The Torsen Roar

[TheLion]

I just got done doing a rear end swap on my 2016 ecoboost. I put in a loaded GT PP rear diff (3.73 Torsen). However I also installed the steeda performance (black or stiff) differential bushings and aluminum sub-frame bushing stiffeners. It's obvious that there is markedly more noise, I hear all the drive train slop / backlash when starting or stopping at lower speeds, so please take note of that.

However I'm not familiar with Torsen differentials and what's normal and not. Basically I can only describe as a roaring or binding noise (similar to a tire rubbing inside a wheel well, but more metallic) when taking sharp corners are low speeds under moderate throttle (which happens some what often).

It does not occur on larger more sweeping turns and lessens the harder I am on the throttle, obviously if I floor it in 2nd going around a corner the torsen does its job and both rear tires break loose and fishtail the car (where my standard EB base diff would just produce inside wheel spin).

It's quite loud at times. The loaded differential was never disassembled, so it has factory shimming and pre-load on the diff bearings. The drive shaft flange was removed and swapped with the ecoboost flange that was on my stock diff as they are different (but mate to the same 30 spline pinions). The pinion bearings were set with proper pre-load and even so it only occurs during sharp cornering while under light throttle (aka daily driving), not in a straight line (no noise what so ever other than a barely audible whine at 77mph, but not a big deal). Coasting around a sharp corner it's either non-existant or barely noticeable as well (aka the diff is under no load). When I had the car up on stands, after I re-seated and alighned the sub-frame and reconnected the drive shaft, I did a rotation check and was easily able to rotate one axel (with the other axel rotating the opposite direction like an open diff) without any noise or binding, smooth as butter. I was also able to rotate the drive shaft easily (car in neutral) and both axles turned smooth as butter with no noise. So I verified there nothing external binding anywhere on the drive train or bearing issues just to be clear. This is coming from the torsen internally and it's more audible because of the bushings.

I'm running AMSOIL 75W-90, but I have not added in the friction modifier yet. AMSOIL said I their severe duty gear oil didn't require modifier but I could use the ford modifier or another (which I forget what it was called) if I have gear noise (although I think they were referencing gear whine, which is related to the pinion and ring gear).

Now I doubt I would hear much of that noise if I had stock diff / sub-frame bushings as they transmit quite a bit less noise (hence why you get wheel hop also). But I would like to quite it down some during sharp corner without changing to the softer red bushings if I can. Anyone notice this noise in your torsen (especially if you do diff / sub-frame bushing upgrades) and have you had any luck with friction modifier quieting down the "torsen sharp turn roar"?

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[wildcatgoal]

I have this, too with same mods only I have red bushings. Red bushings won't solve it. It is a normal sound. At first I could not be convinced of this, but I have been told this by numerous people at Steeda, two dealerships, and a differential shop I decided to go to for shytes and giggles (that works on diesel trucks) and the guy that explained everything to me drag races a fox body. He was really great. As for the clunks and what not, he said he can help me get rid of that by fixing lash in the differential and suggested a solid driveshaft only if I did the lash fix, but he said I'm probably better off just living with it because it seems like there's slop all along from the transmission through the differential if if he tightened up the back, it might get stressful to the transmission. He said he didn't trust the MT-82 and said probably just not worth the money. I guess that made some sense, and it wouldn't have been cheap to have him do the work so I just said f'it and decided to live with the lack of refinement there. To note, he also suggested what he does which is to somehow raise the rear differential so the half shaft joints are more straight... I didn't quite get that. He does that on his car.

I added Ford's modifier to my BG oil which is supposed to have friction modifier in it already, and the noise reduced a fair amount. Hopefully that's not bad that I did that... haha.

 

[EXP Jawa]

Depending on what you are hearing, modifier might be of help. This type of differential does characteristically make what has been alternatively described as a moan or a "rusty screw noise" in sharp turns, especially at low throttle levels. This might match what you're describing. This noise is a quirk of friction in the gearing, and is almost always alleviated with friction modifier, and why Ford uses the modifier in the OEM fill.

If you are getting something that more resembles a clunk, click, or whine, that wouldn't be normal. Those sort of noises are typically not helped by using modifier.

 

[TheLion]

Depending on what you are hearing, modifier might be of help. This type of differential does characteristically make what has been alternatively described as a moan or a "rusty screw noise" in sharp turns, especially at low throttle levels. This might match what you're describing. This noise is a quirk of friction in the gearing, and is almost always alleviated with friction modifier, and why Ford uses the modifier in the OEM fill.

If you are getting something that more resembles a clunk, click, or whine, that wouldn't be normal. Those sort of noises are typically not helped by using modifier.

I get a bit of Ring and Pinion hum at high speeds on the highway, but it's very low key and not a bother, barely audible with no music on and the windows up. Turn on music, crack a window or even turn the air on high and you can't pick up the ring and pinion hum / whine (which 3.73's are known for).

This is only when turning sharp corners under moderate throttle, so it's related to the diff internally. Good to know also about the steeda red bushings not helping so I don't waste more time swapping those in, in place of the black ones (although the red ones may quite down back lash a bit, but the back lash doesn't really bother me, yah it's definitely there, but it also is only while starting or stopping, while cruising or at moderate speeds aka 35ish or higher it's non-existent).

But, that torsen sharp turn roar is loud, it's louder that the back lash, although less frequent. Another noise I would liken it to is similar to a bad wheel bearing, that loud roar, but again more metallic (given the worm gears are a carbon steel).

I have AMSOIL Severe Gear 75W-90 snythetic gear oil. AMSOIL makes some of the best lubricants on the market and while they do have modifier already in it, I had contacted them prior to ordering to ask about adding modifier if I have gear noise and they said I could use 4oz of either Ford's or their modifier. They also do note that some drive trains do need additional modifier even with their gear oil.

Good to hear the modifier reduces the noise. I would be ok with it if it was at least 50% reduced, to a dull back ground noise slightly less intense than the thudding / clanking of the drive train back lash. I'd consider this a 100% success then (right now it's like 90% lol). Thanks.

 

[xXANCHORMONXx]

The diff bushings are the issue.


Imo if you don't want the nvh from the diff do the subframe stuff only.

 

[wildcatgoal]

Um. Except that the noise exists without them installed. Louder perhaps with bushings inserts, but still there.

 

[xXANCHORMONXx]

Um. Except that the noise exists without them installed. Louder perhaps with bushings inserts, but still there.

Something is not right then. The oem diff is quiet as far as whining goes.

 

[TheLion]

Something is not right then. The oem diff is quiet as far as whining goes.

Not as far as my research as led. I found all kinds of GT500's, GT PP's etc. with the torsen and the "roaring / grinding / moan" noise complaints. Most of them were resolved by friction modifier. A few the modifier solved the issue temporarily.

I poured in the bottle last night and drive around. The diff is much quieter during the low speed sharp turns. You can still hear the "rubbing / roaring" sound, however it's very muted and far less noticeable than the drive train backlash / slop. As long as it stays this way I think this issue is generally solved.

I did notice however it take a bit more throttle to get the torsen to start biasing, it stay open diff under light very light throttle. That's basically what the modifier does is keep the worm gears from grabbing against the casing walls more so than just the base oil would. I'm guessing it modifies viscosity a bit to accomplish that. It's a trade off, but yes the torsen still locks under any significant throttle. It is a bit less linear however, it seems to suddenly start biasing as opposed to more of a linear progression so again it is a bit of a trade off but unless your in serious competition, for any hobbyist it still works very well and is immeasurably better than the fiction plate diff that was in there (basically useless under any power during turns).

Those sub-frame bushings really "locked" the rear end down and the car now feels like it's on rails as opposed to "floating" around a bit or the "rubber band" feeling some describe. The sub-frame bushings I would recommend for anyone as I don't think they really add the noise, at least according to Ford Performance. Most of the added noise is through the diff bushings which matter mostly for drag racing (I plan on doing both auto cross and occasional drag strip).

So I would call this a success.

 

[EXP Jawa]

What friction modifier does is it brings the static coefficient of friction and the dynamic coefficient of friction within the differential closer together. Think about this: if you try to push a piece of furniture across the floor, it might be difficult to get moving, but once its moving, it becomes easier to keep it sliding. That's because the amount of friction to resist sliding is higher when its sitting still (static) than when it starts moving (dynamic). That's really true of pretty much anything.

In a limited slip differential, what it means is that the friction surfaces (clutch plates, helical gears, etc) stay bound until the static friction is overcome, then they pop free, then as the energy reduces, slow down, bind up again, pop free... This results in a stick-slip-stick-slip sort of behavior that the driver would perceive as "chatter" or, in the case of a helical gear unit, moan. Friction modifier brings the static friction down to near the level of the dynamic friction, which smooth out that behavior and smooths out the operation.

The downside of friction modifier is that by lowering the static coefficient of friction, the overall amount of friction generated by the differential is reduced. LSDs create friction to be able to resist wheelspin, to bias torque to the higher-traction side. By reducing the overall friction somewhat, you also reduce that functionality somewhat. Usually it isn't a huge difference, and the average consumer probably wouldn't discern the change. It takes a more sensitive driver, or more severe conditions (like track use) to really feel it.

 

[TheLion]

What friction modifier does is it brings the static coefficient of friction and the dynamic coefficient of friction within the differential closer together. Think about this: if you try to push a piece of furniture across the floor, it might be difficult to get moving, but once its moving, it becomes easier to keep it sliding. That's because the amount of friction to resist sliding is higher when its sitting still (static) than when it starts moving (dynamic). That's really true of pretty much anything.

In a limited slip differential, what it means is that the friction surfaces (clutch plates, helical gears, etc) stay bound until the static friction is overcome, then they pop free, then as the energy reduces, slow down, bind up again, pop free... This results in a stick-slip-stick-slip sort of behavior that the driver would perceive as "chatter" or, in the case of a helical gear unit, moan. Friction modifier brings the static friction down to near the level of the dynamic friction, which smooth out that behavior and smooths out the operation.

The downside of friction modifier is that by lowering the static coefficient of friction, the overall amount of friction generated by the differential is reduced. LSDs create friction to be able to resist wheelspin, to bias torque to the higher-traction side. By reducing the overall friction somewhat, you also reduce that functionality somewhat. Usually it isn't a huge difference, and the average consumer probably wouldn't discern the change. It takes a more sensitive driver, or more severe conditions (like track use) to really feel it.

So friction modifiers reduce static friction as opposed to motive friction, which is why it reduces the light load condition which basically sounds like a wheel rubbing the inside of a fender well. It's 'gritty" because of the static friction coefficient, stick, pop slide, stick, pop, slide in probably a couple hundred to maybe a thousand or so Hz frequency.

Functionally as I stated the diff performs a bit better without the modifier, but for street / drag strip and auto cross even with the modifier it still performs very well. I think if your car is a dedicated competition car your better off without the modifier to achieve maximum biasing, but with the modifier you still have a high level of biasing but with much less noise.

Now, if only I could mute the drive shaft slop...sounds like I'm towing a ball hitch trailer...but the power delivery with the differential bushings is impressively smooth. The IRS collars / bushing supports impacted handling the most while the differential bushings resolved wheel hop (which I expected).

Anyone try the red steeda diff bushings? I'm curious as to how much stutter / hop would return vs drive shaft slop noise is reduced. It's not really an issue when cruising at constant speeds, but stop and go or at low speeds (25 zones even some bumpy 35 zones) its some what frequent. Boy does this thing drive on rails now, I'm quite impressed at the difference just the aluminum IRS bushing collars made.

 

[wildcatgoal]

I have the red bushings; I get driveline slop noise for days. I had it before any bushing inserts anyway, albeit a little less clunky and more "muted" on account of the OEM rubber.

 

[MaverickGT]

I don't have the noise and I didn't do the diff bushings, only the subframe support bushings.

 

[wildcatgoal]

Congratulations!

 

[MaverickGT]

Not sure if your being sarcastic or not. The noise may be from the diff bushing. I haven't heard of any other PP cars with the 3.73 torsen rear having this problem. I know when I tried to use the transmission bushing insert it caused so much noise and vibration in the cabin that after 15 miles I turned around, put it back on the lift and took it out. I've heard diff bushings cause a similar effect.

 

[EXP Jawa]

Well, the noise you hear/feel is very dependent on the transmission path into the cabin. Bushings are a big part of that; anything mounted on bushings as vibration dampers is done so for a reason. So, if you change that, you have to accept the trade off...

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