Not your typical Gear Whine

[Stitch]

I've been having a real loud gear whinish noise happen from 50mph to 65mph but only when i'm at that sweet spot where you're not accelerating or decelerating. I could be cruising at 55mph in 5th, push in the clutch, and the noise is gone. I accelerate, noise is gone. I decelerate, noise is gone. I honestly can't tell if its the rear end or the tranny.

I may sound picky but when everything else is quiet and this noise comes through pretty loudly and its pretty annoying. My car's a DD so these things get annoying after awhile.

The rear end has 4.30's put in but the noise didn't start until aluminum front diff. bushings were put in. This was done to help adjust the pinion angle to elminate vibrations over 70mph that were pretty strong. My pinion angle with the stock bushings was pointing by 2* or so after the swap. I never got a measurement before the gear swap so I'm not sure what the factory pinion angle was.

Also, the tranny was raised at the rear tranny mount with 4 washers (so about 3/4" if that) to help line up the crankshaft angle with the pinion. Again this was done to eliminate the vibrations as ford specs state that pinion angle and crankshaft angle should be no different then 1*.

Thoughts? Help appreciated.

 

[Stitch]

No ideas?

 

[viperbluelx]

Very simple, aluminum bushings cause more NVH, take the bushings out and put stock ones back in if you don't like the extra noise.

 

[RoyWoods]

I've got an almost identical problem, with a similar setup (4.30's, MM Aluminum Diff Kit, etc.). I'm not much help right now, because I'm still working to figure mine out too. I hope to have the car back together in the next couple of days, and can then tell you what I did and the results. If you do switch the bushings back to the stock rubber ones (which I will eventually try if necessary) be sure and switch them all (i.e. the front ones and the rear one). I've seen a bunch of posts saying that having different materials at the front and rear of the differential is a very bad idea.