Oil change at rear axle

[The German]

From my other cars I´m used to change the oil of the rear axle every 60 to 80 K km (BMW). So I now looked into the Buick Chassis Service Manual and found nothing about periodically oil changes of the rear axle oil. - Is that okay ?

I would like to get your knowledge about that question :
- do you change that oil periodically ?
- if so, what periods are recommended ?
- if not, why should it not be changed after years and thousands of miles ?

The procedure of changing that oil is not shown or described in my manual, so this also is a question for me. Guess one has to open the gearhouse rear plate, right ?
And if so there will be a special seal which has to be peplaced, correct ? - Where to get such a seal ?
Last question : which oil should be used for a normal rear axle ?

Thanks in advance for every information you could give regarding these questions !

[EEE]

I think the life of the oil in the rear axle is quite long, it wouldn't surprise me if most of our old cars never have that changed. One reason could be that the differential doesn't go through the same heat cycles an engine does, so the oil doesn't degrade in the same way. The differential would only get really hot if there was no oil in the housing (I've tried that and ruined an axle; shot a bearing, and melted the brake hose at the attachment point on the top of the housing ).

To change the oil you'd have to take the 12 bolt cover off. I'd recommend you undo the bottom bolts first and work your way up. That way you get a controlled spill coming from the bottom once the cover starts getting lose. Maybe also work in a small screwdriver or similar to open the bottom section if it is stuck with the gasket.

To close it back up, you clean off the old gasket remnants and use RTV silicone to seal it (unless you can locate another gasket). Then open the plug on the side of the passenger side of the differential housing, it has a square head and takes a 1/4 inch socket holder I think it is.
Hmm, maybe start with losening that screw before you start taking the cover off, since you don't want to have an empty housing and not be able to open that bolt because it's stuck for some reason.

Once cover is back on and screw is out, just dump gear oil (it's like 80-90 or something like that in weight), probably around 2-3 quarts of it, and then PUT THE SCREW BACK IN! and that should be it.

Since Adam had that car before you, the gear oil has probably been changed 5-6 times so I wouldn't worry too much about it

[The German]

Thanks for your input, Kimson, especially for your tip to use RTV silicone to seal the gearhouse if I couldn´t find a fresh correct gasket !

As far as I know from several of your postings here you are used working at these big old cars and you have a lot of experiences. So if you never heard of oil changes at our differentials as a periodical necessity it´s probably an early GM "lifetime filling" of oil in these differentials. This could be the reason why there is nothing written about an oil change at the rear axle in the service manual.

Guess the best is to wait whether Adam will tell us something about my axle. If he would have changed the oil during the years he drove this car the axle might be okay for lots of miles, if not I first will screw out the filler hole plug and suck out some drops of oil to let it be examined somewhere. Perhaps the old oil still is good enough ; I only want to be sure it is !

And I hope we will get some more information if there is someone reading this thread who knows more exactly whether such an oil change is recommended or not and/or perhaps has own experiences with such an oil change.

[Smartin]

I never changed the oil in that particular differential, Rolf. It wouldn't hurt anything to change it, just to be safe.

[The German]

Thanks for your information, Adam !
If there will be no other inputs to this topic here I will do it as I said in my last post - first check the oil and then probably change it. - A winter work.

Guess after 38 years this old oil will have some water in it (only from the up and down of the athmospheres pressure which brings little amounts of humidity into the differential and following into the oil every year). Also some micro parts of metal or rust will be part of the oil now so it´s high time to change it.

I wonder whether I can find a gasket for the rear cover.

[Robroy]

Rolf, number one is to keep track of the oil level which is easy done by taken off the level plug and sticking down a screwdriver through the hole.
It doesn’t hurt to change the oil as well sometime during the cars lifetime

If I’m not mistaken there is difference in which oil to use depending if it’s a posi or not.
On a non-posi like mine I used SAE 80 GL5 oil according to the manual.

In case you have a twelve bolted cover on your car I have a brand new gasket that you can have for free, only shipping cost added

[The German]

Hey, that´s cool, Per, my car has the 12-bolt-cover !
I´ll send you an Email.

I looked for the oil level just after I had the car in my garage in winter of 2006/7; it was okay and the gearhouse kept dry, so that the oil level should be okay. My axle is not a positraction one, I will take the same gear oil as you did. My question regarding the oil was aimed more to get information whether we could use modern oil or whether we should search for specialities (may be some specifications are designed for newer materials which are used in our days now but perhaps not so good for the old gears).

Thanks for this info, Per !

[Robroy]

Hey Rolf, I got your email and will get back to you soon.

I’m glad that gasket finally will come to use. I took a chance when I ordered it believing I had a 12 bolt, but then it turned out I had a 10 bolt cover

[Gum,beest]

Hi guys
Same question as Rolf had but now for a posi
The owner manual states that Special lubricant GM partno.1051022 or equivalent has to be used and no interval
So please can anyone tell me what is the equivalent lubricant (SAE) and the change interval

Thanks

[The German]

My service manual says the same, Erik, but in the first chapter of the book there is a so called "Lubrication Chart" where they wrote for the positraction differential:
"Change lube at 1st oil change only. Maintain at Filler Opening to 1/4" below - flushing or seasonal change is NOT recommended. Use TL-SAE 90."
An interval for changing of the oil is not declared.

Only for the positraction differential they give a "Flushing Procedure" with 7 steps for the case that the wrong oil was added.
So I would do that if I would change the oil at a posi. - seems to be better for that axle and could make feeling safer with it !

[Gum,beest]

Thanks Rolf
I haven't got a "Lubrication Chart" in my owners manual
Can you scan the Lubrication Chart and the Flushing Procedure for me please
So if i understand you correctly i only need to change (flush) the oil if someone put in the incorrect oil
I have no indication of that and it still works like a charm (no noise what so ever)
It only came up when you asked about the change interval
In the winter i always change all my fluids but haven't done that for my differential last winter
So now it was a good time to ask you guys
And as Kimson stated the oil in our diffs are probably never been changed So i think i will discuss this with the oil guy (Castrol) on my workplace if there is an expiration date on TL-SAE 90 and if he can supply the oil for me if needed ( still dutch you know)

[EEE]

There's a bottle/tube of posi gear oil additive that you can purchase here at any local auto shop. If you have a posi rear you just dump that stuff in there first, and then fill up with the regular gear oil. I'll see if I have a bottle/tube in the garage I can take a picture of.

[The German]

Erik, here you can see the lubrication chart and the part with the info regarding the positraction rear axle and further the flushing procedure.
It´s from my 1971 Service Manual !
My advice : buy such a Service Manual; it´s worth the money !

[The German]

Erik, ... ...
My advice : buy such a Service Manual; it´s worth the money !

Erik, I had too little time when I wrote this last post and so I didn´t explain why I´m convinced that the service manual is a "must-have". It´s a very thick book and I only need perhaps less than 20% of all its content; may be only 10% were important for me but if I wouldn´t have had that information I´m sure I would have made mistakes or not found the correct way doing some inspection works because I was a "greenhorn" with all these things when I started with my Centurion. So this service manual saved me from bad experiences and saved my money also.
Next is that I could understand several discussions here and with other people at different meetings much better when reading the special parts in this book afterwards. Meanwhile my knowledge has grown a lot.- Okay, I´m still far away from being such a specialist as some of us here really are. But without that manual I would still be the bloody early beginner - that´s for sure !

You seem to start on a higher level compared to me but I´m sure that the service manual will have several specific good information for you also. It often is for sale at Ebay for around US$ 50 - so it´s not expensive compared to what you will get for ! It´s filled with diagrams and pictures, with descriptions and special data of any kind ! Most of them you probably will never need but the ones you want to have you could get very easy with that manual.

All in all : I really recommend to buy such an basic information book - in spite of the possibility that you can ask special questions here and would get all what you need ! Sometimes it might be necessary only a short look into the manual and you will have the answer - faster and more comfortable as to write a post for. I´m really lucky to have one !

[Gum,beest]

Rolf
No explanation necessary documentation is always a good starting point and a must have for a novice like me
I've got a owners manual that came with the car and i have bought a Haynes repair manual for fullsise GM cars incl. ours (can't find it though)
The manual you speek of is that the CD version or the book
I prefer the cd version and i have yet to buy that, as is the fisher body manual
Further more is this forum the place to get hands on experience from more experienced ethousiasts that sometimes differs from the book or is not mentioned in a book

[The German]

Erik, I´m with you. I have the book and also the Fisher Body Manual book. I had a manual on a CD but it doesn´t work anymore. On the other hand I prefer the books because you can place in some "post-it"-papers with further infos and you can take it to the car to compare the things etc. ... ! For me it´s easier than always being forced starting the PC and printing out what is needed.

[The German]

Hey Rolf, I got your email and will get back to you soon.
I’m glad that gasket finally will come to use. ... ...

Yesterday I changed the oil of my rear axle. The old oil was BLACK but it flew out fast and there was only little sump at the bottom of the inner gearhouse. The oil had no metal particles and the gear wheels looked clear and without wear. But I found that there were two scratches in the metal left side at the gearhouse right on the surface where the gasket shall ensure that there is no leak. I had no leak before but when I saw that I drove to the maintenance center of a near Opel car dealer and asked for what I should do. They said that it would be better instead of useing the paper gasket buying a special silicone which will close every little grap. So I followed their advice (which was Kimsons advice here also) and had no further problems. Only I now still have the gasket I got from you, Per, unused as a spare ; I placed it into the box of parts which I have for the car - perhaps it will come to what it´s made for some day ... .

I took SAE 80-W90 GL-5 oil.

Thanks to all who gave their advices !
Special thanks to you, Per, for sending me the gasket - sorry only that I couldn´t take it ! Seems as if sometimes things don´t want to be used ... .

[Robroy]

Feels good doesn’t it when you finally get things done that’s been on your list for while

Main thing is that you got the oil changed and that the seal is tight Rolf!