I have a 2006 GT with 70,000 miles on it, I replaced the wheels and noticed the pinion seal was leaking. I had a guy replace it with a NAPA seal and I picked up a bottle of synthetic gear oil to top it off figuring I caught it early. He told me it took most of the bottle to top it off. When I was driving to work the other day I notice what sounds like tire hum when I coast in gear around 30-50 miles an hour! It goes away when I give it gas. It also goes away if I push in the clutch or coast in neutral. I'm not sure why its there but it wasn't there before I had the seal replaced. I'm thinking it might be the new tires since it all happend at the same time but I thinking its not since the sound is not present when coasting in neutral or engaging the clutch. Any thoughts and thank you for any feedback??

 

does anyone know if adding almost a full bottle without additional friction modifier would create the hum??

 

Did the oil have friction modifier in it? It normally takes 4 oz of friction modifier with new oil taht doesn't have it added. If you lost roughly a third of your capacity then I would say you are down about 1 to 1 1/2 ounces of friction modifier. You should add some and see if the sound goes away.

Also, what did he torque the pinion nut to? If that's too tight it could cause a hum.

 

Possibly the drive shaft also. If it's not torqued correctly, it may vibrate at certain speeds.

 

How was the pinion nut tightenned? Was preload taken before removal and used when tightenning it back? Probably not.
A quart low would be really really low. Should be no 'humming'. But of the pinion nut wasn't torqued properly, you'll get noise. You may be hearing the pinion bearings due to improper preload.

 

This is why I haven't had my leaky pinion seal replaced yet. I worry that I'll end up with bigger problems afterward.

 

Just doing the seal is a pain to do without ending up with gear whine which is what you have based on the coasting vs power applied noises. The ring and pinion must be set with the correct amount of preload/torque.....this is when new gears are installed. When dealing with used gears, you have to match the old setting when you re tighten/torque the nut. This is not an easy task but some many have had success. Most would have counted the number of threads showing and marked the position prior to pinion nut removal and set it back to that same position......not dealing with torque. This puts the mesh pattern of the old gears back to the original pattern which should eliminate any noise. I say should.

Since yours is now making that dreaded noise, the only real way to get rid of it is a new ring and pinion set. The gear teeth wear into a pattern and when the setting is different, a new pattern is now attempting to wear on top of the old pattern. Good reason to put in some fun gears.....

I would also find a different shop to do the work.

 

from what i have read on this i did not porperly torque the pinoin nut so does anyone know the torque setting for the pinion nut, and if i continue to drive before i have it torqued properly will it cause any major damage to rear end.

 

The proper setting is determined by checking preload prior to disassembly. You're not looking to tighten the nut to a particular ft-lb spec. It's not that simple.

Preload is set by achieving a small but precise amount of rotational drag, and is checked with an in-lb beam-style torque wrench. The nut has to be tightened a little bit at a time, and rotational drag has to be frequently checked until you arrive at the correct figure for proper preload.

Here is a lengthy but thorough post at Corral.net, outlining the procedure. Improper preload will damage the bearings, and cause uneven gear wear.

 

I found the leak and after a few years had a shop replace it. The guy that did it tightened the nut too much and for the last three years have had gear whine... Was told its a new pattern being worn in to the gears and the only fix is a new set of gears. I've lived with it so far.

Any idea what to do now that the initial and proper preload is lost?