The 1947 - Present Chevrolet & GMC Truck Message Board Network

Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > General Truck Forums > Engine & Drivetrain


Thread Tools Display Modes
Old 01-18-2008, 02:29 AM   #1
Registered User
KShortell's Avatar
Join Date: Oct 2003
Location: Chesapeake, VA
Posts: 634
Rear end lube and noise

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!

1986 Chevy Suburban C10 Silverado
350 SBC / TH700R4 / 3.73 / P235/75R15XL
Semper Paratus
KShortell is offline   Reply With Quote
Old 01-18-2008, 02:56 AM   #2
Senior Member
BarryB's Avatar
Join Date: Jul 2006
Location: Blountville, Tn.
Posts: 3,905
Re: Rear end lube and noise

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
*We could learn a lot from crayons... Some are sharp; some are pretty;and some are dull. Some have weird names; and all are different colours;but they all have to live in the same box.

* You may be only one person in the world, But you may also be the world to one person.

* Some mistakes are too much fun to only make once.

Two rules in life.
1. Never sweat the small stuff!
2. Everything is small stuff!

Last edited by BarryB; 01-18-2008 at 02:59 AM.
BarryB is offline   Reply With Quote
Old 01-18-2008, 10:25 AM   #3
Registered User
pistolpapa's Avatar
Join Date: Feb 2006
Location: Nogales, AZ
Posts: 27
Re: Rear end lube and noise

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.

His: '71 K5 Blazer
Hers: '66 Volvo 122S
Theirs: '98 Wilderness Travel Trailer
pistolpapa is offline   Reply With Quote
Old 01-20-2008, 10:32 AM   #4
Registered User
KShortell's Avatar
Join Date: Oct 2003
Location: Chesapeake, VA
Posts: 634
Talking Re: Rear end lube and noise

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.
Semper Paratus
KShortell is offline   Reply With Quote


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

All times are GMT -4. The time now is 04:03 AM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2018, vBulletin Solutions Inc.
Copyright 1997-2013