911 suspension bounce

[DanPez]

Hi all,
I purchased a 73 911 about 2 years ago, haven't driven it much, and was wondering if anyone could explain to me if the bouncing is normal or not.
The previous owner installed fairly new Koni struts in the front and I replaced the rear Bilstein with Classic Koni.
When I had the rear shocks out and compared the Koni with the Bilstein, the Koni's had really hard damping.
Installing them on the vehicle with the weight of the engine .... the response seems odd.

If I were to put weight on the vehicle, whether it be in the front or the rear, it drops 1/2" or so and when I let go it repositions itself without a bounce.

If I were to take the front or rear and push / pull the vehicle up and down it oscillates (bounces) till I let go and continues bouncing 2 or 3 hops.

At slow speed, 30-40 mph, with cracked paved roads the vehicle feels like a bucking horse.
At higher speeds its just seems fine.

Cornering or braking has hardly any front pitch.

Should I be thinking of changing shocks?

Thanks in advance

[midnight911]

are you sure it's not your seat. one time (a different car) I was struggling to settle the car. changed the seat and the problem was gone. just sharing my lame experience...

[Tidybuoy]

When I first bought my '74 911, I thought the front was excessively bouncy. I eventually replaced the front struts and bushings. During this project, I discovered that one of my shocks was sticking and not rebounding like the other side. In addition, my front rubber bushings were frozen up. I diagnosed this when I jacked up the front end and it took about 30 seconds for the suspension to fully extend.

I highly recommend replacing the '73's old bushings. mine were toast and Elephant Racing makes very good factory replacements. I then changed out my Koni's with Bilstein HD front and sports on the rear and my car now rides very well and definitely feels in control.

[Tidybuoy]

One more thing:

What's wrong with this picture? I thought it was very cool that my car could get the wheels off the ground until somebody on this board pointed out that this was a clear sign of suspension binding up.

Notice in the 1st photo that the passenger wheel is not extending. This was also the case when I would jack up the car and it would take about 30seconds for the wheel to fully extend. After I replaced the suspension, my bounciness went away.

[twistoffat]

+1 on the shocks. I tested a 73 years ago when looking for mine. Especially with an empty tank it felt like the front end was attached to a trampoline. Had a PPI done and they confirmed the shocks needed replacing.

[DanPez]

Thanks for the info.

midnight911 ..... LOL, just laughing because the first time I sat on the drivers seat and weighing over 200lb I sank in as if I were sitting on a bean bag.

Vern ..... I did have all four wheels off the ground and did check for bindings.
I remember the first time I lifted the rear, from a distance, I saw my right side dropping lower than my left. Figured out that the Bilstein were different.
Beginning with 72 models the length and diameters are not the same.



This is why the Bilstein were replaced with Koni's 82k 1756..... and also to have them all the same manufacturer.

twistoffat ..... I'm questioning that myself but on all 4 shocks?
I'm grabbing the body of the vehicle in the front center and then in the back center ....... pulling / pushing up and down .... it oscillate till I stop and does 2 or 3 bounces.
If one of the wheels would bounce more than the other ...... I would probable say "OK this shock needs replacement" but its the whole car.

Could it be all 4 shocks?
The ones in the rear were just purchased and never been used. On the bench the damping is really hard.

[jpnovak]

It sounds to me that your Konis were not setup. The factory setting is usually with the rebound damping set soft. The rebound damping is adjusted by disconnecting the top of the shock, compressing the damper rod until it bottoms out (snubber removed), turning slightly until the adjuster mechanism engages and then rotating. Generally CW is more rebound damping, CCW is less rebound damping. Some of the shocks have a detent ball that marks off "clicks" of adjustment. Generally I start setting up Konis by 2/3 toward full damping from full soft. This gets you started. Then you have to fine tune based on wheel size, car weight and other factors related to preference.

To fine tune you will want to find a suitable "bump" in the road that the car unweights and then compresses. The car should rebound to a single "set" meaning it will compress and quickly return to normal ride height without any oscillations. If you have too much rebound damping you will end up in a situation like Tidy, above where the suspension remains in a compressed state because the shock does not rebound fast enough. That is not a good situation to be in.

The fact that you drop the car on the ground off the jack and it sags, then recovers is completely normal. Koni shocks have inherently softer compression damping than Bilsteins or Boge. This means they will compress farther (and easier) under the same load.

I prefer the softer compression on early cars. They are lighter weight and you get more suspension travel for the same force impact (bump). Spend some time to set them up correctly and you will enjoy the handling. If you are not capable, find a shop that is.

And yes... rubber suspension bushings have most likely surpassed their end of life. Its likely past due time for replacement.

Consider a full suspension overhaul at this point.

[Driven97]

Remove one (or both) front shocks and move them by hand. They should be difficult to compress quickly, then should slowly return to fully extended on their own.

If they compress / extend without much effort, or do not extend on their own, they're dead.

[jpnovak]

Sorry Matt. Not entirely true. Koni Classics are not gas charged and will not return to original length without being pulled out with an external force (usually hand on the bench) or spring tension on the car.

[DanPez]

It sounds to me that your Konis were not setup.
I think you hit it on the nose jpnovak!
I've seen one shock or maybe two go bad but all 4 I found it odd.
My bad ....
I found the pdf for the rears and this info that confirms what you mentioned.
The fronts are probably the same



Thank you all.
Cheers

[Driven97]

Wow, thanks! I've never even seen a non gas charged shock. Mean something new every day.

So what compensates for the shaft volume?