LSD DISCUSSION

Stage 3 Proto

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If you have a factory open differential, adding a friction modifier
is useless, just in case. You didn't mention what kind of DIFF
you had; Open, LSD. I guess we're to assume a limited slip,
but just in case, OPEN diffs don't have anything that the additive
would benefit.

Whining is for a different reason, it's a mechanical issue... Whining
on deceleration is a pinion bearing preload issue. Whining on acceleration
is worn carrier bearings. Generally, worn out pinion bearings can create
whirring noises at various speeds, be it may during deceleration and/or
acceleration. If the pinion bearings are the problem, they create more of
a whirring noise than a rumble because it turns several times faster than
the carrier assembly.

If you have removed the two weights on the axle ends, the drive-line
may whine. They were put there as dampers. They are tuned to
absorb the frequencies produced by the drive-line.
You seem to know your LSD's Do you know if a bad or worn LSD can cause a very loud noise that sounds like a small bomb went off in my back seat when under extreme acceleration. I have a 2011 Roush stage 3. I have eliminated everything from the clutch back to the rear end. This sounds strange but it almost seems like the pinion gear is jumping one tooth when this bang occurs. Is this even possible? Any help is appreciated .
 

Stage 3 Proto

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What rear gear do you have, 3.73 3.31 etc ?
3.73 LSD

I want to take the rear cover off and at least visually inspect the gears but now I'm worried about what lube oil to put back in it !

Anti... what year and model do you have?
2011 Roush stage 3 with two motor upgrades done by Roush Performance for a total of 675 HP at the crank.

I have had the pinion gear jump teeth, but that was in a Geo tracker.
No other RWD car I had, had ever done that before, nor after. The
ring gear wants to climb the pinion gear every time you stomp on the
gas, that is what changes the pinion angle when you accelerate. If the
pinion gear is loose, bad bearings, or pre-load, it can go crooked when
you stomp on it, and jump teeth. It's not all THAT common, but it has
happened.

Banging is usually too much play in the drive line, which happens as soon as
you step on the gas. Too much lash in the diff, or bad universal joints. I just
had a set go bad in my Silverado. Stepped on the gas, BANG, and it wouldn't
move... BOTH the front and rear U-joints broke...

However, I suppose a tooth jump can sound like that depending on how it
travels through the car... It's like a very VERY loud "tang" or "ting" sound,
depending on how the sound transmits through the drive-line.

New one piece Ford Racing drive shaft with new U-joints. Also, all new BMR uca and mounting bracket.
 
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Racer47

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ck the bushings at both ends of the upper rear end link, also called the 3rd link, top center of diff.
 

08MustangDude

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ck the bushings at both ends of the upper rear end link, also called the 3rd link, top center of diff.
HE said, NEW BMR UCA, so one end is fine, obviously. He would have seen
the other one on the diff housing if it were bad, when putting on the BMR Link.
 

RED09GT

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HE said, NEW BMR UCA, so one end is fine, obviously. He would have seen
the other one on the diff housing if it were bad, when putting on the BMR Link.
That bushing can be torn but look fine to a visual inspection. Mine looked fine but when I pried at the center, it maybe had a half inch of rubber holding it in place, it was torn almost all the way around.
 

Wingrider

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Something could be moving under acceleration back there as load is put on all the components. could be bumping against the pinion snubber, or as others have said, bad / loose bushing / link. Could also just be a new noise you just get used to after swapping out the UCA and bracket.

I know when I switched to my Cortex suspension there were all sorts of new sounds that after I double checked, I just learn to accept in trade for the benefits.
 

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