Chasing a ghost. rear end noise.

[wutang61]

I'm having a hell of an issue with rear end noise. And it's becoming quite the Bastid to trace what in the heck is actually causing it.

Car has a built rear end. True trac, mosers and a motive 4.10. Ford racing install kit.

I originally setup the rear end but it howled pretty good. So I bit the bullet and took it to a local race shop to have them take a peak on what exactly was going on.

They gutted the rear, inspected everything with no signs of issues. Reinstalled everything and the gear noise is still on the verge of insanity. They're to the point of being completely lost at its cause. Pattern and backlash are perfect. (Checked in 3 places) wear pattern on the gear itself looks good. Bearings look perfect.

Actual quote was around "it's dead nuts perfect. It's just screaming and there is zero indication of why.

Car does have spherical differential side bushings with stock upper control arms and MM extreme duty lowers. Anyone have a simpler setup? They are pretty forceful on the bushings being the only cause of the noise.

Which I feel they are correct to a point. But I do not believe that sphericals on the diff side would cause gear noise to be so loud it resonates in the cabin at 50-55mph. (Also a whoop whoop whoop on coming to a stop)

My plan of action: ditch the motives for a ford racing gear. Replace inner and outer pinion bearings and carrier bearings. I also have stock rubber replacements for the Diff. so that is another option as well.

Novel over. Thoughts?

[DSG2003Mach1]

i also have a true trac with the noise youre describing on decel but do NOT have any gear whine or other noises at all. Im starting to think its the nature of the beast in that aspect

[sutyak]

I also have spherical housing bushings and spherical UCA bushings with Precision 4.10 gears. Yes it's pretty loud. I think the spherical bushings have a lot to do with it. Leaving in the back seat and sound-deadening mat helps significantly. I had FRPP 4.56 gears in my previous Mach 1 and they were even louder.
The whine is slightly annoying, but I can certainly talk to a passenger normally at highway speeds.

[311-420]

A 75w140 royal purple gear oil will help some. MM heavy duty lowers are great for a street car. Id swap those extremes out for the hd's and add the heavier, more robust, gear oil and go from there. If the problem is still unbearable, ditch the tru trac and get a ford racing limited slip diff with carbon fiber clutches. A 3.73 will probably be quieter as well as alleviate some traction issues and give more top end speed back to the car. Now you have my setup!

[j rick kirby]

My FRPP 32 spline diff with RP 75w140 and 373s is silent.

[32VALVR]

I had a Tru trac for a while, it made an awful noise on decell only. My girlfriend said " Sounds like you've got a box of marbles bouncing around in the trunk". That was it for me, I called Eaton a couple of times and finally got a guy to admit " some 8.8's have it and some don't. when asked what was the cause dude said they didn't know. As mine was only in for like four days, they gave me a refund.
I've had an Eaton posi blow that up so bad it locked the driveshaft destroying my 3650 tailshaft.
I stick with Fords trak loc. they seem to last.

[wutang61]

The little bit of diff noise I hear isn't an issue if that's what the little whoop sounds are on decel. I've been back and forth with a local shop about this for days now and they are pointing the finger hard at the solid diff bushings.

The plan of action at this point is to get rid of the solid diff joints and stick rubbers back in. The interior noise at acceptable speed limits (50-60mph) is enough to wanna drive it off a bridge. If that doesn't work then the motives are getting torn out for a FRPP gearset.

From my ear and the few guys I've had ride in it it's undoubtedly pinion related noise. The lowers are mounted at the end of the axle tubes and are pretty isolated compared to the upper mounts which ride right on the pinion itself. Side loading the car in corners doesn't change the pitch or volume so I don't think the extreme lowers are the issue.

From my digging motive gears make noise more so then any other brand across many forums...So that with my solid uppers I feel is having a compound effect.

Again internally the rear is dead nuts perfect.

I'll definitely update this thread with the be all end all solution to this issue. But in the meantime keep the feedback coming. All of it helps paint a clearer picture for the correct angle of attack.

[gfong]

My car has close to what you have. Car has a built rear end. Truetrac, Mosers and a Motive 4.56 gear.

Noise since first installed, I had Ford racing 4.30's and Ford racing 4.10's in the car before and they were dead silent. (same guy did the install on the 4.10's/4.30's/4.56's)

The 4.56's have been in and out 3 times to quiet the noise. Tried all different oils and right now it has non syn oil in it and it did dull the noise a bit. Mine is bearable but the way you are describing your noise it would drive me batty!

I made a post on here way back as I contacted Eaton and they told me not to run synthetic or use Ford friction modifier with the gear set and their Trutrac. They even posted a FAQ about it on their site.

Q: What kind of oil should I use? Can I use synthetic? Do I need friction additive/modifier?

A: A quality petroleum/mineral based oil works best in the Truetrac units. We do not recommend synthetic oil. Friction additive/modifier is not required.


So... there is one option to try, can't say it will work for you but it did dull the sound on mine a bit. Good luck... ear plugs could be option 2 or SLP loudmouths like I have! (joking)

[wutang61]

Originally Posted by gfong

My car has close to what you have. Car has a built rear end. Truetrac, Mosers and a Motive 4.56 gear.

Noise since first installed, I had Ford racing 4.30's and Ford racing 4.10's in the car before and they were dead silent. (same guy did the install on the 4.10's/4.30's/4.56's)

The 4.56's have been in and out 3 times to quiet the noise. Tried all different oils and right now it has non syn oil in it and it did dull the noise a bit. Mine is bearable but the way you are describing your noise it would drive me batty!

I made a post on here way back as I contacted Eaton and they told me not to run synthetic or use Ford friction modifier with the gear set and their Trutrac. They even posted a FAQ about it on their site.

Q: What kind of oil should I use? Can I use synthetic? Do I need friction additive/modifier?

A: A quality petroleum/mineral based oil works best in the Truetrac units. We do not recommend synthetic oil. Friction additive/modifier is not required.


So... there is one option to try, can't say it will work for you but it did dull the sound on mine a bit. Good luck... ear plugs could be option 2 or SLP loudmouths like I have! (joking)

Yea i read into the non-synthetic oil issue myself. contacted eaton directly regarding it and they couldn't present a "what will happen if you do" answer.
So i just opted to use it due to it smelling slightly less terrible. lol

The issue has been located. The gears themselves were the problem. rear end was setup perfect along with a perfect gear pattern.... TWICE. Changed to ford racing 4.10's and its dead silent.

moral of the story: STICK WITH FORD GEARS. it will save you time, money, and a hell of a headache. or at least avoid the motive option. Much better gears out there for the $$.

[DSG2003Mach1]

The thump on decel is gone too?

[gfong]

Originally Posted by wutang61

Yea i read into the non-synthetic oil issue myself. contacted eaton directly regarding it and they couldn't present a "what will happen if you do" answer.
So i just opted to use it due to it smelling slightly less terrible. lol

The issue has been located. The gears themselves were the problem. rear end was setup perfect along with a perfect gear pattern.... TWICE. Changed to ford racing 4.10's and its dead silent.

moral of the story: STICK WITH FORD GEARS. it will save you time, money, and a hell of a headache. or at least avoid the motive option. Much better gears out there for the $$.

Glad you got it figured out. I'm with ya on the the stick with Ford Racing. I could not get them at the time for my 4.56's. Good luck.

[sutyak]

Glad you got it figured out!

[wutang61]

Originally Posted by DSG2003Mach1

The thump on decel is gone too?

Yep. Even with solids on the axle side the interior noise is just exhaust now. I can't tell any increase in NVH Whatsoever.

Going from an airplane taxiing for takeoff to what is now is pretty astounding.

[DSG2003Mach1]

Interesting, my gears are 4.10s from ford racing and don't make any other noises

[311-420]

Congrats wutang. Glad it was simple!

[mikeracing]

The more helix the gear the quiter the gear set will be the trade off being robs more hp. Most racing gears are going to be loud just for this fact. Ford racing gears are not really a race gear they are for the street thus they can afford to lose 1-2hp for extra helix.

If you are ever around to look at a winters quick change ring gear almost no helix loud but the less helix makes up for the loss in hp of the second set of gears

[rich1]

Motive gear always made noises whenever our shop installed them. Off road guys like them but cant hear them over the tire noise.