Rebuilt 4-Speed, what are you guys using for gear oil?

[RSI700VIPER]

I was going to use 90W synthetic gear oil but wanted to hear from the experts.  What are you guys using? 

[moparchris]

Best results for me have been using Pennzoil Synchromesh.  It is NOT synthetic.  Stay away from synthetic in an older manual box.  The synchros do not work well with synthetic lube.  You will probably have a hard time finding the Pennzoil on the shelf at your local store.  I order it from either Amazon or Summit Racing. 

[70gtx440dana]

I just researched this and decided to go with this product for my 18 spline:

https://www.drivenracingoil.com/go-80w-90-conventional-gl-4-gear-oil.html

My biggest consideration was to find a suitable GL4 oil as recommended for these older transmissions.

[birdsandbees]

20W50 motor oil. Has never shifted so smooth and I've been driving it for 43 years. OE gear box, never rebuilt. I filled it with this after my restoration. Only issue I have is a minor input shaft seal leak, but an easy fix and it is 51 years old afterall.

[cdr]

if you are in a cold climate gear oil will make it hard to shift. I always used atf in the mopar 4 speeds.   

[70sixpkrt]

Sta Lube 85-90 GL4.

[RSI700VIPER]

Best results for me have been using Pennzoil Synchromesh.  It is NOT synthetic.  Stay away from synthetic in an older manual box.  The synchros do not work well with synthetic lube.  You will probably have a hard time finding the Pennzoil on the shelf at your local store.  I order it from either Amazon or Summit Racing. 

I was able to find a couple of quarts on Penzoil Syncromesh at my local advance auto parts.  I've read elsewhere that it is a 0W-30 weight non-synthetic with a GL-4 modifier.   

[John_Kunkel]

Stay away from synthetic in an older manual box.  The synchros do not work well with synthetic lube. 

From my anecdotal experience that's a myth. Been using Red Line 75-60 NS in 833's for years; smoother shifting than any conventional lube.

[c00nhunterjoe]

Thats a 2nd here for redline. I used the mtl which is a 75w80, gl4. Flat shifted my 383 at 8k for a long time with it. Good stuff. Only leak i ever had was the reverse light switch.

[Rolling_Thunder]

if you are in a cold climate gear oil will make it hard to shift. I always used atf in the mopar 4 speeds.   

I've run ATF in my 4-speeds before as well...    if excessive chatter then I run something a bit thicker - I believe in the later OD trans they were filled with ATF (so I've been told)

[c00nhunterjoe]

I tried atf4 in my 4 speed. Was awful.for daily driving and hardcore speed shifts, the redline is the way to go. Gas on the floor, never lift, yank gears over 8k. Its a beautiful sound.