Ever since I changed my clutch, I have had constant rear end whine while at highway speeds in 5/6th gears. It was really loud and would quiet down just a hair when the car warmed up. However even while warm it was very obvious and annoying on my daily driver.

Some folks mentioned that there was something wrong with my diff because a whine is usually an indicator of internal issues. Other folks mentioned that they too had picked up a whine after changing their diff mount from factory to aftermarket. I had indeed changed my diff mount to an HPI design at the same time I swapped the clutch.

I wanted to go back to a rubber mount to see it that would be the source of the issue so tonight I picked up a new mount from my local AutoZone to give it a shot.

I am thrilled to report that going back to a rubber mount did indeed completely eliminate the diff whine I have had for about a year now



I figured that rather than putting in my 20+ year old crusty mount I would pick up a new fresh one. The new mount was cheap, immediately available and only took about 15 minutes to pick up locally instead of waiting on an Amazon delivery.

Here's the part number:





New mount on left:




The HPI mount would probably work much better for those folks who don't daily drive or otherwise wouldn't be bothered by the additional NVH this brings to the cabin






If anyone is looking for an HPI mount, hit me up for a good deal

 

You isolated the whine, didn't fix the whine. The whine is indeed an indicator of internal issues, but I know from multiple experiences it can get SUPER LOUD and still not be that big of an issue so if this helps you live with the car long term until it finally bothers you enough to actually fix it, then there is not really anything wrong with that.

 

Sadly, I believe you are correct. The sounding board effect that amplifies the sound has been removed. It could be, however, that the sounding board effect may make a perfectly set up diff whine the way his was. But I doubt it. If it was my car, I'd drain the lube, inspect for foreign objects, change the diff lube, and send it......

 

Interesting. i have an PHADT which is similar in design to the HPI. Diff whined when I bought it in all gears. PO had had the diff 'built' with 4.1 gears by an incompetent shop, and did not break it in properly. I had it rebuilt by a good shop, broke it in properly, and zero whine. Dead silent.
Whine in only certain gears is not the diff, it's the trans. ie constant 60mph, a whiney diff will whine whether it's in 4th or 6th, it doesn't care.

 

At one point I bought an aftermarket stock-style diff mount from RockAuto. It was cheap, and I threw it away because it felt so flimsy. How does the Duralast feel in your hands compared to the stock mount? Similar weight?

That's a good point. Also with the whine being in 5th and 6th, that leads me to think it could be a loose 5/6 cluster gear on the T56 mainshaft. This is a super common thing: https://www.google.com/search?q=t56+...6+cluster+gear
My T56 MN12 with only 72k miles had a 5/6 cluster gear that could slide off by hand... it's supposed to be an interference fit. Granted it didn't have a whine beforehand with a stock diff mount.

Texas Drivetrain Performance offers a mainshaft repair service where they build up the 5/6 journal so that the 5/6 gear can go back on tightly as it's supposed to. After this repair my 5/6 gear went back on what seemed like excessively tight, but at least it won't ever loosen!

 

I suspect that's what OP has....

 

While you guys may be correct, all I know is that my car had no whine whatsoever before going to the HPI, whined terribly after installing the HPI, and now has zero whine after returning to a stock rubber mount setup.

I have seen other recent posts stating that they picked up a whine after installing an HPI mount when before they had none. ¯\_(ツ)_/¯

Either way I am satisfied with my outcome.

 

I had the same thing happen after installing AMT mount. Did it right before clutch install and almost blamed the shop who installed the clutch. It was so bad I didn't want to drive my car at all. Put the stock mount back on and night and day difference. Easy enough to change for a trip to the track. I was only worried about wheel hop. I am hoping the Koni's I put on will be enough to cure the severe wheel hop I had last time at the drag strip and won't need a stiffer mount...