Harvey Cohen wrote:
> Does anyone dnow how excessive negative camber is
> corrected in the rear wheel of a TR6?
And Scott Suhring replied:
> More than likely the trailing arm mounting brackets are
> put on incorrectly. The knotches must be facing up and
> the brakets with two knotches go on the outside while
> the brackets with one knotch go on the inside.
And Jim Hill further replied:
>That's may well be the stock configuration, but there are actually at least
>three different brackets (1, 2 and 3-notch), all with a slightly different
>offset between the mounting holes and the holes for the trailing arm
>bushings. In addition, the brackets can be installed upside down if
>necessary to adjust the camber (which may require different combinations on
>the left than on the right).
>With a total of some 36 possible combinations of brackets and mounting
>configurations, it's possible to make substantial alterations in camber.
>Some time ago Brian Lanoway posted measurements of all the permutations -
>perhaps he'll post it here again.
Thanks Jim for remembering my post on fixing a bad (and lopsided) case of
rear wheel camber. Here's my post from last August again. Snip:
It's now taken me 2 years, but I finally think that I've got the camber
on both my rear wheels right and I thought the list might benefit from
some of the 'science' I've applied to the task. There's been some
traffic on the list last spring about this subject, but I haven't seen a
comprehensive approach to this yet. I hope this helps.
First some background. Last year, I installed new trailing arm up-rated
rubber bushings, springs and rubber spring packings, only to find that
the rear camber was still excessive - with the driver's side sagging
more than the other. This spring, I mixed and matched the trailing arm
brackets - using the same mirror-image combination on both sides - the
net result being the proper camber on the passenger side with some sag
still remaining on the driver's side. Finally, I remixed the brackets
on the driver's side alone to get that right. I now have both sides at
the proper camber angle - primarily through using various trailing arm
bracket combinations.
Since there are 36 possible trailing arm bracket combinations with the
one notch, two notch and three notch brackets - either in the 'up' or
'down' positions, I measured the bracket and trailing arm geometry,
applied some trigonometry, and then created the following table to
determine the range of camber adjustment possible using the 36
combinations. Please note that the camber angle shown in the table is
the RELATIVE angle between bracket combinations, the actual angle you'll
end up with depends on the camber angle you're starting with. By the
way, 3U means positioning the bracket with the three notches up, etc.
Here's the table:
outer bracket - inner bracket - relative camber angle (degrees)
3D - 3U - 0.00
3D - 2U - 0.98
2U - 3U - 1.50
3D - 1U - 2.11
1D - 3U - 2.42
2U - 2D - 2.49
1D - 2D - 3.40
3D - 1D - 3.49
2U - 1U - 3.61
1U - 3U - 3.80
3D - 2U - 4.40
1D - 1U - 4.53
1U - 2D - 4.78
2D - 3U - 4.93
2U - 1D - 4.99
3U - 3U - 5.91
2D - 2D - 5.91
1U - 1U - 5.91
D - 1D - 5.91
2U - 2U - 5.91
3D - 3D - 5.91
1D - 2U - 6.83
3U - 2D - 6.89
2D - 1U - 7.04
1U - 1D - 7.29
2U - 3D - 7.42
3U - 1U - 8.02
1U - 2U - 8.21
1D - 3D - 8.33
2D - 1D - 8.42
2D - 2U - 9.33
3U - 1D - 9.40
1U - 3D - 9.71
3U - 2U - 10.32
2D - 3D - 10.84
3U - 3D - 11.82
The actual angle you achieve may differ somewhat from that listed above
because the rubber bushings distort when you force the bushing bolts
through to meet the new bracket holes.
I found that it's best to change only one bracket per trailing arm at a
time. If you want to leave the ride height alone, change the inner
bracket. If you want to raise (or lower) the ride height while changing
the camber angle, change the outer one. To use the table, figure out
which bracket you're going to leave as is and then find the next
combination that allows you to do this while achieving the approximate
camber angle change desired.
In my particular case, the combination I ended up with was: passenger
side; outer = 1D, inner = 2U, driver's side; outer = 3D, inner = 2U.
I should point out that it is very possible to change out a bracket
while leaving the rest of the rear suspension intact. To do this, place
the rear of your TR on jack stands, jack up the trailing arm so that you
can support it (and take the spring pressure) with a secure support
under the trailing arm, place your jack under the arm where it joins the
bracket, remove the bushing bolt, remove the nuts on the bracket to
frame bolts, raise or lower the jack so you can get the frame bolts out,
remove the bracket and install the new one. Make sure you replace the
alignment shims as you found them. There is some grunt work involved in
getting the trailing arm back into the new bracket and aligning the
bushing bolt holes (I've found that a pipe clamp is a great help in
forcing the trailing arm back into the bracket) but the whole job can be
accomplished in about an hour and a half.
Couple of cautions: make sure the trailing arm is securely supported
while you do this; that rear spring can cause a severe injury if it lets
go. Secondly, go this bracket change-out route only after you've
renewed the trailing arm bushings, springs and packings as required.
unsnip.
back to lurking....
Brian Lanoway
73 TR6 CF6985U waiting to come out of winter storage
Winnipeg
PS: as a final note, I did try the aluminum spacer route before this, but
elected to do a proper job because the spacer fix was rather 'course' and it
upset the ride height of the car.
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