9 inch differential question

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Jun 5, 2010 | 11:45 PM

xlt4wd90

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From: SoCal

9 inch differential question

I hope someone here can enlighten me on this.

Last year I replaced the pinion seal on a Ford 9" differential (on an old Mustang) because it seemed to have been leaking most of its life in the hands of previous owners. This required pulling the yoke off of the pinion. While in there, I noticed the 40 year old gear lube looked like tar, so I pulled out the entire third member and cleaned out what I could. Then I assembled with new gaskets and copper washers, and filled with 75w90 Mobil 1 lube. Without having driven it much over that last couple of months, I noticed a slow leak coming from the center of the yoke, where the pinion sticks through and the nut fastens on. The areas around pinion seal, main seal, and those copper washers are all dry, so the leak is definitely coming from between the yoke and pinion.

So I'm wondering, is there some kind of seal like an O-ring or something else that goes between the flange and the pinion? Or should I apply some RTV in there as well?

Jun 6, 2010 | 01:53 PM

mark a.

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Make sure the axle vent is clear.

Jun 6, 2010 | 04:54 PM

xlt4wd90

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From: SoCal

Thanks Mark. The vent is clear; but it's leaking just sitting there, without being run at all.

Jun 8, 2010 | 01:31 AM

mikeo0o0o0

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From: Stanley, VA

The pinion nut comes with a coating of sealer on the flange and threads. If you reused the old nut you need to coat it with sealer on the threads and the bottom of the flange.

Jun 8, 2010 | 03:09 AM

xlt4wd90

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From: SoCal

Thanks Mike, I'll try it. I won't be able to get into it until this weekend.

Jun 8, 2010 | 07:34 AM

60F100

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From: Cantonment, Fl

If you replace the pinion seal how tight should the nut be torqued so that you don't mess up the crush collar?

Jun 8, 2010 | 07:56 AM

gfw1985

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From: Raphine, Virginia

There is an O-ring on the pinion shaft and preload washers. Edit: Trying to be clear here. When you pull the whole pinion gear, not removing the yoke, is where the o-ring and preload washers are.

Last edited by gfw1985; Jun 8, 2010 at 08:03 AM. Reason: Clarify

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Jun 8, 2010 | 03:10 PM

xlt4wd90

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From: SoCal

60F100: I could not get a consistent torque reading on the pinion when trying to check the bearing preload. So I punched little marks on the nut and the end of the pinion before loosening the nut. When I re-assembled, I just torqued the old nut back to the position where the little marks lined up again. I figured this should be close enough, since I did not change bearings or crush collars.

GFW: Are you talking about the pinion carrier and the O-ring around it? There are spacers there that set the pinion depth. But I did not change any of those, and that's not where the leak is. I do not recall finding an O-ring around the pinion shaft itself. If there was one, and I forgot it, maybe that's why it's leaking now.