I am installing a posi unit, and realize now that I bought one without a plug. My housing does not have a plug. So, I will be adding through the axle tube. If I buy diff oil labeled for posi rear ends, do I need to add an additive as well? How much? If possible, I would like to get it right on my first try so I dont have to pull the axle again. This is the first time I have had a posi, so I dont know what I am doing to some extent.
If the gear lube is labeled for a posi-traction or traction lock differential you can use it without an additive. How do you plan on checking or verifying the fluid level? That 8" center section without a fill hole is from and earlier unit with the fill hole in the housing. They are not as strong as the center sections in the Mavericks and Comets. Just so you know.
Fill spec is 4 pints... You could add 3½ pt and see if it has excessive chatter or clunk... If OK add the other ½ pt through the vent tube, if not add the friction modifier... When I re-clutched the 8.8" T-L in my Bird it had fits on the "supposedly" posi gear lube, had to add the modifier... As far as checking level in future, if it isn't leaking, not necessary to add...
Thanks for that info, I didnt know they were weaker. Probably will be fine in current set up, but very good to keep in mind. You guys are so smart.....I didnt think of adding through the vent. I was looking forward to (not!) pulling an axle to add that modifier. I am certain no more than 2 quarts came out, so the 4 pint number agrees with that. Frank, I will post up a pic, because I should know by now that what looks like a simple third member to me actually holds at least a paragraph of good info from those in the know!
FYI, the hole inside the vent tube is only 1/16" and is designed for venting only, trying to pour 80W gear lube will be next to impossible.........you can unbolt the vent tube from the housing and use funnel to add lube. Be careful as the vent tube also secures the rear brake distribution block. Clean the area of any dirt/debris to avoid falling through hole once vent tube/bolt is removed, should be 5/8" Also, if vent hose is still original, with crimped on hose clamp, you may want to unbolt the clamp securing the hose to the body, to prevent twisting and thus breaking the hose, while unbolting the vent tube which has approx. 3/4" of threads (15 or 16 threads, so will take at least that many complete turns to remove). David
Good observation, I did remove vent tube when I added the modifier to my Bird(things we forget)... Heating it to around 120*F will make the lube/modifier much easier to pour...
Never met an oil that lasts as good as an additive package and use GM's additive on ALL clutch(friction) style posi units. Occasionally gives new life to ailing units too.
