Very interesting. I'm going to be doing the brakes on my S4 soon, and would have probably just tossed the old rotors, but this may be a good justification for keeping them around.

Great, just what I need, more stuff! Heh heh...

 

Great thread, Bill!
*subscribes*

 

I know they can move either way, but in the quote I provided from your guide, the highlighted text seems to say you want them all the way forward for optimal caster, then it says all the way back later on. When I look at the lower balljoint and the caster eccentric I get confused easily.

I gather on the 928, the minimum caster attainable is about 4 degrees and therefore you generally just drive the eccentric to set caster at the minimum (unless you have the odd car that can adjust lower) then make sure both sides are equal. So, which end of the range do you want the lower ball joint itself (understanding that the eccentric end of the carrier moves oppositely): All the way forward or all the way back? Earl doesn't spell this out and although I scrutinized a bunch of basic caster information to figure this out, I'd like this spelled out here. If the upper balljoint is behind of the lower, then you would try to get the lower balljoint all the way back, right? So, in your orginal text, the first instance of the word forward should be changed to back, right? Sorry to be a pest.

 

I'm going to try doing some of my own alignment since I'm not happy with the last place I took it to. These are all good write-ups and I've already started making the toe gauge setup like Dr. Bob and the Capt. describe.

Will also buy an alignment turntable.

Was wondering if anyone has tried this camber/caster gauge. Looks pretty good for $150. There is a video that shows how to use it.

http://www.spcperformance.com/PROD_D...OOLFASTSM.html

The tool looks pretty good.

Brent
89S4

 

I'm most of the way through the "how to make the toe-in fixture" write-up with the assembly diagrams and all. Should be formatted and proofed by the weekend for sure. I did figure out how to get all the AutoCad drawings into MS Word, but need to go back and redo some line widths so the drawings are more easily readable. Right now they come up pretty faint as imports into Word. It is coming together though.

In the meanwhile shop for a 7' stick of 2" Al box tube 1/8 to maybe 3/16 wall, and a 3' stick of 1.5" aluminum angle stock with at least 1/8 thickness.

 

I see the same device at Summit Racing. They quote a spec of 0.25 degree accuracy. That's not good enough. You need to get 0.1 degree accuracy.
http://store.summitracing.com/partde...part=sps-91000

 

Will this thread make to the Nichol's site or the 928 DIY forum? I just checked the 928 DIY forum, last post there was May 2005.

 

I guess we've seriously neglected the DIY forum. This could go there. Master threads should be kept more readily available, such as a DIY forum or made sticky here or linked in a sticky master thread master link post in the Read First FAQ sticky.

 

OK, just a bit of my primitive understanding of caster setting to clear up which way to adjust the eccentric, the question I asked above.

As Jim indicated, we have positive caster, wherein the upper balljoint is positioned behind the plane of the lower balljoint as shown here. Positive caster provides straight-line stability and self-centering of the steering wheel at the expense of some extra steering effort.


The spec for caster in the 928 is 4° +1 (so, max 5). A common observation is that on many cars it is difficult to get caster down to the 4° spec. So, a common solution is to set caster to the lowest value available common to both sides. Make sure both sides are as close as possible to each other to prevent pulling to one side. So, if one side will go down to 3.5° but the other will only go down to 4.8°, set them both at 4.8°. Caster is measured indirectly by calculating from camber at +20 and -20° turn-in, as described in Captain Earl's guide and Jim M's detailed post above.

The caster adjuster in the inner (closer to the car centerline) of the 2 eccentrics on the lower ball joint carrier (unless you have an OB that happens to still have the recalled aluminum balljoint carriers), as shown here:


To get caster to its minimum, you would turn that eccentric so that the lower balljoint moves as far rearward as possible. Note that changing caster will affect toe, but not vice versa. So, if you make an adjustment to caster, go back and redo toe.

 

Since this is a master thread, here are the standard alignment specs from the WSM. You should align as closely as possible to the exact center spec if there is a range and minimize side-to-side variations. That is not to say there might not be special settings that differ from this, such as toe out for quicker turn-in on the track, but it is very rare that these are desirable.

 

I agree with the midrange recommendation whwre the spec shows a +/- range. For caster, they give a target number and suggest a + variation only from that target. FWIW, a larger amount of caster makes the car a little more sensitive to road camber, but seems to reduce tramlining some, especially when combined with correct and even camber adjustments.

The specs that alignment techs use seem to allow side-to-side variation between the wheels, and that can easily lead to pull to one side or uneven tire wear. To keep the car going straight and to minimize tire wear, it's very important to have the right and left sides identical. For example, the WSM camber settings would seem to allow one wheel to be at -20' and the other at -40' (one-third of a degree negative on one side, two-thirds of a degree negative on the other.) To get the car to track perfectly with the steering centered would require an offsetting difference in caster; that would cause problems at steering angles other than centered though. The conclusion is that you can adjust the wheels within the factory tolerances, so long as they are both the same.

 

Hi Bill,

great initiative to pull all the great information into one master thread.
My car is only roughly adjusted to a toe value close to 0 to avoid uneven tire wear before doing the complete adjustment.
Which will be a project in a near future.
And thanks to all contributors for all the details and great ideas.

Cheers/Peter

 

Trapezoid calculator..
http://www.analyzemath.com/Geometry_...alculator.html

More about it's use for toe adjustment later.

 

Two cars visited me for a toe check in the last two days. In both cases you could eyeball that they were toed-out. The first measured 0.8ş toe-out. The second started out at 1.6ş toe-out! As you can see from the spec chart posted earlier in this thread, total toe should be 15' (or 0.25ş) toe-in, or 0.12ş toe-in per side. Egad! Tire wear had been an issue on one car and the other was not stable on the road and tended to wander.

We used the following "equipment":


Laser level bonded to 1" aluminum square section tube, with 1" angle feet. (see detail shots below) One foot is 7" long, making two-point contact with the wheel rim, and is glued and pop-riveted in-place while the other foot is only an inch wide and is adjustable by way of a slot cut into the square tube base. So, we have a 3-point base. The laser level also has bubble levels to aid in making sure the instrument is in a level plane fore-aft. It would be ideal to have TWO of these. You could leave them bungee-corded on the wheel while you measure and adjust. I will make a second after I'm happier with the design. In the meantime, I move it from wheel to wheel and just hold it against the rim for measurement - not ideal, but it works. Please see my heretical commentary about this tool after the detail pictures below.

Laser Targets. I used 4 of my kid's stand-up school project display boards. I set them up as shown in the diagram 1 further down in this post. If you can establish the exact distance between the ends of the laser level beams, as dr. bob does, as shown in diagram 2 you would only need one pair of target. Marking pen not shown.

Tape measure. I hope to dispense with the mickey mouse targets and the tape measure and build a single, wide, ruled target.

Alignment turntables. You could just as well use homemade slip-plates from two linoleum-type floor tiles with grease between them. Since the turntables raise the front end about an inch, I used a 1x6 board under the rear wheels (not shown) to keep things level or close to it.

22mm open-end wrench for tie-rod locknut and 15mm wrench for the tie-rod adjustment flats.

Here are some closer shots of the laser tool. I used silicone goo to glue the laser to the tube. I think the long foot end of this is fine as I did it, but I'm trying to make a spring-loaded adjuster for the adjustable foot. dr bob has discussed calibrating and adjusting the lasers elsewhere.




I'm going to be heretical here for a moment and say that making the rim mount for the laser does little more than allow to use your hacksaw, file and drill. Before I made the mount, I used to lay the laser across the tire face. Front to rear, the tire should be even and not have bulge like the lower portion of the tire on the ground. So, if you haven't made a fancy mount, don't sweat it. A laser across the tire face will get you very close.

Here's a schematic diagram showing the lasers mounted on the front rims shooting forward at two pairs of targets. The near targets are moved out of the way to shoot the far targets. You measure the distance between the right and left dots on the rear and the front target pairs. If you are toed-in, the laser dots on far targets should be closer than on the rear targets. Diagram 2 shows dr. bobs method.




You can plop the numbers into this on-line trapezoid calculator.
http://www.analyzemath.com/Geometry_...alculator.html
I've labeled the diagrams above to correspond to the on-line calculator. Here is a screen capture with some hypothetical numbers that happen to hit the spec.

Note that I theoretically introduce a small error by measuring the distance between the far and near target boards (sides a and c of the trapezoid) perpendicularly rather than precisely from dot to dot. You could not measure a difference between those two dimensions if you used a micrometer. It's just much easier this way and the error is below miniscule (less than 0.001ş).

The adjustment itself is pretty simple.
- Roll the car up onto the turntables (and board for rear tires) or slip plates. If you have neither, you will have to roll the car after each adjustment.
- Pull the lock pins on the turntables.
- Take your initial measurements.
- If adjustment is needed, loosen the 22mm lock nuts on the tie-rod outer ends, near the ball-joint, counter-holding the tie-rod adjustment flat with a 15mm wrench.
- To move toe from positive to more negative, the rear of the front wheel must move outward. So, turn the tie-rod tube by the adjustment flat so as to expose more threads and lengthen the arm. From behind the tie-rod, this would be DOWN on the driver (left side) and UP on the passenger (right side). Be very careful not to lose your bearings and turn the wrong direction.

The adjustment is pretty sensitive. If you are way off, as with the two cars I mentioned, a full turn may be a good start. But after that, 1/4 then then 1/8 and 1/16 will be needed to get the toe on the money.

This is a simple approach that ignores some fine points, such as the effect of driver load. You can account for those by weighting the front seat. For some driving situations, you may not want factory spec toe-in, but that is an exception.

Toe has the most profound affect on driveability, handling and tire wear of any of the alignment adjustments. As was the case with the two cars, it is OFTEN way out of spec due to improper previous alignments, from raising the car prior to alignment. Make sure the suspension is settled and do any ride height adjustment days before adjusting toe. If need be, apply the WSM procedure for drawing down the front suspension, as mentioned in the first post in this thread. although it's best to just avoid it.

 

Man that hurts my head!!