jhowar

I have 2008 NC with LS3 conversion by V8 Roadsters. I'm trying to figure out the correct volume of gear oil for the Ford 8.8 rear end from the Mustang Cobra. Diff case is aluminum with steel back cover. Filling up to fill hole results in puking oil out of the pressure vent on top of the case. Does anyone know how much oil to use in this set-up?

pj_mcgarvey

I have a Cobra 8.8 diff as well, and have only filled it up to the fill hole. Same with the diffs in my Jeep. Easier than measuring out fluid.

Oil coming from the vent at the top is interesting... are you pushing the fill bottle into the fill hole thereby pressurizing the diff case when filling and then maybe the pressure is being relieved through the vent hose (as it is designed to do)? Otherwise, that's a weird issue.

tbone heller

Put a longer hose on the vent tube.

jhowar

Thanks pj. To clarify: oil comes out of top vent as I'm driving if I fill up to fill hole (about 64 ounces). After car is parked, oil will continue to drip on the garage floor. Oil is not coming out of vent as I fill the diff. I reduced oil volume to 55 oz, and that decreased leakage, but did not eliminate completely.

jhowar

Thanks tbone. I've got 8 inch hose attached to top vent and it runs upward toward charcoal cannister as high up as I can get it. I put a small K&N breather cap on end of hose.

pj_mcgarvey

Maybe a longer vent tube, as well as a loop in the tube? Though it sounds like maybe oil temperature is causing the overflow, or maybe it's frothing? Either one sounds like an issue with the oil itself, maybe wrong weight, or missing an additive? The Cobra 8.8 I have requires a small bottle of friction modifier. Not sure what the symptoms are if you don't add that.