Corner balance questions

[Jameel]

I just finished redoing my entire suspension with a stock "restoration" package from Elephant Racing. Rebuilt the calipers, new brake lines, the whole nine yards. So the car is sitting in the garage right now waiting for corner balancing and alignment. I've been reading up on the process and have a few questions I didn't find in searching.

First, some baseline info on my setup.

1983 SC Coupe. I used all stock bushings from Elephant. The only upgrade I made was to swap out the stock Boge shocks for Bilstein HD, using the existing Boge spindles with Bilstein inserts.

FRONT: I didn't touch my new (as of last year) turbo tie rod settings. I also marked the shock towers precisely so I replaced the camber plates pretty much exactly as I removed them (had the car aligned late last year-- so hoping to keep the setting) I also marked and replaced the adjusting screws for the t-bars as before. Not sure what the corner weights were, so this will be off.

REAR: I measured the spring plate angle after removing the lower stop collar and recorded it. They were both very close to 34 degrees. When I reinstalled the t-bars, I set each plate at 34 degrees, which is according to the tech spec book for '83, which was the year they set US cars at "Euro" height. I also positioned the adjustable spring plates right in the middle of their adjustment range, hoping that would buy me enough movement that I won't have to reindex splines.

Questions.

1. I've read a lot by Wil Ferch and Chuck Moreland, but couldn't find this so-called "in depth" discussion thread that has been referenced, but never linked to in various threads. I've love to read it.

2. Every link for Wil's calculator that I found is broken. Is it still around?

3. I know that the front adjusters lower the car when backed out (loosened), but what about the big hex eccentric adjusters out back? I don't remember which way those turn to raise or lower. Knowing that would perhaps save me an adjustment cycle when I go to corner balance.

4. Were the cars corner balanced on the assembly line? I would think with the spec for the rear plates that the worker would simply install the plates on the correct splines to get the degree spec, then torque everything. I can't imagine in a factory setting that they were pulling plates off (early non-adjustable) but I could see them using the adjustable plates since it would be much easier in a production setting.

5. I've read that one should disconnect the sway bars before corner balancing. Makes sense to me for free movement during adjustment, but couldn't the sway bar influence the weights?

Thanks.

[Knockdown]

Here’s a link to a rear spring plate angle calculator.....

https://www.elephantracing.com/tech-topics/spring-plate-angle-calculator/

I recently updated my suspension, used the string method for f/r toe, digital angle level for camber/caster. Got the car close to desired ride height, leveled the car, aligned toe, caster, camber. Used floor tiles to level and grease in gallon baggies under the wheels to relax the suspension after jacking. Ended up purchasing a set of corner scales, got the cross weights close and rechecked all of the alignments. I have adjustable sway bars so it was easy to disconnect.

[Bill Verburg]

Originally Posted by Jameel

I just finished redoing my entire suspension with a stock "restoration" package from Elephant Racing. Rebuilt the calipers, new brake lines, the whole nine yards. So the car is sitting in the garage right now waiting for corner balancing and alignment. I've been reading up on the process and have a few questions I didn't find in searching.

First, some baseline info on my setup.

1983 SC Coupe. I used all stock bushings from Elephant. The only upgrade I made was to swap out the stock Boge shocks for Bilstein HD, using the existing Boge spindles with Bilstein inserts.

FRONT: I didn't touch my new (as of last year) turbo tie rod settings. I also marked the shock towers precisely so I replaced the camber plates pretty much exactly as I removed them (had the car aligned late last year-- so hoping to keep the setting) I also marked and replaced the adjusting screws for the t-bars as before. Not sure what the corner weights were, so this will be off.

REAR: I measured the spring plate angle after removing the lower stop collar and recorded it. They were both very close to 34 degrees. When I reinstalled the t-bars, I set each plate at 34 degrees, which is according to the tech spec book for '83, which was the year they set US cars at "Euro" height. I also positioned the adjustable spring plates right in the middle of their adjustment range, hoping that would buy me enough movement that I won't have to reindex splines.

Questions.

1. I've read a lot by Wil Ferch and Chuck Moreland, but couldn't find this so-called "in depth" discussion thread that has been referenced, but never linked to in various threads. I've love to read it.

2. Every link for Wil's calculator that I found is broken. Is it still around?

3. I know that the front adjusters lower the car when backed out (loosened), but what about the big hex eccentric adjusters out back? I don't remember which way those turn to raise or lower. Knowing that would perhaps save me an adjustment cycle when I go to corner balance.

4. Were the cars corner balanced on the assembly line? I would think with the spec for the rear plates that the worker would simply install the plates on the correct splines to get the degree spec, then torque everything. I can't imagine in a factory setting that they were pulling plates off (early non-adjustable) but I could see them using the adjustable plates since it would be much easier in a production setting.

5. I've read that one should disconnect the sway bars before corner balancing. Makes sense to me for free movement during adjustment, but couldn't the sway bar influence the weights?

Thanks.

Your precautions may get you close but you will need a corner balance and alignment to get it right

[Jameel]

Thanks for the link Knockdown. Looks like my base setting of 34 is within half a degree.

Look forward to hearing if anyone else has thoughts on my other questions.

Bill, I am planning to corner balance and align. Just trying to get some things learned before I dive in on the corner balance, which I'll be doing partly on my own.

[Driven97]

Originally Posted by Jameel

3. I know that the front adjusters lower the car when backed out (loosened), but what about the big hex eccentric adjusters out back? I don't remember which way those turn to raise or lower. Knowing that would perhaps save me an adjustment cycle when I go to corner balance.

Depends on which way you have it. They're cams. So if you have them set to the middle right now, each one is either pointed straight forward or straight back.

Originally Posted by Jameel

4. Were the cars corner balanced on the assembly line? I would think with the spec for the rear plates that the worker would simply install the plates on the correct splines to get the degree spec, then torque everything. I can't imagine in a factory setting that they were pulling plates off (early non-adjustable) but I could see them using the adjustable plates since it would be much easier in a production setting.

Not sure about the factory question, but you can corner balance a 911 by only adjusting the front. Hell, you only need height adjustment on any one wheel to corner balance a car.

Originally Posted by Jameel

5. I've read that one should disconnect the sway bars before corner balancing. Makes sense to me for free movement during adjustment, but couldn't the sway bar influence the weights?

That's where adjustable end links are supposed to com into play. You're screwed in front with the under body bar so that has to stay put regardless. Maybe worth your time to measure your height differences left to right, so it'll help you determine where to raise or lower. Not much you can do.

Corner balancing only makes a car handle in left turns the same it handles in right turns. I guess if you really screwed it up it could also affect wheel lockup in heavy braking too.

[chrismorse]

Hi Jameel,

I have only cornerweighted one car. I did bars, springs, shocks, bushings and was able to borrow a set of scales from the local sports car club. If you don't have access to a set, you might want to consider having a shop finish the car, rather than put out $1000 or so on a set of scales you might only use once or twice.
Do you have a really level floor?? If not, you get to play around with shimming up the scales so they are all on the same plane. If I can find it, I will post the rube Goldberg set up I cobbled together.
I am going the same route as you, only adding adjustable rear drop links, SwayAway, adjustable spring plates, new MC, brake cooling, 21-28 T bars and a Quaife 2.5 "quick rack".
There is an unavoidable bit of chasing one's tail, redoing the corner weight, or height because of something you did on the other end of the car/side. This can get frustrating.
I think it is important to have a good overall target in mind before cranking on the heights or alignment. IMHO, getting height and alignment specs from Chuck Moreland would be a great time saver, since he has a good idea of your objectives and equipment.
I am going back to "stock Euro ride height", because that is what the factory engineered for things to work out well for a sporting street car. Before moving from "stock", it is important to understand the compromises/costs you will be encountering.

So:
To make the suspension work the same, (camber changes, toe/roll steer ect, ect, you need the heights to be the same, side to side.
This means you need to replicate your weight in the drivers seat, (concrete bags), disconnect the anti-roll bars, so they aren't loading the suspension. You need a half tank of gas and any equipment you "normally" carry, spare tire, jack, fire extinguisher, tools, spares, so you have a close to reality ability to get the weights right
I have been told that you can shim the chasis mounts for the bars if they do not have adjustable drop links.
Since I have a 74, the drop links were not adjustable and I got a later Carrera bar that can use heim jointed drop links, (also from Chuck). I will also drill one or two more holes in the rear bar arm to enable fine tuning with the rear bar.

Are you going to use something like the "smart string" alignment system or farm out the job to a good Porsche shop? I am considering it too.

Best,
chris

[Jameel]

Thanks Chris and Matt for the input. I'm having a shop help with the corner balancing, but I'm playing an active part, thus the couple questions. I'll have another shop with a Hunter and 911 experience do the alignment itself.

[Jameel]

Originally Posted by Driven97

Depends on which way you have it. They're cams. So if you have them set to the middle right now, each one is either pointed straight forward or straight back.

Yeah, that's what was dancing around my head. I was trying to remember how I oriented them when I reassembled.

[911pcars]

Originally Posted by Driven97

".......Not sure about the factory question, but you can corner balance a 911 by only adjusting the front. Hell, you only need height adjustment on any one wheel to corner balance a car.

..........."

Maybe, but corner balance depends on the ride height setting at each corner. The process usually includes going back and forth between ride height and corner weights to arrive at the preferred combination.

Sherwood

[Alan L]

Instead of scales, I purchased a speedway weight checker. It has a piston and pressure gauge attached to a lever. You place it under the rim (topside) and lift the wheel until a shim plate under it just moves free - total weight on that wheel and no more. record each wheel/corner and proceed from there. Works perfectly.
Yes you need a guaranteed flat surface at the corner points - or you have a few mm of pre load somewhere. Bags of sand or whatever (I used cartons of wine) placed in driver position, near your weight equivalent. For street work, not worth getting too anal about it - as soon as you put a passenger in it, the balance is skewed by more than you would consider acceptable tolerance if trying to balance. For that reason, and variable driver weights, I doubt they were corner balanced at factory.
Alan

[Trackrash]

Also interesting is there is no mention of corner balancing in the original, up to the '71 edition, of the Workshop Manual. However it did state that the front ride heights should not vary by more than 5mm from side to side and the rear should not vary by more than 8mm from side to side.

I think Porsche has a specification for corner balance. When did it come into play?

[gduke2010]

Btw, I lived in Iowa City when I bought my car and after adjusting ride height and corner balancing, I took the car to Kelly Moss Motorsports in Madison, Wisconsin for alignment. i think it cost $400. I think Bill V. is right you can get close. But, take it to a professional for fine tuning.

You're car will handle so, much better with the new bushings and shocks. I would also, consider turbo tie rods.

Good luck you will really enjoy driving your car this summer.

Gary

[Driven97]

Originally Posted by 911pcars

Maybe, but corner balance depends on the ride height setting at each corner. The process usually includes going back and forth between ride height and corner weights to arrive at the preferred combination.

Sherwood

Right. I like to use a wobbly restaurant table as an analogy. You only need to shove a packet of sugar under one foot to stop the wobble. That's cross weights, and what the scales will tell you. This is also what has the big effect on handling.

You can stop the table from wobbling, but still have a table your pen will roll off of. That's heights, and that's what a measuring table will tell you. This is primarily cosmetic unless you're really off.

The important thing for OP to know is that you can't adjust anything except cross weight with corner balance. No matter how much you raise or lower the rear, a 911 is still going to be 40:60. Likewise you can't make the left side sum lighter or heavier.

[911pcars]

Originally Posted by Alan L

Instead of scales, I purchased a speedway weight checker. It has a piston and pressure gauge attached to a lever. You place it under the rim (topside) and lift the wheel until a shim plate under it just moves free - total weight on that wheel and no more. record each wheel/corner and proceed from there. Works perfectly.
Yes you need a guaranteed flat surface at the corner points - or you have a few mm of pre load somewhere. Bags of sand or whatever (I used cartons of wine) placed in driver position, near your weight equivalent. For street work, not worth getting too anal about it - as soon as you put a passenger in it, the balance is skewed by more than you would consider acceptable tolerance if trying to balance. For that reason, and variable driver weights, I doubt they were corner balanced at factory.
Alan

I have the same weight checker. Caveat. The lift point isn’t compatible with the shape of any wheel. I assume users would fabricate a lift bracket bolted via the lug nuts (not so simple with Fuchs lug design).

I fabricated a moon-shaped block of billet aluminum that fits the contour of the wheel at 12 o’clock; the other side has a drillled hole to accept the lift pin. In addition, I insert a thick piece of leather between the wheel and the aluminum block to cushion and avoid any trace of the lift assy. on the Fuchs.

Speedway (and others) also sells a liquid level kit to measure and adjust the car’s footprint so they’re all the same.

Sherwood

[Alan L]

I place a hunk of solid rubber between the lift pin and polished Fuchs.
Mine seems to fit straight on rim OK. Yes - I purchased the water level kit too. I think this amount of precision is only applicable to track work tho. the minute you throw a passenger and/or some luggage in the measurements are largely out the window as far as any precision goes - eg passenger would add another 80+kg largely to one side of car.
Alan

[911pcars]

Great idea and much simpler. My mind didn’t stretch that far. Thanks for sharing.

Sherwood

[Jameel]

I did the corner balance yesterday. It went pretty well. It was off by about 60 pounds corner to corner initially. Ride heights were within about 1/4" or so of the typical 25 / 25.5 measurements. I didn't put a weight in the driver's seat because I'll often have a passenger. No autocross or tracking of this car. Just regular sports car driving on public roads so I didn't think it mattered that much. I wanted more predictable braking than handling (or so I've read) It really paid off measuring everything before I rebuilt the suspension. We only had to make one adjustment of the right rear spring plate, lowered the car down, and got these numbers.



We put the scales away and drove to the alignment shop. Pretty happy with this result.

One question.

I think my front height may be a little low now, like 25-1/4". Should I leave it alone? I'm afraid I might have a little bump steer. If I decide to raise it up 1/4", can I turn the front adjustment screws precisely the same amount and not screw up my alignment and corner balance?

[Lyle O]

Originally Posted by Jameel

I did the corner balance yesterday. It went pretty well. It was off by about 60 pounds corner to corner initially. Ride heights were within about 1/4" or so of the typical 25 / 25.5 measurements. I didn't put a weight in the driver's seat because I'll often have a passenger. No autocross or tracking of this car. Just regular sports car driving on public roads so I didn't think it mattered that much. I wanted more predictable braking than handling (or so I've read) It really paid off measuring everything before I rebuilt the suspension. We only had to make one adjustment of the right rear spring plate, lowered the car down, and got these numbers.



We put the scales away and drove to the alignment shop. Pretty happy with this result.

One question.

I think my front height may be a little low now, like 25-1/4". Should I leave it alone? I'm afraid I might have a little bump steer. If I decide to raise it up 1/4", can I turn the front adjustment screws precisely the same amount and not screw up my alignment and corner balance?

If you are perfectly precise, you can maintain the corner balance, but the alignment will still be thrown off and need to be re-done.

As to whether to change it now at all, do you have a bump steer kit installed? There is a relatively inexpensive version that adds spacers to the steering rack, thereby bringing the tie rods closer to parallel. It should improve your bump steer issue and allow you to keep everything else in place.

[tobluforu]

Do not touch it, if you raise it you will change the balance.

[Mahler9th]

For a street car, I doubt a change of 1/4 inch in ride height will create any noticeable change in bump steer behavior.

Any resulting change in front camber, caster and toe will likely be acceptable from a handling and tire wear standpoint.

But only you can define "acceptable."

Of course if you have a way to accurately and precisely measure toe changes versus ride height you can plot a curve and experiment with your own driving sensitivity.

In my experience, few, if any of us amateur 911 racers bother to go through a process of optimizing bump steer. What seems more typical is the installation of rack spacers, and tie rod end solutions with known specs.

For example, if you go to a service provider like JWE for an alignment, the measurement and adjustment of bump steer is not likely part of their standard service. Typically a static toe setting is all that is done.

My application is racing, and I have 100's of hours of experience with alignment and CB with my 911-based race car and those of several friends. After a while you develop a feel for the sensitivities of these things.