furylee:

No, the SAE 10 oil was not a winter thing. It was an all rear round thing. Additionally, I just found an old service bulletin from 1953 and it states that ATF type A can be substituted for the SAE 10 engine oil. In fact, my memory says that all 53 and later standard transmissions (up to 58 when my direct experience ended) came through our dealership filled with type A. Of course, type A is not available anymore, but I think Dexron would do just as well. The gear sets in a modern automatics handle a lot more torque than was ever available from the old engines. In addition the gear sets are smaller today. There are no excessive gear wear issues with any automatic trannys that I am aware of.

I just can't believe that people want to put hypoid gear oil in transmissions for which it was not developed and not intended. Of course, some other manufacturers might have had such poorly matched gear sets that the hypoid oil was required to keep them quiet!

I'm getting ready to put an overdrive in my 41 coupe. I just had it all rebuilt with new bearings/gaskets etc., and I put a full synthetic gear lube (Castrol 75W-90) in both the tranny and overdrive.  My mechanic buddy did that to his 53 convertible 20 years ago, and it still performs like the day he put it in.  He said the 10w motor oil was winter thing, and how many of us drive them in the winter?

The Ply is a 40 PT105 with optional 4 speed, and the Dodge is a 49, B1D-with 4 speed.

John:

What vintages are your pick up and truck? If the PU is mid-thirties or later and a half ton it should have the same transmission as the cars. In that case it should have synchro on 2nd and 3rd, although the cones may be worn and not effective. If that is the case, then I would not hesitate to use SAE 10 oil in it. If one or both transmissions are the heavier duty four speeds, then I am not sure. I cannot remember if engine oil was recommended for them or not. I think non-detergent oil was used originally, but I cannot see that it would make a difference.

would 10 wt oil help my sometimes inept gear changes in my Ply PU and Dodge truck which have completely non-synchro gears?  then i guess the next question would be--- detergent or non?    I found that switching from 140 to 80-90 helped in cool weather.

Thank you for the information.  I learnd something.

jd2ksilver:

All "modern" final drives utilising a hypoid crown and pinion assembly require the use of a hypoid 80 or 90 gear lubricant. Any time a drive gear engages a driven gear off its centre line (known as hypoid gearing) very great pressures are developed between the teeth of the gears. Engine oils cannot withstand these pressures and would be squeezed out leaving metal to metal contact. Standard transmissions with their straight cut or helical gears do not develop really high pressures and engine oil lubricates them well. there are definite advantages in terms of shift quality to the use of engine oils in Chryco transmissions. I have a 36 Dodge and when I overhaul ther transmission I will use SAE 10 engine oil in it also. There aren't major differences between my 36 transmission and those used in the fifties.

Both the owners manual and the service manual I have indicate SAE 90W Hypoid Gear Lubricant in differential(Use SAE 80 below minus 10 degrees F).  Thanks for the confirmation of the 10W motor oil for transmission and overdrive.

If it is true to change to 10w, then how about the differential?  This is the first I heard about such a low number gear oil in transmissions.

Yes, engine oil for both transmission and overdrive.

Yorel:

SAE 10 engine oill is the correct lubricant. Hypoind 80 or 90 causes harder shifting and can also cause the syncromesh cones to slip when shifting causing a gear grind. All standard transmissions back to the very early '40s function very well with SAE 10. Our garage changed literally dozens of them to engine oil with never a problem.

I recently purchased a 52 Belvedere with overdrive transmission.  I bought an owners manual, and a 1946-1952 reproduced service manual.  The fluid in transmission case is very low.  I checked the fluid in the case immediately behind the transmission and it is also low, and the fluid seems really thin.  The manual says to put SAE 80 gear lubricant in the transmission, and the service manual says to use SAE 10w engine oil.  Which is correct?  For both cases?  Seems to me when I was working at a service station in the late 50's, I always used 80 gear lubricant, but thats been a while ago.