Rear differential pinion seal replacement.

Dealing with all subsystems specific to the diesel powered Datsun-Nissan 720 pickup trucks.

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claybodie
Posts:51
Joined:14 years ago
Location:Corvallis, OR

#16

Post by claybodie » 14 years ago

Great - Thanks a lot for the info. That's really helpful.
There isn't an internal seal. The only "seal" other than the axle seals and pinion shaft seal, is the housing gasket. Even if it leaks, a much easier fix for a leak at that gasket is external application of sealant.
I was actually talking about the gasket when I said 'seal.' The external application of sealant sounds like a good idea.



Clayton
1982 Datsun 720 w/ sd22 running on B100.

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asavage
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#17

Post by asavage » 14 years ago

On other rigs, I have seen leakage around one or two of the studs, where the diff carrier bolts to the axle housing -- this was fairly common back in the day on Fords & Chevrolets. I spray them off using a lot of aerosol brake cleaner, wipe & let dry, then RTV over the nut. On a non-pressurized assy like the diff (which is separately vented), you can get away with that. Works less effectively on pressurized assys like a timing chain cover.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.

claybodie
Posts:51
Joined:14 years ago
Location:Corvallis, OR

#18

Post by claybodie » 14 years ago

Ok, so it looks like this job may be possible by marking the nut and ignoring preload measurements (assuming I can get the nut off).

Could someone describe a little more clearly how to mark the nut and its relation to the rest of the differential? If I, say, put a permanent mark on the top, and I retighten it so the top is up, how do I know it doesn't need one more 360 degree rotation?
That may be a really dumb question, but then again I'm not working with really powerful tools at the moment - I may not be able to get it back on tight enough.

Thanks everybody.

Clayton
1982 Datsun 720 w/ sd22 running on B100.

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asavage
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#19

Post by asavage » 14 years ago

First, I have to emphasize that the mark you make should be large and robust, so that a casual blow won't obliterate it. A pin punch or center punch will do, so will a Dremel mark, and probably a small cold chisel will work. A scratch with a screwdriver is not sufficient.

You ask a good Q about "how do I know the nut doesn't have to go another turn". Unlike other bolts you've tightened, the torque will come up quickly on the pinion nut. The pinion is not very elastic, unlike, say, a head bolt. In this regard it's much like a lug stud on the axle. Imaging match-marking a wheel's lug nut to its stud. When you put the lug nut back on, you wouldn't mistake tight-and-marks-line-up with needing a whole 'nuther turn, and this is the also the case with the pinion's nut.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.

claybodie
Posts:51
Joined:14 years ago
Location:Corvallis, OR

Keeping it Simple

#20

Post by claybodie » 14 years ago

So in the interest of keeping things simple, if you are thinking of undergoing this operation, check the air bleeder screw on the rear axle and see if it's plugged up. Mine was completely stuffed full of junk and absolutely useless. It would make sense that if pressure built up in the diff that it would come out of the pinion seal if necessary.
Anyway, I cleaned out the air bleeder screw with a safety pin (blowing it out with air would be a good idea) and it seem to decrease significantly the amount of oil leakage. It almost completely stopped it, but still a small trickle - not enough for me to change the pinion seal at this point.
1982 Datsun 720 w/ sd22 running on B100.

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asavage
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#21

Post by asavage » 14 years ago

Wow, your truck must have had a rough life, to plug the diff vent.

I've seen that before, on a customer's Toyota 4x4. I ended up taking the "hat" off the vent, putting some fuel line on it, up to the bed bottom, then a metal U and finally a fuel filter, to keep the crap out of his diff.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.

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