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Manual Transmission Gear Oil - 85 Nissan 720


gryffinwings

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There have been mixed information regarding if it's truly safe for brass. I went down that rabbit hole and there were some responses from the manufacture that claimed it was safe. But really, for $20 you can get GL4 from napa. Sta-lube gl4.

MAN I WAS JUST ABOUT TO ASK ABOUT THE STA LUBE! 26 bucks on amazon. It's gl 4. And a gallon, according to the fsm, will be enough for the transmission and transfer case.
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Transfer case and diff do not require GL4.

I double checked the manual, gl4 for transfer and transmission. Gl5 for diffs. And weirdly enough, dexron for power steering. I have to refill the power steering after I install the new line. Guess I'll return the quart of power steering fluid I bought today
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There are no syncros in the transfer case? Why GL4?

 

It's not just the brass synchros. Differential gears transmit power differently that transmissions and transfer cases. My guess is differential geras transmit force through a 90 degree corner. The gear teeth need more sulphur anti scuff additive protection, about 6%. Transmissions are axial, with the input and output in the same plane less anti scuff protection, about 4%. You might think 2% difference? How is it that different? Well if you think about it 6% is 50% more than 4%.  

 

The sulphur additives form a molecular bond with the steel gear teeth to keep them from steel to steel contact. When GL5 is used on brass it bonds to the copper and forms a super hard layer that cannot be supported by the soft alloy beneath it. The top layer cracks and flakes off and the process repeats slowly eroding the brass rings.  

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  • 4 years later...

IF (the little word with the BIG meaning), if the seals in the transmission, diff, or ? are new a synthetic oil probably won't be any problem. But, if all the seals in the transmission, diff, or ? are  not new, then the synthetic oil will most likely leak.

 

Don

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Ok. Yeah I know nothing about what the previous owner did to the truck, but I am going to assume nothing, as far as new seals. Was just making sure before I go and buy oils for the transmission, transfer, and diff. So probably stick with a Sta-lube or something similar.

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  • 2 years later...

The fill bung is about half way up the side of the transmission, usually on the left or driver's side. In rare cases it's on the right just behind the reverse light switch.

 

If you don't know when the gear oil was changed last it's better to just change it. 80w GL-4 NOT GL-5!!! It takes 2 liters which is just over 2 US qts. Good for 30,000 miles but few owners keep to this so this is the best reason for changing it now.

 

The procedure is to remove the drain bung on the bottom usually with the square end of a 1/2" ratchet. The bung has a magnet on it that collects ferrous powder from wear. A black/gray paste is normal. Wipe this clean so next change you have the wear from this change. Secure the drain bung and remove the fill bung. I use a dollar store kitchen funnel and a three foot length of garden hose.  Run the hose down from the engine compartment and into the fill hole. When you can't put more in... it's full.

 

 

 

If checking, you should be able to dip your little finger in the oil. 

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I change mine yearly.I use Red line MT-90.I just changed mine back in May. I paid 20.79 for each quart.It takes a hair less than 2 quarts.Mine was full.But it was dirty.I only put about 7500 miles on it.I buy mine from Ebay.I use the Harbor Freight 10 dollar pump.You will need to put in a oil container with a big opening cause,the Redline has little openings in there containers And the pump end won't stay in the Red line containers.Everyone has there choice of gear oil they use.I use a 1/2 inch drive to get the drain plug off.You will need to tap it with a hammer.The fill plug takes a wrench.It is a square plug.I had no metal in the magnet drain plug cause I dont grind my gears.The reason I change my oil often cause I know how hard these transmissions are to find and no one wants to rebuild.When I changed it,it was almost 2 quarts.Every so often,check it.You can get a piece of card board a little less thin than the opening,and stick it in there a little at a time till the oil gets on the card board to tell how much is in there.Put the new oil in there till it starts coming out.Write the date and mileage down to keep records of it.

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Edited by Thomas Perkins
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Can anyone tell me how much oil I need to replace the front and rear differential on my ‘85 720? I’ve never done a differential oil replacement so any tips would be greatly appreciated too. I’m changing gearbox oil today with Valvoline conventional 80-90. It’s the only GL4 I found at my local auto parts store, hoping the viscosity works with what I’m doing. Photos attached for reference.

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On 7/16/2023 at 5:35 PM, Meesh said:

Can anyone tell me how much oil I need to replace the front and rear differential on my ‘85 720? I’ve never done a differential oil replacement so any tips would be greatly appreciated too. I’m changing gearbox oil today with Valvoline conventional 80-90. It’s the only GL4 I found at my local auto parts store, hoping the viscosity works with what I’m doing. Photos attached for reference.

image.jpg

image.jpg

 

 

Viscosity is good. 

The diffs you just drain and fill, nothing special that I can think of. 

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On 7/16/2023 at 5:35 PM, Meesh said:

Can anyone tell me how much oil I need to replace the front and rear differential on my ‘85 720? I’ve never done a differential oil replacement so any tips would be greatly appreciated too. I’m changing gearbox oil today with Valvoline conventional 80-90. It’s the only GL4 I found at my local auto parts store, hoping the viscosity works with what I’m doing. Photos attached for reference.

image.jpg

image.jpg

 

Can't see where it says it's GL-4 on the bottle. GL-5 has 50% more anti scuff additives in it than transmission GL-4. The anti scuff additives are sulphur based and break down and become acidic which is fine in a differential which contains no copper/brass parts but is bad for brass synchros in transmissions. Any gear oil that says it's good for transmissions and differentials is somewhat suspect.

 

I believe all synthetic transmission oils come from the same stock and maker. A dye is added for the seller.

 

Front R-180 differential ........... 1 liter 2 1/8 US pints.

 

Rear H-190 differential.............. 1.25 liter 2 5/8 US pints

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