Frankenvette

I'm thinking about synthetic lube along with 1 bottle of GM posi-additive. Is this acceptable, or is GM lube better? If synthetic is ok, what is the correct type?

7t2vette

I am putting in synthetic 75w 90 with 1 bottle of additive, I don't see any reason not to.

Mike Ward

You can use it if you want but there's no practical benefits (like all synthetics).

rihwoods

How about whale oil ? Heh.

AlwaysWave

I recently read in Chevy High Performance that the OEM's were putting synthetic gear lube in for the proven friction reduction, aiding in fuel mileage.

GrandSportC3

I'm using Mobil 1 synthetic 75W90

MsVetteMan

Tech or general?

BSeery

Was it "oil" ??

I heard it was something else........

rihwoods

Got this from the.....internet:

"Thirty to forty years ago, we had the perfect ingredients for long transmission life: low heat demand and a ready supply of whale oil. Most of the cars in junkyards arrived with functioning transmissions. We did not have the heat demands on the motors we have today. In previous columns, I’ve written of the increase of thermostat temperatures - and that the transmission oil used typically was almost perfect. Mechanics never changed the fluid until fixing a leaking gasket or seal. Worn out and failed transmissions were rare. There were not as many franchised transmission shops back then.

The trouble was, thousands of sperm whales were killed every year to acquire the almost 29 million pounds of whale oil used in ATF. Sperm whale oil is an almost pure ester, not really an oil at all. So the Endangered Species Act of 1973 was brought about partly by automatic transmissions."

I once put two pounds of hamburger in a car rear end to quiet it down for a trade-in. It worked.

Kalway

I've heard of "good ole boys" using saw dust.

Eddie 70

I also used Mobil1 75w90 in the rear setup in mine. Works nicely and quietly for the last 5 years or so.

flood

jimcork1

I used synthetic 75w90 Castrol in the differential of a big ford 5 years ago. After 50K miles the wheel brg went out and I pulled the C clips to remove the axle. What I found was the surface hardening had worn off of the gear face into the porosity of the casting. The gears were worn out due to scuffing. IMO I don't think the syn. gear has sufficient EP additive to take the shearing stresses in a differential between the pinion and ring gear. I won't use anything but standard oil in the diff. I have never had a gear failure with standard EP gear oil,, but have with synthetic.

99 Nassau Blue

kdf1986

I bought a 72 this week that had some differential grinding noise. I pumped out the old fluid and added 1 bottle of Mobil 1 Synthetic 75W-90W gear oil and 4 oz. of Anti Slip Additive. It quieted the grinding noise some but not all. My plan is to replace the gear oil again next weekend to get rid of all the old oil, and that should do it.

kdf

VETDRMS

I am using Royal Purple 85-140 MAX gear oil in my diff along with a bottle of GM posi additive.

0Tpls 69

I've been using Royal Purple Max Gear on both my C 3's, for the past 7 years. Are you sure your manual called for 85w-140? My manual calls for 75w-90, or 80w-90.The 140 may be too heavy for the tolerances allowed for C3's of that era. You also don't need to add the GM posi fluid, as Royal Purple say they already put an anti slip additive into the gear oil. Using the GM additive w/ RP's shouldn't create a problem though.

82Vette'ster

I was considering using one of the wide range fully synthetic gear lubes also, like 85w-140. I think I've seen 75W-130 also. It doesn’t match the manuals, but it wasn’t around when they built these cars. I think it might be a good option for the hot environments, like here in Arizona with our summers. The 85W (cold measure) is probably the highest viscosity the 85W-140 will reach. Which is probably fine. I would be very surprised if the 140w on the hot side was thicker than the 85w cold. Remember the scale isn't flat.

The first number is the viscosity when cold and the second number is the viscosity when hot (Sorry, I don't have the actual temps they measure at here). It's not a level scale, it's relative to a straight weight oil. So 85W-140 has the same viscosity on the cold side as 85 straight weight standard oil when it’s cold and the same viscosity hot as 140 straight weight standard oil is when hot. It's still going to get thinner (lower viscosity) when it gets hot, but just not as much. Usually holding viscosity is a good thing, although higher viscosities do lead to slightly higher drag losses.

NHvette

Everyone is adding one bottle of additive.
I thought two was recommended. I bought two.
Should I just save one ?

Matt Gruber

whale sperm works better, but you have to cozy up to the whale to get it