Rear differential assembly repair not easy, but doable

My 1998 Dodge half-ton 4x4 pickup started making a growling noise, which comes from its rear end and doesn’t vary with load. I removed the cover of the rear differential assembly and found several rice-sized chunks of metal at the bottom. Everything else inside looked normal. I’m thinking it’s the ring and pinion. A shop I called wants about $1,500 to fix it. Any ideas or suggestions? I’m driving it only for short trips until it’s fixed. I’m handy at fixing lots of things but a differential is something I’ve never done before. — Dave

It’s difficult to say what has failed inside your rear differential assembly. The metal chunks could be from a carrier bearing or side or pinion gears. They’re probably not coming from the ring and pinion, as the noise doesn’t change with load. My concern is additional metal particles may have ground through all of the components, causing the noise you’re hearing and wreaking havoc.

I wouldn’t recommend tackling a rear-differential rebuild yourself, especially if you haven’t done it before. There’s quite a bit involved in getting pinion depth, gear patterns and bearing preloads right, and special tools are needed. Since you are a handy gent, have you considered a recycled complete differential unit from a dismantler? Rear ends are typically bulletproof and plentiful, running around $500 or more, depending on model. Because you have four-wheel drive, it’s essential the gear ratio of the replacement unit matches your front one. Wrestling the hefty component is a handful, but it’s probably a four hour job at most to make the swap. With any used component there’s always a slight risk of getting a bad one, but the most you’d be out would be your time and trouble, with the dismantler offering an apologetic replacement.

My car’s check engine light is on, and the on-board diagnostic system is reporting a trouble code of P0440. How big a deal is this to fix? Will it hurt anything to drive it until I can take it to be fixed? — Zach, Reno, Nev.

Sounds like you’ve got an evaporative system (fuel vapor) leak. Possible causes include a loose or faulty fuel filler cap, a leaking or inoperative vent or purge solenoid, a cracked or leaking fuel vapor canister, and a leaking hose, fitting, or fuel tank filler neck or seal. Try snugging the fuel cap and waiting through three separate cool-start road trips (fuel level between one-quarter and three-quarters of a tank) to see if the check engine light turns off. The system tests under these conditions and needs to see three successful trips before turning off the light. The code remains in memory for 40 trips before it auto-clears.

If the light stubbornly remains on, professional help will be needed. This type of fault will not cause damage or problems if you drive for a bit prior to repair, although you will likely be emitting somewhat greater hydrocarbon emissions than normal.

Depending on the vehicle, your diagnostic tech will employ various methods to isolate and identify the offending component, typically using a scan tool to command control solenoids to direct or divert vacuum, pressure, or smoke throughout the system, while observing changes in the fuel tank pressure sensor reading or watching for emitted smoke.