What Do You Look For In A Junkyard Rear End?

I went looking for a rear end today. With Tape measure in hand I crawled under a lot of cars and realized that- I really had no idea how to guess at the condition of the rears I was looking at.

I unexpectedly found a Mopar 8 3/4 that would probably fit (I still want to measure twice again). I took off the drums and eyed the nice dry internals, but what else can you do to make sure you aren't buying a can 'o' worms?

 

One thing is to grab the pinion yoke, and rock it in both directions, and see how much slop there is between it and the ring gear.

 

I'll check that.
Any other advice?

 

Check see if it is a posi unit, listen for dry bearings or clunking when you spin the gears, feel for anything funny like a ratcheting feeling.

 

Make sure its straight.
Took a 9 inch home once, found it was crooked and i would have been drivin around in circles

 

along with the housing being straight, make sure the axles are not bent.

Sure is nice to be able to pull the cover off or pull out the 3rd member and see how it looks....

Also figure out the ratio, if it's not a posi and you turn one wheel two turns exactly, the number of turns of the pinion yoke is the ratio.

 

Add to those, excessive gear oil leaks. The pinion seal and axle seals should be dry. If it is a ten or twelve bolt GM and the cover leaks a bit that can be fixed easily.

On the GM C clip rear ends I'd pull the cover and check the pin that holds the spider gears and the bolt/pin that holds it. That seems to be the biggest cause of failure in those particular rear ends.

 

whats it from? and what you puttin it in?

 

If you're going to that much trouble, also pull the pin out and look at the axles where the wheel bearings ride, if they're shot (like most of them are) you might be able to negotiate a discount.

 

It's a Mopar 8 3/4" out of a 65 Coronet 440, and it would be going into a 38 Chrysler. I've gotta measure twice more because I want to have room for my

 

If it's a Mopar, look at the last three digits of the drop-out case part number. They're on the side, easy to see.
If they're -489 your great. If it's -472, that's not a bad unit either. If it's a -471, leave it. They have a small diameter pinion stem. I'm 90-percent sure I have those numbers correct (-472 and -471), but the sure-fire way to tell is the weaker pinion version will have a big "X" cast right on the housing, on the side of the area that houses the pinion, behind the yoke. That "X" is like Mopar telling you "Don't bother with this one."
Now, that being said, if it's a limit slip differential in there, DO get it, because the actual differentials themselves (the part the ring gear rides on) will fit in any of the rear ends.
All Mopar rears are also 30-spline axles.

If you can crack open the drain plug, look at it and see if there are any metal shavings in it.

Obviously, the more you can take apart in the junk yard, the better off you're going to be.
Check the axle flanges to make sure they aren't bent from hitting a curb, check the brake drums for excessive wear or grooves, of the pinion seal is shot, you may need to replace the yoke as well... With a car that pretty, I'd be hesitant to get a junk yard rear end as anything but a core for a starting point. Plan on replacing all the bearings and setting the center section up again. I don't think you're going to find one ready to go.

-Brad