I tap the differentials for every customer that wants them, both NCRS or non NCRS members. There is a point where practicality should take precedence. My mostly original 72 has a tapped diff, my 69 has both a tapped diff and Muncie. However, I don't judge my cars so it doesn't matter to me. Interestingly enough, many NCRS guys opted for tapped diff drain plugs.
Whale oil I believe was outlawed by 1972? Joe can confirm, but I believe there has been several revisions of the GM additive over the years. Part numbers and packaging for sure, chemistry I can't say but can say I have seen a difference in performance about 10-12 years ago. With a tuned posi, one bottle was all that was ever needed. After one of the packaging and number changes in that time frame, I did have a posi that chattered. I still had some of the previous additive and replaced the diff oil and used this additive and it resolved the issue. Since then I have been advising using 2 bottles of the additive, in this case the GM stuff since that is what I use. I haven't had any issues since. Again, I build posi's in the non traditional way, no spring pack at all. Axle end play 005-007"
Also the clutch type will make a difference. Eaton never warranties a posi where synthetic oil was used, steel clutches or the new Fiber type.
Whale oil I believe was outlawed by 1972? Joe can confirm, but I believe there has been several revisions of the GM additive over the years. Part numbers and packaging for sure, chemistry I can't say but can say I have seen a difference in performance about 10-12 years ago. With a tuned posi, one bottle was all that was ever needed. After one of the packaging and number changes in that time frame, I did have a posi that chattered. I still had some of the previous additive and replaced the diff oil and used this additive and it resolved the issue. Since then I have been advising using 2 bottles of the additive, in this case the GM stuff since that is what I use. I haven't had any issues since. Again, I build posi's in the non traditional way, no spring pack at all. Axle end play 005-007"
Also the clutch type will make a difference. Eaton never warranties a posi where synthetic oil was used, steel clutches or the new Fiber type.
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