rear gear whine

[tarafied1]

I bought this old 72 as a driver for my boys with plans to fix it up if it survived them. It's been doing pretty well but I haven't really used it as a truck until last weekend. I bought two 69 Mustangs out in Eastern KY and used the 72 and my dad had his F250. We drove for hours just to get to them but shortly after leaving the house with the trailer hitched up, the rear started whining and was really hot. I checked the lube and couldn't feel any so I put a pint in and that filled it. I stopped frequently to check the rear and see if it was till getting hot. It seamed better but still noisy. It made it all the way out to Eastern KY and back loaded with a 69 Mach 1 and lots os parts. I let my dad tow the heavier load with his 250. The rear doesn't make much noise around town or with no load but as soon as I work it it is really loud. I think it might be the gears because if it were a bearing I would think it would be noisy all the time.

[terry b]

You need to pop that diff cover off and take a look around sometime when you git some time. Look at the whare pattern on the gears. Then match it to photos on the internet. That should tell you if it loose or tight. Also is it a ten bolt or a twelve bolt cover?

[tarafied1]

I am not sure if it is a 10 or 12. I will have to check. Maybe this weekend I will pull the cover and change the lube.

[terry b]

It sounds to me that it may be a pinion bearing. Is it leaking any gear lube around the seal?

[tarafied1]

no leaks. The noise is only under load. When I don't pull the trailer or if I let off the throttle it gets quiet.

[Keith Seymore]

Gear mesh frequency is a "high frequency pure tone" (aka "whine") in the 370 Hz range (depending on axle ratio). It is load dependent and can whine on coast, steady state driving, or accel (or more than one of those).

Bearing noise is usually more of a low frequency "rumble" (trashy, white noise; not a pure tone) and is not as load dependent.

I'd pull the cover and check the pattern and lube. If everything looks ok and it's quiet during normal use I wouldn't worry about it.

K

[chevy72blu]

Could be a number of things with the pinion... lash is frequently set incorrectly by DIYers. Did the OP recently replace it?

[tarafied1]

Originally Posted by chevy72blu

Could be a number of things with the pinion... lash is frequently set incorrectly by DIYers. Did the OP recently replace it?

no, it's a one owner truck. I got it from a field where it had been sitting for a long time. As far as I know it is pretty much all original except for the things I have been replacing or fixing.
I have been driving it as a car (no loads) and mostly in town driving. This was while I was getting the bugs out from sitting. It has been getting more reliable so I decided to use it to tow with. I didn't notice the noise until I had the trailer (empty) and got up to 55+ mph. It is more of a tone I would say. It it very load sensitive. The noise (even with trailer) will decrease or go away when coasting or going down hill, let off throttle, etc. It isn't really noticeable until over 45 mph and seams the loudest or worst at 60 to 65. On the interstate I tried to stay under 60 because it was quite annoying above that.

[tarafied1]

Originally Posted by Keith Seymore

Gear mesh frequency is a "high frequency pure tone" (aka "whine") in the 370 Hz range (depending on axle ratio). It is load dependent and can whine on coast, steady state driving, or accel (or more than one of those).

Bearing noise is usually more of a low frequency "rumble" (trashy, white noise; not a pure tone) and is not as load dependent.

I'd pull the cover and check the pattern and lube. If everything looks ok and it's quiet during normal use I wouldn't worry about it.

K

I'll pull the cover this weekend. It's a solid truck but has been used as a truck so it is well used. It has about 120,000 miles on it.