1991 xjs v12 irs oil leak& hot diff

[dave01]

When I bought this car the diff was covered in road grime and oil,which had also got onto brakes,this was removed with de-greaser, all was fine for 1500 mls untill it desided to drip oil . Is there a breather on these diffs,if so where is it? and how warm should a v12 rear diff get after a 40 mile trip driven reasonably briskly at 30-90 mph it seems to be very warm

 

[dave01]

oh and by the way the oil drip was from drive shaft oil seals.

 

[dave01]

Forget that the oil aint coming from shaft oil seals its leaking from above the level plug ......dont just view REPLY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[vettedog72]

Dave:
I don't have any idea about your diff and the vent. It seems that diff's on other cars do not get hot in 30 or 40 min of driving. I am sure some one with an intelligent response will enlighten us all.

In the mean time, if there is a concern about the level of oil in the diff. you could pull the filler bung, assuming there is one, and let any excess drain off. If the car is level when you do the drain off, you should not have any over flow from a vent with hours of hard driving on the street. You know SCCA requires catch tanks for all vents in race cars so if you are racing, all bets are off.

 

[Michael J.]

Let's rule out whether there is too much or too little oil in the diff. Pull the level plug on right side of rear cover avout 1/3 of the way up. Oil should be to bottom of threaded hole. Diff oil must have additive for positraction added before adding oil. It is a GM P/N for a small bottle that you add to a quart of 80/90 wt oil.

Up higher on the right side is the speed pickup. The vent, at least on my 90 is on the L/H side of the rear cover.

Unless you know the history of the car, you dont know who might have added oil, or how much.

 

[dave01]

The oil was changed by myself about 3 months ago and the level is fine.

 

[Michael J.]

Were you able to locate the vent?

Is there any unusual noise or slipping from the diff that you have noticed, especially when going around curves?

Have you checked the rear cover bolts along the top for tightness? You might want to consider draining the oil and pulling the rear cover to replace the rear cover gasket.

Any fluxuation on speedometer readings? There is some type of seal where the pickup installs in the cover with one or two bolts. Feel around the pick-up to see if it is wet with oil. The leak may be there.

 

[dave01]

The oil is definitely coming from breather only if the car is driven fast,the oil level is correct and there are no leaks coming from end cover gasket or shaft oil seals.

 

[Michael J.]

Automatic Transmissions will leak transmission oil from the vent if overfilled and the fluid is whipped into a foam.

With the car sitting level on Jack stands, pull the drain plug to see if any oil runs out from the fill plug. I realize that you said the level is correct, but humor me.

Have you driven through any deep standing water before the onset?

If some water entered the diff through the vent, the oil would float on top, raising the level. Maybe causing it to foam?

Try loostening the bottom drain plug a few turns. What leaks out, water or oil? If you have water in the diff, it will drip off the loostened drain plug first. If it is oil, you have two choices. Consider that someone added the wrong oil at some point, hence the foaming. or simply drain the oil and replace it with new 80-90 wt oil mixed with the G/M additive. At that point, you can repeat the high sped runs to see if the oil continues to vent out of the breather.

The breather should be an "L" shaped pipe. It should have a vertical section about 1 1/2" long. If yours does not look like that, perhaps it was broken off somehow?

Compare what your vent looks like against the illustration in the parts catalogue.