[68Catalina68]

Okay I have a 68 or 69 GTO rerun, 3.55 gear ratio with limited slip. What gear oil should I use and do I need an additive?

Picture shows when I was told to use previously.

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[Schurkey]

Should be fine. The "limited slip" additive is already in there. Possible that your differential would need more, but there's no point in buying the additive if you don't need it.

[steve25]

Both of those you have in the picture have the needed additive in it.
I hope your axle seals are good because with synthetic fluid your Brake shoes will know if the seals are good real fast!

[68Catalina68]

Originally Posted by steve25

Both of those you have in the picture have the needed additive in it.
I hope your axle seals are good because with synthetic fluid your Brake shoes will know if the seals are good real fast!

Great, now I'm worried it's an old year-end that probably has never been serviced. I saw that I had a few drops on the ground so I decided to replace the gasket but now I'm worried about the fluid I picked.

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[ANDYA]

I'm about to do the same job on the rear of my 65 GTO. Going with 80w-90 or 75w-90 conventional oil and a bottle of GM additive to be sure.

[68Catalina68]

Originally Posted by ANDYA

I'm about to do the same job on the rear of my 65 GTO. Going with 80w-90 or 75w-90 conventional oil and a bottle of GM additive to be sure.

I found these in my garage, not sure how old lol



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[Half-Inch Stud]

Redline "Shockproof" synthetic for all yuur valuable Rear Diff needs.

[68Catalina68]

Originally Posted by Half-Inch Stud

Redline "Shockproof" synthetic for all yuur valuable Rear Diff needs.

I guess you didn't read the rest of the thread, I'm worried about my old seals leaking if I use synthetic.

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[ANDYA]

When our cars were brand new there was no such thing as synthetic oil, just plain old conventional oil. The shop manual states that rear differential oil only needs to be changed if the rear end is overhauled. In most cases that gear oil stayed in there years if not decades. I have a 67 Firebird that I got from the original owner who was a good friend of mine. I am 100% positive the gear oil has never been changed. There are no leaks and I have never had a problem where I felt it necessary to change the oil. I can see synthetic oil in an engine but IMHO is not that important in a rear. If your worried about leaks just use conventional oil and don't worry about it.

[geeteeohguy]

Originally Posted by ANDYA

When our cars were brand new there was no such thing as synthetic oil, just plain old conventional oil. The shop manual states that rear differential oil only needs to be changed if the rear end is overhauled. In most cases that gear oil stayed in there years if not decades. I have a 67 Firebird that I got from the original owner who was a good friend of mine. I am 100% positive the gear oil has never been changed. There are no leaks and I have never had a problem where I felt it necessary to change the oil. I can see synthetic oil in an engine but IMHO is not that important in a rear. If your worried about leaks just use conventional oil and don't worry about it.

I agree. I drained the original gear oil out of my '67 GTO at about 220,000 miles when I did a pinion seal replacement. The oil and gears looked like new. For a limited slip rear, in all my GTO's for the past 40+ years I have always used mineral based 75/90 with a bottle of the additive and have never had an issue. Many cars, many years, many, many miles.

[i82much]

i thought the BOP 8.2’s had a cone style and did not need the friction modifier? had my truetrac so long now i may have forgotten!!!!

[68Catalina68]

Originally Posted by i82much

i thought the BOP 8.2’s had a cone style and did not need the friction modifier? had my truetrac so long now i may have forgotten!!!!

That's what I also just read, this shouldn't be this hard lol

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[propuckstopper]

Originally Posted by steve25

Both of those you have in the picture have the needed additive in it.
I hope your axle seals are good because with synthetic fluid your Brake shoes will know if the seals are good real fast!

This one confuses me. I think the implication here is that in the event you have bad axle seals, the synthetic fluid will find its way to the brake shoes. That part is entirely correct.

The truth is, if you genuinely have bad axle seals, conventional fluid will get through to the brake shoes through the same area of the compromised seal just the same as the synthetic fluid.

I am not going to get into a debate about how much faster synthetic fluid will go through a compromised seal than a conventional fluid. If your axle seals are not good, differential fluid will find its way to the shoes nonetheless. Change your seals.

Wet brake shoes are not good period. A brake shoe soaked in synthetic oil is no more slippery than one soaked in conventional oil.

[68Catalina68]

I'm a if it's not broke don't fix it kind of a guy. Seals aren't leaking now with conventional so that's what I'm gonna use. I didn't put any additive in it because I read the cones did not require it.

now I'm thinking why would the Factory attach a tag to the outsidefor for no reason at all then to tell everyone it's a limited slip differential?

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[chuckies76ta]

Moser rearend from manufacture says no synthetic oil. Conventional oil only with friction modifier. 80w-90

Charles

[i82much]

Originally Posted by 68Catalina68

now I'm thinking why would the Factory attach a tag to the outsidefor for no reason at all then to tell everyone it's a limited slip differential?

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maybe to let the guy in the assembly line know which axle to put in which car?

[Half-Inch Stud]

80-90WT go fir it...generates metallic powder film on all non-contact surfaces (like right away), for a reason. Get full of hard-metal powders for improved gear and bearing grind. Runs good-n-hot at the pinion bearing during and after a highway drive.

Redline Shockproof Synthetic look NEW after 150,000 miles, no metallic coating on surfaces.

Just providing information, so you all know, and... enjoy your choice.


My GTO Dana60 leaks at the original Strange Pinion Seal with both types of oil. A bit annoying. Both original Strange Wheel Bearing Seals nice and dry. Rear Discs doing quite well.