Overdrive

R

Robert Legner

Member
I have a 1950 with a stock 8Ba with a column shift, 3 speed w/overdrive. The overdrive works although the kick down switch may not work. Don't know because I have not tried it. The real question is how is the overdrive unit lubricated. Does it have it's own oil? If so is there a place to check the oil level? Or is it lubricated with the transmission lubricant? The owner's manual does not address the overdrive lubricant. Thank you in advance for your response.
 
On the 49 Merc O/D transmission there is a fill plug on the B/W tailshaft for adding lubricant. Other than using that location to fill the B/W unit after I had rebuilt the trans I’ve not figured out why its there since there is a common passage between the tailshaft and the transmission case which allows for the passage of the lubricant between the two. This sentence in the Lincoln/Mercury shop manual would seem to indicate that routinely checking the fluid level in the B/W unit isn’t necessary.

“If on checking for the lubricant level in an assembly that is in service, check level at transmission fill plug. If only a small amount is required, it is satisfactory to fill at the transmission plug only.”

Your Ford O/D trans may be different, but a quick check of the B/W tailshaft will show if there is a fill plug on it. SAE 80 lubricant is recommended for the Lincoln/Mercury transmissions. SAE 90 for extreme conditions-hard driving in hot climates. “NEVER USE A HYPOID AXLE TYPE LUBRICANT” - this is from the manual.
 
Both the Ford and the Mercury overdrive transmissions have fill and drain plugs for both sections of the complete unit. Typically, the Ford version has a small drain plug on the OD housing, with a hex socket......they’re usually pretty tough to remove and often the hex will strip out.

The others are correct in stating that there are common passages between the OD and the regular 3 speed sections where the oil can travel back and forth. Trying to fill the OD section through its own filler plug is an exercise in frustration because the ring gear is pretty much blocking the opening. The best way to fill these transmissions is to use the 3 speed fill plug opening for both sections. If the trans is totally empty, fill to the opening and let it sit overnight. Then come back and top it off again. You may want to do this a third time to ensure that you’v got it completely filled. When checking the trans gear oil level from then on, use the 3 speed filler plug for the whole unit.

Because the overdrive gears sit a bit higher in relation to the cluster gear, they will be the first ones to run dry when the oil level gets down. For this reason, it’s important to stay on top of checking this more frequently than a regular 3 speed (non overdrive) transmission.

Ford recommended GL-1 gear oil (90 weight) back in the day. Any name brand GL-3 or GL-4 oil is good as well. With the GL-5 oils you may wish to check the label for its compatibility with the brass components in your transmission.
 
Borg Warner made a lot of that stuff for Ford but Ford wasn't the only customer for the design. They all have some carry through but some carry through faster than others. I figure they put the fill port there to insure there was a place to fill the aft section or at least check the level of fluid back there.
 
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