[T3] rear wheel alignment

[Jim Adney]

On 5 May 2018 at 12:00, David wrote:

> Then on page 76, Table 1. Rear Wheel Alignment, it says the rear wheel toe
> spec on a squareback is "-5 degrees 0 minutes, +/- 0 degrees 10 minutes".
> If I read this correctly, this means the rear wheels are toed out 5
> degrees.
> 
> So my first question; Is this a misprint where it instead should read +5
> degrees 0 minutes?

Such a simple question; such a complicated answer.

I've now looked thru about 10 different sources to see what they have to say 
about rear wheel alignment. Only about half of them bother to deal with 
alignment specs at all, but those that do, show the toe as 0' +/- 15' (for an 
IRS Square.) At first I thought this was a misprint, where they had used the 
apostrophy instead of the degree sign, but at zero, they mean the same.

Look at the table in ch. 7, pg. 37. I think those numbers are correct. That's 
the front axle chapter, but that's where they give the most details on rear 
wheel alignment, and those numbers agree with the other numbers I find.

Note that Squares, (Fastys & Notchs), and Type 3 Ghias all get different 
numbers, plus swing axle and IRS cars are different, plus Squares with and 
without the Z-bar are different, plus there's some difference for very early 
cars. I don't have the relevant official shop manual, so this is about as good 
as I can do.

To answer your question: Yes, I believe there are typos in the chart in the 
rear axle chapter. The toe specs in the first 3 columns should read:

-5' +/- 10'   |  -5' +/- 10'  |  +5' +/- 15'

The 4th column, 0' +/- 15', is correct as-is for your '72 Square. Since this 
table is in the brown Bentley '68-73 Type 3 manual, note that the swing axle 
numbers are only good for '68 Fastys and '68 Squares with the Z-bar. Similar 
'67s are probably the same. If you're looking for good specs for a different 
car, let me know, and I'll see what I can come up with.  

Yes, 5 degrees of toe-in would be WAY too much.

Toe-in is done to correct for the effects of camber. When the tops of the 
wheels tilt out you need toe-in. When the tops of the wheels tilt in you need 
toe-out. The reason for this is impossible for me to explain in typed text, but 
I'm thinking that it would be a good topic for a tech session, as it comes up 
so often and is so little understood.

For now, keep in mind that for both swing axle and IRS the toe doesn't 
change much as the tire moves up and down with load and road, while 
camber changes drastically on swing axle cars but only slightly on IRS cars. 
In both cases, the toe setting is a compromise, but it's a much larger 
compromise for swing axle cars than for IRS cars.

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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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