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Transmission Fluid and Differential Fluid Change


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#1 Seaway

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Posted 06 January 2017 - 09:51 AM

I am going to change the trans fluid and differential oil in my 1985 720 2WD 5 speed manual. From what I have gathered, I should use the following:

 

GL-4 75W90 for the transmission - 2.5 qts, roughly.

 

GL-5 for the differential - 1.5 qts.

 

 

Are these quantities correct?  What weight do I need for the differential? Can I use GL-4 in the differential?  I would like to be able to just buy a gallon of gear oil and use it for both, if possible.

 



#2 ]2eDeYe

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Posted 06 January 2017 - 10:02 AM

That is the correct qty. 

80/90 weight for both

 

You can use GL4 in the diff. 

 

Do not put GL5 in the trans. :)


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Whenever I think that I'm out of my mind for putting this much time and money into an old Datsun, all I have to do is look some of your threads to know that I'm not nearly as whack as you are.

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#3 Seaway

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Posted 06 January 2017 - 10:05 AM

That is the correct qty. 

80/90 weight for both

 

You can use GL4 in the diff. 

 

Do not put GL5 in the trans. :)

 

Perfect, I appreciate the response.  



#4 datzenmike

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Posted 06 January 2017 - 12:34 PM

GL4 only in transmission. 2 liters

 

GL5 only in the differential 1 liter. Sorry Steve GL4 will not provide enough protection.


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#5 Seaway

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Posted 06 January 2017 - 12:37 PM

Sounds good, thanks.  I was about to place an order for a gallon of GL-4, so I am glad you chimed in!



#6 RasselFlassel13

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Posted 06 January 2017 - 01:50 PM

Correct mi if I'm wrong but gl-5 in the transmission will not slow down the Sysco gear the time need to slow down in between shifts?

1984 Datsun 720 2wd Z24 dirft truck 1986 Nissan 720 4x4 Z24 daily(broken piston)


#7 ]2eDeYe

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Posted 06 January 2017 - 01:53 PM

Correct mi if I'm wrong but gl-5 in the transmission will not slow down the Sysco gear the time need to slow down in between shifts?

 

 

It will eat the syncros. 


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Whenever I think that I'm out of my mind for putting this much time and money into an old Datsun, all I have to do is look some of your threads to know that I'm not nearly as whack as you are.

You're going to skin a few knuckles, stand up too fast and bump your head, hunt around the floor for the nuts and bolts you dropped, invent a few new cuss words and when you're finished you'll say "That wasn't so hard after all!"


#8 datzenmike

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Posted 06 January 2017 - 02:14 PM

80w90 GL4 is the same thickness as 80w90 GL5 and would shift the same. However differentials need extra scuff protection on the tooth faces that transmissions do not. This anti scuff additive contains a sulphur compound (you may have noticed the smell when changing the oil?) that in GL4 is in an amount (about 4%) that does not bother the copper/brass.bronze synchronizer rings. GL-5 oil contains it in about 6% concentration, which is 50% stronger and will over time tarnish and erode the copper.

 

GL4 is more than enough protection. GL5 is not good for Datsun transmissions.

 

Even GL4 should be changed at the recommended intervals. About 5 years 30K miles


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#9 RasselFlassel13

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Posted 06 January 2017 - 02:23 PM

Really mi shop teacher just said you can't shift unless you double clutch which makes sense then

1984 Datsun 720 2wd Z24 dirft truck 1986 Nissan 720 4x4 Z24 daily(broken piston)


#10 datzenmike

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Posted 06 January 2017 - 02:39 PM

You do not need to double clutch. Tell your wood shop teacher he watched The Fast and The Furious too many times.

 


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#11 flatcat19

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Posted 06 January 2017 - 03:00 PM

YELLOW-SAFE GL-4.

Some GL-4s are not safe for the brass in Datsun transmissions.

Sta-Lube from Napa is a good bet.

You can't hang if your nuts haven't dropped...it's physics


#12 datzenmike

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Posted 06 January 2017 - 04:58 PM

 

Some GL-4s are not safe for the brass in Datsun transmissions.

 

 

I've heard this also. If this was 30 years ago you couldn't go wrong with GL4 rating. Today, you'd better read the label.


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#13 kelowg

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Posted 06 January 2017 - 07:19 PM

Royal purple is safe for syncors. Expensive but seems to work great in mine. Replaced 25% with lucas oil stabilizer and leaks



#14 datzenmike

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Posted 06 January 2017 - 07:46 PM

It leaks or because of the Lucas it leaks?

 

Synthetic oil is thin and very slippery. It will pass old or worn seals where thicker 80W90 won't. You can replace the seal and this often solves the problem.


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#15 Seaway

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Posted 09 January 2017 - 04:25 AM

I picked up a gallon of GL-4 only Sta-lube from Napa (they only had one gallon bottle, no quarts) and a quart of GL-5 for the differential.  It was about 15 degrees all weekend so I didn't make it over to my unheated garage to change it out.  Hope to get it done this week when the temps are supposed to get back up into the 50's.  Thanks for the replies.



#16 Draker

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Posted 09 January 2017 - 10:11 AM

Your transmission will thank you for the GL4 later! 


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#17 Seaway

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Posted 09 January 2017 - 10:31 AM

Your transmission will thank you for the GL4 later! 

 

I am interested to see what the fluid that is in the truck now looks like.  I can't imagine it is good.  I got the truck for $250 and it was in rough shape.  I have only put about 3000 miles on it in 9 months, but it has come back from the dead nicely.  There is a slight whine in the trans (I think that's where its from) at 50 mph and above and I am hoping new fluid will help it out.  I use it as an in town parts hauler and runs very well considering where it was when I got it.



#18 racerx

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Posted 09 January 2017 - 10:43 AM

One of the first thing I do when I get an old car is check all of the fluids and change when necessary.



#19 Seaway

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Posted 09 January 2017 - 11:15 AM

Me too, usually.  I was so surprised I was able to get this running and driving that the trans fluid slipped my mind.  It has had oil changes, a coolant flush and a brake fluid change.  I haven't changed the blinker fluid, but it's on the list.



#20 datzenmike

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Posted 09 January 2017 - 02:08 PM

30K miles is the usual change time so look at the mileage and imagine that the first owner may have done this. Second owners and successive ones don't want to sink money into a 'junker' and skip this.

 

Generally it will be thick (90w) and dark but clear honey color with a sulfurous smell. The drain bung has a magnet on the end that collects ferrous metal. A black paste is normal. Clean this off so you have something to gauge next oil change. 


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