Can anyone tell me which is the preferred gear lube for a Muncie M21 transmission?
Thanks in advance,
Mark
'66 SS Coupe

GL4 is right. GL5 will eat your sychros.

parts plus carries it on the shelf

Sta-lube gl-4 avail from intrnet or napa.

Or redlines mtl or mt-90 gl-4 both mfg with specific friction enhancer's.

Thats to ensure proper syncro operation as was an issue in the past with older generation syn oil in muncies not designed for it being too slick causing improper synco operation which isnt an issue anymore with redlines mtl/mt-90 gear lubes per info directly from the oil engineer's on redline's site.

Using a gl-5 lube in a muncie wont cause it to self destruct/corroded the yellow metals syncro's are made of overnight.

But in certain situations the additonal extreem pressure additives gl-5 lube has over gl-4 lube can do that over a long period of time in the right circumstances of non use our classic cars see .

BTW,DONT BE INCLINED TO USE PENNZOILS WHAT THEY SELL AS " SYNCROMESH " GEAR LUE BECUASE THATS FOR NEWER GENERATION MANT TRANS AND IS LIKE WATER VS THE PROPER 75-80 LUBE OR THERE ABOUTS FOR A MUNCIE.

Scott