Mr D.

Does Mobil 1 synthetic gear lube or any synthetic gear lube require the limited slip additive? I had read somewhere that it does not. I at the service rear end and trans part of my 69 project and have decided to go with synthetic gear lube in both the rear end and trans. Thanks

Jvette73

I used the Mobil1 gear oil in mine without the additive and have had no problems or noises. Even if you dont put it in to begin with it can always be added at a later date. The additive is only a few oz's.

pws69

I had the same question when I converted everything over to Mobil 1. My research said to use it as it really doesn't contain LS additives (as opposed to the Redline products that DO contain LS additives) - you can't lose by doing so and it will save the hassle of adding it later (which you probably will have to do anyway!).

GTR1999

I use regular old dino 90wt gear oil in the diff and trans along with 2 bottles of GM additive. I looked into the synthetic oils and spoke with an engineer at US Gear and TomWatt. They both said NOT to use synthetic oil in the diff.

I haven't had any problems with the dino oil and it had proven itself over the course of use in these cars. When I rebuild a diff a add a drain hole so it's just easier to to an oil change in the future.

Gary

GDaina

What was their reason for saying that? I'm sure if using Mobil 1 or any other synthetic brand caused damage, the products would not be on the shelves to be sold.

GTR1999

The US Gear guy said he was concerned about heat and the abuse the differential would be under. Tom Watt is a pretty straight forward guy his answer was "I don't use them in my differentials,use 140wt for all applications" end of story. I reasoned that if both men were against using it and have been building and designing differentials for years why change?
I heard also of oil leaks from using them but haven't confirmed this,may just be rumors?
Gary

gkull

I've been using the Valvaline syn 110w-140 or something close to that oil weight for years with two tubes of GM posi lube.

My 4.11 richmond gears still look nice 100,000 miles later.

burners

I've been running Mobil 1 for about 40,000 mile in the diff with no problems. I didn't add any additive. I remember when I researched it (before I switched to it) that I found that it contained what was needed. Switching to Mobil 1 actually cured a posi clutch chatter problem I had (once I did the requisite 5 tight 360 degree circles in each direction).

jimcork1

I won't say what won't work, but I ran synthetic diff gear oil in my wife's car. At 100,000 miles I changed a rear wheel brg. and found the ring gear to be worn through the surface hardening into the porus steel underneath. This required the gears to be replaced. THis car only used the synthetic diff oil for 35,000 miles. At 70,000 diff cover gasket was replaced and no wear was noticable on the gears. The syn lube was installed and the wear found after 2 years of normal driving. (major brand name intentionally left out) If you would like to know you may email )