Speaking of aluminum ...

In comments on my last post, we discussed the amount of aluminum you find in today's cars. I had this big, fat, late model Chevy pickup (2500 series) in the shop today and what do I find on it? Aluminum brake rotors. Granted, they're aftermarket and this guy threw a buncha money in the trash buying 'em, but you see these a lot on hybrids and the micro-minis the car makers are pumping out these days to save weight and increase fuel mileage.





The reason I had this load in the shop today is for a vibration that came on at 40 mph and continued up to highway speed (kept up no matter how fast I got it on the highway). Now what possessed this guy to put these huge tires on it when it hardly sees any dirt is beyond me but the things have the most aggressive tread to still qualify as a street tire (noisy as a fuck). The whole wheel/tire assembly weighed about 60 lbs which is why I said he wasted the money on the drilled aluminum brake rotors.

The idea behind the aluminum is to reduce "unsprung weight". That's the weight of the parts of the vehicle not controlled by the suspension - "anything below the springs" in our parlance (wheels, tires, brakes, axles and differential housings sometimes, control arms sometimes). The idea is the less weight below the springs, the better handling the vehicle is and is less susceptible to "bump-steer" - the wheels reacting to bumps and divots in the road. It's why they put steering dampers on off-road vehicles - to absorb the shock to the steering gear and undesirable inputs coming back through the steering wheel. The weight savings over iron rotors compared to the aluminum ones is negated by the heavy wheels and tires.

The reason you see a lug nut with washers under it is because I was running the beast up in 4WD on the lift without the heavy ass wheels and tires on it (trying to rule them out as the cause of the vibration) and I had to keep the rotors from flopping around and destroying the pads, calipers, and mounts.

After running it up while having Nunzio watch the driveshafts and anything else that rotated while driving, we looked at the front axles (it's got an independent front end) and found the inboard constant velocity joint in the left front was binding. The hubs stay permanently locked (the shifting to 4WD is done through a solenoid on the New Process Gear transfer case) so you get it in 2WD as well. I slapped a new axle in it as soon as I could get one sent up and the vibration went away. Thankfully, I only had to take the wheels and tires off twice. I hate working on trucks.