Correct manual transmission gear oil

[gunsmith]

I have 1984 720 4x4 5 speed manual transmission.  What is the correct gear oil to use in it?  Specific manufactures name would be very much appreciated.

 

[weldingrod]

I use 80/90  GearLube. in any gearbox.

[gunsmith]

Is GearLube a specific brand name like STP or Mobile or Royal Purple, etc?  

[Crashtd420]

1 hour ago, gunsmith said:

Is GearLube a specific brand name like STP or Mobile or Royal Purple, etc?  

Any one of those is fine, I think all that really matters is that its yellow metal safe, I believe it should say GL4....

I personally use the royal purple.... 

[datzenmike]

It came with API GL4

80w90 for up to 100F continuous driving. If it sees temperatures constantly above 100F and does not go below 50F in the winter, then 140 is advised.

 

I've had very good luck with GM Delco Friction Modified Synchromesh Transmission Oil. It is a semi-Synthetic so if the transmission is old or worn it may begin to seep out the driveshaft seal. Replacing it with a new one usually fixes the problem. The oil is thinner and the synchros engage faster so shifts are quicker with the same effort and especially so on the first few shifts when the transmission is cold and also in winter weather. Another benefit I noticed is the transmission will down shift without grinding now. I think in the states it's about $10 at Lordco and $12 at the dealership. I paid $17 at Lordco in Canada so that sounds about right. Truth be told, I imagine that the base stock lubricant only has one maker (Shell) and it's just colored red or purple and a different label slapped on the bottle.

[Stoffregen Motorsports]

I use Redline MT-90 in all of my manual transmissions. It is about $60/gallon.

[datzenmike]

$5 a quart mark up for the red pigment. ?

[bottomwatcher]

I have been running the syncromesh  for several years as per Mikes suggestion and all has been fine.

[Stoffregen Motorsports]

Brawndo has what plants crave. It's got electrolytes.

 

Redline is one of those name brands that helps put customer minds at ease.

[datzenmike]

The 80w90 is, I'm sure, thicker. It was always stiff to shift for the first Km or so, mostly 1st to 2nd but fades away as the engine warms up. Very noticeable as you get down to freezing. Upshifts were fine until you change to the Delco and  can see they were slow. Not that I shift fast but it shifts faster with the same effort. It might be my imagination but the shifts seem to click louder now. It's very mechanical, positive and reassuring. I like it. I stopped down shifting entering a corner in town until at the slowest speed possible or you would hear the teeth rumble together as they mate. At higher speeds I would have to straight arm it hard and there was a lot of resistance and a small grind. That all went away with the Delco oil. I can only assume that thinner and slipperier allows the synchros to engage faster.  It's a miracle how fast it is.