Rear End Noise...did research still need help

[Methodical]

I've research the forums and gotten some info but I thought that I needed to post my particulars.

After I reached about 85-90 mph, I can hear a moan - a hollow moan (resonance) - but not a vibration coming from the rear. If I drive normally to 85-90mph I don't really hear the moan but if I go WOT to 85-90 I really feel or hear the moan. I don't think it's the drive shaft. I've had bad U-Joints and now they can shake you out of the car. The moan was there for awhile but not really noticeable until I recently installed the upper (FRPP stock replacement) and lower control arms (MM w/spherical end) along with the complete coil over kit, now the moan is even louder. I had 3.73s installed back in 1995 or 1996. I read that these particular LCAs would create road noise but I think l something going on in the rear differential but need a sanity check. Oh by the way, the car is lowered as follows (wheel fender well to ground) Rear = 26.25", Front = 25.875". Also, when the car is in the air, I notice that there is play in the rear wheels when rocking the wheels front to back (i.e. a little slop). I think this is normal but not absolutey positive.

Now during my research, these were 2 responses that caught my attention. These were responses to particular posts.

1. If the rear gears are installed incorrectly, noise and vibration would be felt all of the time thru out the rpm range and not sometimes.

2. Folks suggested removing the dogbone (mine still exists) after installing aftermarket gears.

Below are my questions:

1. Should I remove the dogbone?

2. Could the pinion angle be screwed because the car has been lowered?

3. Is the statement in in No. 1 true or not?

4. What diagnostics should I try?

Thanks for your help and insight

 

[94-302-vert]

I have the exact same as what you are saying... The resonance kinda oscillates, like when driving near another car with a loud exhaust you get the bwough kinda sound...

Mine started with my gear install last year. I have since replaced the DS with an alum one.

I have talked to a couple of buddies who went from not hearing anything then put in poly bushings and now they hear a ton of road noise. I am attributing mine to the road noise coupled with the exhaust....

 

[Methodical]

I have the exact same as what you are saying... The resonance kinda oscillates, like when driving near another car with a loud exhaust you get the bwough kinda sound...

Exactly. Could not have described in any better. Did you remove the dogbone?

 

[JOEGTS]

I have the exact same problem. I installed the Ford racing uppers, Steeda lowers and Lakewood shocks. My noise mainly occurs when I am decellerating in gear. I took my cover off and my gears are making contact accross the entire tooth front and back. I believe I need to take some clearence away from the pinion? The noise was there before the suspension install but you could hardly hear it. I am just going to replace the ring and pinion and all new bearings.

 

[final5-0]

I can't be certain but, most peeps I've seen who seem to know about suspension stuff say, "when you move away from the oem stuff, you gotta expect some NVH."

Perhaps that is all that you are hearing and nothing is wrong

Grady

 

[94-302-vert]

I did remove the dogbone... No change...

Now my story gets worse as my gears were installed wrong and I wiped out a bearing (1k miles on the gears at this point). The guy then re-did all of it (I bought all new bearings and seals) and he re-used the same gears. then I had no confidence in it as it was still making a TON of noise so I checked the rotational torque of the pinion and it was like 2 in-lb. This was another 600 miles later... so we tightned down the pinion nut until we had the right value for enw bearings... Since then I have been into my diff 3 times and each time the gears look perfect so I have stopped driving only below 80 and now figure it has to be either NVH from the poly or just a bad wear pattern on the gears.

I also know I have excessive backlash because I get major banging due to the slack in the gears...

 

[Methodical]

I can't be certain but, most peeps I've seen who seem to know about suspension stuff say, "when you move away from the oem stuff, you gotta expect some NVH."

Perhaps that is all that you are hearing and nothing is wrong

Grady

What it is Grady (smile). A little old school on my part. Yeah I figured that and if that's the case well I guess I gotta hook up the ole' stereo system to drawn out the noise. I just hope there's nothing wrong with the gears. Like I said no gear whine etc. I will remove the dogbone to see what happens. I removed the pinion snubber years ago even after lowering the car. No bottom out issues. I think because the shock I insalled had bump stops.

 

[JOEGTS]

What is the dogbone?

 

[Methodical]

I removed the dogbone today. I won't get a chance to test it 'til Friday. Hopefully it makes a difference Will update.

 

[mo_dingo]

What is the dogbone?

Underneath the diff there is a sorta dogbone looking thing. Can't even remember why it's there, someone here knows ford's crazy logic.
Scott

 

[bill302]

Rear End Vibration Damper - That heavy bone shaped thing on the front of the rear end snout is the factory vibration damper. Each one is tuned to a frequency that corresponds with the factory gear ratio to cut down on noise, vibration, and harshness (NVH). Turns out the thing is no longer at the proper frequency if you changed the rear end gear ratio. Take it off and throw the bottom bone shaped part in the nearest trash can. Keep the top sheet metal part and reattach it to the rear end with some shorter bolts. This gives the pinion snubber something flat to hit against.
copied from http://www.jason.fletcher.net/tech/freetips/freetips.htm