jb78L-82

I have been using Mobil 1 75W-90 for 25 years now with zero issues-no problem with engine braking, synchros not working correctly etc BUT have decided now that I am upping the HP substantially on the engine-100+ more HP-why tempt fate with a GL-5 and will be switching to Redline GL-4 before the new engine install or shortly after. I don't want any more big projects like a head and cam change morphing into a complete engine rebuild!!

Mike Ward

This is also an otherwise dead three year old thread that got dug up for unrelated reasons.

rays699

I GOT 6 QT. FROM AMAZON FOR MY 69 VETTE

pacecar620

. . . YET. Mobil-1 motor oil does not have the EP additives that protect gear tooth faces.

Jason Staley

I'm using Redline's MT-90 75W90 GL-4 Gear Oil that they recommend for manual transmissions. This oil is great, and the shifts are SOOOO much smoother than any gear oil I have tried before. Little pricey, but absolutely great stuff to use.

ctuinstra

After reading this entire post, I've decided to go with your advice and use the Redline also. I might use the MTL which is nothing more than a slightly lighter weight. I'm pretty convinced this is the right way to go.

Eddie Van Vette

Restoring my 1979 C3,350,I have the Borg Warner trans out along with the engine, Cleaning up both, Wondering what oil to use in the transmission, debate is ATF Or 85W90 gear oil,drained the trans, gear oil was the oil in it, I suppose this is the proper type to refill, I am waiting for a shop manual to confirm.

hugie82

Ford was big on the ATF in their transmissions. I suppose it was to gain an extra 2 hp and make the EPA happier with 1/2 MPG but I've always used the 85/90w gear oil. As long as you keep the level correct and change it every 10,000 miles of hard driving, you should have many miles of fun without problems.

Sayfoo

Just a couple of thoughts here:
Just because a specific lube was required 30-40 yrs ago doesn't mean it's the best now. Also, doesn't mean it's not good now. Just means it was the best compromise lube for the whole country.
Where you live--temperature--can have a major impact on your car. If you live in Minnesota, and you use gear lube and your trans is hard to shift when cold, it makes sense to use a lighter weight lube. I've found this to be true even in Southern Calif. when the temp drops below 50 deg.
How you use your car makes a big difference also. If you're tracking your car and your gear box is thoroughly warmed up, you have a different situation then just running your car for a few miles in cold weather.
I use the thinnest/thickest fluid/oil/lube that works the best. If you notice a difference/problem between hot and cold performance, go thinner.

TO_Vette

I'm planning to perform an oil change on my 1981 vehicle, which has a manual 4-speed transmission. I've been browsing through the comments here and synthetic oil seems like a good option, although it's a bit perplexing.

Firstly, I don't race my vehicle; I mainly drive it around Southern California so it doesn't experience extreme heat. I'm looking for a suitable oil to maintain a quiet and smooth performance since it's primarily a weekend driver.

Let's say I decide to go with a Mobil 1 product. I've noticed they have a 75W-140 and a 75W-90 option. Can I use the same oil for both the transmission and the rear-end, or should I opt for a heavier oil for the rear-end? Additionally, do I need to use any additives?

Thank you in advance for your assistance.

ddawson

Just use a quality 80W-90 Conventional GL-4 Gear Oil.
I use Driven https://drivenracingoil.com/i-304977...-gear-oil.html

TO_Vette

Ok, but that doesn't answer the question.

pacecar620

My '78 is an automatic, so transmission lube is already determined by Chevrolet. It's just a matter of choosing a reputable brand. As for the rear gears, I will defer to the recommendation by Chevrolet for the Corvette Positraction and use 80W-90. My choice is Amsoil Severe Gear 80W-90. Amsoil claims that their fluid does not require the addition of additional friction modifier. Amsoil does post the following disclaimer in their catalog: "AMSOIL synthetic gear lubes do not require the use of the (Slip Lock) additive. However, not all differentials respond the same and if chatter is noticed, the addition of AMSOIL Slip Lock will eliminate it."
Hope that's somewhat of a help.

rmrtrex

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I would stick to GM products. This is for diff. Remember with these cars patience is a virtue. LOL.

cottoneg

When I put in my new clutch, I used Redline this time. It was much thinner than the 75W-90 I used to use.

TO_Vette

Quick question on an older response of yours.
If I understand, you are using Mobil 1 75W-90 for your manual transaction.
What are you using in your rear end? The same?

I'm looking at replacing fluids in both my Manual 4 speed transmission and the rearend. Thanks in advance.

MelWff

Unless you have a noisy rear end, use the 75W90 conventional gear oil for both providing the bottle says for limited slip differentials. Valvoline is an example.

TO_Vette

Noisy! The car is old and everything noisy so what is too noisy.

So you don't recommend a synthetic like Mobil 1?

MelWff

Correct, conventional fluid. The rear would make noise when applying and releasing the gas pedal, a distinct whining sound.

TO_Vette

No noises like that. To ask one more question, what do you run in the manual transmission?