76 L48 manual.
I noticed that the diff cover was broken (see pic).
I hear the wheel rattling on this side

So how bad is it?

Can I live with it or do I have to replace that part?

How involved is the removal of the part and should I plan for some heavy 'while I am at it' type of actions?
Knowing some of my OCDs, I am already prepared for a lot of 'while I am at it'...

 

Yeah.. you need a new diff. cover. Problem is that is how the differential is also mounted to the rear cross member.

Seen several cars with this issue. Not sure what causes it. Could you get away with it... most likely. But since you have seen it and if your keeping it I would suggest changing it before it lets you down as you only have one more bolt left towards the back holding the spring to the diff.

How much you change while in there depends on how deep you get into it (and what you find bad). Its a little crunchy under there so you have some old parts that are gona want to stay right where they are.

The hardest thing to get to is the 4 upper diff. cross member bolts but if you dont mind pulling up your rear carpet and putting a hole in the floor just over the crossmemeber you can make life a lot easier for yourself (You can use some plastic furniture desk plugs to close them up later). Then you gotta drop your exhaust, spring , strut bar bracket and the diff from the front mount. But you could most likely just drop those items and then replace the cover with the diff still connected to the half shafts in the car. All depends on how creative you are and what else is worn out (Ujoints, trailing arm bushings, trailing arm bearings, stub axles, cracked eaton carrier, strut rod bushings, spring bushings, spring on and on if you want while I am at it itus). Change as little as you need to make it safe again..... You could turn this into a body off event if u want.....

Look up trailing arm bushing bolt removal horror stories if you want to wield a sawzall on your car... the strut rod lower shock mounts are real gem on rusted cars as well. Trying to quite that while your at it itus for you.....

 

actually, my first thought was: let's clean that up and weld it back while still mounted...

Being so close from the fuel tank is what made me think again: I would need to drop the tank (again!)...

I will get a closer look at it. It may have been here for years, left unnoticed, and may not be the origin of the rattling noise.

Could the full assembly be dropped in one piece (i.e., cross member with diff and others still assembled to it)?

 

remove the spring, disconnect the half shafts and axle, remove the 2 bolts holding the cross member and drop the whole thing

 

Dropping that upper cross member is a real bear... Those outer bushings are near impossible to separate from the car. You might get lucky and it could go easy for you. Certainly something to try.

Welding cast iron is tricky... my understanding is you have to heat it prior to welding it and carefully control the heat to ensure a good weld. Not sure you can do that while its on the car.

 

Can't weld cast iron(I know some specialist can but it'd cost more than a HD replacement). Those halfshaft u-bolts look pretty ruff, your gonna replace a lot of stuff and might be a good time to do some other upgrades. I just put over $1700 of parts into my rear, about $300 of that in hardware and I didn't touch the trailing arms or the center section(pig).

New solid Spicer u-joints are about $100 alone. Not trying to scare yah but I'd estimate $1000 plus in parts if your doing mostly just stock replacement parts, once things start to crumble as you take it apart. Torches would help a lot if you got em and if not you can take it to someone with some. I'd remove the rearend crossmember with the pig and leave the halfshafts connected to it as well load it up and hit it with some heat.

 

$2k was my quick look estimate of how much it would cost to replace most of the parts. With your data, I am probably looking at 3k.

Scary...

Bummer, this happening at the beginning of summer is annoying. As a winter project it would be fine...

 

Good luck, that looks like a tough job...done it so it will take patience.

 

FWIW I just happen to have a NOS Muskegon HD diff cover that needs a good home (decided to fit mine to a batwing). PM if interested.

 

My $1700 included
-$450 PST alum halfshafts with all new spicer solids
-$360 VBP composite spring
-$320 QA1 single adj shocks
-$240 dragvette basic drag kit(no longer sold)

So I still think $1000+ is doable if your not replacing everything Like I did and not pulling apart the TA's. Well the camber rods I'd be surprised if you could reuse them. Unless you can get just the diff cover and crossmember out, but idk if I'd try that myself.

 

They're not hard to pop loose. The problem is if you try to pry them from one side with a crowbar, they bind up and don't want to budge. But if you use a big 2 or 3 jaw puller to pull them straight down, they come right out with surprisingly little effort.

 

Thank you all for your suggestions and encouragements.
I had a closer look yesterday. I also started soaking the bolts in WD40.

I like the idea of a gear puller: one of them on each side, slowly but surely working at them. I will keep the crow bar in case of...
First, I will try to fix the issue without removing everything as suggested above, if that fails, I will remove the whole assembly and fix only what needs to be fixed.

I will keep you posted, thanks again everybody!

 

Gear puller is the way to go. I tried everything on mine and the gear puller was the only thing that worked. I just used one gear puller and worked each side with it.

 

It seems like a great way to do it. What are you guys doing to keep from breaking the weld nut off inside the sombreo bushing bracket?

I still like the idea of removing the 4 bolts on the diff. cover from inside a hole in the floor of the car (you still have to take them out anyway)... that no one would see with the carpet laid back down.... but to each his own.

 

I do as well, I just have not come to term with making holes in my C3 yet.

After a few hours of frustration, I may lean that way tho...

 

No need to chop up your vette when simple tools are readily available to remove the cross member. My cross member came down with little difficulty using a crowbar.

 

Mine cracked in the same place, if you look at diff covers from most vendors you'll see the stock one and the HD version, which was a fix for this very issue. It's going to take a day to trade out the cracked one for a new one and while your at it, this would be a good time for a new spring ( I'd recomended a comps it ). Don't forget to add ac Delco positive Trac additive when you refill your diff.

 

It might cost more and be a pita to tear it apart, but from the looks you could prob use some new halfshaft u-joints and it's only gonna get rustier.

 

Hope that helps, Moose

 

Yup, once you get in it ...theirs no turning back .......can't fix that cover and ignore all the other chit that is worn out.

Typically what kills a C3 .