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Corner Balance Help

So for the first time I have the car on the scales. It's in my garage and I have levelled all the scales. The readings are not encouraging. I added weight to the drivers seat to approximate me, disconnected both sway bars and rocked the car continuously to make sure the suspension is settled.

DF 416 PF 659
DR 1009 PR 746

I've lowered the front corners a few ways amd jacked and raised the rear corners and I can't seem to get any indication of where to begin getting it closer to optimal.

Ideas?

John
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Last edited by North Coast Cab; 04-13-2006 at 04:29 PM..
Old 04-13-2006, 04:15 PM
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Jsut a thought to make sure your scales are all calibrated equally, did you try to change the scales positions? ie. take teh front ones and put them in the back and then take your measurements again...so on so forth.
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Old 04-13-2006, 04:18 PM
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Are those numbers the corner weights ?? Incredible. Obviously I canīt offer any intelligent suggestions since I am a total newbie. I am just amazed and looking forward to what promise to be a very educational post.
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Old 04-13-2006, 04:23 PM
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I moved the scales around as well as the cables. Everything came back the same including the total weight.

John
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Old 04-13-2006, 04:23 PM
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no quick answer will work.... hoo boy !!

try raising LF (or RR)...OR ..... lowering RF (or LR)

Make sure the height adjustment "pawl" for the fronts are engaging about the same length along the screw shaft... if not...reset so they do..and start over and re-do these checks.

If all that fails.... re-index the bars ( rears too) and make sure you try to get tooth engagement the same on both sides, and the two piece spring plate should have the height adjustment in the same location in the slot...left to right, compared. Free hanging "droop" should be the same on both sides

Depend less ( or maybe not at all) with any height adjustment screws in the rear ( if weltmeister).

Wil
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Old 04-13-2006, 04:24 PM
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WIl,
If I raise the LF o RR those numbers go down. If I lower the RF or LR those numbers go up.
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Old 04-13-2006, 04:28 PM
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For starters, make sure your ride height is where you want it, and that all adjusters are centered. Then make sure to check that the scales are level to each other as well (not just individually level). Also check tire pressures, and make sure you have around a 1/2 tank of fuel in addition to the driver's seat ballast.

After that it is basically a cat/mouse to get you close to optimal.
From your measurements, it looks like you are "teetering" on the LR & RF (should be more weight on the LF & RR).
You might try Thom's CB calculator to get you general target weights:
http://rennlight.com/cgi-bin/balance.cgi

Old 04-13-2006, 04:46 PM
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Eric,
I 've done everything you suggested in the first paragraph. I can start by lowering the LF/RR or raising RF/LR, but my issue is I feel like I have to move the corners so much that the ride height will be bizarre. Does this sound logical?

John
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Old 04-13-2006, 05:05 PM
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If you lower the LF/RR you are taking MORE wieght off, transferring more to the RF/LR. The same as if you raise the RF/LR. If you try to raise the LF corner using the adjuster you are in effect pushing the wheel down. This has to INCREASE that corner weight, right?
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Old 04-13-2006, 05:28 PM
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If corner weight adjustment results in a lowered ride height on one corner,I would lift the front or back at the center and use the tripod method to set ride height at the opposite ends first to level the car . I think then you should be closer to ideal corner weights and can fine tune with scales .
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Old 04-13-2006, 05:32 PM
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WOW...that is way way off...

Almost as if the fronts (or rears) should be reversed from side to side. Not to sound stupid, but have you reversed the cables somehow? How abot weighing the same item (like a couple or 3 of cinder blocks or yourself) on each scale to see if there's not something wrong with the scales?

Man...over 500#s difference in cross weights is huge. Helluva a lot of wedge in there

Last edited by Dueller; 04-13-2006 at 05:44 PM..
Old 04-13-2006, 05:39 PM
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I know you probably already looked at this article, but thought I'd post it just the same:

used following principle from Bruceís book, Porsche 911 Performance Handbook 1st edition, page 174, I quote Bruce;

"Assuming the 911 has a weight distribution of 40/60 front to rear, forty percent of the left side weight should be on the left front wheel, and sixty on the left rear" end quote. Thanks Bruce, hope You donít mind me quoting You.

Mike Piera wrote some time ago, I quote Mike;

" When you find which diagonally opposite corners have too much weight (they will each be heavy by the same amount if you calculated right!) you should lower the 2 heavy corners, and raise the two light corners slightly, all by the same amount, then drive the car and measure again." end quote. Thanks Mike, hope You donít mind me quoting You.

I was not able to get weight transferred to right front and keeping car level. After I leveled the car, and 8 hours of adjusting, the car is level, but the weights are way off. LF 718, RF 561, LR 903, RR 933 (lbs) I did not drive the car after adjustment, adjusted with wheels on ground, rears hard, but it can be done with 2 people. After adjustment, bounced the suspension and the HEIGHT adjustment was logical. I adjusted a little, car HEIGHT changed in proportion.

Mike, I donít completely understand Your wording; "they will each be high by the same amount", please clarify.

<< Your weights are accurate, I can tell because the diagonal corners are all off by + or - 52 pounds. Here is your car (front of car is top)

718 1279 561 (LF, Front, RF) 1621 3115 1494 (Left, total, right) 903 1836 933 (LR, rear, RR)
Here is your carís weight distribution :

41% 52% 48% 59%
To calculate the desired corner weights, multiply the front or rear percentage times that sideís weight, i.e. for left front 41% (front) x 1621 (left) = 665 pounds. You have 718 on LF so you need to reduce weight on the left front by 53 pounds.

When you calculate the other corners you will see that EACH corner is off by 53 (or so) pounds - and the diagonals are the same, i.e. right rear (diagonally opposite of left front) is also 53 pounds heavy : 59% (rear) x 1494 (right) = 881. 933 - 881 = 52.

In order to KEEP YOUR CAR LEVEL and at the current ride HEIGHT, and change all four corners to the correct weight, you need to LOWER the left front and right rear a bit (reduce weight on a wheel by lowering/loosening the torsion bar), and RAISE the right front and left rear by the same relative amounts. By doing so the car will stay level and at the current ride HEIGHT.

You can also change the corner weights by just adjusting two diagonals, i.e. just lower the LF and RR and then drive the car to settle it in and weigh it again to see if you did enough. This will lower the entire car however. But if you did want it a bit lower then this is just the trick to do! Likewise if you want to raise the whole car a bit then just raise the RF and LR. If you need to keep the ride HEIGHT the same then do all four corners.

Then if you do everything right you should have a perfectly balanced, level car that weighs:

665 613 956 881
Of course this is easier said than done and may take a few trials but if you are within 10 pounds or so youíve got it! Good luck and let me know how it turns out!
Old 04-13-2006, 05:54 PM
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Quote:
Originally posted by North Coast Cab
WIl,
If I raise the LF o RR those numbers go down. If I lower the RF or LR those numbers go up.
Try doing both.

lower the RF & LR, and raise the LF & RR by the same amount.
Basically, you need 125# less at the RF & LR corners, and 125# more at the LF & RR corners.

If you still can't get close, then it sounds like you may need to do as Wil suggested and re-index the T-bars.
Old 04-13-2006, 06:21 PM
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I think Eric is on the right path...

I crunched the numbers:

Right now, your LF and RR are too light and conversely (consequently) your RF and LR are too heavy.

I would probably do it sequentially on the diagonal and check the weight with each diagonal adjustment. If you lower the driver's rear and lower the passenger front by the roughly the same amount you will accomplish 2 things: You will transfer weight while maintaining close to the same ride height. Keep in mind, when you lower the drivers rear you are generally going to see a rise in passenger front ride height so hypothrtically it will even out. After you've made these two adjustment, weight it and see if its going in the right direction.

If it is still off, then raise the driver's front and raise the passenger rear and measure again.

Keep in mind that relatively small adjustments (especially on all four corners) can yield significant weight changes.

If I had to guess looking at the weights, you may have the front ride height set a bit too low overall (or the rear too high) because you're ending up with a 38%/62% f/r ratio and it should be somewhere in the range of 40/60. Still its pretty close.

One last thing: Has this car been in an accident where the tub is possibly substantially twisted? I know the dirt tracK boys will literally twist a chassis on a frame machine to build in some wedge.

Last edited by Dueller; 04-13-2006 at 07:30 PM..
Old 04-13-2006, 07:11 PM
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* CORNER balanced - numbers from this...and the weight
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Old 04-13-2006, 07:23 PM
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Boy, that thing should turn left like gang busters.

BTW, the quantity of wedge in the car won't change the front/rear weight split by a noticable percentage. You would have to jack it up like a funny car to change the percentage a noticable amount.

The have a bit more weight in the rear and if the tank isn't full it will skew it a bit more. (plus any other changes in the weight of the car...)
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Old 04-13-2006, 07:40 PM
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I agree with johnsjmc.

Your corner weights are too far off to conveniently adjust using the minimal adjustments provided.

Let's assume your scales are accurate. First, record the total weight of the car. According to your scales, it's 2830 lbs. (1075+1755). The F/R proportion is 39%/61%. This proportion won't change no matter how you jack the weight around (unless you move your driver's seat, battery or gas tank). However, the right side F/R weight proportion is currently at 88/12% while the left is at 41/59, not very even. Your target is around 40/60, F/R, each side and at your desired corner heights.

Lift and support the car as a tripod. The tripod method removes one end from the equation and eliminates any effect it has on the opposite end.

Adjust the front ride height and corner weight first (adjusting the front is easier). The scales under each front wheel will give you the total (1075). Adjust each and aim for roughly an equal split for now (537/537) and ride height. The exact weights will change later on because the driver's side is usually heavier than the right side (proportion remains the same).

Repeat for the rear. Place the car on all four scales. That should get you closer with all four scales. Let's hope your current RF and LR ride heights are higher because it seems you need to lower these corners to give the LF and RR corners more weight to support. If not, your chassis might be tweaked; for example, the corner weights are proportioned correctly, but the ride heights are way off.

Refer to Thom's calculator for target corner weights.

Hope this helps.

Sherwood
Here's a paper-based chart to record your settings
http://members.rennlist.org/911pcars/cornerbalance.htm
Old 04-13-2006, 07:48 PM
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Quote:
Originally posted by johnsjmc
If corner weight adjustment results in a lowered ride height on one corner,I would lift the front or back at the center and use the tripod method to set ride height at the opposite ends first to level the car . I think then you should be closer to ideal corner weights and can fine tune with scales .
It might not get any closer. I have to think that there is more to this. What chassis work has been done on this car? Rust repair? Accident? To have a CB'd car that is wedged, when it's balanced, visual ride height may be off at the bodywork. that's not a good measurement anyway as fenders get mounted high and low due to accident tweaks.

I determine my visual height at the bottom of the car in several places. You can then check at a wheel arch and see it high, but the pinch seam nearby down under is the same as the one across the car. This is a fender problem, not a balance problem.

If a car has a body problem where one corner is up higher, then you will go round and round with this. So, if you find the exact center on both ends and raise the car to equalize the one axle and then the other and the chassis is bent, you will see some subnormal numbers. And when you jack the thing to rectify what you think is the problem, you get some more weird numbers.

You should be able to eventually get your balance even if the camber settings go away. The highest arch will point the way to the previous damage/condition that started all of this.

I have been conviced by a pro or two that CB should be done on a frame machine or referrece surface to understand what the chassis is doing.
Old 04-13-2006, 09:20 PM
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Quote:
Originally posted by North Coast Cab
WIl,
If I raise the LF o RR those numbers go down. If I lower the RF or LR those numbers go up.
Are we speaking about the same "raise" and "lower"? Maybe a problem with symantics.

Wil's advice is (as usual) spot on! But something is wrong with the language here.

When you INCREASE ride height on any given CORNER (that is, make that corner HIGHER), you will transfer some additional weight to that same corner, AND, at the same time, transfer some additional weight to the DIAGONAL corner.

For example, on your 911 if you were to INCREASE the ride height on the LF (that corner of the chassis is now higher off the ground), that would transfer some weight to that corner, AND also transfer some additional weight to the RR. The net effect of this, obviously, would be to REDUCE some of the weight on your LR, AND on your RF.

As you are playing with this, give one of us a call if it still does not appear to be working. We are at 607-535-4237 (New York).

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Old 04-13-2006, 09:47 PM
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John,
You have some great advice here from people that know this backward and forward.
However it is easy to confuse yourself.
First have you measured from the ground to each fender arch?
If the measurements right to left are within 1/8th inch right to left something is twisted.
The measurements should be off right to left.
Second you indicated you added some weight to the drivers side. How much? It should be 150 to 180 pounds.
Your numbers indicate right to left weight close. There should be more left total.
Once you know what the fender arches measure out just write it down.
Now before you touch a single adjustent, put some 1/2 inch shims under the left front scale and the right rear scale.
Remeasure the weight. The cross weights should be closer.
Continue adding shims under the left front and right rear until the cross weights are close +-25 pounds or less.
This will show you how much you need to move your suspension to get the weights correct.
The nice thing is you hven't touched anything yet. No unecessary work.
You might even want to post the results with the shims before you try to adjust anything.
With the experience on this board you will get great advice.
When you are comfortable to adjust, start with the front.
Back off the right side adjuster one turn, tighten the left side adjuster one turn.
Now reweigh with the scales level, no shims. You will be getting closer.
Look at the adjuster screws, don't back one out too much or run one in too much.
We are just trying to see if you can get most of this with the fronts. Much easier than the rears.
Get as close as you can without getting the front screws too far different.
At this point put the car on level ground and check the fender arches.
You will be surprised how little they have changed.
This will also guide you as to whether you want to lower or raise the front or rear to correct any further error.
Bottom line here is the shims under the scales will show you what is possible and how far you need to adjust before you touch any adjustment.
There may be some adjustment available to you at the rear.
As you get comfortable with the tweeks, you'll get there.
Don't forget to have an alignment done when you are finished.
As far off as this is the alignment will be off. No high speed driving until it is aligned.
Please post your progress. We are all interested.
If I was close I'd at least come by and kibbitz.
Have fun,
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Last edited by 2.7RACER; 04-13-2006 at 11:24 PM..
Old 04-13-2006, 11:12 PM
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