A few years ago, a 2007 Toyota Tundra 4×4 was donated to the automotive program at the school where I teach.
This vehicle had been used in a “Ride and Drive” event that had introduced the new bigger, heavier-duty Tundra. A Ride and Drive event is where anyone interested can drive a new vehicle on a closed course or track to check out the vehicle’s capabilities. During these Tundra events, Toyota dared people to abuse the truck to prove how tough it was.
This truck had been severely abused over several months of “Ride and Drive” events. The truck was then used by Toyota Technical Training centers for a few years and then donated to our automotive program. This truck has a 5.7L engine, 6-speed automatic transmission, and 4.30:1 axle gears! This is a burnout machine!
When we received the Tundra, I noticed that all tires had feathered edges and were nearly worn out, especially the right rear tire. It was evident that many “One Tire Fires” had been performed with this vehicle. For those of you who do not know what a One Tire Fire is, it is when a vehicle without a limited-slip differential does a tire burnout. That means that all of the engine power is transferred to the right rear tire rather than to both rear tires. 4×4 trucks typically do not come with limited-slip differentials (although optional); many 2WD trucks do.
This truck has a severe vibration and terrible noise coming from the rear axle. I used this truck in a manual drivetrain class because I wanted to teach vibration diagnosis with it and teach rear axle overhaul to diagnose the abnormal noise.
When attempting to disassemble the differential case (the part that the ring gear bolts to), we noticed three things:
The differential pinion pin lock bolt was broken off. We unscrewed it, and it was just a stub. We were able to remove the broken remains of the lock bolt by driving it out from a hole on the opposite side of the case.
The differential pinion pin did not come out of the differential case
The differential pinion pin would rotate with the right-hand side gear.
We used a hydraulic press to press out the differential pinion pin. It turns out that the right-hand side gear had friction welded itself to the differential pinion pin. I had never seen that before, and I wondered how that could have happened.
During a “one tire fire,” I realized that the right-hand side gear on an open differential would spin at twice its normal speed. As the differential side gear rotates, it spins on the differential pinion pin. There is very little lubrication provided to the side gears under normal conditions, so if someone performed a very long “one tire fire,” centripetal force would allow any remaining lubrication to be flung away from the gear and pin. Under these conditions, extreme friction would occur and the eventual welding of the side gear to the pinion pin. Once the gear was welded to the pin, the lock bolt would shear off.
To summarize, the severe noise and vibration from the rear axle were caused by the side gear welded to the differential pinion pin and rotating as one assembly. This type of vibration is tire speed-related, especially while turning corners, even slight turns or curves in the road. The NVH app includes detailed differential and axle diagnostic information.
There are close to 300 possible vibration sources on a typical vehicle today. The NVH app eliminates the guesswork in vibration diagnosis and guides you step-by-step through the entire diagnostic and repair procedure. Get the NVH app today by clicking on the link below.
THE NVH APP IS HERE!
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