Transmission and rear axle grease recommendation
 

Hi Fellows,
So mine is a '66 C-20. I am wanting to change the fluids in the trannie and the rear end. Can someone tell me what is a good modern day available grease and viscosity to use? Capacities would be helpful also.
I know, I need to get a shop manual for this info but the forum is so easy.
I promise, I'll write it down for next time. Lol.

Probably should have included the transmission is the four speed.

Re: Transmission and rear axle grease recommendation
 

80-90w gear oil with API service GL5 rating

A gallon should just about do both. Maybe a little more or little less.

Re: Transmission and rear axle grease recommendation
 

Ok, great! Heading out this fine Saturday morning to get the good stuff.
Thank you for the info!

Re: Transmission and rear axle grease recommendation
 

https://www.rymax-lubricants.com/upd...gl-4-and-gl-5/

Apparently GL5 may not be so good on the brass components of a gearbox. I always get the GL4 for my old junk.

After getting all the sand (or walnut shells) out of one that I bought and changing a few bearings the 3.07 diff seems to work OK now.

Re: Transmission and rear axle grease recommendation
 

The guy who rebuilt my old school 4 speed recommend GL4. Specifically this stuff. https://www.summitracing.com/parts/j...MaAuaREALw_wcB

Re: Transmission and rear axle grease recommendation
 

Just out of curiosity, I wonder what the the designation was for the original stuff that went into these back in '66. Or was there such a designation?
G-4 or G-5?
Not saying it's snake oil, but I bet there was only one available back in the day.

Re: Transmission and rear axle grease recommendation
 

I dunno, but this guy built my tranny and here's a quick autobio on him. https://www.5speeds.com/word.html With his experience, I'm taking him at his word.

Re: Transmission and rear axle grease recommendation
 

From the '63 shop manual under "General Information and Lubrication" ...

Re: Transmission and rear axle grease recommendation
 

I have been using GL5 that also says MT1 and limited slip performance with the API service rating and not have had any trouble but after doing some reading perhaps the synchro metals are wearing faster than they would with GL4.

I run a 318, several 420s and a 465 and all seem fine with the GL5, MT1, limited slip performance.

Several of them have been rebuilt and run this oil (one of them 18 years ago) and its still shifitng fine.

Maybe I should find the GL4 for the transmissions instead based on other members onput and readings provided.

Re: Transmission and rear axle grease recommendation
 

For the rear end, any GL5 80W-90 (or 75W-90 if you prefer synthetic). Here's what I run in the old 4 speed:

https://www.tractorsupply.com/tsc/pr...l?cm_vc=-10005