The Stovebolt Site Forums The Shop Area Driveline New rear end hum

Well after a few hrs of driving. My new 3rd member has a low hum and is a little hot to the touch. Hums when accelerating stops when I Coast.

Before installing I did the best I could to find any slop or wear. The gear had almost no wear and so we installed it. Everything sealed up fine and the front seal shows no sign of leaking but maybe too soon to tell. The front section is where most of the heat is located.

Where do I start?

Don

Well I guess I. On my own on this one.

I’m going to open up the rear cover and check the backlash. Should be between .005-.008. .005 seems really tight. If it needs more I can remove the locking clips and turn the left hand adjustment nut out two positions and turn the right hand adjustment nut in. Then check with a dial indicator. Piece of cake.

Don

Don, when you say “front” that says pinion bearing to me. Also if your differental has a side thrust adjustment I’d check that adjustment. It’s been discussed here a few times, search should turn up helpful info.

Good Luck, RR

It a new to me member. Could be the pinion bearing. If it is I will have it professionally rebuilt as that will be too involved for me. Adjusting the ring gear is not that hard to do and can be done in place. If I lose the hum I’m going to drive it to fail.

Thanks Don

Don, when I say "side thrust adjustment" I'm speaking to the adjuster bolt (that may be) on the right hand side of the housing when viewed from the front. It's on all HO72 and some HO52 Eaton units. You can see it in the image below.

A low hum would have the frequency of the tires, axle, etc. if it is a pinion bearing hum, it would have a higher frequency of the driveshaft/engine, so identifying the frequency should give a start.

Ed

Yes I understand there is an adjustment bolt. It goes in tight against the ring gear and then backs off 1/12 of a turn. I my mind this is a very strange aspect to have on a rear end. This should be set only after the backlash is set. Other wise it could hinder shifting the ring gear.

When I discuss the hum with other guys we all agree that the hum is from either the gears are to close and need to be opened or the pinion bearings are bad. Or at least this is the best place to start.

Thx Don

There is a VERY important break in procedure when a diff has new parts. Are you aware of this?

YUKON GEAR AND AXLE CO.

New Gear Break-In
All new gear sets require a break-in period to prevent overheating damage. Any
overloading or overheating will break down the gear oil, which will cause the ring
and pinion to fail. This can be determined by inspection and will void the gears’
warranty.
Please follow these guidelines to insure proper break-in.
Avoid heavy acceleration during the break-in process.
Drive the vehicle lightly for the first 15 to 20 miles and stop. Let the differential
cool before proceeding.
Avoid heavy acceleration for the first 100 miles.
Drive the vehicle at least 500 miles before towing to retain the gears’ warranty.
When towing for the first time, drive for a very short distances (less than 15
miles) with the full load and stop. Let the differential cool for about 20 minutes
before proceeding. Repeat this procedure two more times (45 miles total) to
fully break in the gears.
Change the oil after the first 500 miles. This will remove any metal particles
and phosphoric coating shed by the gear set during the gears’ break-in period.
These towing instructions may seem unnecessary to most people, but we have
seen many differentials damaged from being loaded before the gear set was fully
broken-in.
OVERLOADED OR OVERHEATED GEAR
OIL WILL BREAK DOWN
AND DESTROY THE RING AND PINION!

Does the "new" unit have brand new gears and bearings, or is it just "new to you" as in a used assembly that you have just installed? A gear whine on a used unit is virtually impossible to correct, at least that's been my experience in the 55+ years I've been building rear ends. Once a wear pattern that makes a noise is established, there's virtually nothing that can be done to change it. Any adjustment you try to make can only make things worse. Unless it's making noises that change from pull to float to coast, pinion bearings probably aren't the problem. Rough carrier bearings cause a steady hum that doesn't change with load, and gets louder as speed increases.

OK- - - -just re-read your original post. A hum on acceleration only is probably a bad pinion bearing. The front bearing is fairly easy to change, only requiring the removal of the driveline flange and the bearing retainer. If you decide to change both pinion bearings be sure not to alter the pinion depth which is set by shims between the pinion carrier and the main housing.
Jerry

Not saying it’s a bad idea ....but......So does any one ever “break in” their rear end on their brand new truck or car ? Or change the rear diff oil after 500 miles?

Depends on what the owners manual says. Probably not. Just informing what all the gear sellers say as FYI.
After only a few hours it was humming and hot. This is what always scared me about doing my own. Lots of parameter's to cover. I finally did one and have not run it yet.

I was also curious when I did my 3.55 gear change last year. Checked the temp on the first 25 miles and found it barely warm to the touch. I did change the diff oil since the build upgrade.

[quote=Hotrod Lincoln]Does the "new" unit have brand new gears and bearings, or is it just "new to you" as in a used assembly that you have just installed? A gear whine on a used unit is virtually impossible to correct, at least that's been my experience in the 55+ years I've been building rear ends. Once a wear pattern that makes a noise is established, there's virtually nothing that can be done to change it. Any adjustment you try to make can only make things worse. Unless it's making noises that change from pull to float to coast, pinion bearings probably aren't the problem. Rough carrier bearings cause a steady hum that doesn't change with load, and gets louder as speed increases.

OK- - - -just re-read your original post. A hum on acceleration only is probably a bad pinion bearing. The front bearing is fairly easy to change, only requiring the removal of the driveline flange and the bearing retainer. If you decide to change both pinion bearings be sure not to alter the pinion depth which is set by shims between the pinion carrier and the main housing.
Jerry

Sounds like I will need to rebuild the pinion bearings. If it’s too much for me to do I’ll look for someone that can. Thanks for your response Don