CARspec had the opportunity to address a howling noise while driving on a 1999 Toyota 4Runner. The owner, on his way up north next week, was concerned he wouldn’t make it safely and asked our technicians to diagnose the noise. After driving the vehicle in the air and listening to the drive train with a stethoscope, the rear differential pinion bearing (the bearing that supports the main driving gear inside the rear differential) was failing. After a discussion, both the 4Runner’s owner and the technician agreed that replacing the rear differential was the best course of action.
A rear differential is major drive train surgery – both rear axle need be removed, the brakes disconnected, and the entire rear differential carrier be removed. Because this 4Runner was equipped with a locking differential, the technician put the truck in 4LO and locked the rear end before starting the repair. If you do not lock the rear differential the select collar that engages the lock won’t allow the rear diff to fit out the front of the rear axle assembly. Here’s what the rear axle looks like with no carrier, axles, or hubs installed:
Toyota is unique in that the differential comes out the front of the axle instead of the rear – there is also no access panel on the back of the unit. The entire assembly comes in one piece, ready to be installed. After removing the old and installing the new, the technician tore down the failed unit to find the root cause of the howling noise:
While the root cause of the bearing failure remains unknown, the best safeguard against differential and transfer case failure is routine fluid replacement. As Eden Prairie and Chanhassen’s independent Toyota and Lexus repair shop, we stock all the fluids to service late model Toyota, Lexus and Scion all-wheel and 4 wheel drive systems. If you’ve got a noise, are concerned about the condition of your differential fluid or would like advice on maintaining your drive train give us a call at (952)426-4798 to make an appointment today!