Re: Front lower control arm replacement

["ksgrimsr" <knut.s.grimsrud@xxxx>]

--- In dmcnews@xxxxxxxxxxxxxxx, "David Teitelbaum" <jtrealty@xxxx> 
wrote:
> A very informative post. Just 2 quick questions, did you weigh the
> origional and the S/S arms to see what the difference is?

> And how did the alignment set up (you did go to a front end
> shop and have the alignment checked didn't you?)

> I would also keep an eye on the bushing that went in loose.
> Maybe a spot of paint or nail polish as a witness mark...


I did not explicitly weight the control arms, but the new arms were 
noticeably heavier than the originals. The weight of the originals 
and of the stainless replacements is not substantial in either case, 
and the arms are a few pounds each.

I have been monitoring the bushing to ensure there is no motion 
since I had one press fit that was not as tight as I would have 
preferred. Your suggestion to mark it is a good one that I will make 
use of.

As you note, any time you do work on the suspension that has the 
potential to change the geometry, it is important to have the 
alignment checked/corrected. The following are the alignment figures 
from my realignment with the new control arms.

LEFT RIGHT
TOE -0.02" -0.02"
CASTER 3.67deg 3.84deg
CAMBER 1.36deg 0.01deg

As most folks are aware, only the TOE is adjustable when performing 
an alignment and all the other parameters are fixed by the geometry 
of the setup. In case some folks are not aware of the exact meaning 
of the three common alignment parameters, here is a brief tutorial 
(and my commentary on my specific values):

TOE: This refers to whether the two wheels are parallel to each 
other along the direction of travel. If the wheels are "cross eyed" 
it's referred to as "toe-in" and if they are "wall-eyed" it's toe-
out. Most alignments are set up for zero toe. The 20/1000th error in 
my alignment is in the noise as there is that much variance in the 
wheel rims to which the alignment equipment is attached. Since this 
is adjustable you'd expect that this can be adjusted to yield good 
values.

CASTER: This refers to whether the axis about which the wheels pivot 
for steering is vertical (i.e. perpendicular to the road surface). 
The caster is affected by any modification in the ride height of the 
front of the car, and if you lower your front a little the caster 
will also change since the car will not be parallel to the ground 
any longer. I don't have the alignment report from my previous 
alignment, so I cann't tell if the caster has changed, but the 
caster measurement is reasonable in light of the DeLorean's overall 
configuration (larger wheels in the back) and the fact that my front 
is slightly lowered.

CAMBER: This refers to whether the front wheels are closer together 
at the bottoms than at their tops. As you can tell from my readout, 
the camber of my left front wheel is different from my right (it is 
perfect on the right side). A positive camber as measured for me 
indicates that the bottom of the wheel is closer to the centerline 
of the car than the top of the wheel is. This positive camber will 
tend to make the car pull to the left (the car will drift towards 
the side with the most positive camber).

Because the camber problem coincides with the side of my car that 
had the catastrophic control arm failure, it is possible that the 
discrepancy is due to a deflection of the mounts caused by the 
failure rather than due to a tolerance issue with the new control 
arms. I'll be taking my car to a frame shop to see about any 
straightening of the structural mounts (we're talking pretty small 
amounts of correction).

The slight camber offset I have is not noticeable in any pull of the 
wheel, and my car tracks perfectly straight. I'm not sure what 
effect the weight of the driver in the car has on the overall 
geometry, since the alignment is usually done with noone in the car 
(and most cars are driven with at least the driver in the car). With 
the driver in the car, the driver's side suspension will compress a 
little bit, and depending on the geometry of the suspension travel, 
this may impact the effective alignment while the driver is in the 
car. I'm also not sure if the camber changes with suspension travel 
for the DeLorean geometry (in some setups it is common for the wheel 
to tilt inward at the top slightly as the spring is compressed in 
order to provide good tire contact with the road during cornering).

Overall the car feels good to drive and it tracks straight without 
any drift and without any pull of the wheel. Because most roads 
around here are not perfect, it's difficult to make any real 
determination based on the feel since, the crown in the road likely 
has more effect on perceived alignment than the variance I have in 
my setup.

Knut