, just need to get a few things sorted. I saw the PSS10's but they are for a C2 and unfortunately I don't think they will work on a C4 otherwise I would get them. Those Bilstein B16 shocks are at the top of my list, although I would really like the damptronic ride control versions but I don't know if there is a 996 version of them, I haven't found any yet anyways..

Nice car. Looks really good. Hope you enjoy. Where are the classified adds???

Replace your motor mounts

@hotrodaxel1976:Thanks The classified are at the top of the porsche discussion forum page https://rennlist.com/forums/marketplace/parts/search/ @dporto: I had the car in the garage a few weeks ago installing an IMS solution among other things and was told the motor mounts were still ok. Why do you think the motor mounts could cause this issue or at least be a contributing factor?

Had a back end bump ten years ago. Did you know this fact before you bought the car? That might just be the contributing factor to the handling problem at speed. You just may be throwing good money after bad trying to fix the bad handling at speed. I hope you are not thinking of tracking the car when you know it has had a back end pile driver no matter what the guy who did your pre purchase inspection is telling or not telling you. Motor mounts are a cheap enough DIY job but do not expect a miracle. I would take notice of the typing across the alignment result (Handling and safety problems may result). Anyway good luck with your endeavor.

The "water sloshing around in a bucket" feeling is one of the first things I noticed while taking quick turns. Replacing the motor mounts fixed it. This is not to say it's the only thing going on with your car, but I bet it's a contributor at least.

When I first got my car, I thought the shocks were shot or something else was wrong. Turned out that my 996 was just very compliant and floated a bit over bumps. But on the track driven hard, my car felt planted. I nearly replaced all shocks, struts, springs, motor mounts, etc. All I ended up doing was performing an alignment. My car only has 50,000 miles. Since your car has a known issue - the shock - I'd address that. And take it to a place where they can laser-check the body and frame to make sure it's straight.

@Hurdigurdiman. That's my biggest concern is throwing away money chasing problems around. I was planning on autoxing it but not before I figure out this alignment issue (I may go to one to get other peoples opinions on the cars handling). I did know about the accident before buying and did what I could to verify that it was OK before buying. I did get a very good price for it so it was a risk I was willing to take given the information available at the time. @dporto. Thanks for the info, I didn't realize that engine mounts could be a contributing factor. I'll have to look into it some more. @murphyslaw1978 (good username! seems appropriate now..) I haven't owned too many vehicles, only just bought my first one in 15yrs about 1.5yrs ago. It was an gen2 Audi TT and it had a much harsher ride going over bumps and I expected the porsche to be similar. I think maybe my first step should be to get a laser-check on the unibody, I was hoping the wheel alignment check would have been sufficient to point to any major issues but it seems that I may have to go further (laser alignment check wasn't possible at the time of purchase). Then if that checks out OK or at least not too severe then I'll change the rear shocks and see what happens. Does anybody else feel that the rear is perhaps a bit looser feeling than other vehicles?

Assuming the tire pressures are all good and the tires all match, then my recommendation is to replace the "B6" strut/shock with the correct new strut/shock. In fact my advice would be to replace both the "B6" strut/shock and the other side. After 100K miles the other side is probably going to perform differently than the new strut/shock on the other side so if you just replace one strut/shock you could just end up transfering the the floaty feel from when taking left hand corners to when taking right hand corners. Then get the car properly aligned. Not at the shop that told you those numbers were ok though. Give that shop a miss.

Hi Lexvortex, I had a really lose rear end, and it was shocks. At high speed on autobahn the expansion joints would make the rear go scary. At rest the shocks seemed fine. Changing them out made a world of difference. Given the age, I would change other suspension parts while in there. my alignment was coming back perfect each time. Would recommend a Porsche/race alignment specialist. transformed the car

I definitely want to replace all the struts, but I figure if I'm going to go through the hassle of doing it, i might as well upgrade the suspension and replace the bushings but before I spend a lot of money on suspension I would like to know if the chassis is ok. What does it usually cost to check the frame alignment on these cars? I want to thank everyone for the feedback and responses here, it has really helped me to figure out a path forward. Cheers, Dave

Hmmm.... I don't remember reading that you had 1 different shock in the rear. That's not good. Since you already have the H&R lowering/sport springs. I'd recommend the Bilstein B8 struts/shocks. They're matched to the sport springs and are a little stiffer than the stock B4's... Good luck

My '02 C2 has rear pressure recommended at 44psi. Are the Gen I's different?

Quotes source post: 14267537

Nope, 44 psi is correct afaik

So I've put in new engine mounts, stock version, and upped the tire pressure to 44psi and the car does handle much better, thanks for all the input. The new engine mounts definitely helped the most. Dporto, water sloshing around in a bucket analogy is an accurate way to describe the feeling before the new engine mounts. The car feels much better when accelerating through a corner than it did before and feels much smoother in general. I'm still looking into new shocks, I have a few options that I've started a new thread on.