My 3.89 isn't loud (or at least I can't hear it). And I have an aluminum carrier, which they also say is loud.

Proper R&P setup, machining quality/tolerances and gear tooth design will be larger factors than tooth count.

 

In recent history (the last 30 years) I can only speak to the 3.89:1 , the 3.50:1 and the 2.79:1 ratios.

they were all Ford original factory gears and all as quiet as a mouse in church..

when I was restoring a ‘66 GT350 and a ‘65 K code, I tried the Motive gears as the Shelby already had 200,000 miles on the original gear set.

The Motive gear noise was incredible. We tried a couple of different settings. No soap.

The guy setting them up was no novice. He’d been doing it since 1975 (when got home from Saigon (1975) as part of the marines who oversaw the Embassy evacuation by helicopter). And this was 1999 when he was doing my work, 24 years later.

anyway, they were loud. I tried another set of new Motives just to be sure it wasn’t an anomaly on the first set being bad. Nope. Just as bad.

so I took the advice of more experienced professionals and searched for a set of good used Ford gears. The wear on the ones I found was superficial and they worked very well for the next 100,000 miles I had the car. And they were quiet.

when restoring the k code (3.50’s) and the Galaxie 500 (2.79’s) I just searched for good used Ford gears and they worked out just as good.

Z

 

I've heard that too, that some of the aftermarket gear sets are way noisier than the Ford gears. Maybe it was you how mentioned it? It goes to show that high volume manufacturers really can make good stuff when they set their minds to it.

As for the Embassy evacuation in Saigon: by pure coincidence this also came up as a side note in a book I was reading last night. Funny how these things go sometimes.

 

I don’t remember any noise from the 3.70’s I had in the car years ago. Can’t hear the 4.11’s in the car now.

 

I think the bigger issue is the maker of gear and where they are made…..just had a Chevy axle done, was talking to the owner of the shop and the quality control just isn’t there….still some old inventory that works but the new stuff is hit and miss

 

I did a couple of 4.11 for a friend last year they were summit gears. he said they were quiet

 

I put Motive Gear 3.25-1 in my 8” housing. Using the factory manual.
I set them up with shims not the crush sleeve. I broke them in as per Motives recommendations.
I have no noise complaints.
I saw an article a while ago about a micro polishing process for gears, I wonder if that would help break in and noise.

 

if using ford gears some sets need to be timed. see the shop manual

 

On my Mustang I've used only Ford gears in 2.50, 3.25, 3.50, 3.70 ratio. The only noise was from the 3.70 set which we couldn't get to stop howling thru several adjustments.

 

I know enough about this to be dangerous. A big part of the noise is how thick the gears are, how well they're made, and all the things you might expect. But one other factor makes a big difference: hunting vs. non hunting tooth counts.

If you run a multiple or divisible number of teeth on the pinion with the ring gear, then the same teeth will touch over and over and over, and they form regular wear patterns, and will often make more noise even from the first time you run them. For an example, let's say you have 10 teeth on the pinion, and 30 on the ring. That's a simplistic example of a 3:1 ratio (not one you'd see in a car or truck). With that setup, the same ten teeth will mesh with the same 10 teeth on the ring, over and over and over, three times per axle revolution. If the number of teeth on the ring and the teeth on the pinion share a common denominator, they are said to be "non hunting".

If, on the other hand, you run prime numbers for the teeth on both, or at least they're not evenly divisible, then you will be trading wear partners every single revolution of either gear. That's a "hunting" gear set, and all the teeth will wear more or less evenly over time, even if one or more has minor imperfections. A good example of this is the 2.79 gearset so common in 8": it's 19 teeth on the pinion, and 53 on the ring.

 

when I had the original leaf spring/ford 9 setup with 3:50s it didn't make noise, possibly a low hum at certain speeds but that was it.

until I went with SOT 3-link, it didn't whine until I went over 80, but I think that was the 3rd link harmonizing the sound from the rear end housing. I did have strange engineering build a ford 9 with 350s, but it whined like crazy, after we pulled it, gears were toast after 500 miles and strange rep said this was normal sound due to "tight tolerances" lol. I will be rebuilding it with 370s, but need to find a set that won't whine.

 

I use those Motive Italian gears. 3.50 on a Yukon locker and a heavy duty aftermarket case.
I forgot who made it.
I set them up and have about 10,000 miles on them.
They don't make noise and run pretty cool.
I have given them the beans with a 427 sideoiler stroker Tunnel Wedge and
a wide ratio Top Loader.
I tell peeps it has Italian Racing Gears.

 

Gear whine (if set-up and meshed (timed or indexed) to the proper teeth), is caused by the mesh of pinion to ring gear teeth, and if they all mesh or only certain ones. If only certain teeth mesh, then only those teeth are lapped together in manufacture, and must be aligned during setup. The ones that are most prone to noise are the sets with a low common factor of pinion to ring gear teeth.

A common factor of only 1 with no other common factors (no other common factors) is great as every pinion tooth eventually engages every gear tooth, and no indexing is required during setup. You can calculate for common factors using an online calculator, such as this: Common Ratio Calculator

Of note is the common factor determines if the gear set is 'hunting' where all pinion teeth are hunting-for and mesh with all gear teeth eventually, and do not require indexing in setup; or if they have 2, 3 or more common factors they are 'non-hunting', mesh only with certain other teeth and require specific marked teeth to be meshed during setup, else noise is a high probability.

Note while some sets are more prone to noise, any set can make noise in any configuration, and proper setup simply reduces that potential. Hope that helps.

From DIYFord.com:

 

Gear whine (if set-up and meshed (timed or indexed) to the proper teeth), is caused by the mesh of pinion to ring gear teeth, and if they all mesh or only certain ones. If only certain teeth mesh, then only those teeth are lapped together in manufacture, and must be aligned during setup. The ones that are most prone to noise are the sets with a low common factor of pinion to ring gear teeth.

A common factor of only 1 with no other common factors (no other common factors) is great as every pinion tooth eventually engages every gear tooth, and no indexing is required during setup. You can calculate for common factors using an online calculator, such as this: Common Ratio Calculator

Of note is the common factor determines if the gear set is 'hunting' where all pinion teeth are hunting-for and mesh with all gear teeth eventually, and do not require indexing in setup; or if they have 2, 3 or more common factors they are 'non-hunting', mesh only with certain other teeth and require specific marked teeth to be meshed during setup, else noise is a high probability.

Note while some sets are more prone to noise, any set can make noise in any configuration, and proper setup simply reduces that potential. Hope that helps.

From DIYFord.com:
View attachment 943020

That chart and the comments below especially with the aftermarket 3.70 gears being loud kind of sums up what I've heard over the years. I want to do the 3.70's but will do the 389's just to be safe.

 

I found a local-ish place to do the gear swap and have the oil draining out of the housing as we speak, but still can't commit to a certain ratio. The math says 3.70 will fit my needs best but I fear the whine they are known to have. I don't mind pulling the T5z to swap the tail shaft gear if I go with 3.89 but that would be too short in second if I ever autocross again. 3.50 is really close to the 3.25 I'm currently running. I have a huge on/off throttle clunk since I swapped to the 9" rear end, so I'm having everything looked at.