Greengear

Plasticfreak

You really should get someone to look at your car....................

Gordonm

The posi case and the open case are 2 different cases. You cannot just simply remove the posi clutches and make it an open diff. Why not just repair the posi if that is the problem.

MelWff

"Im having issues where the posi grabs after exiting the freeway while in low speed turns."

Are you sure the problem is the posi, the posi only kicks in under load, are you accelerating while going through these low speed turns?
Exactly what is happening that you think the posi is the issue?

Dynra Rockets

You'll have to remove the rear and/or crack open the housing either way. Might as well just fix it right.

Silver spurs

I have posi and non pozi complete differentials if needed

Greengear

GTR1999

Posi chatter, very common and shows up typically when the oil is hot and you stop then turn. Getting another diff could be the same,since it all depends on how the posi is setup. If you completely changed the oil out , used 2 bottles of GM additive and a quality gear oil, and still have the problem then you have to correctly setup the posi. There is no reason a correctly setup posi won't last you a very long time. I have diff's with over 100k miles on them and no posi chattering. I change out the oil every 8-10k miles, use non synthetic oil and only GM additive. Posi locks up straight, no binding fully tuned. If you do your homework you can take the diff apart, polish and tune it and it will be fine.

Who ever told you the additive spins out of the clutches is clueless on how these work. The additive is mixed in with the oil, the posi is always in the oil- unless it leaks out and the bearings burn up. Using the wrong type oil without the additive will cause it to knock and chatter all the time. I recall about 35-40 years ago buying a well known oil that had the additive in it, I tried it and within 300 miles it was chattering all over town. I added 1 bottle of the GM additive, the good old stuff, and that resolved it. Today use 2 bottles.

The posi spiders have ribs to hold the clutches, an open diff does not and only has a thin shim behind the side gears. If you remove the clutches, plates, and springs you can make a open diff but why? Fix it right and it will be done. Go on Youtube and look up Tom's posi tuning. Follow it to the letter, don't cut corners, and it will work better then any stock posi with springs.

HeadsU.P.

The figure 8 thing is old school for conventional rear axles with hollow tubes. The idea was to slosh the newly added lube from one end of the axle tube to the other so it was thoroughly mixed. And on some models that was quite a distance between axle bearings
Now lets look at a Vette rear axle, (or WHAT rear axle?) How far is the fluid going to mix / slosh around doing figure 8s? A half inch to the left. Then a half inch to the right? There's no room in there. Its tighter than a can of sardines. But some people insist on doing the figure 8s. Old ways are hard to break. The mixing of lubes are done before you pull out of your driveway, because there is so much turbulence in there. And that was shown in a video this past summer.

stingr69

Figure 8's are to rotate the posi clutch disks in the steels. Figure 8's rotate the clutch packs in alternating directions. Distributes the additive mixed lube between the plates so it can work.

HeadsU.P.

I understand, but that's pretty much what backing out of the driveway does too.

Greg

oh well.

Greengear

Greengear

Greengear

Greengear

7t9l82

I wouldn't for a variety of reasons. I'd just fix it right or buy a good used unit from someone.

68notray

Absolutely not. Do it right do it once.

BUT make sure to have it all set back up in proper spec (not that hard). See the "good" stub axle side? Look how much gap behind the snap ring clip - that is way too much. Leads me to suspect badly worn posi clutch plates to get that much room.

GTR1999

Ok so you have it out, good. From what I see you have an original 77 diff with the very common issue of worn axle faces. This is how they all were from 1972-1979 it created a market for rebuilt axles that make people a lot of money and provided a good replacement part. The issue the past few years has been QC or lack of it. Whether new or rebuilt I have seen issues with these that should never have been sent out but also at the same time some come in that are pretty good, so you have to check them when you get them and if no good return them. I agree you shouldn't have to do this but that's the way it's been for awhile.

Sounds like you are capable of doing the work and possibly have access to a machine shop? I know guys have built up axle faces with hardened rod and fit them, others have faced and bored the axle face and bored them to press in a hardened tip- that is exactly what a rebuilt axle is. To save money these are options, most guys won't have that option though. I have a machine shop and I still use rebuilt or the best new axles because it saves me time. Your time is worth something so you would have to decide on that.

If you just want to get the diff back in the car and go you get a better axle in it and go. I certainly would not do that but it's your call. What many here just don't know and I have typed out countless times is axle endplay is dependent on 3 things. Just replacing the axle will not typically count the endplay down to where they should be. For instance, many of these diff's are out there with 030-040-050" etc endplay in them. You swap out the axles and you're at 025-030" let's say and off you go. That is still more endplay then I like to see but for an otherwise good diff it will work.

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.

Good luck, with this said I am signing off of this thread. I will watch to see how you make out but I am done typing out long explanations. I am off to build a 68 435 diff and using the original axles!

DUB

Worn clutch plates is NOT what is causing the snap ring groove to be where it is at in that photo. It is because the end of the side yoke wore down and he is pushing in on the side yoke to make it contact the pinion shaft.. I see this ALL the time on side yokes that have worn down that badly..

Not saying that the clutches are also worn out but ...but bad clutches is not what is happening in that photo.

I guess how you feel you can repair the side yoke and not spend money on them is all up to you. I have no clue on what your capabilities are and if you have the equipment to do it correctly and harden the end correctly to the correct Rockwell hardness due to there are companies that DO IT. So if you feel you have it all figured out....have at it. You have only yourself to either pat on the back if you get it right or blame if it grenades. I would get a new pinion shaft due to I would guess it is worn and NOT smooth and would begin to eat up your repaired side yoke ends.......unless you feel you can repair that one versus buying a new one from GM.

DUB