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Hagerty Employee

Choose your oils wisely: Transmission gears and differential gears have different needs

Tom Marrin writes: I have a 1954 Chevy Bel Air with a three-speed transmission. I recently had the rear axle bearings and seals replaced, along with the torque tube bushing. I have been using MasterPro GL-5 80W-90 or GL-5 85W-140 gear oil in the transmission and in the rear end, but my mechanic just told me not to use it in the transmission. OK, so what oil should I be using in each place?


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If you choose to use synthetic, Red Line MT90 would be the correct viscosity instead of MTL (which is 75W80). 

Pit Crew

I agree, MT90 is the better choice. I also use it on my Triumph Spitfire.

I enjoy the setting up and timing of a points and condenser ignition as much as the next person, but I can testify to the current lack of quality in the conventional parts available (even from such a vaunted name  I recently had a condenser go kaput after less than 6 months of use.  What did I replace it with?  Another B piece.  Whadda ya gonna do?


I am using SAE 140 API/GL-4 in my 1939 Ford (I don't drive it in winter).  It is a Sta-Lube product.  The label says it is suitable for auto, truck, and bus standard transmissions and differentials, and that it is not corrosive to copper, bronze or other non-ferrous alloys, bearings, and bushings.

Pit Crew

Dealing with points and condensers was wearing on me for years. I've finally switched my last old Mopar to electronic ignition. Now all 4 of my 60s Mopars are the same. 1965 Dodge and Plymouth and 1969 Dodge and Plymouth. At least now I can interchange the ignition boxes when one of them breaks down. Easy peasy lemon squeezey.


Jeez I've been using the same 90/140 in my diffs and gearboxes for 40+ years. None have been daily drivers but I've never noticed any problems. As for points versus electronic ignitions: the second most important benefit of breaker points (after ease of diagnosis and repair) is that they very gradually fade away before they strand you. Barring some catastrophic failure, there's always time to drive to a safe harbor.


I have to agree with Tinkerah. The points set-up is (usually) easily fixed on the roadside (even if only temporarily) to get you moving along again. A spare set of points & condenser in the glovebox (takes up no room) is all you should ever need in an emergency. The rotor & cap can always be cleaned/re-used. Electronic can leave you stranded. NEVER happened to me with points!