Is it possible to have noise coming from a differential one month after adding gear oil?

Here is the scoop...I had my 2001 Mustang Gt in for an oil change. At this time there was no problem with my diff. When the mechanic is under the car he notices that I have a rear pinion seal leak. So I ask him to fix it and on the bill it says added gear oil. About three weeks I start getting a really loud noise coming form the differential. So I bring it back in and the mechanic says all the damage was done prior to the pinion seal change and that it just took a little longer for the gears to wear out. My question is....Is this even possible to have no noise then have service done to it then all of a sudden have noise back there. It seems weird that oil was added and then the noise appears. It would seem to me that they made a mistake and didn't add any gear oil after the seal was changed and that was most likely the cause. Any help would be great as I now need a new differential and they are not cheap.Is it possible to have noise coming from a differential one month after adding gear oil?
Yes it is possible, was the noise on acceleration or on deceleration, if it was on deceleration then your pinion bearing is gone, if it was on acceleration, (or all the time) than your gears are worn out and this was probably caused by previous issues. Some diffs have a crush sleeve in them that might need to be replaced when a pinion bearing is done or the preload on the bearing can be off casuing a loud howl on deceleration.Is it possible to have noise coming from a differential one month after adding gear oil?
Yes, it's possible, in fact likely that the damage was done prior to them doing the service. They took off the back of the differential, drained the fluid and replaced the seal and then put more oil in. Unfortunately, the damage was already done. Draining the old fluid removed a lot of ';sludge'; (basically metal shavings from the gears) and then the new gear lube compounded the problem because it has a detergent in it that makes sure the gears stay good and clean. Good in a good differential, not so good in one that's severely worn. Simply put, the sludge was what was keeping the thing working and they cleaned it out. The only real question is how long would it have taken to fail had you not touched it? Certainly it would have lasted longer but how much longer? A week? A month? Maybe even a year or two? Hard to say. But the flip side is also true, what if it wasn't too late to replace that seal? If they caught it just in time they may have saved you this expensive repair . . . unfortunately, there's no way to know ahead of time.





You're just stuck with the same advice my dad always used to give me when I complained about break downs and repairs ';Cars are expensive, aren't they?';
they probably never touched it and charged you for it. you have to watch those people.if they filled it then it should have been ok.