Intricacies of corner balancing - and they are?
 

I'm probably going to get "corner balanced" in lieu of my track day on the 21st of this month. I want to get a good baseline of my suspension before the trackday. After that, I figure I'll have an idea of the mods the suspension might need (if any) afterwards. So I figure a corner balance and alignment will be prudent.

With that in mind, what on a 911 causes a car to become unbalanced? I know that if one drives into a curb or a deep pothole, they could knock their alignment off. But corner balancing has remained a mystery of enigmatic proportions.

How's it done? What is balanced?

Help me see the light, oh brothers...

A 911 is corner balanced in order to have as close to equal side to side weight distribution. A small amount of change to front - rear weight distribution can also be obtained. I would say that rarely a 911 requires a corner balance caused by wear or damage. Though some uneven sagging in suspension componets may eventually lead to poor balance. The majority of the time a corner balance is required because suspension components have been removed or the car has been lowered. When ever the spring plates or torsion bars are removed the original corner balance is lost. My car required a corner balance because I both removed and restored the suspension and lowered the car.
When a 911 is corner balanced the vertical oriention of the rear spring plates on the torsion is changed in order to alter the load of the desired side. The front balance is adjust by tightening a bolt which preloads the torsion bar.
Corner balancing is a bit complex but here is a quick run down of how it is done.
On a level surface the car is placed on four scales to determine the load on each wheel. Next the car must be jacked up and the spring plated removed in order to rotate it the required number of torsion bar splines (down to increase load or up to decrease). Changing splines also changes ride height which must be done set while balancing. Once the rear is balanced side to side the front can be balanced by moving the adjustment screws. One thing to keep in mind is that increasing front preload by tightening the screws shifts weight back and to the opposite corner. Some times changes to the front bars alter balance in the rear and changes have to made again. It is just a slow process of changing a little at a time untill it is close enough. For me at 4 in the morning the night before it was going in for an alignment I decided it was good enough.
-brad

The later cars can be slightly adjusted using the built-in rear adjuster screws...

-Wayne

I currently have no adjustable spring plates on my car, which is a '74. However, I do have adjustable SC springplates in a box in my garage. Will the adjustable springplates make the corner balancing process any easier or more accurate as opposed to using the non-adjustable I have on my car now? Is there a difference?

Thanks Brad. Thanks Wayne.

(Wayne - you on for the Mulholland Run on the 24th? - Bring the F-car)

dd74;
The adjustable spring plates make it a lot easier and faster to adjust the corner balance. At the end of the day I doubt that it's more accurate, at least in a real world sense.

The trick with adjusting the "non-adjustable" pieces is that you have to take them apart and move the T-bar 1 tooth in one direction and the spring plate 1 tooth in the other direction. This is because the inside of the T-bar has 40 teeth (9 degrees per tooth, as in 9 * 40 =360 degrees) and the outside 44 teeth (8 degrees 10 minutes or 8 1/6 degrees). So if you move them one tooth in either direction, you'll have moved the spring plate 9 - 8 5/6 = 5/6 of a degree or 50 minutes. The shop manual and BA's book will tell you this and so you'd think that smallest increment is 50 minutes. Actually you can adjust the spring plate by 10 minutes if you rotate the T-bar 180 degrees and then the spring plate by 1 notch. So you CAN adjust "non-adjustable" pieces to a very small degree, most likely smaller then you need to.

The trick of all of this is to measure, record and check. If you keep track of every change and the outcome you'll be able to zero in on the desired settings within 5 or 6 trys at most.

You've been around a while (or at least you've got more posts then I do), so I'm sure that you know that the actual nuts and bolts process of cornerweighting a car has been discussed here at length, so I'm not going to bother repeating it.

Sweet! I didn't know you were going to make it on the 21st.

Just take the car to Tyson w/ beer in the passenger seat and twentys in the glove box. It's all good!

Chuck Mooreland and I have previously engaged in lengthy discussions on corner balance..do a search on our names and topic.

The REAL target in corner balancing is to get each corner to carry the weight it SHOULD, by the weight it actually carries at each corner. If it doesn't, it is "weight-jacked".

Huh?

The basic front/rear balance of a typical 911 is 40/60..and the typical left/right balance is about 0-2 % biased to the left ( for non English cars).

The "short-form" basis that Chuck worked out ( vs. my equally accurate but more involved "long-form") targets LF/LR=RF/RR.

Tips.
1.) The TOTAL weight of any two adjacent wheels will NEVER change as you change corner balance. Thr total for the front two wheels.... left side two wheels.....back two wheels....right side two wheels...will always total out to the same value.
2.) If you increase the weight of the (say) RF..it will increase the weight of the opposite diagonal ( LR). Same if you decrease the weight on any one corner. This begins to make more sense if you combine this with tip #1.
3.) The target is NOT to get the diagonal totals equal. This works for symmetrically built Formula type cars...but doesn't work for our "tin-can" cars.

More in the archives....

Wil Ferch