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Mark42 · 12-10-2009, 08:02 PM

Ok...
The Owners Manual for 1998 bird says the rear takes 1.75 quarts of SYNTHETIC oil (75w90), and if the OEM posi is installed, use 4 oz less and add 4 oz of posi fluid.

The differential that is being installed is the Eaton Truetrac. Eaton says to use what the automobile manufacturer says to use. Posi additive not needed.

The gear install doc says to use what the automobile manufacturer says to use. The also say to drive for 15 -20 minutes, then let cool fully. The important part is not to over heat the gear lube so it fails during breaking. Gear instructions say the first 15-20 minutes of break in cause high oil temps as the gears are wear hardened from use. Then keep speed under 60 mph for the next 500 miles.

The reason I asked if regular lube or synthetic lube should be used is in the past I have read where synthetic is not good for break in, because its just too darn slippery and doesn't let the parts wear in properly. But if no one has info saying regular lube should be used during break in, then synthetic will be used.

12-10-2009, 08:02 PM	#21
Mark42 Join Date: Oct 2009 Posts: 443 iTrader: (0)	Ok... The Owners Manual for 1998 bird says the rear takes 1.75 quarts of SYNTHETIC oil (75w90), and if the OEM posi is installed, use 4 oz less and add 4 oz of posi fluid. The differential that is being installed is the Eaton Truetrac. Eaton says to use what the automobile manufacturer says to use. Posi additive not needed. The gear install doc says to use what the automobile manufacturer says to use. The also say to drive for 15 -20 minutes, then let cool fully. The important part is not to over heat the gear lube so it fails during breaking. Gear instructions say the first 15-20 minutes of break in cause high oil temps as the gears are wear hardened from use. Then keep speed under 60 mph for the next 500 miles. The reason I asked if regular lube or synthetic lube should be used is in the past I have read where synthetic is not good for break in, because its just too darn slippery and doesn't let the parts wear in properly. But if no one has info saying regular lube should be used during break in, then synthetic will be used. __________________ 1998 Firebird Coupe Mods: 3.73 Gears, Eaton TrueTrac, PCM Tune, LS1 Aluminum Drive Shaft, Cold Air Intake, 180 Thermostat, Magnaflow Cat-Back Exhaust, Moog LCA busings. My Firebird Projects : Click Here Last edited by Mark42; 12-10-2009 at 08:04 PM.