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I've had my 83 for several months now but because of a cross country move and other things in the way I've only put a few hundred miles on it. I am the 3rd owner and the car has just 62,000 miles on it.
In all those 300 miles the car has never felt "right" and has always sat 1.5-2" lower in front than most 928s I have seen pictures of.
When I say it has never felt right, I mean to say that the front end never seem planted. It would get upset over uneven roads, pull to one side or the other, the shocks seemed to bottom out if I had my wife and son with me, just never felt the way I would think a 928 should.
I knew the alignment was off. Even though the wheel was straight, the tire wear on the front tires was insane. Looking at the car head on you could see a crazy amount of negative camber. The previous owner had bought new tires and an alignment in early 1997, the car had only covered maybe 6,000 miles since then.
So I have driven it sparsely, waiting for a time when I could address the front end. I assumed since the ride height was low I would find worn shocks, and maybe worn ball joints.
I went ahead and ordered new Boge shocks, Lemforder iron ball joints, the correct bracket, new eccentrics, new tires, and new pads/rotors.
This weekend I pulled the shocks and was surprised to find that the front shock are already newer Boge replacements (they say Made in Germany on them) and that the lower ball joints, while the original aluminum units were still tight. Upper ball joints are fine, and I am not replacing those. I was also surprised to see that my 83 didn't have the adjustable collars on the front, but have been told that it wasn't originally equipped with them.
I am going ahead and replacing the shocks, they have to be nearly 20 years old anyway, and I already have the steel ball joints installed on the lower arms. This leaves me wondering if all the "problems" with the cars ride height and strange handling were all due to a messed up nearly 20 year old alignment.
I'd appreciate any thoughts or experience with this. I'd really like to get this right and finally enjoy driving the car without the fear of bottoming out on every bump in the road!
Heres a picture the day it as delivered to my house. Yes, its dirty! But you can see how the top of the front tire is tucked into the fender, in most 928s I have seen pictures of (even more so with the early cars) there is at least a half inch gap between the top of the tire and the fender.
But you can see how the top of the front tire is tucked into the fender, in most 928s I have seen pictures of (even more so with the early cars) there is at least a half inch gap between the top of the tire and the fender.
Your car was probably aligned after being lifted onto an alignment rig and not properly pulled down to settle the suspension.
This is a very common mistake and most will say: "You need to find a shop that will not lift the car".
That's the "easy" way but as you can see in the WSM pages, not the proper way. It's best to find a shop that will properly pull down and settle the suspension prior to doing the alignment. Since you are concerned about ride height this is especially important since you really should have the wheels off the ground to make the adjustment.
A "typical" modern alignment comes with the motto: "Set the toe and let it go" - this applies even to the dealership. Since this is the #1 factor that effects tire wear, it works for most, even if the other adjustments are "wrong".
If you want it done right, find a shop willing to follow the WSM.
As for ride height with other 928's, here is my 79, no issues with tire wear, these are 18" wheels and the front suspension is not fully settled yet. No, that is not my H2.....
I had searched pretty extensively and am aware of he "no lifting" issue. Plain to see the last alignment was improperly done. I contacted a local Porsche specialist and talked with then about the alignment. I'm taking the front shocks into them to swap out the mounts and springs to the new ones to cultivate the relationship so to speak and to talk with them more before the car goes in for the actual alignment.
I was thinking of taking in the WSM, but not sure if that was threading a fine line and don't want the shop to think I am implying I "know more than them".
My concern is that I might be missing something before I go ahead and put the car back together.
My previous experience tells me that the negative camber I was seeing woudn't lower the car as much as it seems to have but thought it would be a good idea to discuss it with the knowledgeable people here!
I was thinking of taking in the WSM, but not sure if that was threading a fine line and don't want the shop to think I am implying I "know more than them".
A good shop will appreciate having the information on hand.
its obvious too much toe in or out. nothing will wear it like that, bad shocks dont do it. lose stuff on the steering tie rods can do it, and that usually is inside edge wear .(toe out). toe in gives you the wear on the outside edge.
When these are decayed and let the rack move around you can get the situation on uneven roads where the toe for each wheel is different, and constantly changing according to which sort of undulation is being encountered by each wheel.
To check this, lift the front of the car so the wheels droop. With hands at the 9-o'clock and 3-o'clock position on a front wheel, push-pull horizontally. With even a small amount of wear in the rack bushes you'll get 1/4 - 1/2" of play without the steering wheel moving.
Get underneath and have a helper move the wheel and you'll see the rack move vertically.
There may also be some play in the front wheel bearings just to add to the fun.
When these are sorted and you've accurately set the ride height using the tripod method, get the alignment set as follows: Castor: 4deg or less; Camber: neg 1/2 degree; Toe: +2mm included.
To check this, lift the front of the car so the wheels droop. With hands at the 9-o'clock and 3-o'clock position on a front wheel, push-pull horizontally. With even a small amount of wear in the rack bushes you'll get 1/4 - 1/2" of play without the steering wheel moving.
Get underneath and have a helper move the wheel and you'll see the rack move vertically.
There may also be some play in the front wheel bearings just to add to the fun.
HTH.
Thank you for that, I will check this once the car is reassembled before putting it back on the ground.
I did check the wheel bearings, they are fine.
The front tire wear you show is typical to a toe'd-out condition. You've seen the guidance on not lifting the car before alignment, and you have first-hand knowledge now of the results. Excessive camber will wear the tire across the whole face, with more wear on the insides. The scrub from toe-out will chew through the inner tread like that, leaving the rest of the tire relatively intact.
Since you are replacing the shocks and springs, consider updating to later the adjustable lower spring perches. These are available used from 928 International at a reasonable cost. You'll want to restore the height to within the factory's recommended range. This will help with the toe change on road irregularities, get the car up into the normal dampening range for the shocks (will ride much better), and reduce the amount of vertical rack displacement that UpFixen mentions above.
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Relatively early in my stewardship period, I took my car to a highly-recommended shop for alignment. I sat there with the tech under the car as he made all the adjustments, and verifed the readings on his machine. Then chewed up a set of expensive front tires in just a couple thousand miles. Replaced the tires, settled the car, took it back to the same shop. They put it back on the alignment machine, where all settings showed perfect. I took it upon myself to make some laser alignment fixtures, spent some serious time getting the fixtures themselves "dialed in", then found that the toe and caster were off. It took a few tries and some patience to get everything perfect, but it is now. The difference between even "just a little bit off" and "perfect" is significant in both driving feel and tire wear. You can really tell when it's all just right.
Not replacing the springs, just the shocks. Is there an issue with the springs sagging? Once the new shocks are installed and the alignment corrected shouldn't the car come back to its proper height?
I'm so lucky to have a good Porsche shop where they work on 928s routinely and have their own alignment rig that they know how to use! I just got my new steering rack put in and the alignment they did feels incredible. None of this Tires R Us alignment for me. "Set the toe and let it go", I just love that.
The shocks don't hold the car up, the springs do. The shocks just dampen vibration. If the car is low (and it looks pretty low...) you'll need to do something to get it back up closer to correct ride height. The later adjustable spring setup uses shorter coils IIRC, but you should ask the question when you talk to 928 International. They will know exactly what pieces you'll want/need to restore the height. I've installed a few spring/shock units, a couple with adjustable pieces from them. The parts come looking and functioning like new, definitely worth your while in my opinion.
There are several articles here on measuring and adjusting ride height. You'll want that knowledge as you fit up your parts.
The more extreme negative camber is an effect of the car sagging, not a cause. Camber changes with the difference in length between the upper and lower control arms. The shorter top control arm has a smaller radius to work in, so it pulls the top balljoint in more than the same vertical displacement will move the lower balljoint in. This causes the tire to stand more upright in a hard corner, when the suspension would be compressed.
Camber is adjusted by moving the lower balljoint in and out relaitve to the centerline of the car and the position of the upper balljoint. Adjusting camber directly affects the toe setting, so be ready to do the rest of the alignment once you dink with the camber. Adjusting camber to a less negative number will cause your toe setting to go more towards toe-in, if you make no changes in the tie rod lengths. Adjusting camber this way means that the pivot pont for the adjustment is the upper balljoint centerline. You can look at the angle of the axis thru the two balljoints, and the distance between them. Then a little trig will tell you that you'll see a bigger change in ride height from tread depth difference than you will from making that axis more upright. (difference in arc cosine between current axis angle vs new angle, both as degrees from vertical). It's miniscule.
Thank you for that, I will check this once the car is reassembled before putting it back on the ground.
I did check the wheel bearings, they are fine.
My pleasure Mr Zilla.
When you've been back on the road for a few hundred miles check your tyres for tread feathering. (Hope I'm not telling you what you already know).
It's a condition where one side of the tread blocks have a slightly upturned sharp edge, and can be felt by sliding your hand against the 'feathers'.
They're caused by the tread blocks being forced to slide, bending them backwards, with the rearmost section deflecting upwards and thus getting the least wear, so once the block is unloaded that 'unworn' section returns to normal size and it can be felt as a 'feather'.
So look at where the blocks are feathering and think about what would cause them to be dragging instead of rolling.
Understanding this will give you early detection of alignment problems.
09-02-2014, 11:36 PM
Improper alignment and effects on ride/handling
