need advice on swapping out rear end

[GRB101]

Hello all,
My '07 Envoy 4.2 4wd w/ 3.42 rear end has developed a "roar", pretty much overnight that sounds like I'm driving on winter studded tires. There does not seem to be any vibration. The noise is in the driveline and changes with the speed of the truck and not the engine. I have looked for rubs and friction points, I have rotated the tires. I have checked the fluid in the transfer case and the differential. Both front hubs are fairly new and the noise does not change when turning either direction. I recently replaced the pinion seal, and it is possible that I over-tightened the pinion nut. I did that repair about 800 miles ago, in May. There is no "clunk" going in or out of gear and there is no play in the rear driveshaft. There does not seem to be any leakage from the axle seals, but I wouldn't know the difference between an axle bearing going bad, or the sound a diff makes when something is bad there, and either way, at this point, I am considering replacing the rear end altogether because I just don't know what else to do or check.
unless someone has some other advice, my next problem is that the only junk yard near me is a "pick&pull". They have several Envoys/Trailblazers of various years to pick from, but I would need to know A: what I am pulling, and B: What is the best all around rear end (if I have a choice). I won't be towing more than 2,000 lbs and I do mostly hwy driving. I don't do much off roading, but i don't want to short change myself in that area - I want a capable truck.

 

[Brian K]

Have you checked your U-Joints? Mine went bad almost overnight. The Envoy felt really weird when driving it. I took it to a shop because I couldn't figure out what was wrong. Pricey though but now i have U-joints that I can lube. I changed the front drive shaft U-joint my self since it turns too.

 

[Mooseman]

What about the front diff?

I would put the truck on jack stands on all four corners, put transfer case in neutral and I would rotate each wheel and listen for the noise.

Have you opened the rear diff and examine the fluid? That would be telling of what is going on.

 

[flyboy2610]

If you do swap out the rear diff make sure you get one that has the same gear ratio as the front diff. Otherwise the first time you put it in 4WD you will not have a pleasant experience.

 

[GRB101]

Thank you Flyboy, I didn’t know that….you saved me from a huge mistake (I thought I could put in whatever I wanted)

 

[GRB101]

Does anyone know the RPO code for my 3.42 or have a reference where I can look it up? …. I’m gonna need that at the junkyard.

Also …would over tightening the pinion nut lead to this kind of problem or should I look elsewhere? (Before I go crawling around in the dirt…)

I replaced the diff fluid when I did the pinion seal in May and the little bit I drained off the top last night seemed ok…

The universal joints are all tight ( but being able to lube them myself would be nice so I'll look into that

 

[GRB101]

I’ll have to check the front diff…I changed the fluid, also in May, when I did a cv axle
(it’s been a busy year keeping up with this truck… I’ve also replaced a hub and the radiator…it’s been a bad run lately )

 

[azswiss]

Does anyone know the RPO code for my 3.42 or have a reference where I can look it up? …. I’m gonna need that at the junkyard.

RPO Master List attached.

 

[budwich]

OP, seems like a lot of potential work to do a rear end without confirming that the problem. As mooseman suggested, put it up on stands and carefully listen while turning wheels. My guess is you have bad front wheel hubs.
Having said that when you did your work on the rear end, did anything look "ugly" at the time?

 

[Mooseman]

Gearing RPO codes

Even though the front hubs are "fairly new", new doesn't mean good. I've had some name brand hubs self destruct within months. And the proliferation of CCC (cheap Chinese crap) parts, it wouldn't surprise me if a hub has already died again.

Just throwing parts at a problem will not necessarily fix it. Diagnose it first.

 

[GRB101]

Thank you for the code list…I will try to keep this one!

I raised the truck on all four and found a squeak or a whine up at the front of the front differential…right near the valve body for the transmission.

One of the front CV axles has a click…(bummer because I will have to fix that and I don’t think it’s the problem.

I don’t know what I’m looking for here and I certainly don’t know what the squeak indicates. There is a tiny amount of vertical play in the front driveshaft at the front differential…no side iti side…even when I spin it….it was not in 4wd

Thank you all for the help so far. I think I have eliminated the rear end as the problem…no indication that there are any bad axle bearings and the differential sounds and looks good to me… but I’m no expert and I know very little about the drive line…I’m learning.

 

[GRB101]

I ordered my Cardone CV axle from Amazon. It will be here Tuesday instead of Thursday from Rock Auto and $5 cheaper.

 

[Mooseman]

Do you happen to leave the transfer case selector in Auto all the time? If so, you may have worn the front driveshaft U-joints as they would be spinning all the time. Same for the front differential.

 

[TJBaker57]

Actually the front driveshaft spins all the time regardless of 4WD or not.

The PID is $3162 for the front propshaft. $3163 is the rear propshaft speed.

In 2Hi the front driveshaft spins slower but still spins due to the internal frictions of the transfer case forward clutch plates.

 

[GRB101]

No, I rarely take it out of 2wd… I left it in auto for awhile and simply decided it wasn’t worth the wear…I put it in 4wd from time to time just to check things out. The squeak sounds like a dry seal … not friction oriented or mechanical.

 

[GRB101]

The front driveshaft u-joints look difficult to access, but I shook them and found no play

 

[Mooseman]

For the squeak, did you check the brake dust shields? A common issue is that they will rust or bend and rub on the rotor. I`ve also had squeaking from the rear brakes with the shims rubbing. Also check the rear parking brakes. Checking all four wheels off the ground should help pinpoint the noise.

 

[GRB101]

i mentioned where I heard the "squeak"

unfortunately I had to take on an "out of town project" so I'm not able to install the CV axle. I will update when I get home and do that.

Thank you for all your help!

 

[Mooseman]

I raised the truck on all four and found a squeak or a whine up at the front of the front differential…right near the valve body for the transmission.

I missed this post. Not sure what you are calling "the valve body for the transmission" as that is inside the transmission in the pan. Or do you mean the transmission cooler in the radiator? If the front diff is indeed making noise, I would open the fill plug and try to look inside. A borescope would be useful here.

Hopefully it is an axle shaft as those should be dead silent. If the new axle shaft doesn't fix it, before ripping the front diff out, which is a difficult job, I would pull both axles and the driveshaft and check for the noise. Spin the diff's pinion to see if the noise is there.

If it's confirmed, you have a couple of options. Replace the diff however it's a difficult job, which you would have to do twice if pulling one from the Pick-n-pull as well. The other option would be to remove both axles and the driveshaft and use it as a 2WD only. Since you mentioned that you never take it out of 2WD, this could be an option for you. The wheel hubs are designed to run without axles in them as they are also used with 2WD models.

 

[GRB101]

Thank you. This is very helpful…is it difficult to remove the front driveshaft or is it just a matter of taking apart the u joint?

 

[Mooseman]

I've done it multiple times to replace the seal in the transfer case. It's just a matter of removing the strap bolts on the pinion, prying the u-joint out of the pinion and navigating the diveshaft past the diff to slide it off the transfer case shaft and tilt it to remove it.

 

[Brian K]

Watch some Youtube videos on how to do it. As Mooseman says, it is pretty easy. After disconnecting the front U-joint bearing cap straps, it should lift up and toward the battery and slide forward enough to allow the rear splined connections at the transfer case to move forward. You might need to use a hammer to slide it forward off the spline. Slide it toward the front of the vehicle and it will drop down. Be careful once the front U-joint caps are loose so that you keep the needle bearing caps on. I did mine while the vehicle is up on ramps.