Differential Rebuild / Service - XK-140 when is it needed? ...and at what cost?

My XK-140 SE is in mid restoration after sitting unused, not running, in CA for 30-40 years. (Approximately 40,000 miles on odometer) The current issue is the Differential. Fluid is black but no indication of metal chips or damage. Not looking to be a show car but rather a high end reliable driver. Should I have the differential rebuilt? …any Idea as to what that should cost? Engine has been professionally rebuilt, body and chassis are being chemically stripped and e-coated. Any advice is appreciated. …would love to save cost somewhere - Yikes!!
Tom A

The Salisbury 4HA is a virtual clone of the Dana/Spicer model 44. Hundreds of thousands of Dana 44 axles were used in Ford trucks, station wagons, Studebaker cars and trucks, Mercury wagons, International Harvester Scouts and Jeeps of every description. Find yourself a shop that specializes in off-road Jeeps. They will be very familiar with it.

I was not aware of that so thank you for that information. I am sure a Jeep / IH / Ford facility will be much more reasonable than some exotic / import service facility in my area. Thank you, I will check that out!!

Tom A

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I would drain the fluid, replace the axle seals and fill it back up.

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The 4HA is not known for a lot of failures, with one exception. That is the bolts that hold the crown gear to the differential carrier. I have one on which all the bolts were sheared off. Pull off the rear cover and have a look at them.

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That is interesting. Wow, I wouldn’t expect that. Appreciate the information, I will take a look at that.
Tom A.

That may be the logical course. Appreciate your thoughts.
Tom A

I second that. I’ve seen several 4HA diffs with sheared ring gear bolts. About the only difference between the Salisbury and the Dana is the Dana uses larger ring gear bolts.

When I do an inspection of a differential I measure the backlash movement of ring gear with a dial gauge and run a pattern check with Engineers blue

If there was no other reason for concern, and after inspection of all parts, I would not rebuild it those two checks are ok.

I believe the backlash max is .008" but that should be in the FSM

You do not say what you intend to do with the pinion seal

I cant see how it would hurt to replace the ring gear bolts