Originally Posted by MattG
While I don't dispute that logic, I do wonder...how does one check the torque of the inner a-arm bolts without removing the wheel? Or should we just use a jack to raise the hub / compress the spring in this case to close to ride height?
You have figured out the Catch-22...
You can use a jack to raise the hub/compress the spring - many people do that. Or, an simpler way is to lower the car/wheels onto RhinoRamps so the weight is on the wheels. The slide under the car and use the torque wrench.
This is one reason that when
I get a garage lift, I'm getting a four post drive on lift. Now I just need a bigger/taller garage so I can fit one...
You can always check the torque on the bolts with the car in the air - if they are tight, you won't be changing the position of the bushings. But if they are loose, then you need to put the car to ride height prior to tightening.
A little background about suspension bushings.
The suspension does not actually rotate about the bolts that hold the A-arm to the chassis. The rotational movement of the A-arm is accomplished by the twisting of rubber in the bushing.
The bushings are made with two sleeves (cylinders) of metal, with rubber bonded (the Black and Gray in the diagram below) between the two. The outer sleeve (Orange) is pressed (it's a very tight fit) into the end of the A-arm (Blue). The "pivot" bolt (Green) (in this case the end of the Toe-Link ball joint) passes through a hole in the chassis (Yellow), through the inner sleeve of the bushing (Red), and through the other side of the chassis bracket (Yellow). When you tighten the bolt (Green), the sides of the chassis (Yellow) clamp down on the inner sleeve (Red). This clamps the inner sleeve of the bushing to the chassis and prevents any rotation of the inner sleeve. Note that the inner sleeve sticks out slightly from the rest of the bushing - this makes sure that the only part of the bushing to contact the chassis is the inner sleeve, preventing metal to metal rubbing of the suspension parts and chassis (only the Red and Yellow come in contact and they are clamped together so they can't move relative to one another).
Since the outer sleeve (Orange) is a press fit into the A-arm (Blue), it is not free to rotate relative to the A-arm. The only movement is the twisting of the rubber (Black and Gray) between the inner and outer sleeves of the bushing.
If you tighten the bushing with the suspension "drooped", things will be clamped in that position. When the car is settled on the suspension, the rubber bushing will be in it's twisted state. This causes a couple of problems. One, the rubber tries to untwist, "lifting" the car - it will try to act as a bit of a spring. Two, and more importantly, the twisted rubber is under strain, and will degrade fairly rapidly (consider a rubber band that has been stretched around something for a few months - it will no longer be flexible and will tend to easily break if you twist it or pull on it). Three, since the rubber bushing is already twisted a considerable amount, it will be strongly resisting being twisted more - this will reduce the ability of the suspension to move upward when you hit bumps, etc. It will act as a strong spring (if you want stiffer springs - add the metal kind, it's more predictable). Four, the car will feel "floaty" as you drive it.
Bottom line is, tighten (clamp) the bushings with the suspension in the ride position to avoid problems. This is also why you shouldn't store a car over the winter months "up on jacks". Leaving the suspension drooped for long periods of time will have the same effects, and cause the bushings to degrade more rapidly.
Oh yea, the reason the rubber in the bushing "Black and Gray" in the diagram is that Lotus has used a bushing that has a plastic ring (Gray) in the middle of the rubber (Black) bushing - this limits the twisting of the rubber, making the bushing "stiffer" without the harshness of using a hard plastic material (such as polyurethane) as is often used to make stiffer bushings.