I had a u-joint and seal replaced in the rear end about 4 months ago. The garage replaced the lost fluid with their regular gear oil, the receipt just says "shop supplies". I think they used 80W-90, but don't know if it was GL-5 and they did not put in any additives. Everything seemed fine until the weather got cold. At -10 celcius there's a fairly loud noise, but at milder temperatures the noise is quite faint. It's not quite a howl or whine, and not really a grinding sound. More like a really rough humming. It's quite loud accelerating, and winds down as soon as you take your foot off the gas and I don't feel any shaking or vibration. Once I've driven enough for everything to be warmed up the noise gets a lot quieter. Seems like maybe the oil is too thick when it's cold? I don't really know if I have a locking differential, a regular diff or limited slip. The garage says it's a regular diff, but my RPO code is G80 and I think it's a locking diff. I don't want to bring the Blazer back to the garage and pay them more money, to fix something that might be caused by them using the wrong fluid. I'm wondering if putting in some additive would solve the noise problem, or will I have to flush out the rear end and replace the fluid? Worse yet, could this be an entirely new problem? I greatly appreciate whatever help with this anyone can provide. Thanks.

 

I’m replying to myself because I couldn’t figure out how to edit my post.
I went ahead with getting the lubricant in the rear end changed, hoping that the noise would go away. Bought the oil at a dealer to make sure I got the right stuff. Even with my VIN they couldn’t confirm that the rear end is limited slip, but they told me to go ahead and use the additive because it won’t hurt anything. They also suggested that synthetic gear oil is a bit lighter and better for cold weather. I had the work done at the garage today. Turns out that once the diff cover is off, it is limited slip which is good to know.
Sadly, the noise is still there and the garage says I need the left rear bearing, plus because the bearing will be wearing a groove in the axle I’ll have to replace the axle too. They told me that in cold weather the gear oil gets too heavy to spray along the axle and lubricate the bearing. Could driving around for 4 months without limited slip additive in the diff be why the gear oil got too thick to lubricate and is that why the bearing has failed? It doesn’t make sense to me that I never experienced the diff oil being too heavy to lubricate until this year. Either way I need to get it fixed, but am I now paying for a repair because the garage messed up, or is this normal wear and tear?
It seems like every time I walk into the garage the mechanic’s eyes go ching-ching as he starts counting how much money he can make from me. Since I’m a woman I feel like I’m at a real disadvantage. I have no way of gauging how long this extra work should take or what it should cost. It would help me a lot to know if anybody else thinks the mechanic might be making excuses to cover his butt for not using additive in the first place. Also, how many hours should the job take?
Since I can’t do the work myself I probably should not have posted to this category, but I’m hoping to learn as much as I can. I am really glad to have found this site. I’ve already learned a lot of information from those of you who generously share your knowledge. Thanks again.

 

As I said in my last post I replaced the 80-90 gear oil with synthetic oil plus the additive I bought. The garage charged me 150 bucks for the labour (and I had to return it to them because it was leaking, they had missed 1/2" of the silicone gasket when they put it back together). Anyway, on my way to work I thought I felt it clunk twice which scared me, so I brought it back to the garage. They said I would have to replace all of the bearings in the rear end, and he wanted to replace both axles too. I said that when they took the truck apart I wanted them to call me if the axles were bad before they did any more work, because I did not want to spend an additional 1500 bucks or more for axles. They did all the bearings, and I've just given them another grand for that. But, when I picked up the truck (the battery was dead because they had left the hatch open) they said there was no guarantee on the two wheel bearings because they don't know how long they'll last, since there is some wear on the axles. If that's true, I don't quite get why they never called me about that when they took them out.

Is there anyone out there who can tell me if these bearings went because when they did the u-joint and seal in September the mechanic put in regular 80-90 gear oil instead of synthetic, or because they did not put any additive in. My Blazer has limited slip and when I went through my receipts I see that maybe they should have known that, because they replaced the diff fluid a couple of years back. What's done is done, but it's cost me a lot of money. I need to know if if all of this trouble is coincidental, or am I paying my garage to make mistakes and then to fix them? I'm just looking for an unbiased opinion, should I still be trusting these guys?

i'll be grateful for any advice I get. Thanks.

 

If they put in the wrong fluid they should be responcible for any damaged done but proving it would be difficult.Usualy the loud humming would be a sign that the axel bearings are bad.
Should you trust the 1 mechanic you took your vehicle to I would say no.Find one who is more reputable and get references.
Welcome to the forum.

 

Blazers only came with an open differential or the g80 (which is a locker, not a limited slip). If you have the g80 code, you have the locker that does NOT require additive. I agree that the cause would most likely be the axle bearings. Just my .02

edit: or maybe they installed your ujoints/driveshaft wrong (if that's even possible?)

 

Yes it is possible. The propeller shaft can be out of phase if not installed the way it came out. But that causes more of a "buzz""shudder" or "vibration". Not sure it matches the symptoms she is describing.

But that shouldn't matter at all based off of temperature.

 

as mentioned above the g80 is only a locker and not limited slip, so the 80-90 is correct. but even if your axle bearings are shot and eating into your axle, as long as it didnt eat to the point of its going to snap, witch i HIGHLY doubt. They make repair bearings, that moves the new bearing off the worn spot on the axle shafts. so you dont have to replace the axle shafts. i installed them on my jimmy. and due to the fact of where the fill plug is on the axle, as long as the axle is full, there should be fluid all the way to the end of the axles at all times, regaurdless of the temp.
Also if your worried about a mechanic taking advantage of you. try and take it to a different mechanic and just tell them what wrong/the symptoms and not what the other mechanic said and see if they say the same thing is worng.

 

Thank you all for your replies. I'm shopping around for a new garage. It looks like garages who are part of the Tech-Net Professional Auto Service group offers a 24 month warranty on repairs, so I'm going to try and find a shop that's fairly close to me. We had a severe cold spell here and i'm happy to say that the diff hasn't been making noise. I'm hoping the wear on the axles won't cause a problem with the rear wheel bearings, at least until spring. When I start hearing noise from them I will follow Blade_24k's advice about using repair bearings instead of replacing the axles. Thanks again to everyone for the advice. Take care, Tracer.