Super stiff control arm after new bushing
 

I just replaced all the bushing in my control arms. Bolted things back together with proper torque today, and its STIFF. Haynes says torque for these 3 nuts is from 34 to 49 ft lbs .. I got it to just over the bare minimum at 35 by holding the bolt end with a wrench and torquing the nut end. Even with only 35#, it seems already too tight. It now requires A LOT of pressure to articulate the hub up or down. I could tip the other side up with the pressure required. The bushing kit I used is the IL Motorsport competition rubber that FM sell. It did say 40% stiffer, though I assumed that 'stiffness' referred to less unwanted lateral movement, and not normal articulation of the control arms ...

Did I do something wrong ?

https://cimg7.ibsrv.net/gimg/www.mia...c8314d9dfc.jpg

The only rotation you will see from those joints is the give of the rubber. So if the rubber is stiffer then the articulation will be stiffer.

Ideally you want to avoid preloading the rubber bushings, so it's better to torque them when the car is sitting on its wheels.

--Ian

^what he said.
Assuming you have the car on jackstands, lift the hub with a jack until the car just lifts off the closest jackstand. Then tighten the nut.

Thanks. I just looked into 'loading' the suspension during reinstall. Problem though is that this is an Exocet build, so I'm just reassembling my PPF right now. It will take about another week to get the frame on to lower the car or lift a corner.

From my understanding now though, seems that this will change the range of movement for the rubber bushing, but won't make it any easier to articulate up and down. Meaning if I torqued it now unloaded, the right arms will be incorrectly articulating up and down from 3 to 5 oclock ( for example ). If I torqued it with the suspension loaded, it will instead articulate in the correct 2 to 4 oclock range. It doesn't change the range of movement ( about 2 hrs on the clock or 30 deg in this example ) nor the amount of weight / force required to make that movement. That's changed due to the stiff material of the rubber.

Is that correct ?

Rubber bushings are in effect acting like an additional spring, for the suspension to move it has to twist them, and they will tend to try to return it to the position that it was in when they were torqued. The spring rate of the bushings is fairly low compared to the rate of the spring itself, but it's high compared to the amount of force you can exert on the arms just by pushing. Still, you want the "neutral" position on them to be close to the normal ride height of the car, so as to minimize the effect of this additional spring.

But yes, you can't get rid of that effect when using rubber bushings, it's inherent to the way they work. Polyurethane bushings will (briefly, when well-lubricated) give virtually zero resistance to motion, and when disconnected from the upright will actually droop down under their own weight. The problem is they don't *stay* well-lubricated, relubricating is a serious PITA, and when not properly lubricated they get stiction and bind. Delrin bushings are self-lubricating, but are too stiff to use in the pickup points with alignment cams and will bind if used there. Heim joints are very smooth, but are expensive and have a short lifetime. The new hotness is urethane with oil-impregnated metal bushings inside them instead of the traditional solid sleeve, which theoretically allows for enough deformation to not bind the alignment cams, but also smooth motion without being high maintenance.

--Ian

Thanks for that explanation Ian! Learning a lot from this project.