Hi everyone,
I hope somebody can help with this, but I seem to have a problem with the diff out of my '72. The trans is out of the car so I can turn the axle shaft flanges by hand and they're as smooth as can be, but when I turn one flange and hold the other flange steady, it feels "rough" and sort of makes a "grumbling" noise. Any ideas what that might be, please? Thanks.

Differential carrier bearing.

Why is it out of the car? Was there a problem when it was in the car?

If I understand your post it’s running smooth when you rotate both axles simultaneously, the same amount of rotation on each axle.

Then when you hold one axle fixed but rotate the other it’s feels and sounds sounds grumbly?

Did it make any noise in the car when making very tight turns?

When you spin one axle the other turns opposite due to the spider gears in the differential doing their job. They aren’t moving more than the output flange on the other side. When you either impeded one axle, or rotate both in the same direction you are now moving the actual differential. This moves the pinion, which moves the rest of the gear stack. Even in neutral, there should be some resistance and noise as you are slowly moving all of those components. What I can’t tell you based on your description is if the amount of noise you are getting is Normal or not. Also, it’s difficult for me to describe normal or not in words.
Why is the trans out? Did it have problems? If so, what were they?

There is precious little you can diagnose with the trans just sitting there and not torn apart. Pretty much only major catastrophic stuff like broken gear teeth, seized stacks, sheered roll pins, stuck in gear.

Hi Doc,

The trans is out of the car as I've just replaced 1st/2nd/3rd synchros and dog teeth (with the help of your DVD!) as - typically for a teener - the shift in those gears was diabolical! I sloshed about a cupful of 90 Gear oil into her to keep things oiled, as the car's waiting for paint and I don't know when she'll be back together.

I'm trying to post a movie clip illustrating what the problem is, but my cinematographer isn't on form these days! Please watch this space.

Hi Super,

The trans is out of the car as I've just replaced 1st/2nd/3rd synchros and dog teeth as - typically for a teener - the shift in those gears was diabolical! I sloshed about a cupful of 90 Gear oil into her to keep things oiled, as the car's waiting for paint and I don't know when she'll be back together.

I'm trying to post a movie clip illustrating what the problem is, but my cinematographer isn't on form these days! Please watch this space.

Please take look at the link and turn your volume up to max.
https://imgur.com/a/ZuTIyyS Thanks.,

Please take look at the link and turn your volume up to max.
https://imgur.com/a/ZuTIyyS Thanks.,

I don’t think there is much that can be inferred from the video.

First is that the transmission doesn’t operate in that position. I suspect you don’t even have oil in it? Does it have oil in it?

Even if it did have oil (and not leaking out the input shaft seal and the vent) the oil is not in the right place. It will have drained off all the proper gear and bearing surfaces due to the vertical orientation. Likewise when spun, it’s not picking up oil out of the oil bath properly to distribute back to the gear sets and bearings.

In the first video, then only thing I think I hear is a dry gear set spinning when you hold the output flange.

I’ll gladly defer to Doctor Evil but would want to see what it does with it oriented horizontally, properly filled with oil. I suspect having oil on gear teeth will likely quiet it right down.

Hi Super,
I said in a previous post that I'd put a cupful of 90 wt. and sloshed it around a bit, just to (hopefully) keep rust at bay, even though it's indoors. That seems to have made quite a difference and shut it up a lot!

Thanks to all who replied.