1977 L48 Automatic

I have been putting off changing my differential cover until the weather cooled off so I am out of excuses. I purchased a Muskogen HD Cover for it months ago but since I have to tear down the entire rear end I wanted to get some feedback on what else I should be checking and replacing while I am there. I am going to replace the U-Joints, struts and shocks also when it is apart.

I had a few questions before I begin:

Is there a way for me to check/test the differential prior to dropping it? I wanted to put in 3.55 gears in but if it is not broken I was going to leave it alone aside from replacing the cracked cover. I don't want to have to drop the cross member again in the future if I can help it.

When I drop the cross member there are some large bushings I believe, where I am going to have to use the jaw puller to get it off. Will these need to be replaced or ok to re-use?

Since one of the differential brackets is broken on the differential cover the leaf spring layers are twisting, can a leaf spring be rebuilt?

I have heard people talk about snubber bushings, is there a way to check to see if it needs to be replaced prior to dropping everything?

Anything else that should be checked or replaced? The fun begins next weekend so want to get any parts I don't already have en-route, I don't want the car apart more than two weekends if possible, preferably just one.

 

I'll address your questions one at a time:

There isn't any easy way to check anything in your differential when it's still mounted to the bat wing.

After you remove the two 7/16" bolts that secure the bat wing to the large rubber bushings the bat wing will remain stuck to the bushings. Just use a pry bar to un-stick it

Leaf springs can be rebuilt but wait until you have it removed from the cast iron cover to see what it looks like with no load on it. It is probably okay as is.

The snubber bushings will need to be replaced because they squash over time and if yours are the originals they will be squashed.

The differential side yokes are likely in need of replacing because every time you make a left or right turn the spider gear cross shaft scrubs against their ends and wears them. There should be about 1/8" of splines showing past the snap ring and yours are very likely worn down to (or close to) the snap ring. Only buy the quality side yokes from one of our supporting vendors; not low priced E-Bay yokes unless you know their quality..

Good luck.

 

If the pinion seal is leaking now would be a good time to replace it....There is a real good "How To...." post here on the forum.

Brian

 

If it is an original untouched 77 then you should check the axle endplay as mentioned, they were soft and worn down in about 30k miles or less. If they hit the seal lip they will start to grind into the housing and then you will have a problem. The clutches were snowflakes and not too good but if it was a low performance automatic car they are probably still intact but you won't know unless you pull the posi apart.

At a min replace the axle seals and pinion seal along with the cover. I would check the ring gear bolts and if you see flange head bolt remove them, clean with acetone and use #271 Loctite on them. Retorque them and you can install socket heads in the bearing caps for under $5.

 

77 = NO Bat Wing

 

Gary is completely correct. You should DEFINATELY change both the stub axles to rebuilt units that have had hardened tool steel inner ends added to them. The C3 design has the stub axles sliding in and out of the differential and bearing internally. Without improved ends, they will wear and leave the diff full of metallic trash. Eventually, you will have too much negative camber and will be unable to adjust it out.

While you are doing this, you might also consider changing your strut rods to a threaded sleeve adjustable type with rod ends. This will keep your rear end firmly planted.

Finally, I found removing the bushings from the cross member supporting the diff to be VERY difficult. I finally used a torch to burn then out and replaced them with new after POR 15'ing everything. I also installed the aluminum reinforcing discs when reinstalling.

 

JayRay: I was very leery about the crossmember bushings being badly stuck on the frame the first time I had to drop the differential and came up with this method, which I have posted before.

..............
An alternative method to get the differential out without removing the crossmember is to use a flat ratcheting wrench and a deep hex socket as shown. See below. This just fits the narrow gap between the body and the crossmember and you do need to be a little adept with your fingers, etc.

Additionally some long bolts with the heads cut off and loosely held serve to reposition it going back in.

Why might you choose this? Well when I pulled the body off I had to pound on my 45 year old crossmember with a sledge to get it out. These things don't just pop out. And of course going back in you'll want new rubber insulators so that is certainly a consideration, as they also are a bitch to get out. And course if you really really want to change out the bushings, installing the aluminum pancakes is a nice upgrade.

The only real downside is you can't correctly torque the mounting bolts. But in 10 years of hard use, it never loosened on me.