Who is running a aftermarket rear that is quiet?

[Sieg]

Originally Posted by 69x22

As it stands I have about $3800 to $4000 in this noisy piece of junk, and it still howls.

Sorry to hear it.

My car is running silent OEM 3:31's in the original 12-bolt. The T56 mag needs 3:73's but this throw-the-dice noise issue isn't exactly motivational.

[HIFLYR]

I am glad this post was posted before I bought my rearend. I simply do not believe that if you buy a complete rearend from moser it should make noise because it is aftermarket. Moser should have complete control of their parts sourcing and ensure the end product is a good one when you buy a COMPLETE rearend. Yes there could be problems when sourcing parts from different places and assembling it yourself but not for a manufacturer of complete units.

[4mul8ion]

Setting aside the other design requirements, as far as axle noise is concerned, it takes three things to get axle noise. A source of the vibration to generate the noise, a path for the noise to take and a responder – or speaker – to make the noise audible to the driver.

The sources of the noise can come from the gear meshing but can also come from bearing faults as well. There are different mechanical vibration frequencies that can be the source of the noise depending on what is happening.

There are two paths for the noise to take and the associated speakers: through the suspension into the body that vibrates a body panel or forward into the driveshaft and that set off motions in the driveshaft that travels through the air into the vehicle cabin.

The classic gear noise that drives everyone crazy generally comes from vibrations generated by the first harmonic of the gear meshing that either travel through the suspension into the cabin or into the driveshaft and rings it like a bell. It generally occurs when either accelerating through the 45 – 65 MPH range or decelerating 65- 45 MPH. But not always.

Looking at the driveshaft path first, it is spinning hollow and is now commonly made out of aluminum with various OD’s and tube wall thicknesses depending on the manufacturer. Bare with me here – I’ll try to get to my point quick. It’s supported at one end at the axle and on the other end by the transmission. One end of it has to be able to translate in the vehicle fore/aft direction to allow the rear axle to move in the path dictated by the suspension. It has to take the engine torque, amplified by the transmission gear and sent it through to the rear axle through universal joints. The U joints are optimized to run an included angle between the transmission and driveshaft of no more than 3 degrees and, for best performance, an equal included angle of no more than 3 degrees to deliver smooth rotation from the transmission to the rear axle.

The point is that the driveshaft is allowed to move in its mounting and doesn’t deliver smooth power to the axle. The rotation accelerates and decelerates as the u joint rotates. The ring and pinion don’t mesh smoothly by themselves either. These accelerations / decelerations set up the gear mesh vibrations that forces the driveshaft into various resonant frequencies that you hear depending on the geometry of the tube and amplitude of the acceleration / deceleration of the rotation. The OD, wall thickness and length for a given material determines the bending frequencies and shell modes – or bell ringing – frequencies and the torsional frequencies of the driveline. Changing these dimensions move the resonant frequencies up or down in vehicle speed. Naturally, the OEMs try to increase these frequencies to mask the gear noise by other noises like wind or engine noises that aren’t so annoying or damp out the noise using tuned torsional dampers or inserts in the drive shaft tube. Neither eliminates the source of noise – it just moves the energy around. No free lunches.

The later 4th gen f-body driveshaft had an aluminum driveshaft with a larger OD and had both a tuned torsional damper that was pressed onto the transmission side slip yoke to damp out the torsional resonant frequencies. If you were to tap your knuckle along the axis of the driveshaft, there’ll be spots that will ring and spots that will go thud. Inside the tube, there are inserts to damp out the bending and bell modes of the driveshaft.

[GregWeld]

3:73's -- manufacturers will tell you that for some reason that ratio is "noisy". I've talked with Randy's Ring and Pinion (they're local for me) about this and that's what they told me. The Eaton rep told me the very same thing.


I frankly wonder how much of this is the transmission vs the rear end... the tranny in my '32 Ford is noisy... but I just chalk that up to the fact that the idiots at SAR probably charged me for a brand new one and installed a used one -- or that they ran it dry for a few days.... I'll replace it this winter.

The '32 runs straight cut quick change gears -- and they're noisy... so I might switch to helical cut versions when I do the tranny. s

[Vegas69]

Originally Posted by 4mul8ion

Setting aside the other design requirements, as far as axle noise is concerned, it takes three things to get axle noise. A source of the vibration to generate the noise, a path for the noise to take and a responder – or speaker – to make the noise audible to the driver.

The sources of the noise can come from the gear meshing but can also come from bearing faults as well. There are different mechanical vibration frequencies that can be the source of the noise depending on what is happening.

There are two paths for the noise to take and the associated speakers: through the suspension into the body that vibrates a body panel or forward into the driveshaft and that set off motions in the driveshaft that travels through the air into the vehicle cabin.

The classic gear noise that drives everyone crazy generally comes from vibrations generated by the first harmonic of the gear meshing that either travel through the suspension into the cabin or into the driveshaft and rings it like a bell. It generally occurs when either accelerating through the 45 – 65 MPH range or decelerating 65- 45 MPH. But not always.

Looking at the driveshaft path first, it is spinning hollow and is now commonly made out of aluminum with various OD’s and tube wall thicknesses depending on the manufacturer. Bare with me here – I’ll try to get to my point quick. It’s supported at one end at the axle and on the other end by the transmission. One end of it has to be able to translate in the vehicle fore/aft direction to allow the rear axle to move in the path dictated by the suspension. It has to take the engine torque, amplified by the transmission gear and sent it through to the rear axle through universal joints. The U joints are optimized to run an included angle between the transmission and driveshaft of no more than 3 degrees and, for best performance, an equal included angle of no more than 3 degrees to deliver smooth rotation from the transmission to the rear axle.

The point is that the driveshaft is allowed to move in its mounting and doesn’t deliver smooth power to the axle. The rotation accelerates and decelerates as the u joint rotates. The ring and pinion don’t mesh smoothly by themselves either. These accelerations / decelerations set up the gear mesh vibrations that forces the driveshaft into various resonant frequencies that you hear depending on the geometry of the tube and amplitude of the acceleration / deceleration of the rotation. The OD, wall thickness and length for a given material determines the bending frequencies and shell modes – or bell ringing – frequencies and the torsional frequencies of the driveline. Changing these dimensions move the resonant frequencies up or down in vehicle speed. Naturally, the OEMs try to increase these frequencies to mask the gear noise by other noises like wind or engine noises that aren’t so annoying or damp out the noise using tuned torsional dampers or inserts in the drive shaft tube. Neither eliminates the source of noise – it just moves the energy around. No free lunches.

The later 4th gen f-body driveshaft had an aluminum driveshaft with a larger OD and had both a tuned torsional damper that was pressed onto the transmission side slip yoke to damp out the torsional resonant frequencies. If you were to tap your knuckle along the axis of the driveshaft, there’ll be spots that will ring and spots that will go thud. Inside the tube, there are inserts to damp out the bending and bell modes of the driveshaft.

Lot's of good thoughts here. OEM's spend millions of dollars making their parts mesh for the consumer. We slap some aftermarket parts on our 40 year old cars and wonder why it doesn't work out as we'd hoped. This is exactly where I was going with my original post. Four sets of gears and the noise is still there. It's time to start looking elsewhere for a solution.

I thought my Moser 12 bolt, 33 spline, true trac, with bolt in axles was quiet but to be honest, my exhaust was so loud who the hell knows. I will say that there was always a vibration in high gear in only a 300 rpm range that I could never completely get rid of the life of the car. I swapped out engine mounts, trans mounts, changed driveline angles. I finally just gave up as it was at like 85-90 anyway. I ended up with a rubber passenger mount and that made the biggest difference.

Greg, I told you not to put that POS TKO600 in your car. Nobody every listens.

[Sieg]

4mul8ion - Thanks for the info and education.

Is it reasonable to assume the drive shaft is the primary speaker?

[4mul8ion]

Originally Posted by Sieg

4mul8ion - Thanks for the info and education.

Is it reasonable to assume the drive shaft is the primary speaker?

No. There can be others. The path through the suspension resonating a body panel is much harder to deal with because you're trying to improve the ride and handling by using stiffer bushings. You give up isolation for improved handling. Locating the resonant panel is tough.

That's not all. You can still have amplification of the gear mesh vibrations by the suspension attachment brackets being forced into resonance going into the vehicle cabin. Or the OD and wall thickness of the axle tubes on a salisbury axle going into bending or torsion amplifying the mechanical vibrations going inside. The bushing can't effectively isolate an amplified signal.

My long winded point was that the OEMs spend a considerable amount of time desensitizing their new vehicles to the gear by looking at each and every component in it. I'm sure any of the OEMs who read this post will be overjoyed to hear that their hard work is paying off in strong quiet and durable performance in the field. They often don't get to hear that type of feedback.

There is no way any aftermarket company can compete with that resource requirement. But they have a good handle for their product performance in applications in other ways. Randy's, for example, suggest on their website, applications where OEM sets meet demanding customer applications better than the aftermarket. In particular, they say vans. I'm sure a call to any of the aftermarket companies to discuss a particular application would be useful if you get someone who's been around the block a few times. Did they optimize their aftermarket gear for an off road truck application or a car application?

The gear manufacturers spend a considerable amount of time optimizing their designs and processes too. OEM and aftermarket. It isn't just cutting slots in a ring of steel and slamming it into a case either. It can still be a bad gear for any or all of the reasons you had listed in your earlier post. Or the gear cutting summary wasn't optimized for the process it's in. Or bearing vibrations lighting up the driveshaft or coming into the cabin. Different vibration source, same resonant component will sound the same to the driver.

Point being is that it can be one or more of many things. "It's a bad build" or "It's a bad gear" is just the starting point. Important information to whoever is trying to diagnose what went wrong will want to know other things. Noise on acceleration or deceleration or both? What speed? What does it sound like? Was it always this noisy is it getting worse or did it just happen? Any pics of the pattern before or as it is now?

[Sieg]

I've been intrigued with acoustical damping ever since watching a show featuring an Aston Martin assembly facility on Velocity TV where an "engineer" was strategically applying a material similar to Dynamat Extreme in lightening bolt and wave shapes on interior cabin panels. I've always wondered how much science was behind their application considering the sophistication of their engineering.

I finally found a picture (and a great tour of the facility) tonight.

On these Vantage chassis I was interested to see these reinforcing strips added to the interior, applied as a result of noise, vibration and harshness studies to improve the characteristics of the chassis.

http://www.speedhunters.com/2013/08/...dream-factory/

[Twoblackmarks...]

Personaly I dont mind some whine, it makes the car feel more "racier" As long it is not too much.

I would think leaf spring transfer more sound than 4-link, soft mushy bushings MUCH less or zero sound vs. urethane and such. Frame car vs non frame etc..

I dont think my 87`Olds 442 8.5" 3.73 was very "developed" by GM to be honest. But it has a very "quiet chassis" that is forgiving for everything in sounds. -Super sweet car by the way

78 Camaro With 2.42 -No sound. Put in a used 3.73. Some mild sound when hanging on gear if i remember correct -could be the pinion bearing, or faulty setup, (also had been used...) even when set up by professionally. But to be honest I just think the aftermarket has a little less quality in it, or sound is not their ultimate deciding factor for the parts, but it still is somewhat weird I think, but the parts for US cars are really cheap to buy, so that explains atleast a portion of it. -For many types of parts..

If you ultimately want a quiet ride, install mushy bushings in everything, so they absorb everything you dont want to hear and feel, and lots`o sound deadening. I think that Cures most sounds..

I work With New cars, and they are very sensitive to tire noise, out of round, sounds from drivetrain. If you take the Wheels of an old impala that glide like an boat at 100mph, they could be "oval" without feeling it, put them on a New car and it would feel horrible at 40-50mph and may make a LOT of tire noise.

Because every year they get harder bushing, more Direct mounting in body, lighter spindles, shocks and springs etc.

Now it is really good for driving to get less unsprung weight, but at the same time that unsprung weight act as an vibration/torsional damper, and usually the lighter/less mass an vibration damper have, the worse it "Works"

Since it ability to absorb vibrations, and even sounds lessens, and the more sound and vibrations then go through the modern hard bushings into the body and to the driver in one way or another.

Now I wrote much more than I was going to, I still think rear gears should be somewhat quiet, Stock or not, Depends somewhat though, what type and such. My Moser makes some sound, but not more than my exhaust, so dont know at the moment, and I am ok With it too, so it does not really matter, it is a Hot Rod, not a Rolls Royce

4mul8ion Has great Points.

Here we have a lot of modified cars like Voyager type cars With removed rear seat and changed carpets and different stuff, (because of TAXES!) Many of those complain about noises from everything, since the rear compartment now acts as a huge speaker.

This may be a messy post without much answer, but I still post it, and se what happens

[chr2002ca]

I've purchased 2 new complete 12-bolt rear setups from Moser for my '69 Camaro. The first was a 30-spline unit with Eaton posi and 3.42 gears. It made a little bit of noise after about 3000 miles but it wasn't too bad and I didn't really notice it much. The 2nd unit I purchased which is currently in the car is a 33-spline TruTrac with 3:42 gears again. It's perfectly quiet right now, but it only has about 550 miles on it. Time will tell. If it develops a whine, oh well, it doesn't really bother me. I have sound deadener laid down all the way to the back of the trunk, so maybe that helps.