Dana 41 differential - want to "tighten it up" som

When the gears are manufactured, the final step is to "lap" them together - they are run with an abrasive lapping compound in the contact area so they are basically "worn in" together. All the time since then, they've been doing the same thing, only a lot slower - wearing in, getting used to each other, developing a wear pattern. If you change the backlash, you will move the contact patch out of that wear pattern, and will likely make the rear noisy and accelerate wear.

As Bruce says, some lash is SUPPOSED to be there. The obvious question is "how much?", but we don't have to rely on guess work or feel for this. The manual sets the permissible range between 0.005" to 0.010". 

will measure the lash with a dial indicator tonight and report back!

I have to agree with Bruce. If it isn't broke, don't try to fix it.

I owned and operated a driveline shop for 18 years, and customers would come in from time to time with a situation similar to yours. I would advise them to leave it as it is and just drive it. Some would take my advice, others wouldn't. Most of the time those that didn't take my advice ended up getting new replacement gearsets sooner than later.

Put simply, you can't "tighten up" a ring and pinion setup. It changes the relationship that has already been established at the factory and causes noise and accelerated wear. If you decide to move the ring gear into the pinion to reduce the lash, be prepared to replace the whole setup in a thousand miles or so.

Fourteen or fifteen thousandths lash is not unusual for a gearset that has been in service for several years. Provided that it has the proper lubrication, it should see several thousand miles of service.

Take Bruce's advice to heart, he is telling it to you straight.

Bruce said: When the gears are manufactured, the final step is to "lap" them together - they are run with an abrasive lapping compound in the contact area so they are basically "worn in" together. All the time since then, they've been doing the same thing, only a lot slower - wearing in, getting used to each other, developing a wear pattern. If you change the backlash, you will move the contact patch out of that wear pattern, and will likely make the rear noisy and accelerate wear.
You say that the pinion "has a couple degrees of rational play". It should have some. The proper way to measure that is by setting up a dial indicator on the ring gear and measure how much "rotational play" there is in the ring before it moves the pinion. If it's only a little more than the spec for new gears I would not try to change it. If the case (carrier) is tight in the housing and does not want to come out, it's a sign that the side bearings are not worn. In my opinion from what I have read, I'd say that it's not broken - don't try to fix it.   BW

When there is the proper lubricant in the axle, the lash isn't so noticeable. The front still has oil in it and would be smoother and less noisy.

Depending on whether your rig has had hub-locks on it for most of its life or just drive flanges, the wear could be minimal. If it has had drive flanges, the wear on the front could match the rear. With hub locks and most of the drive time on the pavement the wear might not be very evident.

All of this is dependent, of course, with the proper lubricant in place.

One of the worst things that can happen is to run the axles under water and let that water rust inside the housing. The water can get in through breather openings and can be sucked in through a pinion seal if the axle is warm from use and is cooled down by the water. The rust acts as an abrasive and causes gear oil emulsification which in turn is less effective as a lubricant. If your axles are immersed in water for any length of time, it would be a good idea to drain them and replace the gear oil.   

Konstan, FWIW, My 1959 F150 has 90 degrees of that backlash in its rear axle. It has had the same amount for over 30 years & 275,000 miles so far. I change the gear lube every decade whether it needs it or not. There have been no iron filings in the old lube.

I have had a complete spare rear axle assembly sitting in my barn for the same amount of time. I got the spare for when the original axle fails. I am still waiting for it to fail.

I do use the truck as a farm truck. So it does not get babied. I hope this eases your mind a bit.

Don't forget to put that ring gear bolt back in... assuming you removed it? 

...or get the holes and bolts oil-free and use Loctite.