Extremely Loud "Hummmm"

The Jeep.... 2000 XJ, Chrysler 8.25 Rear, Dana 30 Front. 6.5" RK Long Arm kit. AA SYE, Six Sates drive line.

I had 4.56 gears (Yukon rear, Precision front) installed along with front and rear ARB's. As soon as I hit about 60-65 I start to get a loud hummmm. As I speed up it gets louder. So loud as it really will give you a headache. It is throttle related. As soon as I let off the gas it goes away. I figured it was driveline angle as the pinion looked a bit high. The RK leafs come with 4 degree shims. I swapped them out to 2.5, same thing. So I decided to take them out all together. I got very slight vibrations but the exact same humming sound. I took the front drive line out, thinking it may be front end vibration of some sort. No change at all. I put the 2.5 degree shims back in and now it is smoother (No vibration). Any Idea what this could be? The gears were installed by a very reputable shop here in Phoenix. Thanks for any help.

Tom

Sounds like the driveline shop is going to have to warranty their work. Take it back.

Something must not be shimmed right.To tight?

It is actually the second drive line. Did it with both shafts..... Hmmmm....

yeah, sounds like something is either too tight or too loose. My 8.8 did that after I trashed the bearings.

Check the preload on the carrier bearings. I know of a case where the nut thingys backed off of the bearings and ended up making the gears a bit noisy.

Ok I do have another question now. I decided im going to go ahead and swap the rear drive line, just in case. I have another new drive shaft sitting here I may as well try. Well my Jeep has been sitting for about 30 minutes, plus the time it took to yank the rear shaft. The CV part of the shaft is REALLY hot still. Like, you cant touch it for more than a second..... What is your input on that?

Dohh I guess it wouldnt help that the Cat is right next to the CV..... Im going for a test drive now with the second shaft to see if there is any difference.

You still have to measure the angles and adjust from there!

Ok I have eliminated the drive shaft issue. It has got to be in the rear end. I guess I will be swinging by the shop tomorrow. Thanks for the help.

Tom

live24wheel said:

Ok I have eliminated the drive shaft issue. It has got to be in the rear end. I guess I will be swinging by the shop tomorrow. Thanks for the help.

Tom

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How?Nothing youve posted so far has eliminated anything,how about some actual numbers?

RCP Phx said:

How?Nothing youve posted so far has eliminated anything,how about some actual numbers?

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I have tried no shim, a 2.5 degree shim and a 4 degree shim. With the 4 degree you can see the pinion is 2 - 3 degrees to high. With no shim it looks like the pinion is about 2 - 3 degrees low. With the 2.5 it looks about 1 - 1.5 degrees low. I know "looks" are not actual numbers. A slight vibration can be felt with no shim and a 4 degree shim. It is smooth as can be with the 2.5, other than the noise. I have also tried 2 different rear drive shafts, hopefuly, eliminating any CV issues. I will have them measure it in the morning and post up the results.

:wierd:

live24wheel said:

I have tried no shim, a 2.5 degree shim and a 4 degree shim. With the 4 degree you can see the pinion is 2 - 3 degrees to high. With no shim it looks like the pinion is about 2 - 3 degrees low. With the 2.5 it looks about 1 - 1.5 degrees low. I know "looks" are not actual numbers. A slight vibration can be felt with no shim and a 4 degree shim. It is smooth as can be with the 2.5, other than the noise. I have also tried 2 different rear drive shafts, hopefuly, eliminating any CV issues. I will have them measure it in the morning and post up the results.

Click to expand...

There's half your problem,8.25's can be tough,but do your "own" homework!

Took the Jeep in and the angles are perfect. They are going to tear into the rear end to find out what the deal is.

Are you by any chance running super swampers?? I do, and I get a loud "hummmmm" every time I drive it on the road!!

Nope, BFG AT's.

maybe its just happy and likes to hummm. Cant stop a happy jeep.

I just got new MTRs and regeared, so I'm not sure what's causing my hum either!

Its a really low, but loud hum, and I can see how it could cause a head ache.

i just had a issue like that, ended up having my front pinion preload to the proper spec. ended up grenading my front ring gear. took front shafts out and front driveshaft off and now its quiet as can be no more humm..

I have this exact same issue. Swapped out the D35 with a D44 HD and had it regeared with 4.56 ratios. Initially it had a slight whine under load at slow speed and took it back. They carefully reset everything and checked the pattern and when I got it back the whine was gone. However, I now have the humm/droning noise. It only appears under load and is at it's loudest at about 110 km/h. Same as yours, if I lift my foot from the gas, the humm/drone is gone.
The thing is, previously with my D35 if I travelled really fast (for a boxed shaped XJ at least!) I had a similar drone at about 140km/h. I never really worried too much about it as I never drove that fast and just made it off as a lot of heavy metal turning at high speed. With the regear in the new axle the propshaft is spinning faster for the same speed, hence why it appears at lower speed (this is my theory which is yet to be proven right). What I did was to notify the diff guys about the sound, but under took to first check everything else before I take it back to them. Currently I'm thinking it might be the output shaft bearing on the transfercase...there is a small amount of play there, but I'm not sure if it's normal or not.

Forgot to mention - I'm running without a front propshaft currently so the problem is definately somewhere from the middle backwards.

I got a hummm on my d44 whenever the rpms are areoun 1.5 to 2k rpm after that it goes away. Will a rear end slight hummm hurt anything or is it just anoying?