Transmission Oil
 

So I'm sure this has been asked a million times (but I couldn't find it)
Is this OK to use in my 1939 flathead 3 speed big truck?

https://www.autozone.com/motor-oil-a...art/265000_0_0

Your expertise is always appreciated.
Thank you

Re: Transmission Oil
 

I’ve often wondered about that too. I don’t see why not.
Just to be safe I use something more like 75/140 in my old transmissions.
In souther CA straight 140 should be ok but I think back in the day 90 was used in warm weather and 80 in winter time in cold climates.

Re: Transmission Oil
 

It's fine to use.
I used Amsoil 75-90 Manual Trans oil in mine.

Re: Transmission Oil
 

It’s been stated many time here on Barn. Tranny has yellow metals needs to be GL4.

Re: Transmission Oil
 

There is no SFE weight mentioned. I would stay away from it and use NAPA SL-24238 140W GL-4

Re: Transmission Oil
 

I agree, I don't see any call out of the GL rating, IMO it needs to be GL-4. I would also use a multi viscosity.

Re: Transmission Oil
 

How about the differential fluid type....1934? Thanks

Re: Transmission Oil
 

The Sta-Lube that TerryOH pointed out in post #5 is what I use in the gearboxes because it's GL-4. And I use it in the rears too but more for convenience than anything else. I have a '36 and a '35.

Re: Transmission Oil
 

A big thanks to all of you!!!
I'll get some NAPA SL-24238 140W GL-4.

Something I noticed when I drained the transmission, it seemed to be filled well past the fill hole, and it seemed to be mixed with the corn head grease that I put in the torque tube. Is it possible for the corn head grease to get into the transmission? if so does that mean I'm overfilling the torque tube?

Re: Transmission Oil
 

Check the rear diff fluid level. Fluid can transfer back and forth depending on the rake and gasket/seal conditions. If the trans is overfilled and the rear is low, it's all migrating forward. There will be transfer between the u joint and and trans if you don't have a sealed rear bearing on the trans.

Re: Transmission Oil
 

YES !!!!
If the grease is going forward it probably means your driveshaft seal is working .
If it is not the grease usually goes into the torque tube .

On cars the spec for filling the u-joint cavity is 4 oz .

I just use SAE 140 GL4 in the u-joint , tranny , steering gear and rear end . Works fine if your d-shaft seal is good and the gaskets are installed well .
1933 and 1934 cars .

Many seem to think packing the u-joint cavity full of grease is the way to go . The excess is either going in the tranny or rear end .

Re: Transmission Oil
 

You can use GL-4 or GL-5 in the differential because of the lack of "yellow" metal in the rear axle. But, IMO, GL-4 is a better option because: rear axle lube can end up in the transmission, the gear type in the rear axle don't require GL-5 and it's similar to just use the same lubricant in both the transmission and differential.

Re: Transmission Oil
 

[QUOTE=1939 Tonner;1990968]A big thanks to all of you!!!
I'll get some NAPA SL-24238 140W GL-4.

Yep...Is what I use also.

Re: Transmission Oil
 

David J says he uses 140 in everything.
I checked the weather there last month and it was -20f three times when I checked.
My brother lives in St Croix Falls.
When I lived in River Falls I bought a ‘46 V8 off a used car lot when it was around 20 below zero.
After about 50 moles that day the rear end started to howl.
The local gas station had to use a blow torch to get the gear oil to drain.
I don’t see how he can even steer a car with 140 in the steering gear box.
Oh, and another thing;
If you put GL5 in a gearbox with yellow metals it will discolor the yellow metals after several years. It will NOT dissolve them in a few minutes like most people believe.

Re: Transmission Oil
 

I have mentioned it before, but if you have a Tractor Supply store near you, check them out for trans and rearend oils.
They still carry the Ford tractor transmision oil-- GL-1 for Ford tractors manufactured from 1939-1952.

Re: Transmission Oil
 

Very simple answer .

I do not drive nor start them in cold weather .
Summer cars here .

The one that gets driven nowdays is a 34 phaeton .
Not a cold weather car and it actually still has the straight STP in the steering box Mike ran in FL .
That makes SAE 140 look runny .

Re: Transmission Oil
 

If you put GL5 in a gearbox with yellow metals it will discolor the yellow metals after several years. It will NOT dissolve them in a few minutes like most people believe.

This I agree with.

Re: Transmission Oil
 

Well Im bucking the trend on this one . Ive gone away from using GL4 and have started using the Penrite 85-140 mineral gear oil GL5. They have an additive which is "supposed too be" safe[ish]:rolleyes: . Time will tell. Pretty sure Lawrie has just been using "standard type" gear oils without detrimental effects. I believe the damage come mostly when the oil becomes hot. Most of my driving is back and forth too work so thats not an issue.

Re: Transmission Oil
 

At lot of the GL-5 producers claim they are now synro compatible. I tend to not trust them and GL-4 is easy to come by. It is mild EP, which is what Ford specified and I don't care much for the smell of GL-5. :) I use Mercon myself (T5).

Re: Transmission Oil
 

here the GL4 is hard to come by and expensive :rolleyes: