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Home ride height and corner balance success story

A while back I had posted several questions about ride height and home corner balance following my rear torsion bar bushing replacement. Wil Ferch and several others responded with some solid guidance so I thought I'd give it all a try...worst case I'd end up at a shop and they could clean up my mess.

Before getting started I leveled my floor using some VCT tiles from Home Depot with a water level I made with $3 worth of clear tubing. All of this knowledge was found in the PP archives.

Once I was satisfied with the level of the floor, I went about reindexing the torsion bars using the $7 angle finder level tool in the rear using the so-called "Ferch Triangulation" method. Knowing the OE spec (using hub center to torsion bar cover center) was circumspect, I chose to aim for a 25" rear fender height and 25 1/2" front fender height. But, I concluded that having the suspension balanced should trump the sheet metal height, so I double-checked the torsion bar cover height (measured from the ground) for L-R consistency at the (possible) expense of fender height aesthetics.

Since the rear is far more difficult to adjust, that was my starting point. I removed the steering rack cover in front and both front and rear sway bar mounts were removed to relax the suspension in the case they were preloading it. I measured the distance between the front torsion bar covers and marked the center point on the crossmember (there was a bolt visible on the rear of the crossmember at that point, so it was easy to find after that. Instead of using the 6" wide lifting pad on my jack, I put some steel bar stock in the lifting pad and used it to make contact on the crossmember for more precision. I found it helped to remove the front wheels and then lower the front suspension closer to it's actual riding height (although I could only get close before my jack bottomed out).

I found that my rear torsion bars needed to be reindexed to get within a range that could be fine-tuned by using the eccentric adjustments. I centered the eccentric adjusters and reindexed the torsion bars to the exact same angle, using the angle finder tool and Thom/Wil's online spring angle calculator. I used the OE published weight, since I had never gotten my car on scales and set the angles to those recommended by the calculator.

Many small adjustments with the eccentrics later, I had the rear within 2mm L-R . This is measured at the torsion bar covers while the front was jacked up at the front crossmember center point to triangulate the suspension. The fender heights were pretty close to the 25" I was aiming for, too.

Moving on to the fronts, I raised the rear at the standard engine case jacking poing to create the triangle for the front. The front suspension compresses a bit, so I was using relative heights. The passenger side was closer to 25 1/2" at the fender before jacking, so I looked to level the torsion bar covers L-R at the height that the passenger side was already at. Again, I looked for L-R consistency at the torsion bar covers over the absolute height as my reference. I did not use the OE method, but ensured that my a-arm was no lower than level (it was in fact, slightly sloping down from the pivot point). I added bump steer spacers while I was in there as I had been feeling some bump steer. My front sheet metal was not as close as I'd hoped, but again, I had the torsion bar covers pretty close to equal L-R, providing suspension balance, which I deemed more important than 1/4" in sheet metal aesthetics.

So, with all that done, I was off to my former employer, Hunter Engineering, for an alignment. I had 3 very generous and willing co-workers with $100,000 of their coolest new equipment waiting at our disposal. Man, did I feel lucky.

First we were on to the brake tester. It's actually a drive-on dynamic brake force analyzer. I drove onto it at about 5 mph and hit the brakes firmly. There are four slip plates that measure dynamic braking force at each corner. Luckily, mine were very evenly distributed. That same unit measures corner weights once you've stopped and settled.

Here are the results: My corner weights

Wow, 19 lbs off at the diagonals on the first try! Needless to say, I was impressed. Maybe I was lucky, but I think others can use this method to get corner balance really close at home.

Now the car is aligned, wheels newly balanced on the state of the art Hunter GSP-9700 balancer (a $15,000 wheel balancer that memorizes each wheel's attributes and optimizes balance at each corner with the others in mind), my 21 year old 155k mile 911 is riding on rails, tracking dead straight. My face hurts from grinning on the way home.

I couldn't believe how solid and vibration-free my car feels. Not to sound like a commercial, but I highly recommend finding one of these balancers in your area at http://gsp9700.com/ and seeing what it might do for your 911's balance.

edit: I forgot to mention that I put bags of softener salt approximating my body weight in the driver seat for every measurement. The suspension must be settled in between measurements as well.

edit 2: I chose to use 3/4 full tank of gas as well.

Craig
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'84 Carrera Coupe - B&B Headers and one-out muffler; K&N Cone intake; Steve Wong Chip; Euro height and corner balanced; 171K Miles (9/12)

Last edited by Thrasher; 03-30-2005 at 10:06 AM..
Old 03-30-2005, 09:06 AM
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Craig:

I'm very happy it went so well for you... !

Wil
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Old 03-30-2005, 09:32 AM
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Old 03-30-2005, 09:40 AM
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fantastic
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Old 03-30-2005, 12:20 PM
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You give hope to all DIYers.

Amazing how someone who cares what he is doing can do a job as well as or better than the pros.
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Old 03-30-2005, 12:41 PM
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Now that it's aligned and driving so well, do I go for that last 19 lb difference, or leave well enough alone and call it "good"? It's really a 38 lb difference, but could be remedied by dropping the LF/RR a small amount, moving 19 lbs off of that plane and onto the RF/LR plane.

I doubt I'll feel the difference, but being anal and all...
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Old 03-30-2005, 12:50 PM
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Leave it alone !!!

Real test if "if you can feel it" ...on the road. I suspect you won't...

Wil
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Old 03-30-2005, 12:52 PM
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Thrasher,
I noticed that too. If it's convenient (), go ahead. Amazing the small amount of weight that changes the F/R side proportion from 70% to 65%.

Sherwood
Old 03-30-2005, 01:00 PM
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Very good writeup! Would have been better with a few piccies, but what the hey.

I need to get off my arse and try this myself one of these fine days.

ianc
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Old 03-30-2005, 10:13 PM
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Nice doc Craig.
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Current: '80 Silver Targa w /'85 3.2, '79 Anthracite 930
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Old 11-07-2014, 06:20 AM
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Wow, it's coming up on 10 years ago that I wrote that up. I've been 911-less for about 2 years now due to family matters. Mine went to another Pelican, so I know it's in good hands. I was just thinking on my commute in this morning that I may need to start thinking about my next project... probably still a few years away, but I still enjoy lurking here occasionally and living vicariously.

Glad it was helpful... Wish I'd snapped some pix and put those in for future reference. Maybe "next time".
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'84 Carrera Coupe - B&B Headers and one-out muffler; K&N Cone intake; Steve Wong Chip; Euro height and corner balanced; 171K Miles (9/12)
Old 11-07-2014, 06:44 AM
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Quote:
Originally Posted by Thrasher View Post
Wow, it's coming up on 10 years ago that I wrote that up. I've been 911-less for about 2 years now due to family matters. Mine went to another Pelican, so I know it's in good hands. I was just thinking on my commute in this morning that I may need to start thinking about my next project... probably still a few years away, but I still enjoy lurking here occasionally and living vicariously.

Glad it was helpful... Wish I'd snapped some pix and put those in for future reference. Maybe "next time".
Craig... I did not look at thread date. You can see it has legs. Very well written.

Think I might understand "family matters." Hope all is well.

Am just diving into height-rake-alignment-balance on '80. If you're interested in taking a look to see where project is... and perhaps offer your expertise... would be much appreciated. Immediate challenge to resolve is evening out rear spring plates. One went down further than other. Want to raise the lower side and can't get plate to move. Also have back-end suspension creaks now.

First time height & alignment project - help wanted :)
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Old 11-07-2014, 12:01 PM
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