Car is a '76 L-48/auto w. 142K miles on it. Future plans are for a 5 speed TKX swap and a moderately built 350.

I removed and opened the diff, it looks decent inside and I was happy to find it still had gear oil. I'll install new bearings and seals, tune the posi unit and do something about the yokes.
I haven't taken any measurements yet, I will next week when I get back in my shop.

I rebuilt the Dana 70 in my Dodge last fall, so this isn't entirely new to me.

I have interpon's and leigh1322's rebuild threads bookmarked. I skimmed them but will read them in detail over the weekend.

At first glance everything looked good inside, currently the plan is to retain the factory 3.08 gear set and go with a wide ratio TKX when I get to that part of my build.
Other than backlash are there any other measurements I should take before disassembly?

I felt a slight amount of play in the left yoke, I suspect that was the bearing noise that led me to remove the diff. I'll know more of course when I get it apart.

What would cause the shiny wear patterns on the coils on the right side of the spring in this picture?


I could see no corresponding wear on anything.

Are there any good options for heat treated yokes, or shall I plan on getting mine heat treated if they measure good?
I've read a bit about buttons for the yokes, is anyone currently doing this?

Thanks.

 

I regret not running a pattern contact test to see where it was originally.
take a lot pics!
a real crapshoot on axles, see my thread for help i got from Gary and hardening..
very curious to see your measurements! One looks pretty good!
it looks like the spring kinda sticks out maybe rubbing…you won’t be replacing that anyway?

 

Search the forum for posts by gtr1999 (Gary Ramadei) and watch Tom’s Eaton Posi Tune on YouTube. You’ll see that you won’t need to put the spring packs back in.

Your axles, if original, are likely junk as GM’s QC was in the dumper during those days and the heat treating process (hardening) of the axles fell way short, causing them to wear badly.

I built my differential a couple years ago with Gary’s guidance and could not be happier. You will need some specialized tools to do it right but in the end, you will have it done right.

 

I've read a lot of Gary's posts, and will search for more when I get into this diff.
I need to find Tom's video's, thanks for the reminder.

 

The easy work is done:

A little wear on the bearings, a lot of wear on one side yoke and one broken snow flake clutch.

Now on to the cleaning and polishing, I'm buying some of leigh1322's parts so I'll have steel clutches when it goes back together.
After I get the posi tuned I can check the end clearance on my less worn side yoke to see if it will work.

 

Awesome..here is toms link below..
what are you going to do for yokes? Almost unobtainium..
awesome you will be replacing snowflakes and gratifying something was broke..in a weird way.. it is unreal to me how that end play effected handling imo

 

Bairs Corvette's rebuilt side yokes have been recommended.
I need to contact them to see what I'd be getting.

I have seen supposedly factory yokes on EBay, I could fit them then get them heat treated if Bairs doesn't work out.

 

which were the years the heat treating sucked and which years were the better ones?

 

I think I recall the yoke heat treating was good up until '76 or '77.
I had researched that a bit before removing this differential, I wasn't surprised to see the wear.

I don't know if there is any way of proving what year a yoke was manufactured, even if you find an old differential there is no way of knowing if the yokes are original to it.

 

Not sure your intended use ... I use mine in road racing so achieving minimal yoke end play is a key parameter for me. Just so you know, the part of Tom's video where he is rotating the posi over and over again is meant to knock off high spots in the new clutches and is critical. Don't skip that no matter how painful it is. If you do, you'll find that you have a lot more play than expected after some driving and get to do it over again (it's faster the second time). Don't ask me how I know .... This isn't as critical for a street car. Also, you can never get rid of all camber change at the wheel, there will always be a little bit if you achieve the recommended .005-.008" yoke end play. It gets tighter when it warms up.

 

i suggest reaching out to @GTR1999 as he MAY have a solution (buttons) or best advise.
I think that you would need to get assembled dial in and then measure what size button you need above the circlip if that is a viable route.
No way would i put in yokes and assure not hardened @leigh1322 also had some hardness testers in his kit... it would weigh on my mind and the end play continues. Also Gary's advice I valued.
as far as hardening years.. this is from my thread.. 72-79 risk. My ebay ones the seller said 70 (trust factor here) . and makes sense they were ok.. but it would weigh on me not knowing and a lot of work to change out again... BTW it took me a couple ebay returns as most have no clue about end wear..


edit.. a better summary below of @GTR1999 which tells me i am going in the clutches.
So what are the 3 areas that affect endplay? I am sure many out there now know but it comes down to this:

1- axle face wear. You can clearly see the difference in yours but what is the hardness of the better looking one? They have to be hardened and the 72- 79's were not. They will always ride up against the cross shaft in the posi and that is hardened.

2- Posi setup. These are spring loaded posi's, not a bad design but the spring load also compensates for mass production tolerances building these posi's. MOST of the time the posi is not dialed in as it should be, been a problem since 1965 when the first Eatons were used in a vette. It continues to today with the aftermarket units. Those have different clutches and spiders but the design is the same as it was in 1965. I have taken apart new out of the box posi's and once the springs were removed found up to 030" endplay in the side gears. Are they all like that? who knows they are production built unit, same as always. If you tune it like I mentioned above this will dramatically change the endplay in the axles so those rebuilt axles with face dimensions all over the place may actually work. There seems to be a misunderstanding on the clutches too. Most likely because few have actually taken them apart and just pass on information and that sometimes changes as it passes from one to another. The new carbon fiber clutches will in fact wear, you can rub the material off by hand without a lot of pressure. The original steels do not wear out like that, if you want to go cheap you could measure them and I would expect you to find them in the 068 range +/- 001". They have a diamond stamp pattern on them but they were never a sharp diamond like a deep cut knurl on tool handle would be. Will you see a shiny "ring" on them - yes but that shows up when I am seating new clutches and they are not worn out. Years ago I coined the term "snowflake" clutches, it caught on here and people refer to them all the time. They were an attempt in 1972 to stop the posi chatter common with a spring loaded production built posi. they did not work. All they did was make the posi weaker and those that abused the cars ended up breaking the clutches. Look on ebay and there are still people selling these "original" clutches, they are junk. They are also what you have in a 72-79. Bottom line the best posi's are ones that use solid steels, are fully polished, and tuned. Those will go a very long time and out perform a stock spring loaded posi every day of the week.

3- Posi case cross shaft hole. Not as common as the other 2 items but something to check are the bores. They should not have a step in them and should be round. Extreme cases of wear will allow the cross shaft to move once an axle hits it which is at any turn. If the bore wear is loose but not crazy it can be rebored and a 12 bolt cross shaft fit, you would also have to install 12 bolt spider pinion gears and thrust washers. You could also bush it to original size as well but if I am going to do that work I would use the 12 bolt setup. This is something you have to weigh against just replacing the posi case. Replacing a posi case is another story- that I am not going to type out today.

In addition to having lousy axles and clutches, the 72-79's had issues with the ring gear bolts backing out. Around 1977 GM saved a penny by going from a hardened shoulder bolt and lockwasher to a flanged head bolt. Again with a production built item some were good but many were not and the bolts backed out over time. No Loctite was ever used on them. While some of the shoulder bolts also backed out in the earlier cars it was common to see in 72-79's. I rarely have seen it in pre 72's and even less in pre 68's. Same with the axles used from 63 to 71 or so. I have taken apart 100's of them and most of the time, even with over 100k miles, the original axles are still good. In fact, when used with a correctly tuned posi I have to kiss cut them on a surface grinder. This is only a few thousands so they are still hardened and the end play is dialed in to 005-007" where it should be.

Now you know more about these and can make up your mind. You have the diff out, if you have the tools and experience you can slap it together, sub it out, or build it right. Some will tell you these are harder to build then other diff's of the period and that only tells me that person either doesn't know what they're talking about or worse they are just trying to get your money. The principal is the same, you need to set the backlash correctly on what your are working on - a 77 vette or 77 C10, Camaro, etc to have it last and run as quit as possible. If you cut corners in the build it will not last.

 

street here and i was blown away when pushed into turns how much of a difference in reaction there is.. it is almost like no sway bar to a sway bar.. mine were used snowflakes i did turn them but not as many times like the machine in video..

I think OP went with used clutches solid so i wonder how critical it is to turn if used..

 

I am picking up parts and tools from leigh1322 and have been in contact with Gary for advice.
I intend on doing the full tuning as shown in both of Tom's videos, including the 50 turns each direction once I get the clutch pack shimmed correctly.
I have all the time I need, and can work at whatever pace I want.

I know I don't want to do this again, on this car. If I have to do one on another car that's a different matter.

Intended use is some spirited street driving with a moderately built small block and a five speed.
I had intended on doing some burnouts but I think I'll pass on those, no need to cause more wear than necessary.

This is my first sports car, or performance car at all for that matter. I'm coming from pickups and Jeeps, so anything that handles like this will get used for moderately high speed cornering.

 

I have most of my parts and the posi is tuned and I'm starting the reassembly.

That crush sleeve is a mother. I thought my 1/2" IR impact would do it but it doesn't.
It's supposedly capable of 300 ft lbs. I've read that the sleeve may take 400-600.

I'm thinking of bolting the case to the work bench so I can get a longer cheater on a breaker bar.
I wonder if the studs securing the bench to the shop floor would let go. Or the bench legs may bend...

I don't want to buy a heavier impact. I like buying tools, I hate buying tools I already have.

on edit: However I don't have a cordless impact. Over dinner I remembered that I had talked myself out of buying one a couple years ago.
I have one now, it'll crush the sleeve. Tomorrow I'll get it to spec.

 

post 46
https://www.corvetteforum.com/forums...-advice-3.html

i have the dewalt impact ..no way would I use on that..but you may get lucky..couple jack handles for leverage..and a snack prior..

 

I completely forgot about my jack handles. I have a two foot piece of pipe for the breaker bar on the nut.
I was trying to brace the other breaker bar against the vice, which is when the case started to move on me.

I think the Dewalt impact will work, I took it up a bit tonight.

I still need to buy sealant to put on the splines after I install the new seal.

 

After installing and disassembling new bearings, are they still new?

I had installed the new pinion bearings, then had to drive the pinion back out.
I can get the sleeve crushed enough to get 6 in lbs, that's all the new 20V Dewalt impact will do, it's within spec for used bearings.

Currently I need to get the car out my shop, I'm going to "send it" and plan on being back into this differential again in the future if I need to be.

 

Yes, they are still "new."

 

I woke up yesterday and realized I wouldn't be happy with the job or myself if I didn't get the bearing preload set correctly.
I ordered more tools. A 40" 3/4" drive breaker bar and a 3/4" drive 1 1/8" socket.

Today I got the tools and I drilled holes in the work bench.
These were to secure the diff housing to it, the breaker bar holding the pinion was braced against the vice.

After a couple of good tugs the pinion holding tool bent. Well... insert your expletive of choice here.

I guess I'm building another pinion holding tool. The one I built for my Dana 70 rebuild won't fit this yoke.

 

Yeah that crush collar is a BEAR! Almost made me wish I used a grind to fit solid collar.
Pipe extensions worked for me. I used a big impact gun, for some of it, but just to get the looseness / rattle out. Then I went into "manual" mode.

And remember...... you have to SNEAK up on Gary's in-lb torque setting......You CANNOT go over it and then back up.
I went thru 2 crush collars to get that part correct.
Arghhhhh.....