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Jul 21st, 2025 | | | | Joined: Sep 2013 Posts: 15 'Bolter | | 'Bolter Joined: Sep 2013 Posts: 15 | What is the proper type of gear lube for a 1963 C60 truck with a vacuum controlled 2 speed rear axle? | | | | | Joined: Dec 2018 Posts: 2,451 'Bolter | | 'Bolter Joined: Dec 2018 Posts: 2,451 | 80/90 winter 140 summer or heavy work as much as they hold probably wont change very much | | | | | Joined: Sep 2013 Posts: 15 'Bolter | | 'Bolter Joined: Sep 2013 Posts: 15 | What about the type such as GL 4 or GL 5 or? | | | | | Joined: May 2015 Posts: 9,830 Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums | | Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums Joined: May 2015 Posts: 9,830 | Either would work. GL 4 is for synchro transmissions. I don't believe the 2 speed axles have synchronizers. If they do, that would be the only reason to avoid GL 5.
Kevin 1951 Chevy 3100 work truckFollow this saga in Project JournalPhotos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together. | | | | | Joined: Sep 2013 Posts: 15 'Bolter | | 'Bolter Joined: Sep 2013 Posts: 15 | Either would work. GL 4 is for synchro transmissions. I don't believe the 2 speed axles have synchronizers. If they do, that would be the only reason to avoid GL 5. So what is it about GL 5 and synchronizers that is not compatible? I have been using and maintaining my 1958 and my 1963 Chevy C60 trucks for over 50 years. I'm sure I have added GL 5 to the transmissions not knowing better. I believe it was on this forum quite some time ago where it was stated not to use GL 5 in transmissions. That is what prompted me to ask this initial question about the differential lube. So what is it about GL 5 and synchronizers that is not compatible? | | | | | Joined: May 2015 Posts: 9,830 Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums | | Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums Joined: May 2015 Posts: 9,830 | So what is it about GL 5 and synchronizers that is not compatible? GL 5 contains sulfur, which will attack the brass used in synchronizers.
Kevin 1951 Chevy 3100 work truckFollow this saga in Project JournalPhotos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together. | | | | | Joined: Dec 2018 Posts: 2,451 'Bolter | | 'Bolter Joined: Dec 2018 Posts: 2,451 | 58n63 From what I could understand modern gear oil may be too slick to let the synchronizer rings get enough friction on the gear taper to work like they should,may grind on the way in. If the shift collar dogs have weak worn springs so they don't put enough tension on the synchronizer ring may grind. You sometimes feel the collar go past the synchonizer then if you don't go back to neutral will grind. Always happens up town where people will know you don't know how to shift it !! LOL | | | | | Joined: Mar 2004 Posts: 6,189 'Bolter | | 'Bolter Joined: Mar 2004 Posts: 6,189 | 58n63 From what I could understand modern gear oil may be too slick to let the synchronizer rings get enough friction on the gear taper to work like they should,may grind on the way in. If the shift collar dogs have weak worn springs so they don't put enough tension on the synchronizer ring may grind. You sometimes feel the collar go past the synchonizer then if you don't go back to neutral will grind. Always happens up town where people will know you don't know how to shift it !! LOL I believe the OP is asking about lube for his rear, not transmission... Mike B  | | | | | Joined: Sep 2011 Posts: 1,363 'Bolter | | 'Bolter Joined: Sep 2011 Posts: 1,363 | Manual states "16 pt SAE 90 "multi purpose" gear lube.
Made sure it is for hypoid axle.
I run 85W-140 hypoid gear lube.
BC
1960 Chevy C10 driver 261 T5 4.10 dana 44 power loc
1949 GMC 250 project in waiting
1960 C60 pasture art
Retired GM dealer tech. 1980 - 2022
| | | | | Joined: Dec 2018 Posts: 2,451 'Bolter | | 'Bolter Joined: Dec 2018 Posts: 2,451 | MikeB Well your right kinda jumped the traces there,heard others mention synthetics on gear boxes. Changed my differential 14 pints it then pinion leaked till it got rid of enough is now OK at about i/2 inch below the plug cold. | | |
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