2007 Base - 152K - 5-Speed


Every now and then (call it driving the car every 2-3 times), I experience a very horrific grinding/rattling sound coming from the middle/rear of the car. It sounds similar to when two gears are not quite meshed with one another.

It absolutely never happens at high speed, such as in 5th gear and cruising down the highway. It is always at slow speeds such as when slowly accelerating from a stop up to about 0-15 mph, or when slowing down from high speeds, usually right around the 10-15- mph range. Doesn’t seem to matter whether the vehicle is hot or cold, or if I am applying the brakes or just coasting all the way to a “stop”. It is completely at random at low speeds.

What also seems to initiate the noise is if I hit a speed bump, but ONLY after the rear wheels hit the bump; sometimes the noise will be completely gone, but as soon as the rear wheels bump….boom….the noise comes back, then disappears when I come to a stop. As soon as I accelerate again, sometimes the noise will persist, and other times it will disappear, allowing me to accelerate back up to speed again.

Thing I have already tried: keep in mind while this is throwing a lot of parts at the vehicle, all of these were going to need replaced at some point, so I went ahead and knocked out the following.
1. rebuilt front axle - my pinion bearings were going out, so I had to rebuild it anyways. I did not change out the front CV axles. The noise persisted after the rebuild.

2. New transmission (5 speed) - my original transmission was basically just….getting worn out. I purchased a remanufactured unit online. The car is now much more quiet than before at highway speeds, but the issue still persists under the same circumstances as before.

3. Multiple different transfer cases - my original transfer case I pulled due to it having the plastic shift fork issue, so I bought a donor unit to use for a short duration (an 06 model with 100k miles on it). Once I installed donor case, the rear end noise still persisted under the same circumstances. Once I finished installing a metal fork in my original case, as well as giving it an overall good reconditioning, the noise still persisted. I wondered if the worn out plastic shift fork was allowing the shift collar in the transfer case to move freely from the AWD—>4WD locked modes, and was potentially causing grinding, but since it happened not only with both transfer cases, but also with the metal shift fork, this is obviously not the issue.

4. New Rebuilt Engine - I rebuilt my engine last spring BEFORE the noise started happening, but the noise occurs whether the engine is running or not. The noise did not occur until about 2000 miles after the engine rebuild. Several times I’ve been able to get the noise to rear its ugly head, put the transmission in neutral and shut the car off while coasting. The noise will still persist. Which means, the only thing I haven’t actually taken into consideration or troubleshot was:

5. The Rear Axle / Rear Driveshaft - it has to be something in this area. I’ve seriously replaced/inspected everything else on the drivetrain. I have every intention of pulling the rear axle cover off, draining the fluid, and inspecting the rear differential for damage, but I guess I’m a little stumped on what the heck could be causing this. I always envisioned that when a rear axle goes….well it goes. The rear axle currently doesn’t make any other weird sounds (no humming, whistling, etc.) so without this temporary noise, I wouldn’t never have envisioned there is anything even remotely wrong with the rear end. I changed the fluid at 125k miles with a full synthetic fluid, and there were never any problems up to this point.

Additionally, I always thought that the rear axles on these vehicles were relatively stout. Is this not the case?

Anyone ever seen/heard of this issue before?

If I find the problem, I’ll post an update.

Written from my phone, so I apologize if there are any grammar/spelling errors.

 

How are the rear axle U Joints?

 

Doc, thanks for the reply. When I had the (multiple) transfer cases in and out, I didn’t see any indication that the rear axle u joints were bad on the rear driveshaft. They seemed to move very freely.

Asking for my own curiosity; would a bad rear u joint cause a gear on gear type of grinding? Wouldn’t this be more of a vibration/thumping type of sound?

I pulled the cover off the rear axle today, and there was absolutely no indications or signs of wear. No metal shavings in the fluid, and no metal flakes (large or small) on the metallic drain plug. The wear pattern on the ring and pinion gear was extremely uniform, and I couldn’t find anything out of the ordinary. Except…

I did notice that the spider gears seemed very loose, and they made a noticeable amount of noise when I was rotating the axle with the wheels off the ground. I’ve attached several videos to this post for reference. I’m no expert when it comes to these gears, but they just seemed much more loose than I expected, and definitely noisier than the front axle after I rebuild it.

I didn’t go through all the trouble of removing the wheels and brake calipers/rotors but I did jack up my wife’s H3 Alpha (with 4.56’s) and spun the rear wheels. There was a lot more noise overall due to the tires and brakes still being on the car (and still fluid in the differential), but I didn’t hear distinctive ratchety type of sound that was apparent from the spider gears on my rig.

I’m in the process of checking the rear wheel bearings as well, but I’m hitting a roadblock as I cannot get the 8mm or 5/16” bolt out of the differential that holds the pin for the spider gears in place. Once I get that out I can check the wheel bearings and see if they’re still intact.

does anyone know if this amount of noise is normal for the spider gears?

 

U Joints can clatter or chirp, but often times sound different on or off the gas. I follow the old "easy stuff first." If the U Joints have significant miles on them, or you do not know how many, might be time.

Not sure about spider gear play or noise.

Is your rear a locker diff? If so, are the locking pins and ring worn?

 

Copy, I’ll take a closer look at the U-joints both front and back on both driveshafts. It’s becoming apparent that the previous owner of this car didn’t take good care of it…well at all, so I suspect the U-joints are original and have never been replaced.

My rear diff is not a locker; just the base model open differential.

After removing the spider gears and pin, the pin is definitely showing signs of wear. The hole and small bolt that hold the pin in place were extreeeeemly stretched/rounded, and even when the bolt was fully tightened in the carrier, the pin was still extremely loose and was able to move back and forth quite a bit. There appeared to be a little bit of scraping on one end of the pin, not sure where or what is causing it.

I got a new set of spider gears yesterday and will be installing them later today. Since I had to remove the axle shafts to check them anyways, I went ahead and decided to replace the wheel bearings and seals as well (152k miles, I figured it wouldn’t hurt replacing them).

Since I had the wheel bearings removed, I checked the rear axle ABS tone rings; no apparent damage here, and I never got an ABS light so the sensors/tone rings appear to be working properly.

I guess the only other thing on the drivetrain that I did not replace/tamper with (that I’m kicking myself for not thinking of sooner) is the front driveshaft CV joint; upon inspection, there was a small tear in the boot (but still plenty of grease in the joint). I figured once I install the new spider gears, if the noise persists, I’ll remove the front driveshaft, put the T-case in lock and drive around 2WD and see if the noise goes away.

 

Here's a video I recorded of my rig making noise when the driveshaft u-joints we bad. There was no play or binding or vibration or anything specifically pointing to the u joint, just this noise at low speed.



When I removed the old u joints I found the front was totally dry and the joint had been pulverizing the needle bearings. Shame on me for not noticing that at some point a prior owner had installed a greasable u joint on the front joint of the main driveshaft, but had left non-greasable everywhere else.

 

I wanted to drive the car for a few extra days to make sure the horrific noise did not come back, so I apologize for the delayed post, however after 4 days and counting, so far all is well.

1) I re-checked the U-joints on both the front and rear drive shafts, and all was well. Still plenty of grease, no sticking, no wear/looseness, etc. All looked well.

2) I went ahead and installed a new set of Spider Gears into the rear differential; while I was at it, I installed new rear wheel bearings and new bearing seals as well since I had the axle shafts out anyways. The axle shafts other than being a little darkened otherwise looked brand new, and the bearing area was not scored/rough. I inspected the two ABS tone rings internal to the axle and found they were not broken or damaged as far as I could tell (which checks since I never had an ABS light in this vehicle).

I cleaned up the inside of the differential with parts cleaner the best I could, dried it out, installed a new cover gasket, then filled the axle up with fresh 85W-140 differential fluid (I used 85W-140 since that is currently what I am running in my front axle, and I figured it probably wouldn't be a bad idea if the two fluids matched; previously I was running the OEM recommended 75W-90).

I noticed that the new spider gears had almost zero noise when spinning (compared to the video in my previous post, where the original gears made a lot of rattling noise). They are overall much tighter than my old set as well, which means the overall amount of backlash in the rear differential as a whole (not simply the Ring & Pinion gear) was much less after the new set of spider gears. Comparing the slop in the rear axle with the old gears compared to the new gears, there is much less slop in the rear axle than before.

3) I installed the rear driveshaft only, put the car in 4WD Lock and drove around. One way or another, the car is much more smoother than before; butt dynos are very subjective, but it seems like the car accelerates a little tiny bit quicker than before, and there is a bit less noise than before. Or maybe it's the simply placebo effect; either way, so far the hideous noise has not returned.

But this is only with the rear driveshaft installed. I currently have my front driveshaft out to install a new CV joint onto it (boot was slightly cracked from the old one) and have not yet tested the car with both driveshafts installed. However, since all I did was change the spider gears and remove the front drive shaft, since the noise has not come back yet, that means one of the following items was causing it:

i. The Spider Gears - since they were worn/loose/ratchety before, and the new ones make the rear differential much tighter as a whole. I don't know if it was the actual spider gears themselves that was ratcheting, or if maybe the overall looseness/loose backlash from the original worn spider gears was causing some type of weirdness to occur within the transfer case.

ii. The front driveshaft CV Joint - since when I removed the front driveshaft and drove without it, the noise has not come back. At a glance, despite a little tiny crack in the boot, the CV joint appeared to be tight and otherwise okay. But this is at a glance, and I'm definitely no expert into these things, so its possible that something else was going on inside the joint.

This was one of those frustrating repairs, where something only happens intermittently at the most random of times, because it makes it almost impossible to neck down without going on a wild goose chase. To be honest I really don't know which one of these (if either) was causing the noise. I have never heard of a worn out set of spider gears causing a car to make such a racket (especially when it happens only at slower speeds, and usually when coasting), especially when there was absolutely zero metal shavings in the differential oil, and the differential otherwise looked flawless from the inside. I have also never heard of a CV Joint causing this much noise IF there is still plenty of grease in the boot and the joint is otherwise undamaged/tight. Usually after a repair, you get an "ah-ha" moment where you absolutely nail down what is causing something to go wrong; in this case, I didn't get that feeling.

Either way, for the time being, at least while driving around in 2WD, the problem is solved. Once I get my front driveshaft re-installed, I'll see if it stays this way.

 

Putting a Bow Tie on this thread, but wanted to follow up for future people who run into this problem.

I replaced the CV joint on my front drive shaft, installed the driveshaft, put the car back in AWD, and the noise has not returned.

So it was either the Spider Gears, or the CV joint that was causing the issue. If I had to guess, I would say more than likely the spider gears, but I’m not 100% positive.

Out!