SWB Alignment and Corner Balance Complete!

[304065]

Another item off the checklist!

One of the challenges for original cars which lack adjustable rear springplates is achieving corner balance. On the one hand, early SWB cars need all the handling help they can get-- on the other, the lack of adjustable rear springplates makes the process of corner balancing time consuming, and pretty much impossible to dial in perfectly, due to the discrete nature of the adjustments.

What I mean by this is what everyone knows-- that the rear springplates ARE adjustable, but only through the vernier feature. There are 44 inner splines and 40 outer splines, so to make an adjustment down, for example, you go up one spline on the inner (360/44 = 8.18 degrees) and down one spline on the outer end of the bar (360/40 = 9.0 degrees). The net result is 9.0-8.18 or 0.82 degrees of adjustment down, and iterating both sides in this way will eventually allow you to dial in the correct ride height.

I was able to get it in the ballpark, but I don't have a set of scales, so other than measuring the fender height (not the "factory" way of measuring ride height, but the way everyone does it, because the "factory" way is impractical) I wasn't able to really dial it in.

For help I turned to Tom Florio, owner of Advanced Automotive of New Windsor, in New York's Hudson Valley. Tom has been in business for 24 years and works on many different cars, but is passionate about Porsches. He had six or seven inside and a few more around the shop. Also, in a very similar scene to what I saw at Peter Dawe's place back in August, he had a blown-up 3,6 that had vaporized a couple pistons hanging forlornly from a stand. Missed shift? No, it just let go.

Anyway, here's what Tom was able to achieve:

LF 520
RF 462
LR 728
RR 721
Left Weight 1238 (51.3%)
Right Weight 1183 (48.7%)
Front Weight 982 (40.4%)
Rear Weight 1449 (59.6%)
Cross Weight 1190 (49%)
Total Weight 2431 (with fuel fuel, spare tire and driver)

Not bad-- the front weight differs by 58 pounds, where 50 is negligible for a street car. The cross weight would ideally be 50% which means the car handles equally well on left and right turns, but again, this is a street setup without adjustable plates.

Now to alignment:
Front height 25.25"
Rear height 24.75"

This is approximate to the "Euro" ride height I wanted. I didn't want to go any lower, the car doesn't have a bumpsteer kit, nor do I want to start pushing the limits in that regard.


LF camber (0.6)
RF camber (0.7)

For a street car, big front camber isn't necessary and actually hurts braking performance. The factory spec'd Zero front camber in the revised settings for 1968, but a little negative will ensure that when the car rolls over (it has the stock 13mm pencil front bar and no rear bar) the outside wheel will be more orthogonal.

LF caster 6.9
RF caster 6.9

You want all the caster you can get. I am not currently using the steering damper. The factory did away with the steering damper in 1967 anyway. With these caster settings the car is nicely self-centering and at 80+ mph highway speeds tracked dead straight.

Front toe 0

An appropriate street setting. This car will not see AX.

LR camber (1.1)
RR camber (1.0)

This is right on the 1968 settings which were (1.1).

LR toe 0.08
RR toe 0.08

A small amount of rear toe, per standard. The factory said 0-10 arcminutes per wheeel, 0.08 degrees is 4.8 arcminutes per side (center of range) for 9.6 total. Perfect.

All-in it was a six hour job which I thought was extremely reasonable.

The new Hunter HawkEye alignment machine was particularly slick-- rather than attaching the targets with sharp clamps that go between the rim and the bead, Tom's new machine has targets that clamp to the tire directly-- then transmit light back to a tower on the machine that determines the precise alignment. Much more precise than I could do myself!

It was a great experience, if you're ever in the Hudson Valley and need some service for your 911, I highly recommend Tom, whose phone number is (845) 562-0346.

Now to get driving before the winter starts! Hope this helps those who come this way in the future.

[Gumby]

I saw your car at The Mountain Brauhaus a few weeks back...just beautiful

[SERIES900]

How big is your smile now?

[304065]

How big is your smile now?

About like this.

[Merv]

Great stuff 304065. Just about to embark on the same process with my 68. We seem to have pretty much the same spec. All I need now is someone in my area with the 'knowledge' and capacity to align the front.

[Jetjok]

John,

Thanks so much for your great article on corner balancing. I too had that done about two years ago. I've got a '68 912 soft window Targa and wanted to upgrade to a newer front suspension. I found a whole 1978 911 SC suspension and Jim Newton at Automobile Associates of Canton, here in Connecticut, did the job. I don't know squat about suspensions, nor about casters or cambers, etc, so your article helped me understand some of that stuff. Thanks again.

Here's a copy of the worksheet that Jim gave me, along with the bill, when all was said and done. Now some of it actually makes sense to me and helps me appreciate why the cost was what it was. Interesting the weight difference between an early 911 and a 912.

[merbesfield]

Another item off the checklist!

One of the challenges for original cars which lack adjustable rear springplates is achieving corner balance. On the one hand, early SWB cars need all the handling help they can get-- on the other, the lack of adjustable rear springplates makes the process of corner balancing time consuming, and pretty much impossible to dial in perfectly, due to the discrete nature of the adjustments.

What I mean by this is what everyone knows-- that the rear springplates ARE adjustable, but only through the vernier feature. There are 44 inner splines and 40 outer splines, so to make an adjustment down, for example, you go up one spline on the inner (360/44 = 8.18 degrees) and down one spline on the outer end of the bar (360/40 = 9.0 degrees). The net result is 9.0-8.18 or 0.82 degrees of adjustment down, and iterating both sides in this way will eventually allow you to dial in the correct ride height.

I was able to get it in the ballpark, but I don't have a set of scales, so other than measuring the fender height (not the "factory" way of measuring ride height, but the way everyone does it, because the "factory" way is impractical) I wasn't able to really dial it in.

For help I turned to Tom Florio, owner of Advanced Automotive of New Windsor, in New York's Hudson Valley. Tom has been in business for 24 years and works on many different cars, but is passionate about Porsches. He had six or seven inside and a few more around the shop. Also, in a very similar scene to what I saw at Peter Dawe's place back in August, he had a blown-up 3,6 that had vaporized a couple pistons hanging forlornly from a stand. Missed shift? No, it just let go.

Anyway, here's what Tom was able to achieve:

LF 520
RF 462
LR 728
RR 721
Left Weight 1238 (51.3%)
Right Weight 1183 (48.7%)
Front Weight 982 (40.4%)
Rear Weight 1449 (59.6%)
Cross Weight 1190 (49%)
Total Weight 2431 (with fuel fuel, spare tire and driver)

Not bad-- the front weight differs by 58 pounds, where 50 is negligible for a street car. The cross weight would ideally be 50% which means the car handles equally well on left and right turns, but again, this is a street setup without adjustable plates.

Now to alignment:
Front height 25.25"
Rear height 24.75"

This is approximate to the "Euro" ride height I wanted. I didn't want to go any lower, the car doesn't have a bumpsteer kit, nor do I want to start pushing the limits in that regard.


LF camber (0.6)
RF camber (0.7)

For a street car, big front camber isn't necessary and actually hurts braking performance. The factory spec'd Zero front camber in the revised settings for 1968, but a little negative will ensure that when the car rolls over (it has the stock 13mm pencil front bar and no rear bar) the outside wheel will be more orthogonal.

LF caster 6.9
RF caster 6.9

You want all the caster you can get. I am not currently using the steering damper. The factory did away with the steering damper in 1967 anyway. With these caster settings the car is nicely self-centering and at 80+ mph highway speeds tracked dead straight.

Front toe 0

An appropriate street setting. This car will not see AX.

LR camber (1.1)
RR camber (1.0)

This is right on the 1968 settings which were (1.1).

LR toe 0.08
RR toe 0.08

A small amount of rear toe, per standard. The factory said 0-10 arcminutes per wheeel, 0.08 degrees is 4.8 arcminutes per side (center of range) for 9.6 total. Perfect.

All-in it was a six hour job which I thought was extremely reasonable.

The new Hunter HawkEye alignment machine was particularly slick-- rather than attaching the targets with sharp clamps that go between the rim and the bead, Tom's new machine has targets that clamp to the tire directly-- then transmit light back to a tower on the machine that determines the precise alignment. Much more precise than I could do myself!

It was a great experience, if you're ever in the Hudson Valley and need some service for your 911, I highly recommend Tom, whose phone number is (845) 562-0346.

Now to get driving before the winter starts! Hope this helps those who come this way in the future.

I am getting ready to take my 66 over to Gran Touring here in Atlanta for this service. I luckily have adjustable rear spring plates. My wheels will be 7's. With the adjustable spring plates, does this mean the corner balances should be more even? Or just easier to adjust everything? I have a set of brand new tires waiting as well. I do want to lower the car so I will go with your measurements to start.

[304065]

Mark,

Good, they should mount the tires and set the exact pressure you want to operate with first. A good shop knows this.

Yes, (rapid) adjustable spring plates should allow you to dial in the corner balance more precisely and a heck of a lot faster than the (vernier) adjustables. You still have to get the adjuster in the center of the range, which means some R&R of the rear suspension, but once it's there, you can dial it in more precisely. If you get the cross weight within 50 pounds you are lucky.

[savaden]

Actually, you can have perfect corner balance, or perfect side to side ride heights, but not both at the same time with the standard rear spring plates. Just set both rear spring plate angles to the same value, and adjust the fronts until the corner balance is right and the fender measurements are where you want them. I have achieved cross weights to 1 lb difference. That said, there is enough friction in the bushings that +/- 5 lb is more likely what you get after exercising the suspension. The main benefit of adjustable spring plates is being able to re-adjust your ride height without having to take it all apart. For most people that is not a big deal and the expense and hassle of installing adjustable trailing arms is not justified.

Another thing to note is that you can have correct ride heights and the corner balance could be completely off, if, say someone installed the rear torsion bars with different angles, or the tub got tweaked.

SV

[Jm993rs]

Very good Job