Today I swapped my 01's d35 and lp d30 for a 8.25 and hp d30 from a 97 4 cyl 5 speed with 4.10 gears. During the swap I replaced the ball joints.
The 01's driveshaft seemed to fit in the 8.25 so I kept it.
When I went on a test drive I heard a rumble/howling noise coming from the rear end. Any suggestions on where I should start with this noise? I was building this jeep to be my DD. I replaced the axle fluid also.

The noise is only when accelerating, when I coast it's quiet.

I actually have this same problem and but mine older I swap my older 35non c clip for a 94 8.25 with 4.10 also. It usually doesn't start to happen till about 50 to 55 with driving but on light throttle. When on Jack stands its about 35 and comes front the pinion area. So after removing the 8.25 and putting my 35 back in I noticed the noise again but at 45.
So here is my guess since I'm at a new height at 4 with no tc drop or sye, the 35 driveshaft is longer so it sits in the slip yoke more and is actually vibrating since the 8.25 housing is about 2 longer then the 35 and uses different u joints I think.
I am currently rebuilding the 8.25 and will see if anything changes and will be checking the u joints next and probably doing a sye also.
I'd say a little more info is needed like lift and trans. Can't see since on the app.

Similar problem, I ditched the LP30 & scrappy D35 for a HP30 & 8.25. I believe we all have driveline vibrations. I have a SYE & Tatton. Double Cardin DS, and never had drive line vibrations with the 35. I have to replace front U-Joints & grab some shims for the rear. That should fix the issue. Do either of you have a SYE installed?

My 8.25 29 spline has a slight howl to it and its freshly built (4.56, spartan locker,barely 300 miles on build) with royal purple 75-140, which I was told they will always make noise due to the heavier oil and the pinion bearing getting a work out when there isn't a SYE. As long as it doesn't continually get louder and louder as the miles go on you shouldn't have a issue.

Yours could be several different issues gears not setup properly, to thin of a gear oil, the Spartan Locker itself, not having an SYE or TC drop kit (no mention of your lift height), no shims, etc.

One thing I can tell you is that a proper setup "Does NOT" make an undue amount of noise at least mine never did. Now I'm running 4.56's with Detroit Lockers, 4 1/2"of lift, with an SYE and new driveshaft the only "Noise" I hear is coming from the tires on the highway.

Both my jeep and the donor jeep have about 3-4" of lift. No SYE.

What are the shims you're referring to?

Degreed shims to correct the pinion angle. they go in between the spring pad on the axle and the spring.

I don't have any shims on it now. Will that make a difference?

I agree I have C8.25 29S, 4.56's Aussie locker 4 1/2"lift with SYE, new shafts 4 degree shims. I hear no noise on acceleration or coast but my tires.

OP you need to do some reading on what shims are and driveline 101 stuff. so read away

https://www.cherokeeforum.com/f67/re...estion-125808/

https://www.cherokeeforum.com/f67/wh...-shims-131964/

https://www.cherokeeforum.com/f2/axle-shims-15803/

https://www.cherokeeforum.com/f2/t-c...e-shims-24995/

http://www.4xshaft.com/driveline101.html

^^^ check those out, I'd also recommend getting a SYE (great upgrade & easy to do). That along with the correct shims you should be good to go.

So the noise could come from not having the right angle in the driveline? I don't really feel any vibration just hear the noise. How much will a SYE cost me?

Not sure if I mentioned this but I'm working on making this my DD, not going to wheel it hard.

When you change the angle of the driveshaft such as when adding a lift, you change the geometry of the driveshaft as it relates to the transfer case and pinion. There should be about 3 degrees on either end. When making changes and things go far out of whack, vibrations, u-joints failure, and stress on the output of the transfer case and pinion occur. Read those other threads. There are 2 general methods for the SYE - hack 'n tap (HNT) or open the transfer case to replace the transfer case output shaft. Both require a new driveshaft. The idea is to use a double cardan like the front shaft. The quick and dirty way to reduce the angle is to drop the transfer case by putting spacers between the frame and crossmember. This is a bad idea for multiple reasons such as stress on the motor mounts, exhaust alignment/stress, and reduced ground clearance.

An SYE will run from $200 up depending on which one you choose. The SYE makes a VG option for your DD as it see's a lot of miles at higher speeds.

As the post above stated the pinion angles are very important for many reasons, on my XJ I have both 3* shims and a SYE.

I really appreciate everyone's help. Assuming the problem is from the pinion angle and not the actual gears messed up is it bad to drive it like this for a short period of time while I save up for the SYE?