Is a little suspension compliance too much to ask? (longish)

[ulrichd]

After a year of 911 ownership (78Sc) and quite a bit of suspension work, find myself with a vague feeling of dissappointment about the bone jarring ride and the "there's got to be something wrong" heavy steering.

Before you reply with "Get a Camry!" - I was, in my days (10+years ago) a frequent SCCA autocrosser (DSP class) and almost all of my past cars have had some sort of modification and I have made the occasional trip to the track (BMWCCA). My other ride is a 03 Cooper S with lowered suspension, Koni FSD shocks and 17" wheels. That is a FIRM ride - the 911 is beyond that.

My 78 has:
- new tires (205/225/16)
- new shocks (Bilstein HD, not Sport)!
- Weltmeister rear spring plate bushings replaced (rubber, not polybronze)
- Rear drop links replaced
- Swaybar bushings replaced
- Turbo tie-rods and bump steer kit installed

To do:
- Ball joint replacement (hopefully will help steering effort and cure a wheel shimmy at 70-75mph).
- Alignment, corner balance

Ride height is 25" all around (I have 205/50, not 55 in front). I have proudly done all the work myself. I really need some advice as I am starting to wonder whether I am a "911 guy" after all.

Ulrich

Ulrich

[Rot 911]

No doubt at very slow speeds a 911 takes a bit of effort to turn the steering wheel. As for the bone jarring ride, what air pressure are you running in your tires? Front should be around 32 psi and rears 34-36 psi.

[Chuck Moreland]

Sounds like you know the difference between firm and bone-jarring, so I think we can rule out an over sensitive backside on the driver

Still, I would try to find someone local who has a similar car (SCs are a dime a dozen) - drive each other's cars and compare notes. Or find an experienced Porsche guy to make an assesment to determine if your car is "normal" or has something wrong.

Wheel shimmy indicates you do have a problem, but that may not be related to ride quality.

A little more information would be helpful too:

What type wheels are you using, and size?
Any wheel spacers?
What are the alignment settings?
Tire pressure?
What size torsion bars?
Is the "bone jarring" over minor surface irregularities, or just big bumps?
The car was lowered, was it corner balanced?
Are the bump stops shortened?
Are the US-spec strut top spacers removed?

[ulrichd]

Chuck,
Thanks for the reply.

The car has stock torsion bars, 7&8-16" Fuchs, 5mm spacers in back. Tire pressure is 30f/34r. I removed the US spacers in the front when I installed the Bilsteins. The car has not been aligned or corner balanced, I want to finish the ball joint work first and have a look at my a-arm bushings.

Thanks.
Ulrich

[the]

I don't know the answer, but to give you some encouragement, you should stay on it! SC/Carreras with stock or stock-ish suspension components and settings should have a fairly plush ride, nowhere near "bone jarring" even on relatively rough roads.

And steering should be light, too, at anything over 5 mph. (Are you using a stock diameter steering wheel?)

Something is not right, stay on it, when you figure it out, you'll end up with a very comfortably riding car.

[racer]

How old are the torsion bars and their bushings? If never replaced, thats at the very least some old rubber bushings. Worse case is maybe 1 or more TB's are broken.

I can't recall the stock TB sizes (18f/24r?) but are the HD's "matched" to this small of a TB? Could be the shock is doing more work than it should to control the ride. Just a thought.

[ulrichd]

I prefer to think something is wrong over "that's just the way they are". 911s used to have a great reputation as grand tourers and there is no way anyone would want to cover a great distance that in mine.

Thanks for the encouragement.

[ulrichd]

Originally posted by racer
How old are the torsion bars and their bushings? If never replaced, thats at the very least some old rubber bushings. Worse case is maybe 1 or more TB's are broken.

I can't recall the stock TB sizes (18f/24r?) but are the HD's "matched" to this small of a TB? Could be the shock is doing more work than it should to control the ride. Just a thought.

Interesting thought, but there are not many shock choices. Bilstein HD and Sport, Konis and Boges (do they still have hydraulic fluid in them?). My car came with Boges from the factory. Would they have been a better choice?

Ulrich

[rvanderpyl]

Bilstein HD are pretty Stiff. YOu might be better off with Konis set to the soft end of their range, or if you want a cheap and apparently good riding solution try KYB's

[racer]

Originally posted by ulrichd
Interesting thought, but there are not many shock choices. Bilstein HD and Sport, Konis and Boges (do they still have hydraulic fluid in them?). My car came with Boges from the factory. Would they have been a better choice?

Ulrich

I'm not sure. I redid my 911 suspension years ago but went with custom valved bilsteins to "match" the torsion bar rates. While my ride was "firm" it was not "jarring".

So. how old are the TBs and bushings? I think that may be the problem since they are, essentially, "springs" that carry the weight of the car. If the are broken, sagging, binding up, they can't do their job.

[ZAMIRZ]

I think you're best off returning everything back to stock if you feel the minimal mods you've done are "bone-jarring." No offense, but you've done practically nothing to your car compared to a lot of others on this forum, and you don't hear any of us complaining about it in utter disappointment.

My SC has the following:

turbo tie-rods
Bilsteins (Sport, not HD!!!)
later Carrera sways
Neatrix rear spring-plate bushings
stock torsions in front, 26mm turbo torsions in back.
lowered and aligned, but not corner-balanced.

In the grand scheme of things, I've done just about the most basic mods to my car, haven't even gone through and changed everything to polyurethane or bronze, no heim-joints, no crazy thick tbars, no sways with adj. preload, etc. like many others.

Compared to my other car (MINI Cooper S with Bilsteins and H&R springs) the 911 is more comfortable on the highway, and maybe a tad softer on the street. I'd describe the MINI as extremely firm, and uncomfortable over really bad pavement. Whereas the 911 is firm, but can handle most anything except for a giant pothole or chunk missing from the road.

Something to think about, maybe a modified 911 is just not for you...

[ulrichd]

Amir,
I am not sure what mods you are talking about. Tires, swaybars and torsion bars are all stock. The Bilstein HDs were chosen over the harder Sports. The Neatrix bushings were not a "mod" but replaced tired original factory bushings. I am not sure what I would "return to stock" as you say. As for complaining, I am looking for help which is what this board is about.

Ulrich

Originally posted by ZAMIRZ
I think you're best off returning everything back to stock if you feel the minimal mods you've done are "bone-jarring." No offense, but you've done practically nothing to your car compared to a lot of others on this forum, and you don't hear any of us complaining about it in utter disappointment.

My SC has the following:

turbo tie-rods
Bilsteins (Sport, not HD!!!)
later Carrera sways
Neatrix rear spring-plate bushings
stock torsions in front, 26mm turbo torsions in back.
lowered and aligned, but not corner-balanced.

In the grand scheme of things, I've done just about the most basic mods to my car, haven't even gone through and changed everything to polyurethane or bronze, no heim-joints, no crazy thick tbars, no sways with adj. preload, etc. like many others.

Compared to my other car (MINI Cooper S with Bilsteins and H&R springs) the 911 is more comfortable on the highway, and maybe a tad softer on the street. I'd describe the MINI as extremely firm, and uncomfortable over really bad pavement. Whereas the 911 is firm, but can handle most anything except for a giant pothole or chunk missing from the road.

Something to think about, maybe a modified 911 is just not for you...

[goat]

About a year ago I re-did my suspension.
Prior to doing the work the front end was very harsh.
The culprit... the right front torsion bar was rubbing metal to metal.
Fixing this solved much of my suspension problems.
You cannot tell unless you remove the bar, since it binded under load.

[ulrichd]

Tim,
I pulled, inspected and re-greased my bars when I did the shocks, but at the time, did not know to also check the a-arm bushing (learning as I go). It's next on my list.

Ulrich

[the]

Yeah, you are pretty much at a stock configuration. Your ride should be very nice.

One thing I've noticed on 911s is that they do seem sensitive to ride height. If you take a stock suspension car, and lower it too much, you destroy the ride quality.

And the factory ride height on these cars is much higher than people believe. Post a pic of a car at TRUE "Euro" ride height, and most people would say "Nice car, but you need to lower it." Post a pic of an SC at TRUE U.S. ride height (if you can find one), and all of the "rally car" and "Paris to Dakar" jokes come out.

Although I don't think 25" is excessively low. Can you post a side view pic of your car?

Again, though, stay with it. They aren't "all like that."

[JP911]

When you installed the bump steer kit (I assume steering rack spacers), did you loosen the linkage in the steering to adjust to the new position of the steering rack? It's been awhile, but I remember this being necessary. I drove the car around the block at low speed to get things settled before tightening everythin back up. A search on this board will provide more details.

[Grady Clay]

Ulrich,

I agree.

Bone-jarring indicates something wrong. I’ll speculate something in the shocks. Shock absorbers are sophisticated and complicated devices. It is remarkable that work as well as they do.

Yes, a 911 must have suspension compliance. My 2200# SWB with 20/28 mm torsion bars, RSR struts and substantial sway bars has about 4 cm deflection in compression under normal use. Under extreme conditions, the maximum is about 7 cm (probably with the rubber stops fully compressed). Even with Goodyear race tires on it for track, it has light (911) steering

A simple test is to stand in the trunk and bounce up-and-down. Note the deflection. Note if there is any L-R difference. Repeat in the rear on the engine mounts outboard.

When talking about suspension compliance, look at the effort made with the RS Spyder. The bump response is actually somewhat soft. That is what keeps the tires in contact with the track. The complexity is to add stiffness (roll and other) when appropriate. We don’t have that privilege with our “old” 911s.

Please report what you find.

Best,
Grady

[AES]

older 911s have a lot of stiction compared to more modern suspensions, this leads to a harshness particularly at low speeds

[ulrichd]

AES,
I would definitely describe it as low-speed harshness. Once I get going, and the air cooled motor music is in my ears, all is forgiven. Until the next stoplight. I will try Grady's compliance test.

Ulrich

[ulrichd]

Thank you for the responses. Here is my plan as of right now:
- Do the ball joint replacement. The car has the originals in a 154K miles. We'll see what impact this has on the steering feel.

- Pull and inspect front torsion bars for metal to metal contact and see if a-arm bushings are elongated.

- Do Grady's bounce test when the neighbors are not looking.

Ulrich