Thread: which gear oil is best for ford 9"

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Hello again guys,
Just completed my rear sswap, finally! Question is, I am told not to use synthetic, something about Ford rears not using it. It has a Detroit True Trac. Right now I have 80-90wt Valvoline in there. I have some oil blowing out the vent tube hose which is vacuum diameter and extends about 1 foot up. Also have a super slight rear bearing leak. Am I overfilled? I was told to put 3 qts in. Any help would be much appreciated...Phil.

The Valvoline gear oil is just fine, I would add a bottle of posi traction additive after ya drain it down to the proper level, not sure where ya fill plug is at,but in most cases you should fill till it trickles out the fill hole, My books show 3.75 pints for most 9 inchers...............

So why on earth could one not use synthetic in a Ford rear end? Will it melt? Or will the wear rate diminish to where with proper change intervals you will never have to replace your rear end?

Or is the claim it will eat the shaft seals?

Sounds like advice from the Synthetic Police again ...........

Just curious ..........

Kitz

Sounds like too much lube. Find the filler plug, remove it and let the excess drain out. Make sure the car is level.

Synthetic is fine. Don't forget the posi additive. Most auto supply stores will have it.

I was told I did not have to use a posi additive. The true trac is not a clutch type unit, it has gears, so you do not need it. No? Yes?

If it does'nt have clutches then you should be fine without it .

I have the same rear end as you. Do not use posi additive. I used synthetic in mine--you can if you want to but it is not required.