Datsun 4 speed gear oil, GL4 or GL5 MT-1

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It's clutch time in the 240Z and I am looking for some opinions on modern gear oil in the old transmissions. I'm pretty sure I ruined the synchros in a 240SX running some Coastal GL5 for about a year. I should have done GL4 then and I'm wondering if the Z will be even more fragile. What are some recommendations for an old 4 speed, stick with GL4 or a GL5 MT-1 now days? GL5 MT-1 is definitely easier to find locally for me.

Thanks
 
There are dual-rated GL4/GL5 fluids in 75w90. Motul Gear 300 comes to mind. I found it to be an excellent fluid for year-round use. The VI of 222 is very impressive as well.
 
Yeah I'm aware of the dual rated stuff but was under the impression that even the dual rated stuff isnt as gentle on the brass as the MT-1. I was thinking the GL5 MT-1 was formulated to fix the problems of running GL5 in a GL4 specced trans.

Interesting article for old VWs on the subject:
http://www.ratwell.com/technical/GearOil.html#mt1
 
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Red Line's 75w90 NS is also recommended for MT-1. Not sure if that is appropriate for your trans, though.
 
I think GL-5 MT-1 is for unsynchronized transmissions generally found in big trucks. You might want to look around and find the exacting applications for this fluid rating.
 
I think I'll go with either Stalube GL4 at Napa or Redline MT-90, whatever I can get my hands on fastest before Friday which is clutch day.

Thanks for the recommendations everyone!
 
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Sta Lube from Napa specs:
Applications Auto, truck and bus standard transmissions and differentials requiring API/GL-3 and GL-4 oils
Unit Package Description 1 Gallon Bottle
Brand Sta-Lube
Generic Description 1 Multi Purpose Gear Oil SAE 85W90
Net Fill 1 Gal
UPC Code 072213242393
Unit Dimensions 10.63H x 4.75W x 6D in
Units Per Case 4
Case Dimensions 11.25H x 11.25W x 13.5D in
Cases Per Pallet 55
Case Weight 33 lbs
I 2 of 5 Code 30072213242394
Appearance Amber Liquid
Odor Mild
Flashpoint >302°F
Flammability Non-flammable
Specific Gravity 0.89 to 0.91
Plastic Safe Yes
SAE Grade 85W90
ISO Viscosity Grade 220
 
I run Redline MT-90 in my 71 240Z transmission (5 spd from 280Z).
Generic 80W-90 in the differential (4.11 from 86 Pathfinder)
 
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I would definitely use a GL-4 only oil although my experience is with older BMWs and VWs. Red Line MTL has worked great for me. I have also used something like Sta-lube GL-4 successfully in VW transmissions.

GL5 can either eat up the old syncros or just be too slippery for the syncros to work properly.
 
I went with a gallon of 85w90 Sta Lube GL4 from Napa for $27 dollars. This should be great for the low mileage it gets driven (1000 miles a year is the est.)but the autox's in 90 degree heat. I plan on putting it in the rear end as well (open diff)

I'll give a review after some miles.

Thanks guys!
 
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Originally Posted By: artificialist
Typically the rear diff would need GL-5, and it would probably be SAE90.

So be careful, and check your manual.


This car is 40 years old and I'm pretty sure GL-5 wasn't standard in just about anything Japanese until well after that.
 
Originally Posted By: jayg
Originally Posted By: artificialist
Typically the rear diff would need GL-5, and it would probably be SAE90.

So be careful, and check your manual.


This car is 40 years old and I'm pretty sure GL-5 wasn't standard in just about anything Japanese until well after that.

Not necessarily. My '72 Corolla specs GL-5 in the differential and GL-4 in the transmission. That was pretty standard.
 
Originally Posted By: 72te27
Originally Posted By: jayg
Originally Posted By: artificialist
Typically the rear diff would need GL-5, and it would probably be SAE90.

So be careful, and check your manual.


This car is 40 years old and I'm pretty sure GL-5 wasn't standard in just about anything Japanese until well after that.

Not necessarily. My '72 Corolla specs GL-5 in the differential and GL-4 in the transmission. That was pretty standard.


+1. This car definitely takes GL-5 in the differential and GL-4 in the transmission.
 
BEWARE OF SOME GEAR OILS CLAIMING compatibility of GL5 and GL4 together. If you have yellow metals in your gearbox ONLY use a gear oil that is GL4.


Who else can provide a list of "GL 4 ONLY" SPECIFIC brands we can get fairly easily at chain auto parts stores?
 
Redline MT-90 or whatever the Amsoil 75w90 MTF is. $15 a quart but you don't have to go to all ends of the earth to find it, and its great stuff.
 
So far the $26 bucks of 85w90 GL4 Stalube is shifting beautifully in this car. The rear diff fluid looked new so I left it.
 
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