The Money Pit

This spring I plan to swap in my 4.11 gears, and now am gathering up odds and ends so I'll have everything when the time comes. I plan to drop the trans, swap in the Neil Chance custom converter, do a little clean up while I'm at it....

Question is, has anyone tried synthetic gear oil? Any issues? Do you still need additive for the posi? I have just started looking into this.

resdoggie

Yes. I changed out the diff gear oil on my wife's '13 CTS-V. The diff had a small groan when making turns. Sound familiar? So, I replaced the gear oil with Royal Purple Max Gear synthetic gear oil. Groan disappeared. Also, the Max Gear oil doesn't require the posi additive as it is included in the formulation. I will be switching my 4.11 with Max Gear synthetic 85-140 this spring. Glad I drilled a hole in the 4.11 for a drain plug.

jb78L-82

I have been using synthetic gear oil, either Amsoil or Mobil 1, 75W-90 with no additive in the diff for 25 years with zero issues. All chatter has been gone for years...........No issues!

zwede

I tried several conventional gear oils with posi additive and had horrible groaning from my newly rebuilt diff (new posi clutches).

Finally switched to Mobil1 75W-90 (also added a bottle of the additive) and all noise went away.

jb78L-82

The synthetics I use do not require the additive like conventional gear oil since conventional gear oil does not, on its own, have adequate lubrication qualities for the clutch discs...............

zwede

Very possible I would have been fine with just the Mobil1 and no additive. Next time I change it I'll try it without additive.

The Money Pit

I bought two cases of the Royal Purple trans fluid....not cheap. Plan to use that when I do the converter swap. Guess I'll pick up some for the diff now too.

Thanks guys.

gkull

You do understand that numerically higher rear end ratios create more heat? That is why 85w-140 is what I recommend. I've been using full synthetic from day one on my 4.11 and the Richmond gears still looked brand new after 20 years

3X2

Went to Mobil 1 over 30 years ago. no problems or noises. And.........I have't changed it since. No additive used.

The Money Pit

I just contacted the vender about synthetic gear lube, and he insists on break in with organic plus the additive, then change to synthetic after.

So I guess I too should add a drain plug. Any details would be awesome. Size drill, tap, location...maybe even pics? Mine is an 80, so it might be different, but any insight would be appreciated.

billyride

I use the same oil in both my 67 and 71. No problems at all. I use half a bottle of additive.

Big2Bird

I have an 81. Honestly, just buy an oil suction unit, and skip the plug. $100.

OZGreen69

Does anyone, after using LS synth oil, found their LSD less efficient ? I mean not too much at the light , but in tight corner exiting under full throttle or so, do you feel one wheel spinning more than it should ?
Me too I would like to go synthetic, but Eaton the diff man, say not recommended.

jb78L-82

Rather than take personal opinions like myself and others, you might want to ping Gary, GTR1999, who builds diffs for lots of folks on this forum, and get his expert opinion from him, especially since he sees older diffs for rebuilds and has experience with the different types of lubes.............

OZGreen69

Sorry,I should have name Gary in the first place as he's the man who did my LSD.
But thanks for your advice.

resdoggie

I used an oil pan drain plug I had lying around. Drilled and tapped the hole on the forward end of the housing. Also, used a dab of blue loctite. No leaks.

zwede

Mine locks with any kind of load on it. So in sharp turns with throttle applied the inner wheel chirps because the diff is locked. Using Mobil1 75W-90.

Street Rat

I'm using Amsoil 75w-90w Severe gear oil without additive.

427Hotrod

Been using Royal Purple Max Lube in my Dana 60 IRS for years. Used Mobil 1 before that. Used Mobil 1 in my stock diff. Both work great with no additive...and I'm not easy on stuff!

JIM

OZGreen69

Ok then, thanks Zwede.