I am starting a new post with pictures, because I cannot find the old post. Originally I had a metallic hum that only occurs when pushing on the gas (RPMS increase) itself, coming from the rear and the minute you let off the gas, it disappeared. (also my car idles high, but at 65 it's at 4000+ rpms). and looking up information, some say it could be related to the differential?

The pinion is stamped 15-41 7 5/8. and apparently its standard differential

I was assuming it was the pinion bearings, but I don't know. the gears (to me) don't look overly worn. there is some discoloration at the tips of the pinion (as you can see in picture) and if you jiggle the spider gear housing it jiggled a tad towards the left side (maybe worn carrier bearing?) I was trying to take that bolt out holding the pin in, but it started to strip (as you can see) and so I stopped. it's in super tight. so now I am not sure what to do. even if I wanted to gut it out and replace it all, I can't even get the bolt on..

any opinions, on how it looks, what anyone else thinks, and ideas on getting that bolt out. or should I just send it to the shop? (minus parts, what is the average price for one of these jobs anyway)? thanks

 

trying to get the pictures to show.

 

Here's some pictures

 

More pics

 

A hammer and small chisel on the flange part of the bolt may get it turning. You're going to need to replace it anyway. If the bolt breaks, it normally breaks with about 1/2 thread still holding the pin in. I've used a dental pick to unthread what's left of it.

Other than that, I see nothing unusual in those pictures. 2.73 open diff. May be a good time to upgrade to a posi with some gears in the mid 3.xx range.

 

Unless you are concerned with originality, just swap the rear - they're easily found and usually cheap.

 

For that bolt, use a 6-point box-end wrench; either a 5/16" or 8mm will work fine. Bonk it with a hammer to break it loose. 6-point.

It's a 2.73 non-posi. No big loss if it can't be repaired. People will give you those things for free.

If it doesn't come apart gracefully, button it back up, and start looking for something decent to replace it.

From your description, sounds like it needs pinion and carrier bearings. Probably not worth spending the time money and effort on to replace those.

Your "RPM" problem doesn't exist. What's ACTUALLY going on is, your tach reads high, same as everybody else's. Ignore that.

 

As was said, above, nothing looks all that horrible. A common failure in these rear ends (aside from blowing up) is that the pinion nut comes loose. This lets the pinion move forward and backward ever so slightly in the housing which leads to gear whine only in coast or only under load (rarely both). Acts like worn out pinion bearings but it's not.

If you're gonna dig far enough into the rear end that you are going to replace pinion bearings you might as well think about whether you want to do some mild upgrades like a posi and steeper gears. Anything beyond "mild upgrades" you might want to just save you pennies for an aftermarket rear end assy. and get away from the weak 7.5/7.625 rear altogether.

In my 78 Malibu I swapped in a Buick Grand National rear which is a literal bolt-in from the 7.5. Unfortunately, there was NEVER n better rear end offered in 3rd gens so the only option that exists beyond the stock rear is aftermarket stuff.

 

Sounds like a typical higher mileage rear end. Throw some hush hush oil in it and turn the radio up. You should hear Richmond gears... Them babys howl!