Rear end lube and noise

[KShortell]

Hey all,

It's been a while since I posted something on the forum.

Anyway, I've had a mild nagging moan from the 10-bolt 3.73 rear end in my '86 Sub for a few years, usually only in the "float" or lightest of light acceleration. It's a wee bit louder these days at 145,000+ miles and I got to thinking a bit. This is where y'all come in.

GM specs 80W-90 for the rear diff. I was wondering if running 80W-140 would quiet things down a little. Since I only get 12-13 m.p.g. now, I don't see it hurting fuel economy too much. Anyone ever run a blend? As a kid, I heard about guys running the limited-slip additive to quiet even open diffs like mine.

I do tow a 3,500 pound boat/trailer combo on occasion; I've actually put 7,000 miles on the boat trailer over the years.

I've always just run the factory-spec lubes, but got to wondering. Any advice is appreciated. Thanks!

-Kevin
1986 Chevy Suburban C10 Silverado
350 SBC / TH700R4 / 3.73 / P235/75R15XL

[BarryB]

Ok from what I understand, there are only two reasons a rearend will moan, incorrect gear spacing(worn gears over the years) Or the bearings are worn and have slop.
Your probelm sounds like to me the gears are just worn enough to let it moan.Does you diff. Leak out of the front seal. Tha might lead to another problem. But actually sounds like it might be time for a rebuild or another diff.
Putting in a thicker gear oil, might quiet down the moaning but really I believe it will be just covering up the problem. Just my $ .02

[pistolpapa]

Check your pinion bearing nut.

Mine has been moaning for quite a while at low speeds. While I was pulling the drive shaft for a tranny replacement, I found the loose nut.

Then I read this:

What is this whirring noise?

"Whirring noise only while decelerating at any or all speeds is most likely caused by bad pinion bearings or loose pinion bearing preload, and almost never by bad ring and pinion gears.

A howl or whine during acceleration over a small or large speed range is usually caused by worn ring and pinion gears or improper gear set up.

Rumbling or whirring at speeds over about 20 mph can be caused by worn carrier bearings. The noise may change while turning.

Regular clunking every few feet may indicate broken ring or pinion gears.

Banging or clunking only on corners can be caused by broken spider gears, lack of sufficient positraction lubrication, or worn positraction clutches.

Rumble while turning may indicate bad wheel bearings.

A steady vibration that increases with the vehicle’s speed can be caused by worn u-joints or an out of balance driveshaft.

Clunking only when starting to move or getting on and off the gas might be loose yokes, bad u-joints or worn transfer case or transmission parts. "

__

We'll see when I put everything back together.


.

[KShortell]

I took the truck over to the USCG base today and put it up on a lift at the hobby shop. 85W-140 did the trick. It's hardly detectable now. I actually hadn't seen the insides of the differential in over a decade. The fill plug was stuck last time, so I've had someone do the rear end lube for me.

The good news is that the fluid was still pretty clean. There's a mirror polish on the teeth, so it's just normal wear after 145,000+ miles.

I switched the engine over to 15W-40 since it doesn't get below 10F here and GM says that 15W-40 is good for that heat range. Oil pressure is better on the highway now.

I was so motivated today that I even replaced a bad power window motor on the front passenger side and replaced the dash bezel decal (brushed aluminum) as well. Now, she's just needs a buff and wax...

I will say that doing the differential up on a lift is SO much nicer that doing it in the driveway. I know that my back will thank me tomorrow!

Thanks for the input. It's a boost of confidence in any event.