Axle swap growling noise

Here is the story, my brother bought a 97 XJ for parts. It was a 4 cylinder 5 speed so it had an 8.25 rear with 4.10 gears. It came with no motor and the guy he bought it from bought it from someone else and he didnt know much about it. My brother then bought an 01 XJ that was already lifted but the front end was making noise. So we decided to swap the axles. We swapped the front over and put new ball joints on all ends and swapped axles as the donor xjs axles were iffy. We then swapped the rear over and on the test drive whenever he pressed the gas the rear end would growl or grumble. As soon as he let off it was quiet. The speed of the noise increases with speed. Nothing is rubbing. What could it be? I'm thinking pinion angle. Any other ideas? Gear oil was changed.

Thanks!

If its not a vib but a noise and its only when on the gas then its prob pinion bearings.

^^ this. I suggest that you don't just go in there tearing things out looking for bad bearings unless you have the tools and understanding on how to set things back up. Differentials should be "set up" and to do it right you'll need the tools to set the side adjusters, backlash, and rolling torque of the pinion.

Yep, I'm with the folks above.
Pinion angle issues, in my experience, show up around 30 mph and again as you near 60.
If it's a steady noise that changes with throttle input, most common thing is pinion bearings.
Crawl under there & attempt to move the pinion by hand. Any play you can produce with your mitts is enough to condemn the bearings. Inability to do it by hand doesn't prove their innocence, though.

It is a vibration, one that you can hear at low speeds and feel starting at 25mph. There is not play whatsoever in the pinion or driveshaft. On my last XJ the driveshaft had a little weight on it that was hitting the muffler. This sounds just like that...

Make sure it isn't a limited slip with no friction modifier.

We used mobile 1 with friction modifier included

I put in shims and it still is growling. I got the jeep up to 45 and and it was a very high vibration that I could feel in my head. The angle of the pinion looks like it should he with an SYE. Would that help? This vibe wasn't there before and all that was swapped was the D35 for the 8.25 axle

smalltownbird said:

It is a vibration, one that you can hear at low speeds and feel starting at 25mph. There is not play whatsoever in the pinion or driveshaft. On my last XJ the driveshaft had a little weight on it that was hitting the muffler. This sounds just like that...

Click to expand...

go back to this.........
just because it isnt loose doesnt mean a bearing is bad. it has to make noise for a long time before it wears enough to feel the play in it.
if the only difference is the rear axle, then the problem is the rear axle.

lifted 01 with an 8.25?

how much lift? does it have an SYE?

I ran mine with bad pinion bearings for 4 years, roughly 30,000 miles, and the noise was ridiculous but there was no noticeable play in anything. When i finally got around to fixing it the bearing and race really weren't in that bad of shape. Obviously enough to make tons of racket but it wasn't like they were pulverized into dust.

With an 8.25, if there's noise in the center it's more than likely pinion bearings. Poor design on Chryslers part if I remember right.

From what I've read and seen, Dana 35's usually die horrifically with gears turned into salad and the 8.25's make noise.

Ideally with the stock slip yolk driveshaft, the u-joints run at 1-3 degrees. Rear should be about 2 degrees lower to allow for axle and spring wrap so under load it equals the front.

With a SYE, you set the pinion 2 degrees less than driveshaft angle and as long as the double cardan is within operating range you're fine.

The SYE will give you a longer driveshaft which also reduces the angles.

Its hard to quote exact values because everyone's Jeep is setup differently.

I had bad pinion bearings and races in my 8.25 for a long time when I bought it. It made a lot of noise but didn't feel loose. When I took it apart there was significant pitting in the pinion bearings and races. Chances are that is your issue. Best to replace all of the bearings while it is apart.