Hello fellas.

So here’s my issue. I’ve searched and I can’t find anything like my situation. So I purchased a diff with 410s that was refreshed from a known and reputable vendor. Everything had checked out fine. So I installed the diff and also threw in there a pfadt diff mount and ecs brace. I used redline 75w90 oil with the friction modifier added in the 410 diff. Right off the bat, I started getting what seems to be a rear gear whine. It was present in 3rd and 4th gear. 5th and 6th gear are the loudest. Whines on acceleration, part throttle and full throttle. No whine on deceleration or on no throttle. Driveline felt a lil rough, perhaps some vibration? Not sure. But felt like some unwanted friction was present. Was not smooth at all.

So I decided to remove the diff and install the stock unit. I added the same oil in the 342 diff. Surprise, surprise! I’m getting the same whine on the stock diff when I never had issues with it prior. Everything seems to run Smooth but Whine is exactly the same. Perhaps a tad bit quiet than the 410 diff. But not much changed.

Wheel hubs are fine. The ecs brace is not hitting anything. It may be hitting slightly the driver side exhaust, gotta check on that. But I don’t think it’s the cause of the whine. I could be wrong though. Not sure if the pfadt mount has anything to
do with the whine. From what I found, the mount has shown to cause some vibration on some cases, but im not getting any that I can tell. Who knows. Something else to consider is the transmission, but I was not having any issues with the transmission prior. I’m thinking of removing the brace and mount to see what it does without them. Any suggestions or help from the much more knowledgeable is very welcome and appreciated.

 

The roughness is VERY likely due to the diff mount. I installed a Hinson poly mount when I did my 4.10 gears, and it was BAD with harmonics...car made a "rumbling" type resonant sound...not a vibration, but definitely felt what I would describe as "rough". I swapped it with a stock one and cut 95% of the issue. It's not an issue with all cars, I think it depends on the overall balance of the drivetrain. The TT seems to amplify imbalance, and farther out toward the upper tolerance limit can really cause issues with stiff mounts. If you still have the stock mount, it's easy enough to change out to see if it makes any difference.

Another thing...do you still have the damper installed on the differential? The big weight on the rear? I've read that makes a difference too, and is common to remove with some braces/mounts.

In terms of diff whining, my 4.10's whine just a bit. Part throttle between 75 and 85 MPH. By diff builder said it's normal "gear float" noise and that there's not much that can be done. Noise on accelerating or decelerating indicated improper gear setup. I think it's more common than rebuilders let on since it's so easy to blame "improper break-in" as a way out. Lots of people complain about gear whine after a diff swap.

I had mine built by a local diff shop, and they recommended conventional gear oil for all the time use as opposed to synthetic. They say it keeps it quieter. So I ran conventional for break-in and it wasn't bad. After break-in, I switched to Redline 75w90 as you did, and the whine was quite a bit louder. Ran with that for 1k miles, then changed back AGAIN to conventional and it seems to be quieter. I don't really abuse my car, so the conventional should be fine. I went with Castrol 80w90 conventional with LS additive in it.

Good luck!

 

DetroitPlac: What limited slip additive do you recommend? You seem to know a good bit about differentials.

 

I'm by no means an expert, just dealt with mine a lot.

When I first got my car it was all stock, I changed the diff oil with Redline no additive and added AC Delco friction modifier (comes in a small bottle). I drove it quite a bit, I even tracked the car, and it was fine.

Then when I had the diff rebuilt with new gears and internals, I just bought gear oil with friction modifier already added. Redline sells with and without additive, and the Castrol conventional Ive used also includes it. Diff acts just fine, the same it did when I added the additive before. I've had zero issues with the diff clutches.

It cheaper and way easier to just buy the oil with the additive already mixed in.

 

OK.........Makes sense. Thanks for the reply. I'm getting ready to change mine.

 

Really appreciate the response,seggestion and help. I removed the damper like the mount instructions suggested. Torque tube has just been rebuilt as well. I just don’t understand how both diffs are doing the same thing.

 

The missing damper is probably playing some role here. It would be worth trying to add it back.

 

I’ll add it back, see what it does. If not I’ll remove and put back the mount to see if that’s the issue. See it hard to believe the brace would cause the whine.

 

4.10s should not make any more noise than stock if done right. Mine have been in for probably 1,500 miles and they are no louder than stock. "Some noise" might be considered acceptable by most shops and people, but that doesn't mean it's right haha. A reputable shop did mine and their "secret" to quiet gears is to shot peen/polish them. So far so good.