"Humming" Limited Slip Diff?

[Jamison C]

Hey all. Item for discussion is a Dana 35 with 33" tires.

Last month or so I noticed a "hum" coming from under my jeep when I drive. It's most noticeable when I'm at highway speed and I turn the wheel slightly left or right. Originally I thought it was tires/steering but upon further listening it sounds like it's coming from the rear diff. It's gotten gradually worse at slower speeds, especially driving down little hills while on a moderate turn. On these little hills I'll push in the clutch taking power from the drivetrain and the hum/vibration gets even worse until the road straightens or levels out. I've read that the LSD can hum like that when no friction modifier is added. The guy who regeared my jeep 5000 miles ago put in the LSD (dana/spicer brand) so it's hard to imagine he wouldn't have added a modifier or used the right gear oil with one in it.

Anyhoo...I drained the oil yesterday (looked clean, no shavings), cleaned everything out good, and put in Lucas Oil 80W-90 that has "great for limited slips" stamped in big letters on the bottle. Today I drove it to work and WOW what a difference. My ride was significantly smoother and quieter than I think it has ever been since I bought the Jeep stock. However, I still hear the hum on the normal curvy areas of my drive. It's not as loud or "grindy" feeling, but it's there.

Is this normal for an LSD on pavement use? Or are my clutches toast? Do I need to buy a new one, say a brand new Powertrak no-slip that a friend is willing to sell me for $200 that he no longer needs since he swapped in a 44???

 

[Jerry Bransford]

I suspect your gear installer botched the installation of the new gears. I would not install any lunchbox locker into a rear axle, they're just not well behaved enough when in the back axle. Plus installing a locker into a Dana 35 will very likely result in a broken axle shaft, factory OE Dana 35 axle shafts just aren't strong enough for a locker. Any kind of a locker.

I'm also surprised your gear guy installed the Spicer Tracloc LSD which doesn't have a good reputation. The Detroit Truetrac LSD would have been a much better choice of LSD. The Tracloc's clutch pack only lasts 40-50k, miles, the Truetrac doesn't have a clutch pack to wear out nor does it require any additives to work.

 

[bobthetj03]

Did your gear installer show you the tooth pattern when he geared it?

 

[Rob5589]

Clutch chatter can happen even with the correct oil. If that is what it was and now it's gone, the diff just needed fresh/more/better fluid/friction modifier.

 

[Jamison C]

I suspect your gear installer botched the installation of the new gears. I would not install any lunchbox locker into a rear axle, they're just not well behaved enough when in the back axle. Plus installing a locker into a Dana 35 will very likely result in a broken axle shaft, factory OE Dana 35 axle shafts just aren't strong enough for a locker. Any kind of a locker.

I'm also surprised your gear guy installed the Spicer Tracloc LSD which doesn't have a good reputation. The Detroit Truetrac LSD would have been a much better choice of LSD. The Tracloc's clutch pack only lasts 40-50k, miles, the Truetrac doesn't have a clutch pack to wear out nor does it require any additives to work.

I think he did too, as much as I hate to say it. Which sucks because he’s a good friend and very reputable in our small area. I appreciate the input on the axle shafts because I’ve read that several places.

Did your gear installer show you the tooth pattern when he geared it?

No he didn’t. Called me a couple days after dropping it off and told me it was finished. I trust him so I left it at that. Mistakes happen. He does a lot of classic cars for guys in our area and has been for years. But classic/muscle cars are not jeeps.

 

[AndyG]

I hope it all works out for you .

I love what regearing can do , but it's scary if things go wrong .

 

[Jamison C]

So just and update for you all. I finally bit the bullet and had someone redo my axles. This is what we found...

The pinion gear was set so deep that it was actually digging into the carrier. Ends of the gear had broken off and started ruining the spider gears. On top of that the carrier was not shimmed correctly and had about 1/4” play left to right. Not to mention the break in oil was still in both the diffs. I don’t know how I didn’t run into severe failure earlier but I’m certainly glad I took care of it before that became the case. Rear gears are ruined obviously.

 

[Rob5589]

Those look like machining marks, not pinion contact. Have a pic of said busted pinion gear?

 

[Jamison C]

Those look like machining marks, not pinion contact. Have a pic of said busted pinion gear?

I know the pictures don’t look quite as dramatic but the flash is covering up a lot of the marring. I’ve since tossed the parts but they definitely weren’t usable. The ring gear was pitted really bad too. I had more pictures but my phone from a few weeks ago died and I lost everything. These are the two pictures the shop owner took for his records. I have a video of the slop in the rear driveshaft but I can’t upload it.