Flathead transmission

[Flathead86]

How much oil should I put? Couldn’t find any info on how much oil should I put in my flathead v8 transmission? Any info, Would greatly appreciated, thanks Steven

[Phil Gillespie]

Originally Posted by Flathead86

How much oil should I put? Couldn’t find any info on how much oil should I put in my flathead v8 transmission? Any info, Would greatly appreciated, thanks Steven

What year gearbox? car, truck ?
Phil NZ

[Flathead86]

My truck is a 1948 Ford f1 but not original transmission, I used a car box not sure what year it came out of, motor is a 8ba motor original belt housing,

[Phil Gillespie]

Originally Posted by Flathead86

My truck is a 1948 Ford f1 but not original transmission, I used a car box not sure what year it came out of, motor is a 8ba motor original belt housing,

Ok if it has the filler plug in the side usually fill till it is just begining to flow out the filler hole. maybe around 1.5 to 2 litres, at a guess.
Phil NZ

[Flathead86]

Originally Posted by Phil Gillespie

Ok if it has the filler plug in the side usually fill till it is just begining to flow out the filler hole. maybe around 1.5 to 2 litres, at a guess.
Phil NZ

Ok thanks, that makes sense,

[rotorwrench]

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Many of the old service or owner's manuals give the lube capacity in pounds. If you can put your finger in and bend the first knuckle to find oil then it is usually full enough. Filling it till it pours out is OK too. Manual transmissions tend to find there own level. If it's an overdrive transmission then the overdrive section also has to be accounted for but there is a small passage between the two on most of the Borg Warner OD designs. It just takes a while for the level to equalize.

[19Fordy]

FWIW: I use this as I live in FL.
https://www.amazon.com/Sta-Lube-SL24.../dp/B000M8IHI2

I think this would also be good if I lived up north where winter is cold.
https://www.rvautoparts.com/SL24239-...SABEgI2YvD_BwE

1940 Ford Owners Manual says to use SAE 90 in winter and SAE 140 in summer.

[marko39]

Should take about 2 1/2 pints.

[rotorwrench]

More like 2 3/4 lbs.

[JSeery]

Delete

[Aarongriffey]

140 is just fine if you are in Florida. But gotta use 80 in the north. Got to.
When I was in High school I was so tired of monkeying with my ‘33 & ‘40 that I traded the ‘40 off at the local Dodge, Plymouth dealer for our mayor’s old ‘46 Ford fordor.
School got out at 3:30 and two girls walked down to the dealer with me.
My Dad had been there and taken care of everything. We got in the car and took off for a ride in the country. It was nice. The car was six years old. It was the end of January, in Wisconsin, and the heater worked great!
About four miles and the rear end started to howl. I knew what it was right away.
It was 30 to 35 below zero and the car had been on the lot for several months.
I turned around went back to town.
A local gas station lifted the car and heated the rear end with a blow torch to get the summer gear oil out.
After filling it with 80 I drove it a while as the howl got worse and I eventually put a Columbia in it.

[Automotive Stud]

Just fill it until it starts to come out of the fill hole. Probably less than two quarts.

[jackson]

Use GL1. Not real easy to find.... but you don't want to use hypoid gear oil in an old Ford Tranny.

[JSeery]

GL1 is really not the best to use, Ford after around 40-41 specified Mild Extreme Pressure Gear Oil which is GL4 in todays terms.

[jackson]

I believe GL4 is hypoid gear oil. My 49/50/51 Ford Shop Manual says this:

"Use SAE 80 gear lubricant for all transmission and overdrive assemblies. SAE 90 gear lubricant can be used for hard driving in hot climates. NEVER USE A HYPOID AXLE TYPE LUBRICANT".

The highlighted part is as printed in the manual.

I guess if the Sulphur/Phosphorus additives in todays GL4 is low enough to not cause damage to bronze or copper (syncro's) it would be OK to use. I don't work my Merc very hard...so will stick to non-hypoid GL1

[1948F-1Pickup]

I just put a new stock transmission in my '48 F-1 late last year. I got the fluid from Early Ford Store in San Dimas. Pissed me off cuz I had to drive back and get a second bottle. So in the end, I purchased two 32 ounce bottles. It took one full bottle and about 20 ounces of the second bottle....... so 52 ounces total.

[JSeery]

Interesting Jackson, I believe you will find most of the transmission rebuilders recommend GL4. Some of the gear lube companies now claim GL5 is safe, but not sure I totally buy that. I have never hear a report of transmission syncro issues with GL4. I would for sure what the added protection of the EP additives.

This is from Millers site on classic vehicle lubricates:

GL4 is the first serious level of EP performance and is specified for many gearboxes and final drives from mid 1930’s onwards. Millers produces the following GL4 oils: Millers Classic Gear Oil EP 80w90 GL4 and Millers Classic Gear Oil EP 140 GL4.

GL5 specification is for highly loaded hypoid differentials as fitted to most cars from 1960 onwards. Millers offer the following GL5 oils: Millers Classic Differential Oil EP 90 GL5, Millers Classic Differential Oil 85w140 GL5 and Millers Limited Slip EP 90 GL5 for limited slip differentials.

[rotorwrench]

GL4 mild EP was the replacement spec for GL3 mild EP that they used to use back in the day. The EP additive levels are low enough that it shouldn't be a problem.

[JohnI]

Here is the fill hole?

[Ggmac]

On the side