OK, I understand the importance of using GL-4 vs GL=-5 gear oil in the Muncie manual four speed transmission found in my 1968 GTO...protection of the yellow metals, right? But...how about the rear Safe-T-Track (posi) differential? Paralysis by Analysis is beginning to set in...I have read that GL-4 is not appropriate for the rear, rather GL-5 should be used. I'm wondering is GL-5 was even around the scene 50 years ago? The factory service manuals I have make no such reference to GL-3, GL-4 or GL-5. Seems to me GL-4 should offer the required protection (with an anti slip additive) Very interested to read everyone's thoughts on the subject. Thank you in advance!
GL-4 in differential?
- Thread starter jayvee53
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This guys seems to know about standard transmissions and the like. He has alot of video's that might be of interest to you.,, https://www.youtube.com/watch?v=Z7NpsMZ9pBQ
The 1968 Pontiac Service Manual references "Hypoid" gear oil (page 4A-23), which is the GL5 extreme pressure required for the high pressure "wiping" characteristics of hypoid gears. The service manual for the 1970 Buick Gran Sport (same 8.2" BOP differential) provides a little more information and clarity that you seek. For complete refill you use "Factory Hypoid Gear Oil" (Page 00-11), for top up back in the day you could use a generic MP (Multi-Purpose) gear oil, the same as used in the Muncie transmissions of that period. Bottom-line, you must use GL5 in that differential but minor top up can be with MP gear oil as per the factory. With the proliferation of GL5 today I would suggest you use that both for refill and periodic top up. As you noted, GL4, for the transmission. The information is obscure but was noted back in my 68 GTO manual and my 1970 GS manual. The limited slip differential merely differed, as you probably already know, in that it had a different friction coefficient for the limited slip system (whether a cup and cone style in a BOP or clutches in the McKinnon or C-type). This is referenced in the manuals as Special Lubricant coded TL. If your 68 GTO cup and cone is still functional 52 years later, use the limited slip GL5's available (which is most formulations now).
Originally Posted by jayvee53
OK, I understand the importance of using GL-4 vs GL=-5 gear oil in the Muncie manual four speed transmission found in my 1968 GTO...protection of the yellow metals, right? But...how about the rear Safe-T-Track (posi) differential? Paralysis by Analysis is beginning to set in...I have read that GL-4 is not appropriate for the rear, rather GL-5 should be used. I'm wondering is GL-5 was even around the scene 50 years ago? The factory service manuals I have make no such reference to GL-3, GL-4 or GL-5. Seems to me GL-4 should offer the required protection (with an anti slip additive) Very interested to read everyone's thoughts on the subject. Thank you in advance!
1 quart of 80w90 GL5 then add bottle of GM posi additive, then top off with another quart of 80w90 GL5
OK, I understand the importance of using GL-4 vs GL=-5 gear oil in the Muncie manual four speed transmission found in my 1968 GTO...protection of the yellow metals, right? But...how about the rear Safe-T-Track (posi) differential? Paralysis by Analysis is beginning to set in...I have read that GL-4 is not appropriate for the rear, rather GL-5 should be used. I'm wondering is GL-5 was even around the scene 50 years ago? The factory service manuals I have make no such reference to GL-3, GL-4 or GL-5. Seems to me GL-4 should offer the required protection (with an anti slip additive) Very interested to read everyone's thoughts on the subject. Thank you in advance!
1 quart of 80w90 GL5 then add bottle of GM posi additive, then top off with another quart of 80w90 GL5
Thanks for the replies! Very much appreciated and some confusion is being addressed, GL-5 is the way to go in the differential. Now...what's your thoughts on using one of the many synthetic GL-5's in the differential? (along with the additive)
Originally Posted by jayvee53
OK, I understand the importance of using GL-4 vs GL=-5 gear oil in the Muncie manual four speed transmission found in my 1968 GTO...protection of the yellow metals, right? But...how about the rear Safe-T-Track (posi) differential? Paralysis by Analysis is beginning to set in...I have read that GL-4 is not appropriate for the rear, rather GL-5 should be used. I'm wondering is GL-5 was even around the scene 50 years ago? The factory service manuals I have make no such reference to GL-3, GL-4 or GL-5. Seems to me GL-4 should offer the required protection (with an anti slip additive) Very interested to read everyone's thoughts on the subject. Thank you in advance!
Stalube makes a GL4 gear oil which states on the container for hypoid gears.
https://www.crcindustries.com/products/api-gl-4-multi-purpose-gear-oil-1-gal-SL24239.html
OK, I understand the importance of using GL-4 vs GL=-5 gear oil in the Muncie manual four speed transmission found in my 1968 GTO...protection of the yellow metals, right? But...how about the rear Safe-T-Track (posi) differential? Paralysis by Analysis is beginning to set in...I have read that GL-4 is not appropriate for the rear, rather GL-5 should be used. I'm wondering is GL-5 was even around the scene 50 years ago? The factory service manuals I have make no such reference to GL-3, GL-4 or GL-5. Seems to me GL-4 should offer the required protection (with an anti slip additive) Very interested to read everyone's thoughts on the subject. Thank you in advance!
Stalube makes a GL4 gear oil which states on the container for hypoid gears.
https://www.crcindustries.com/products/api-gl-4-multi-purpose-gear-oil-1-gal-SL24239.html
Last edited:
Stalube makes a GL4 gear oil which states on the container for hypoid gears.
https://www.crcindustries.com/products/api-gl-4-multi-purpose-gear-oil-1-gal-SL24239.html
[/quote]
That's the product I used in the transmission and had planned to use it in the differential, but after collecting opinions of others, now I'm leaning toward using a GL-5 product...perhaps the Amsoil Severe or Lucas Synthetic.
https://www.crcindustries.com/products/api-gl-4-multi-purpose-gear-oil-1-gal-SL24239.html
[/quote]
That's the product I used in the transmission and had planned to use it in the differential, but after collecting opinions of others, now I'm leaning toward using a GL-5 product...perhaps the Amsoil Severe or Lucas Synthetic.
Originally Posted by jayvee53
Now...what's your thoughts on using one of the many synthetic GL-5's in the differential? (along with the additive)
That is up to you if you want to spend the extra money, the old axles do not require synthetic.
I use this in all my old GM muscle cars, regardless of axle type:
https://www.pepboys.com/castrol-hypo-c-80w-90-gear-oil-qt-/product/8078227
You do not need to add any additive if your axle is the original cup and cone posi. If you have put a clutch style in (Type-C, Eaton etc.) you may get away with no additive, try it and if it chatters on slow turns add some of the additive.
If you use an aftermarket Eaton Tru-Trac, they advise against synthetic.
I have noticed the Hypoid / EP designation on the CRC product, which is exactly what I use in all my 4 speed cars. I simply don't use it in the differentials as GL5 (used in all modern hypoid differentials) is readily available and CRC is clear in saying differentials that call for GL4 (moderate to severe duty hypoid use vs GL5 high speed / shock loads and high torque / low speed use - see API-1560 April 2013 for further information).
Now...what's your thoughts on using one of the many synthetic GL-5's in the differential? (along with the additive)
That is up to you if you want to spend the extra money, the old axles do not require synthetic.
I use this in all my old GM muscle cars, regardless of axle type:
https://www.pepboys.com/castrol-hypo-c-80w-90-gear-oil-qt-/product/8078227
You do not need to add any additive if your axle is the original cup and cone posi. If you have put a clutch style in (Type-C, Eaton etc.) you may get away with no additive, try it and if it chatters on slow turns add some of the additive.
If you use an aftermarket Eaton Tru-Trac, they advise against synthetic.
I have noticed the Hypoid / EP designation on the CRC product, which is exactly what I use in all my 4 speed cars. I simply don't use it in the differentials as GL5 (used in all modern hypoid differentials) is readily available and CRC is clear in saying differentials that call for GL4 (moderate to severe duty hypoid use vs GL5 high speed / shock loads and high torque / low speed use - see API-1560 April 2013 for further information).
Originally Posted by jayvee53
Stalube makes a GL4 gear oil which states on the container for hypoid gears.
https://www.crcindustries.com/products/api-gl-4-multi-purpose-gear-oil-1-gal-SL24239.html
That's the product I used in the transmission and had planned to use it in the differential, but after collecting opinions of others, now I'm leaning toward using a GL-5 product...perhaps the Amsoil Severe or Lucas Synthetic. [/quote]
Do your own investigating, I personally wouldn't waste my money on those overpriced gear oils.
Stalube makes a GL4 gear oil which states on the container for hypoid gears.
https://www.crcindustries.com/products/api-gl-4-multi-purpose-gear-oil-1-gal-SL24239.html
That's the product I used in the transmission and had planned to use it in the differential, but after collecting opinions of others, now I'm leaning toward using a GL-5 product...perhaps the Amsoil Severe or Lucas Synthetic. [/quote]
Do your own investigating, I personally wouldn't waste my money on those overpriced gear oils.
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