Hypoid - transmission - overdrive - too much oil

P

Paul Bennett

Well-known member
1950 Mercury
I'm changing ALL fluids so I searched the 'Barn to see what others were using. I bought 2 gallons of CRC GL-4 140W only to find a notice in the MercLincoln bible with Bold print - 'Do not use hypoid oil in overdrive'! Plus I'm finding more references to 90W after having bought 140W.

OK, I'll use the 140W GL-4 in the diff with my lifetime supply. But since it's hypoid oil, guess it's out for my transmission & od. Or it is since this was written way back when oils were different.

But GL-5 would appear inappropriate in the trans because of incompatibility of yellow/red metals in the synchros. Also read there is a common oil chamber between trans and od so they must be the same oil.

I think I could get by with 140W vs 90W as most of my driving will be hot weather. My previous Euro F-car required special RedLine gear oil to shift into 2nd gear when cold, so I'm well aware of the subtlties that oil can have on performance.

But methinks I am making too much of this but I need reassurance or at least some suggestions. I'd rather misspend than do something inappropriate. When I press 'start' for the first time, I want this beast to start. And run. Main question, exactly what oil to use in the trans/od?

Additional aside, what suction pump works well for filling without leaving as much oil on the floor as in the car? Amazon reviews suggest they all suck, literally. Any good Swiss or German designs?
 
GL-4 for the trans and OD. Tractor Supply carries it, and NAPA Auto Parts. The Tractor Supply stuff is 85W90, IIRC without looking at the jug. I use it in my '55 Merc, works great. There is an oil passage between the trans and the OD section. The proper fill procedure is to fill the trans first, then top up the OD. The OD fill plug is a little higher up than the trans fill plug. Most any suction pump will do the job, but you need to be able to get the suction hose all the way down to the bottom of the trans for the best result. It's a messy job. I just put a catch pan under the trans, and spray the trans with brake cleaner and wipe it down with paper towels when I'm done.
 
I had an OD that was stickey. It would not go in to OD sometimes, just not shift. I drained the trans and the OD unit overnight. I filled the trans with 75/90 gear lube, and the OD unit with ATF. It worked great for as long as I owned the car, several years.
 
Sometimes too heavy an oil (or even too 'slippery' an oil) can have ill effects on synchronizer blocking rings. The brass blocking rings act as brakes to slow gears down during gear changes and heavy/silppery oils can inhibit this braking, leadin to extended/difficult/crashing gear changes. Heavy, thick oils can cause OD units to be reluctant to shift. If I remember correctly, B/W preferred a lighter oil than what Ford spec'd but stated to use what the OEM required for their transmission.
 
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