Scary rumble at 70

[Tim Smith]

I recently replaced most of the seals and gaskets on my transfer case and filled it up with some nice fresh Lucas oil. No leaks and it sounds great! In fact, I don't really hear it any more unless I'm really pushing speed limits on the freeway. The problem is, when I let off the throttle or put it in neutral on the freeway there is a new horrible sound coming out of the drive train.

If I keep the throttle down, there is no rumble. If I decelerate (using the engine compression) there is no rumble. It's just when there is no motive power going through the drive train that I can hear this horrible sound.

Now I've tested this sound a little bit and it seems to only start showing up around 45 and gets progressively worse the faster you go. When I first noticed it, I was going about 70 and I thought I had blown the rear end.

It sure sounds like it's coming from the rear diff. I've checked all my connections on the drive shaft and wiggled everything around but nothing looks obvious.

Could it actually be coming from the transfer case and fooling me? Since that is the last thing I touched it would make sense that that this is where it is coming from but it clearly sounds like the rear diff. When I drained the old oil out of the transfer case, there was a good amount of shavings in there but nothing that had me too worried.

I'm going to drain the rear axle tonight and see what the oil looks like. If it does appear that I've got lots of shavings in there, I guess I'll know what it is.

Till then, does this sound familiar to anyone? Is there a common bushing that lets go in the diff or transfer case?

I did have the diff out a few months ago to get the snapped end of a drive shaft out. Maybe there were some shavings/parts left in there that could be playing havoc with me now...

[sven]

You sure its not U-joints? That description sounds like it. I usually jack up one wheel, so that the driveshaft is "unloaded". Makes it easier to feel for play and wear.

[galen216]

Or loose driveshaft bolts, that happened to me a few weeks ago.

[greenmeanie]

It's time to get under your truck and spend a couple of hours poking and pushing. The oil is good for your skin so enjoy it.

First check the obvious things that are visible.
- UJ's are easy and so is the spline joint. You may as well grease them while your there.
- Loose hardaware as described above. You may as well check the drive flanges on the hubs are tight too. If your in the vicinity I'd check the wheel bearings are in good order as a very outside chance.
- Diff pinion. Grab the end of the prop shaft next to the pinion and try and move it both radially and axially. If there is significant movement the pinion bearing has gone. My 101 did this to me and it only manifested itself as rumbling on the over run.
- Transfer case output. Back off the hand brake adjuster (Chock the wheels first please) and then grab the brake drum. Look for radial movement here. This indicates the preload on the taper roller bearings is incorrect. In one of your previous posts you mentioned something about the output shaft but I can't remember what. If it was displaced or showed any signs of movement then these bearings are your culprit.

After that you get into some deeper stuff so we'll wait on your report back on these checks.

Cheers
Gregor

[Tim Smith]

First off, thanks for the quick replies.

A little history. When I was replacing all those seals on the transfer case this past weekend, I also:

• Replaced the boot on the slip joint of the drive shaft. This involved pulling the ends apart, cleaning out most of the old grease in the slip joint, reattaching the ends and then re-greasing the joint. I didn't over do it though because I didn't want to pop the cover plate on the end of the shorter shaft like it was before I started.
• I soaked both UJ's in kerosene and then re-greased the heck out of them. I let a little bit of the old grease come out of the seals just to get rid of the old stuff that was in there.
• I also replaced the wax seal on the end of the output shaft with a felt one (like from the end of a drive shaft). It was a tight fit but I'm pretty sure I got it all in there and seated correctly. The wax seal is on back order.

From the sounds of it, I could have buggered a UJ. When I was under there this morning, everything looked nice and tight. All the drive shaft bolts were tight and there wasn't any slop or play in anything when I pulled and wiggled the drive shaft and parking brake.

Sounds like the far UJ could be the culprit. Now that I think of it, why the heck did I let it soak in kerosene instead of just wiping it down? Oh well. Now I have a few more things to check after work.

Thanks for the pointers!

[sven]

Replaced the boot on the slip joint of the drive shaft. This involved pulling the ends apart, cleaning out most of the old grease in the slip joint, reattaching the ends and then re-greasing the joint. I didn't over do it though because I didn't want to pop the cover plate on the end of the shorter shaft like it was before I started.

Another thought: Did you mark both ends of the driveshaft before you seperated them? It could be out of phase, if you didnt.

[Tim Smith]

Another thought: Did you mark both ends of the driveshaft before you seperated them? It could be out of phase, if you didnt.

You are kidding me. You mean to say that the drive shaft is balanced or something? Oh jeez. How do I figure that out and get it back the way it needs to be?

In case you can't tell, I didn't mark the different ends when I pulled the shaft apart. This sounds like it could be the culprit for sure.

[Terrys]

Another thought: Did you mark both ends of the driveshaft before you seperated them? It could be out of phase, if you didnt.

X2.
As I was reading down thru the thread, I was waiting to see if you made any mention of driveshaft dissassembly. I will bet that you just slide them back together, without aligning the two arrows.

[Tim Smith]

X2.
As I was reading down thru the thread, I was waiting to see if you made any mention of driveshaft dissassembly. I will bet that you just slide them back together, without aligning the two arrows.

Oh thank goodness! There are arrows.

Thanks again folks. I'll let you know what I find out.

[jp-]

Oh thank goodness! There are arrows.

Thanks again folks. I'll let you know what I find out.

Welllll... There might be arrows, might not be. Depends on how rusty the shaft was. I have BTDT as well. It wasn't until I checked the green bible that I realized the stupid thing had to be lined up a certain way.

[BackInA88]

The slip joint should be installed so the yokes are parallel with each other.

http://www.roversnorth.com/store/p-3727-prop-shaft-88-rear.aspx

This means you have a 50/50 chance of getting it right the first time.
If you have been running the u-joints "out of phase" I would replace them to be safe since you are pulling it back out anyway.

They are phased so the cancel each other out while rotating.
If run incorrectly this can put a lot of extra stress on them.

I have always wondered why the manufactures never made one spline wider so you couldn't put the slip yoke back together wrong?

Steve

[jp-]

I have always wondered why the manufactures never made one spline wider so you couldn't put the slip yoke back together wrong?

Steve

As a manufacturing engineer, I can answer this question. It would not be cost effective for them. Sure it could be done easily enough, but then you throw in operator error and you might get a days worth of production that won't go together correctly. If the splines are all the same, and an operator loads a part 180deg out, no big deal; the part can still be used.

Then you would also need to order custom broaches, change your external spline cutting program, make new fixtures to eliminate all possibility of incorrectly loaded parts, etc...

[Tim Smith]

You guys are good! It was the drive shaft being out of phase/balance or whatever you call it.

If it weren't for the fact that I *may have* over tightened the drive shaft bolts on reassembly, this would have been super quick to pull out and fix. As it was, it took me a little longer and a few busted blood vesicles while I switched it out in my drive way. Got dark before I had it out. I wonder if the neighbor noticed me in the light of their front porch while I was looking for those arrows. Once I identified the arrows and switched the drive shaft around, it was quick to put back together and test.

Took it for a drive right after but could only get up to about 50 mph. Still though, it was pretty obvious that this fixed the issue. This morning's drive to work confirmed it. It also seems to have fixed the sub-drive train-shudder that I didn't mention.

This will be one of those "riding a bike" kind of fixes for me. I'll never forget how to identify and fix it.

Thanks everyone for your help!