[purdueboy]

I have a 2003 and just changed my front differential to 75w90 synthetic. I was reading in the do it yourself section that if you switch to synthetic that the vent cap should be changed to a white one? What is the purpose of that? Is it really necessary?

 

[DEWFPO]

Some folks haven't changed caps and have not had any leaks but GM feels the new cap is more compatible with the synthetic fluid and will prevent fluid leaks thru the cap.

DEWFPO

 

[ZL-1]

I have a 2003 and just changed my front differential to 75w90 synthetic. I was reading in the do it yourself section that if you switch to synthetic that the vent cap should be changed to a white one? What is the purpose of that? Is it really necessary?

The '03's and newer models are supposed to have the new white vent cap. '02's and older have the old style black one. If you need one the part # is 12479390.

 

[Evolution]

The '03's and newer models are supposed to have the new white vent cap. '02's and older have the old style black one. If you need one the part # is 12479390.

I confirmed the same info on my latest trip to the dealer for that very thing.

 

[AKTigger99645]

Is this the large (about 2.5 inches) cap on the left (driver's) side of the diff?

 

[Idle_Chatter]

Is this the large (about 2.5 inches) cap on the left (driver's) side of the diff?

Yeppir, big hex in the middle and a hose barb in the center of that with the vent hose attached.

Nice legacy racer!

 

[AKTigger99645]

Cool, mine's white. At least that's one thing I don't have to worry about. Need to change my LF bearing, it's got about 1/2 inch of play, and think about the xfer case pump upgrade.

That's a 1937 Chevy Sedan Legends car. My wife races it, I'm the crew chief. Check out 600 Racing for more info on the program. They're lots of fun!

 

[schulte]

Worst comes to worst, you leak a little diff fluid, even if you had the black cap...

 

[freyguy]

Pictures for reference:

 

[Idle_Chatter]

Worst comes to worst, you leak a little diff fluid, even if you had the black cap...

Actually, a little seepage is not the worst case. Worst case is if your black cap internal baffle (fixed) is in the wrong position, the front diff slings the synthetic lube around in the case and it actually pumps up the vent hose and spews out all over the left side of your engine and the inside of your driver's side wheel well liner. The metal internal baffle in the white cap rotates and always faces down. I've had synthetic lube in my front diff over 5 years and 100,000 miles with my original black cap with no problems. I don't really believe that synthetic lube will eat up the o-ring on the black cap.