rear axle noise?
 

I was hoping to leave the rear axle alone for a while on our 1951 F1 with the 289V8 and the C4 ... but while doing a brake job on the back, I noticed that spinning the rear axle does make a bumping/thumping kind of sound.

I opened the differential up and although there wasn't a lot of lube in there, it does look in decent shape.

I am new to FTE, please tell me that this is a normal sound for these rear ends and that this noise isn't rear bearings. You know I don't want to have to start a new rear end project!

Thanks, Richard

Richard, welcome.
It should make a whirring sound - grinding, thumps and bumps aren't good. Look for something loose that's slopping back and forth excessively. If you can't see where it's moving, have someone else turn it while you listen. If you still can't pinpoint the spot, hold your hand on various parts while it turns. Eventually you'll find where the bump originates. Good luck. Let us know what you find.

How much metal did you find? and when you spin the wheels try disconecting the driveshaft. Mine sounded like that at first but I waited and then my truck ended up tilting from side to side because the ring and pinon went out. Have you had any lumps or spots where it felt like the wheels were not turning?

You may want to also check the rear axle outer wheel bearings.

1951 F1 rearend update
 

Thanks very much for the input!

Let me tell you what we found.

1. I brushed out the differential gears with some kerosene. There is slight pitting, but the wear does not seem excessive. Also, no metal of any kind in the differential.

2. Disconnected the right axle. Then, when I turned the left axle slowly by hand, there is still that tap, tap, tap noise.

3. Then I took out the left axle. Of couse I can only spin the differential inlet then, and the differential spins in some weird movements ... but the main thing is that there isn't any unusual noises.

4. The axles were kind of rusty, but they cleaned up well with some kerosene and ATF we use for parts cleaning ... and a good wire wheel on a 4.5" angle grinder.

5. The bearings in the rear (near the brake back plate) are kind of like pillow block. I was expecting tapered bearings. Anyway, they were kind of dry on the outside with that kind of clumpy stuff that old grease makes, but they turn very smoothly by hand. I don't think that the bearings are the problem ... actually, I am still not sure that there is a problem ... just that sound that I wasn't expecting ... so maybe it is the "whirling" sound that MTFLAT mentioned??

6. So, I suppose that the inner bearings could be bad, but I don't think that both left and right inner bearings would be making exactly the same sound (IE that they would both be going out right at the same time) ... therefore, I am knid of thinking that the tapping kind of sound may actually be normal. There

7. 1Low50, There doesn't seem to be any lumps or flat spots or places where the axle hangs up/drags.

8. I don't really want to totally breakdown the differential. It is a lot of work and I might screw it up rather than fix something. The gear ratio is pretty good (I don't remember exactly but I think it was about 3.6:1 when I divided the numbers). I hate to spend a lot of money on that rear end (four bearing asn seals is expensive and I guess a machine shop has to press the bearigns on ... especially when I can't identify a problem. So, I am thinking of replacing the outer seals and those paper back plate gaskets and putting it all back together with some fresh gear lube ... and dare that bite me someday.

What do you think, am I asking for trouble?

Thanks, Richard

Your noise may be the side gears and differential gears meshing (the four small gears in the middle). If you are turning one axle, these gears are rotating and are quite noisy. They don't turn like this in normal operation. If you turn the pinion shaft and both axles are turning, I bet the noise is gone. While you have it apart, replace both the axle seals and bearings (at the backing plate end). ...Terry