1957buickjim Posted January 11, 2023 Share Posted January 11, 2023 Want to change out the gear oil in my differential and looking for recommendations. It seems that before it had 80W gear oil in it. Thanks! Link to comment Share on other sites More sharing options...
EmTee Posted January 12, 2023 Share Posted January 12, 2023 GL-4 90W? I use this in my '38 Link to comment Share on other sites More sharing options...
1957buickjim Posted January 12, 2023 Author Share Posted January 12, 2023 Thanks EmTee.. Is it available at the local auto parts store or special order? Link to comment Share on other sites More sharing options...
EmTee Posted January 12, 2023 Share Posted January 12, 2023 Yes, I bought it at NAPA. I think O'Reilly's has a house-brand GL-4 also. Link to comment Share on other sites More sharing options...
1957buickjim Posted January 12, 2023 Author Share Posted January 12, 2023 Thanks my friend. I'll head to NAPA and get some. Link to comment Share on other sites More sharing options...
Rusty Heaps Posted January 12, 2023 Share Posted January 12, 2023 Tractor Supply sells a GL-3 that’s marketed for older Ford tractors. I’m using it in my older GM transmissions and rear ends as it is safe for brass bushings. Also it’s a lot cheaper than Sta-Lube. Not that there’s anything wrong with that brand. I’ve used them too. 1 Link to comment Share on other sites More sharing options...
EmTee Posted January 12, 2023 Share Posted January 12, 2023 GL-3 is OK for transmissions, however, Jim was asking about his hypoid differential. That requires GL-4 (or GL-5 for newer cars). 2 Link to comment Share on other sites More sharing options...
NTX5467 Posted January 13, 2023 Share Posted January 13, 2023 If the "GL" code is fine for brass, which ones are which? is GL-5 a syn fluid? I need to do more research to refresh my memory banks! 1 Link to comment Share on other sites More sharing options...
NTX5467 Posted January 13, 2023 Share Posted January 13, 2023 On the other hand . . . check the factory service manual for what they spec'd when the car was new, GL-rating and viscosity. Then go from there. You can also research the lube company websites to see which ones might fit the OEM recommendations. Just some thoughts, NTX5467 1 Link to comment Share on other sites More sharing options...
Bloo Posted January 13, 2023 Share Posted January 13, 2023 (edited) GL-4 is oil for hypoid gears. GL-5 is heavier duty oil for hypoid gears. Either should be fine in a hypoid rear axle from 1957. Old time wisdom suggests GL-5 should be avoided if there are brass or bronze parts. Today you should really read the datasheeet for the oil if there are brass or bronze parts, because a lot of time has passed and the old "rule" has too many exceptions. There are probably no brass or bronze parts in a USA-built hypoid rear axle from 1957. Edited January 13, 2023 by Bloo (see edit history) 1 1 Link to comment Share on other sites More sharing options...
NTX5467 Posted January 13, 2023 Share Posted January 13, 2023 (edited) All that is listed in the 1957 Buick Chassis manual I found at www.hometownbuick.com mentioned an "MIL-2105" spec. Wikipedia had some informaiton on it, but I ended up in the Valvoline website. Any lube brand which can be aligned with current model OEMs in lubes and such, will have either "High Performance" or "FullSynthetic" gear oils. I chose the non-syn lube. From the way the application information read, GL-4 and GL-5 can be used in rear axles (i.e., hypoid), but GL-5 should not be used in transmissions which are "synchromesh", which means no GL-5 for brass items as shims and synchronizers. GL-5, it seems, has more EP additives which make it slicker and can interfere with how the synchros work. So, absent the GL ratings, look for rear axle lubes (i.e., hypoid gears) which include EP additives for wear protection. 90W. Although many will be 80W-90. Items suitable for manual transmission gears should mention that usage, too. Might also seek out non-syn oils, too, for good measure. In the case of engines, some syn oils can degrade the rubber lip seals, over time, so staying with non-syn hypoid gear oils might be advisable. Take care, NTX5467 Edited January 13, 2023 by NTX5467 (see edit history) 1 Link to comment Share on other sites More sharing options...
EmTee Posted January 13, 2023 Share Posted January 13, 2023 Check for evidence of ATF in the rear-end oil. If so, the torque-ball seal should be replaced. 2 Link to comment Share on other sites More sharing options...
1957buickjim Posted January 14, 2023 Author Share Posted January 14, 2023 (edited) Well, so far I'm going with the GL-4 that EmTee recommended. It looks like that type of hypoid oil is recommended in the Chassis Manual. There isn't any ATF in the rear end, as I replaced all the seals (torque ball and shaft) on the transmission when I installed it. It was also rebuilt by Jim Hughes, so it should be good! Thanks all for the recommendations and research Edited January 14, 2023 by 1957buickjim (see edit history) 1 1 Link to comment Share on other sites More sharing options...
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