8 3/4 Vent Blow-By

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Oklacarcollecto said:
In reading the TSB's for 1969 it appears that the differential gear oil was changed. The plate type Sure-Grips were replaced in late 1968 with limited amount of spring loaded cones. 1969 were all spring loaded cones.

"LUBRICATION

Lubricant required for axles with the new “cone” type Sure-Grip differential just meet MS (Chrysler Material Standards) #4893. Chrysler Part No. 2933565 meets these requirements. MS-1569 Chrysler Part No. 2585318 must not be used in these axles.
MS-1569 Chrysler Part No. 2585318 (or its equivalent) must be used in plate-type Sure-Grip axles. These axles have identifying tags stating, “Use Sure-Grip Lube” or “Use Limited Slip Lube Only”.

Conventional Differentials - Part No. 2585317 or 2933565
Plate Type Sure-Grip - Part No. 2585318
Cone Grip Sure-Grip - Part No. 2933565

If you should install a 1969 model differential and carrier in a pre-1969 vehicle and you require using the original drive pinion drive flange, it will be necessary to install the 1969 drive pinion seal guard on the original flange. This new guard is not interchangeable with previous model carrier castings."

I think I retyped all this correct. I have no idea if this will help here but maybe the different oil has something to do with the problem with the Cone Grip Sure-Grip. This is mentioned in more than one TSB in 1969. The differential gurus might know what to make out of this. It appears that the Cone Grip Sure-Grip was an issue. Maybe that is why the housing was modified for 1970. The 1970 TSB has only 1 page on the outer seal replacement on the 8 3/4.
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No I think this had to do with the cone types not needing the SG additive.
 
SGBARRACUDA said:
No I think this had to do with the cone types not needing the SG additive.
Click to expand...

Op said he added SG additive... Wonder what Sure-Grip he is running? I will have to go back and see if he said.

Yes he said cone-type. Could the additive be the problem? I read all over the place that everyone says to use the SG additive but I wonder if it could be foaming when used with this housing?

Ok, I guess I wasted my time. There are a total of 6 pages on this TSB, 3 on another TSB and a reminder for a total of 10 pages in 1969 just fror the 8 3/4. Maybe some guru might read them and see if there is any answers.

I am interested in an accurate answer on this one.
 
I know it has been a while, but I wanted to make sure the problem was really fixed, and to do that I needed to drive the car in the heat of the summer. The cause of the blow-by was the new aftermarket differential vent.

On a hunch I thought maybe it was the vent. So, I searched the web and found an EBay listing for Mopar diff vents, part# 4032798, in the original package. So I bought it, it was cheap ($18 shipped to my door). I installed it a few weeks ago and have driven over 200 miles in the summer heat (mid to high 90s), no more blow-by, not a single drop. The Mopar part looks slightly different (see picture below), Mopar vent is on the left, the aftermarket vent is on the right. However, I'm convinced the real issue with the aftermarket vent is that the pressure relief tension is weak, allowing the vent to stay open too long and/or not closing correctly allowing fluid to blow out of the vent.
 

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Had same problem with mine. Took vent cap off, added 18 inch long rubber hose with cheap lawn mower fuel filter on end, attached it to the upper shock mount, line and filter acts as the breather now, no problems. Old off roader trick.
 
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