Stiff Front Suspension - Which Dampers and Control Arm Bushes?

[mikedsilva]

Several months ago, I went to rememdy a front end that would 'shimmy' at high speeds.

I found that my control arm bushes were quite worn and my front shock absorbers had lots of play too; you could push sideways on the strut assembly and the wheel would rock up and down, similar to how it would move when checking for a worn front wheel bearing. (btw, I had already put all new wheel bearings in !)

I removed the control arms and ordered a set of control arm bushes from my local stockist (they supply the Rennline HD bushes) and sent the yellow Bilstein HD away for rebuilding by our local Bilstein workshop.

With the new components installed along with new tie rod ends and ball joints, my front end appeared to be 'cured'.

However it is now quite stiff. In fact any small bump is quite jarring and tbh, annoying.
Also, at speeds above 100km/h (60mph) the front end wobble in the steering wheel SOMETIMES appears. It's very slight and only on some surfaces. I cannot pin it down but I can be on a stretch of highway and the wheel is perfectly smooth.. and at other times, has an annoying 'jiggle'.

I'm trying to ascertain if that is considered normal feedback considering I have a fairly stiff front end now?

I'm contemplating removing and replacing both my front shocks and bushes again.
This time opting for std RUBBER bushings and the green 34001127 bilstein shocks.

The car is a street car 99%.
Rear shocks are the yellow Bilstein HD.

Looking at the range of options available from our host for bushings, there are loads of options.

Has any one used the URO bushings?
Are the Elephant Racing rubber bushings worth 4x the price of the URO?
I'm inclinded not to use Rennline again.

Any feedback appreciated.
Mike

[Mixed76]

Mike, the stiffness is almost certainly the rebuilt shocks.

Bushings will tell you they're too stiff by increased noise and/ or vibration in the steering wheel.

Sent from my Pixel 7 using Tapatalk

[mikedsilva]

Originally Posted by Mixed76

Mike, the stiffness is almost certainly the rebuilt shocks.

Bushings will tell you they're too stiff by increased noise and/ or vibration in the steering wheel.

Sent from my Pixel 7 using Tapatalk

Thanks for this. Tends to confirm my thoughts that I need to replace BOTH shocks and bushes again.....

It never ends... !

[Ian Comerford]

I understand that Bilstein Green are more suitable for 99% road use than Yellows after researching this for my suspension refresh. The Yellows are firmer which is contributing to your ride being (too?) stiff

[safe]

Yellow Bilsteins are probably the Clubsport/Rennen I variant, there is/was also an ever stiffer Rennen II.
Good for stiffening up the suspension, but they are really harsh, you feel every pebble on the road.
I would go for the Elephant Racing rubber on a street car.
I have the Rennen I on all four corners, but am thinking on replacing the fronts for the normal green on the front because I don't track the car much anymore.

[mikedsilva]

Originally Posted by Ian Comerford

I understand that Bilstein Green are more suitable for 99% road use than Yellows after researching this for my suspension refresh. The Yellows are firmer which is contributing to your ride being (too?) stiff

Cheers for the input.

However, I have found that the colour does not mean quite so much anymore. I had an earlier thread posted last year when I was researching which ones to buy compared to what I already had and someone listed some great resource websites.
See here: https://forums.pelicanparts.com/porsche-911-technical-forum/1144651-79-sc-strut-insert-shock-absorber-confusion.html


I dont have the definitive guide for what is what.. but for example, I think the current B6 HD come in green now, not yellow like before. And then there is the question of which is firmer... 'Sport' or 'HD'? Not to mention that different retailers refer to the same part number shock differently; ie, the same shock with part number 34001134 is called B8 Performance Plus here on PP,but on a UK site they call it B6 Std Type...or the 34001158 is referred here as B6 Performance Rally Setting but the UK site calls it a B6 Sport Type....How are you supposed to choose correctly??

I think I am going to order the Elephant Racing rubber bushes.
The analyst in me, wants to change only one item at a time so I can pinpoint the resultant effect of the change, but it's a pain of a job so I will likely change both shocks and rubbers at the same time. And I'm leaning toward the 34001127 which Pelican calls the B6 Performance, and it is not available on that UK site!

[safe]

Go by the Bilstein part numbers.

Original/turbo: P36-0113 (or P36-0114) / B46-0169
Sportlish strasse: P36-0115 / B46-0975
Clubsport / Rennen I: P36-0116 / B46-0967

The original Bilstein, as I understand, isn't available anymore, only the Turbo.

[Bill Verburg]

Originally Posted by mikedsilva

Several months ago, I went to rememdy a front end that would 'shimmy' at high speeds.

I found that my control arm bushes were quite worn and my front shock absorbers had lots of play too; you could push sideways on the strut assembly and the wheel would rock up and down, similar to how it would move when checking for a worn front wheel bearing. (btw, I had already put all new wheel bearings in !)

I removed the control arms and ordered a set of control arm bushes from my local stockist (they supply the Rennline HD bushes) and sent the yellow Bilstein HD away for rebuilding by our local Bilstein workshop.

With the new components installed along with new tie rod ends and ball joints, my front end appeared to be 'cured'.

However it is now quite stiff. In fact any small bump is quite jarring and tbh, annoying.
Also, at speeds above 100km/h (60mph) the front end wobble in the steering wheel SOMETIMES appears. It's very slight and only on some surfaces. I cannot pin it down but I can be on a stretch of highway and the wheel is perfectly smooth.. and at other times, has an annoying 'jiggle'.

I'm trying to ascertain if that is considered normal feedback considering I have a fairly stiff front end now?

I'm contemplating removing and replacing both my front shocks and bushes again.
This time opting for std RUBBER bushings and the green 34001127 bilstein shocks.

The car is a street car 99%.
Rear shocks are the yellow Bilstein HD.

Looking at the range of options available from our host for bushings, there are loads of options.

Has any one used the URO bushings?
Are the Elephant Racing rubber bushings worth 4x the price of the URO?
I'm inclinded not to use Rennline again.

Any feedback appreciated.
Mike

There are multiple versions of Bilstein and part #s were changed over the years

most are b6 either green or yellow

hd are green b6 and sport are yellow b6

but there are/were shorter versions called b8

all have linear valving


These are the specs provided by Bilstein , but there has been +/-10% variance over the years due to manufacturing and product changes



for a street car w/ 19-22mm t-bars i'd use the green b6
35-001270 current spec 1400/1000

these pair well w/ the sport yellow rears

If having them revalved changing to a digressive valve stack is recommended


Here is a graph provided by Elephant Racing showing the curves for hd, sport and digressive revalve


the left hand side of the curves is maneuver(low speed) and the right hand(high speed) is road irregularities.

KW and MCS come standard w/ digressive valving, but only MCS is monotube

the fancier versions come w/ external cans and have way more adjustments which mostly are over kill for street use.

My guess is that your current issue is related to the shock valving, sport fronts are just to stiff for most street use

I used the yellow sport fronts for a very short period of time on my C3 , went back to stock green hd and never looked back

current front setup is Rennline sport rubber bushes stock C3 sways 20mm t-bars Bilstein green hd
rear is Rennline sport rubber and Bilstein Sport , stock C3 sways and yellow Bilstein sport

225/45 on 8 255/40 on 9.5 x17

If I were to redo I'd be looking for monotube, adjustable and digressive w/ bonus points for raised spindles

[H-viken]

I had Bilstein Sport on my last 911. Too harsh in my opinion

[HarryD]

Unless you are limiting yourself to a track, you want a compliant suspension to soak up the bumps.

IMHO a nice setup is:

Stock or slightly stiffer torsion bars
Soft Sway bars
HD Bilstein up front
Sport Bilstein in rear
Rubber bushes
Lowered

[mikedsilva]

Originally Posted by Bill Verburg

for a street car w/ 19-22mm t-bars i'd use the green b6
35-001270 current spec 1400/1000

these pair well w/ the sport yellow rears

hi Bill
would you know the part number for the shock absorber only, that fits in a Boge strut? suit 1979 SC?

[mikedsilva]

Originally Posted by HarryD

Unless you are limiting yourself to a track, you want a compliant suspension to soak up the bumps.

IMHO a nice setup is:

Stock or slightly stiffer torsion bars
Soft Sway bars
HD Bilstein up front
Sport Bilstein in rear
Lowered

Harry, which is considered stiffer; HD or Sport?

[HarryD]

Originally Posted by mikedsilva

Harry, which is considered stiffer; HD or Sport?

Sport. But in the rear it seems to help with overall compliance when paired with soft torsion bars.

[famoroso]

Another potential cause of your front end stiffness...

Underbody sway bar? Did you replace front sway bar inner bushings at the same time? If so, did you confirm that the sway bar is not binding?

From this thread Sway Bar Upgrade

Originally Posted by Driven97

Hopefully not too late, but make sure you fit your bushings. When putting a front bar on my car, the car suddenly got very pushy, ride went downhill, and I lost a lot of braking performance. The (poly) bushings were pinching the bar so tight it wouldn't rotate, essentially making it work like a lever spring rigidly attached to the chassis.

30 seconds with a belt sander and I regained my front grip. HUGE difference. Since then I do this on every bar I install, favoring slightly loose over slightly tight. I also put a wrap of teflon pipe tape over the bar where it rides in the bushing.

My $.02, ymmv, and all that jazz.

Before:


After:

[PeteKz]

Mike, I agree with Mixed76 that the stiffness and harshness is not the bushings, but the shocks.

I also very much agree with HarryD that you are better off with a softer set up for a street driven car. You can go significantly stiffer on the torsion bars, as long as you don't overdo the shocks. IMHO, most of the aftermarket Bilstiens are too damn harsh.

See my setup in my signature line below. I really like the Koni Sport (yellow) adjustable shocks. Even on my 2330-lb. 1973 car, at the softest setting they provide a compliant ride on the street. At their firmer settings, they work well on the track. Having an external adjustment knob on the top of each shock makes experimenting with them dirt simple and easy. Even if you think you might go for expensive KW or similar digressively valved shocks, start with the Konis and learn what works for your streets, driving style, and tolerance for NVH. At $850 or so for a set of 4 (on sale), I think it's the best option available. You're looking at $thousand$ for the other options.

HarryD and Nickelplated have driven my car, and should add their observations of its street driving characteristics. I have driven their cars, and I think that Harry's is a good street setup, and Nickelplated's car is too stiff for normal street driving; however he lives somewhere that he has lightly traveled twisty roads nearby, and can run it hard without much traffic.

See this video evaluation of Bilstein B6 versus Koni Classic (but I still recommend the Koni Sport):
https://www.youtube.com/watch?v=JzSzoESEhCQ&t=53s

Re the differences in rubber bushings: I'll say up front, I don't know which ones are better and why. But I do know that the differences almost certainly have to do with the material they are made from. Rubber is not all the same. Besides the obvious differences in duromter (hardness) ratings, the amount of natural rubber incorporated into the rubber makes a huge difference in elasticity and how long they last. Cheap Chinesium rubber gets hard and cracks in a few years, if that long. I have seen some rubber parts from suppliers who source in China get hard and crack and crumble in 2 years or less. Whereas, the OE rubber on your Porsche lasts for decades--I have rubber bushings and grease seals on my 1973 that are still pliable and smooth 50 years later. But there is almost no way you can test that, except by buying the parts, installing them, and seeing g how long they last (unless you work for an industrial chemical lab or something like that). I would call ER and ask them about the rubber they use, and where it comes from. Tell them exactly why you are asking, and that you want to get the highest quality rubber, because this is a job you don't want to do again in your lifetime.

Another consideration about the rubber bushings: How do you plan to press them in? This is not trivial. It is very difficult to compress the rubber parts into the metal parts without tearing it. Consider sending your A-arms to ER and have them do it for you with their tools and bushings.

Re the shimmy in the front end: Often that is caused by front wheels slightly out of balance. Since you don't drive in a straight line all the time, one wheel rotates a little faster or slower than the other, and those imbalances go in and out of phase, causing the vibration to come and go. This is especially noticeable in a long sweeping turn on a highway, where you will go from little or no vibration to more vibration and back to little/nothing. If it does that, have your balance checked. Slight out-of-roundness also causes this feeling.

[HarryD]

I will add that tire selection is also a meaningful factor.

I recently switched from Toyo R1R's to Continental ExtremeContact Sports 02 on my car. While the grip with the Toyos was great for track and Autocross, the Noise and Harshness was obvious. I gave up a noticeable amount of grip for a quieter tire that does not deliver a harsh ride (which my wife prefers).

[PeteKz]

^^ This too.

[mikedsilva]

Lots of good feedback above, thankyou.

I agree that tyres (tires) can have a good deal of input here. I borrowed a set of Braid wheels fitted with Yokohama AD09 and found it quite harsh.
I ended up buying a set of Nankang CRS semi slick tyres (wanted to experiment as I had never had sticky tyres) and the ride was noticably more compliant in comparison to the AD09, however the car is still quite stiff.

On my previous car, I used the Bilstein HD front inserts and rubber bushings from ER. Whilst the ride was firm it wasn't jarring.
On this car, I have the Rennline (hard as hell) rubber bushings, and had my front bilstein rebuilt to original HD specs, and it's quite stiff.

So in theory, if they revalved correctly, then the bushings are whats causing my harshness compared to my previous experience.
And when thinking about bushings, surely the firmness must have a lot to do with the feel of the car on the street; why else would they say poly and bronze bushings are simply too hard for a street car? I've driven a couple of cars for a short distance with poly and bronze bushings, and can tell you I couldn't wait to get out.

When I first received these rennline HD bushes, I questioned the seller thinking they were poly- they were THAT hard.


HarryD - how do you like the conti? I tried to find a supplier for those here in Aus but cannot seem to get.

[HarryD]

Originally Posted by mikedsilva

Lots of good feedback above, thankyou.

I agree that tyres (tires) can have a good deal of input here. I borrowed a set of Braid wheels fitted with Yokohama AD09 and found it quite harsh.
I ended up buying a set of Nankang CRS semi slick tyres (wanted to experiment as I had never had sticky tyres) and the ride was noticably more compliant in comparison to the AD09, however the car is still quite stiff.

On my previous car, I used the Bilstein HD front inserts and rubber bushings from ER. Whilst the ride was firm it wasn't jarring.
On this car, I have the Rennline (hard as hell) rubber bushings, and had my front bilstein rebuilt to original HD specs, and it's quite stiff.

So in theory, if they revalved correctly, then the bushings are whats causing my harshness compared to my previous experience.
And when thinking about bushings, surely the firmness must have a lot to do with the feel of the car on the street; why else would they say poly and bronze bushings are simply too hard for a street car? I've driven a couple of cars for a short distance with poly and bronze bushings, and can tell you I couldn't wait to get out.

When I first received these rennline HD bushes, I questioned the seller thinking they were poly- they were THAT hard.


HarryD - how do you like the conti? I tried to find a supplier for those here in Aus but cannot seem to get.

I really like the Contis.

While I have a number of friends who swear by the Michelins for some reason, I have never been totally satisfied with them (granted only non-P cars).

For my 911, this is my second set of Conti ExtremeContact Sports (I tried a set of Toyo R1R's between the two sets and am currently running them on the P-car. My Mercedes C300 is on it's third set of the DWS. Like I tell everyone who will listen: well behaved, good in the wet and dry, predictable, reasonable NVH.

I did an HPDE recently and Autocrossed yesterday. Compared to the R1R's, a noticeable lack of grip but not like I was ice either.

When I got my 911 it had Toyo H4's, they stunk. I put a set of Yokohama ES100's which very better but not great. Then the Conti's.

For several years, on my first set of Conti ExtremeContact Sports, I used Hoosier SM tires for Autocross (take offs from the Miata Spec Racers with 4-6 heat cycles). They were a ton of fun but got tired of aways changing tires for an event.

[HarryD]

As a data point:

My 1973.5 with 184,000 miles has a mostly stock suspension. The upgrades were done years ago. I drive on the street for fun, autocross 5-8 times, and about 6 HPDE's a year.

My suspension has turbo torsion bars (21 mm front/26 mm rear).
Front and rear 19 mm adjustable sway bars.
I replaced my rear spring plates bushes with Neatrix parts. All other bushes are stock and original.
Bilstein HD fronts and Sport rears.
Weltmeister front Strut Brace
The Car has been lowered and corner balanced by a very good local shop.

Everyone who has driven my car (both at HPDE and street) reports the cars handles well.