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How difficult to change rear camber?

Read a bunch of threads. Understand that toe usually gets screwed up...

Have zero rear camber on the 930. Rear tires getting pretty worn on the outside after 6 track days...

Want to add 2 degrees of negative camber, but worried about screwing up toe...

No local Porsche shop to do this, and suspect the local alignment place would be at a loss...

The local tire place willing to try, and said its not a big deal...

Do it myself? Tire place?
Old 05-08-2017, 05:24 PM
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Not hard but finicky. Loosen the toe and camber nuts, plus the two that are hidden by the caliper in this photo. Camber is gained by "twisting" the front of the arm up relative to the spring plate which is what that cam adjuster does. A little does a lot.

As I said in another thread, a smartphone with a free angle finder app can be a huge help here. Measure to your brake rotor before you loosen anything as a datum then subtract two, and adjust to that, should be perfect once it's back together.

Another tip is to pull the cam bolt out completely and put a dot in the outside corresponding to the highest point in the cam. Nice to have a visual.

It will affect your toe slightly, but there's also the danger of the toe cam slipping. So double check when you bolt it all together.

Have fun!
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Old 05-08-2017, 06:10 PM
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The camber and toe adjustments are fundamentally the same thing since the trailing arm is one piece with a single compound angle to it, so if you want to change one you will need to keep track of the other.

I don't mess with the eccentrics. I take them all the way out and use a small jack as a tool to rotate the trailing arm until I am happy with the camber (measure on the ground to know how much you want to change, then get a datum on the rotor when you get the wheel off so you don't have to put the thing on the ground again to see if you went far enough). Toe is then set by adjusting where the trailing arm bolts are in the slotted holes on the spring plate (basically moving if fore/aft).
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Old 05-08-2017, 07:32 PM
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My memory is that you pretty much have to go back and forth between the camber and toe adjusters to get only a camber change. I recall it taking about three or four cycles of that to get my buddy's rear camber and toe where he wanted them.

--DD
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Old 05-08-2017, 08:25 PM
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Thanks guys...

Will play with it next weekend...
Old 05-09-2017, 04:14 AM
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As you adjust in more negative camber, it will toe-out. So you will need to move the control arm forward on the spring plate to compensate. It helps to scribe a reference line on the inside of the springplate where the control arm started.

It will take a lot of back and forth, and don't forget to fully settle the car and rollit forward and bacward before taking measurements of camber and toe.
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Old 05-11-2017, 08:59 AM
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I had the shocks off due to a T bar change, and found the adjusting a bit easier by leaving that way until I had the camber and toe adjusted. That, and dethatching sways, should obviate the settling. But maybe I was wrong.

I keep meaning to purchase toe plates - two aluminum plates with slots in their ends for two tape measures. Not as accurate as some other methods (with slicks at the track I like the scribe the tire and measure for and aft between the scribe lines), but on a treaded tire I think that is problematic. Smart strings, of course, would be great. Old style stringing is OK as an overall check, but a problem with all the iteration of adjusting.

I've welded a tab with a 5mm threaded hole on the tip inside of the spring plate toward the front of where the banana arm part stops. A screw threaded down through this hole to the aluminum helps keep the camber part pretty much the same while messing with the toe.
Old 05-11-2017, 12:31 PM
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Quote:
Originally Posted by Walt Fricke View Post

I've welded a tab with a 5mm threaded hole on the tip inside of the spring plate toward the front of where the banana arm part stops. A screw threaded down through this hole to the aluminum helps keep the camber part pretty much the same while messing with the toe.
That's pretty much how the Elephant CamberMax works, but for a lot cheaper.
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Old 05-11-2017, 12:59 PM
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I remember that Dave Ferguson made a couple of frames out of square tubing that fit into brackets he had installed in the front and rear trunks of his 914-6. The brackets had been located such that the frames were centered on the chassis, and they came out and extended down far enough to get past the centerline of the wheels. Strings wrapped around the downward extending arms of the brackets could be used for checking toe.

It was a very portable and very repeatable set of strings, basically. Referenced to the car's body.

--DD
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Old 05-11-2017, 01:51 PM
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Dave - I made a system which used the front and rear hood pins to hold cross bars, which had vertical pieces welded to their ends so the strings would be at the height of the wheel centers. Worked great, looked a bit weird - as do Smart Strings - putting around the paddock to resettle the car. The trick with Dave Ferguson's approach is finding a place which will let you position the strings at the right height in front of and behind the front and rear wheels. I should see if I can adapt it for my SC. Among other virtues, if it is set up spot on (or with the best compromise the vagaries of the chassis allow), you are getting front and rear toe working off a common straight ahead datum.

Lasers would seem to be great for this, but my experience in the field says that it is too hard to see the spot, and that the spot is wider than a string (which, itself, is about a mm wide, but at some point that isn't going to make a practical difference.
Old 05-12-2017, 01:24 PM
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I've thought of welding threaded bits above and below the rear part of the ride height adjustment system on my two piece spring plates. If nothing else, it would stop what happened with my last T bar rodeo - loosening the bolts with a bit of a load on caused the adjuster to drop to the lowest height position. Since that was close enough, I left it there and made sure the other side matched, but now I have no further lowering ability on that side and am wondering if I should go through the brain damage of redoing things - and resetting camber and toe - on that side so things are set more in the middle of the range. The Elephant two piece system is going to be more positive, and perhaps the bolts are robust enough to raise - and certainly to lower - the car under load. But the stock two piecers, if you are lucky, are a vast improvement over the older method of setting ride height.
Old 05-12-2017, 01:30 PM
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I guess I haven't figured out the technique right but the strings deflect too easily for my liking.
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Old 05-12-2017, 08:36 PM
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Just stretch them tight. I taped a little one dimensional bubble level (the kind you hang on a string) to a piece of tape measure (surely you have broken one and saved the unbroken part of the coil against possible future need) to help with keeping things plumb.
Old 05-12-2017, 09:08 PM
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I was getting frustrated trying to get them tight like a guitar string. Seemed like even with quite a bit of tension the length is long enough that it can deflect by a mm or two pretty easily when trying to use a ruler or calipers or something.
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Old 05-12-2017, 11:12 PM
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Strings for toe are quick (with the right setup), portable, correlate front with rear, and relatively inexpensive. I wonder if there I a home brew laser system which is as convenient and inexpensive. No way to beat a professional alignment system, especially the newest ones, but what to do if you don't want to schlep your 42' long trailer to an alignment shop with 911 experience?

I agree resolution with strings is probably +/- 1mm. That is within a reasonable tolerance, though, isn't it?

A fellow here once showed a way of making rim standoffs to which you attached a laser pointer, which you adjusted so the pointer pointed in the plane of the rim. Hold it to the rim, mark where the dot showed up on the floor 2' in front of the tire center, and 2' to the rear. Do for both sides (per end). Measure between marks. I made one, but setup and a groody garage floor made it too finicky. And with each lifting of the car to adjust you had to do it all over again.

But I'm all eyes/ears on home brew adjustment. I use the SmartCamber system for quick and dirty on camber. I zero the digital angle gauge on the floor right by the tire in question, figuring that will account for sloping floors. With the car up, I can see what the gauge reads, and adjust to add or subtract what I think I want, and setting the car down again comes close despite the geometry effects of this kind of measurement.
Old 05-17-2017, 07:38 PM
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Strings are the way to go for a number of reasons. Fiddely for sure, but accurate.

To the OP make sure that your floor is FLAT. Even 1/8" deviation from one side to the other will make a difference in camber measurements. Use plywood or tile shims to level it out.

You also have to move the car after each change otherwise the tire's friction will prevent the change you seek.

Are you sure you want to add 2 degrees? That's a lot for an initial change.
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Old 05-19-2017, 12:17 PM
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Well, this is on hold...

My gearbox went out on the track... Guess that's now priority one...

I have about 1 degree by camber now. Car rolls a lot in turns, causing shoulder wear...

Probably need to drop the height too...

So many projects, so little time...
Old 05-20-2017, 10:21 AM
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I have had varying success with alignment shops but my own efforts are long dreary and usually unsuccessful. My last alignment left the car with uneven L/R toe and camber 1.5, 1.7 negative and .09, .03 toe in. I have tried using the camber max but they usually break although I give the instructions to the shop.

I have had as much as 2 degrees negative in the rear but not lately. I also can't get the car up high enough to get leverage to loosen/tighten bolts.
Old 08-24-2017, 03:13 PM
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If you can feel the difference on track of 0.2 of camber difference, I applaud you.
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Old 08-25-2017, 03:23 AM
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I was thinking the same thing...I will try it as is and then see if I want more camber.
Old 08-27-2017, 11:14 AM
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