[jhattan]

This is probably a newb issue, but after changing the front diff fluid, I hear a low knock/growl at speeds over 30 mph.

Here's the story: This is the first time changing out the front diff fluid on a 98 TJ Sport 4.0 (Dana 44 LSD rear and 30 front) since purchasing it about a year ago. I did the rear diff a month ago with no issues. I added the Friction Modifier and did the figure 8's as recommended. I used Mobil 1 75w-140 in both the front and the rear.

Procedure:
Drain gear oil
remove cover
spray cover and diff with brake cleaner
wipe down cover and diff as best as possible
scrape gasket
add new rtv sealant
bolt on cover
let sit for 5 min
add gear oil till it overflows from fill hole
replace fill plug

After changing the front, I skipped doing the figure 8's assuming this only had to be done for the rear with an LSD. I hopped in the Jeep and started driving out of town. About 5 miles down the road at about 60 mph, the front diff popped! I immediately slowed down and this is when I noticed the growl. I have driven about 30 miles since the fluid change and have not had any more pops. I did some figure 8's in 4x4, but made no difference.

I'm assuming the growl is coming from the front diff because that's the only thing I worked on, but I cannot isolate the noise. It only happens when in gear driving over 30 mph and stepping on the gas. If I let off the gas, the growl stops.

Anyone have any ideas what my be causing the growl? I tried searching previous topics, but found no similar issues.

Thanks,

Josh

[otisdog]

You didn't leave a pair of scissors inside the patient after sugery did you?
Is there any possible thing that might have fallen in there?
jim

[daveg13]

A simple fluid change isn't going to do any harm. You sure it was your front diff. and not a u-joint?

[jhattan]

I'm sure I didn't leave anything behind, as side from maybe a few tiny particles of the old gasket that may have ended up in the diff.

Like I said, I'm kind of assuming that the growl is related to the front diff simply becasue that's the only thing I worked on. It's possible that the growl existed before and I just didn't notice it.

[jhattan]

One of the u-joints in the rear driveshaft has some movement. I can't check the rear of the front driveshaft without removing the t-case skid plate. I did notice that the entire front driveshaft has significantly more play than the rear. Close to 1/4 inch rotation each way, compared to almost none in the rear. Is this indicative of anything?

[jhattan]

I've read in a few places that removing the front driveshaft and driving around allows you to isolate drive line noise. Is this kosher? Just unbolt and remove the driveshaft? Are there any considerations I need to take?

[jzmtl]

Yeah just unbolt them, no problem

When remove the tcase end of front shaft, look toward the front from behind the tcase, you'll see one or two bolt at a time, unbolt them with a quarter inch drive ratchet, then rotate the shaft for rest of the bolts, this is the easiest way I found.

[jhattan]

Well, it's not the u-joints. I pulled the front driveshaft and drove around. I could still hear the knock/growl, so I removed the rear driveshaft and replaced all of the u-joints in both the front and rear driveshafts. Reinstalled everything tonight, and I still get the noise. Any suggestions on what to check next? I'm clueless!

[J33PIN]

Did you try removing the rear driveshaft and driving around in 4WD, effectively front wheel drive? That would isolate the rear diff.
If it is not the front and not the rear, than it may be the transmission, transfer case, or engine.
Do you hear the sound when you rev the engine? If not then most likely it is not the engine.

Any problems when shifting the tranny? You don't mention whether your transmission is manual or auto.

Any problems when shifting through 4 wheel high and 4 lo?

[DogPak]

Sounds like it's time to pull the front diff. cover and take a look

[Nonya]

i wouldn';t use mobil 1 gear oil if it was free.Its garbage,go buy some 3 dollar a qt at walmart rotella 80-90 gear oil and be happy.Mobile 1 is garbage trust me on this,it might be great for fuel mileage etc but when it comes to heavy duty gear oil stay away from mobil 1.I;ll give you a little example of how crappy mobil 1 gear oil is.My 99 ta was going through carrier bearings ever 10k miles using mobil 1,we switched to regular gear oil and 50k later no more troubles.ITS CRAP trust me on this,go read on the truck forums how many guys end up putting new carrier bearings in after using m1 for a while.ITS HYPE don't fall for it.My wifes 89 camaro had 210k on it using rotella 80-90 no noises or problems.

[jhattan]

Do you hear the sound when you rev the engine? If not then most likely it is not the engine.

Any problems when shifting the tranny? You don't mention whether your transmission is manual or auto.

Any problems when shifting through 4 wheel high and 4 lo?

I only hear the sound while driving in 3rd-5th gear starting at about 30mph. It's a manual transmission. I haven't noticed any shifting problems. 2nd can be a bear to get into sometimes, but that's it. No problems shifting into 4 high or lo.

Sounds like it's time to pull the front diff. cover and take a look

Before I pulled both driveshafts, I removed the front diff cover again just to make sure everything look good. All is well up front.

I removed the rear driveshaft today, took the jeep for a drive in 4x4, and the noise was gone. While inspecting the rear diff and transfer case, I noticed a small leak coming from the bottom of the rear diff. Appearantly I did a crap job on the RTV when I changed the fluid two months ago. I'll pull the cover tomorrow and see what the damage is.

Nonya says Mobil 1 is a no go. Anybody else want to weigh in on this one? Is there something preferable to use?

[Jerry Bransford]

Mobil 1 gear lube is fine and I have used it in my axles, it wouldn't cause this problem. No major brand GL-5 gear lube is going to cause that problem.

[Nonya]

Originally Posted by Jerry Bransford

Mobil 1 gear lube is fine and I have used it in my axles, it wouldn't cause this problem. No major brand GL-5 gear lube is going to cause that problem.

no it wouldn't cause the growling but i wouldn't leave it in there unless you like worn out parts over a short period of time.I know quite a few ford truck guys that had premature bearing failures using m1 75-90.If you use m1 be sure its the 75-140 at least that has a decent additive package.

[Jerry Bransford]

Originally Posted by Nonya

no it wouldn't cause the growling but i wouldn't leave it in there unless you like worn out parts over a short period of time.

Well, only one word comes to mind for that... baloney. I'm not a big Mobil-1 fan but claiming it would cause worn out parts over a short period of time is a pretty laughable and ridiculous claim.