I Have A Diff With Side Yoke Play For One Side At .045 And .065 For The Other Side. This Is Movement From Contact With The Diff Cross Shaft To Where The Snap Ring Makes Contact With The Face Of The Spider Gear That The Yoke Fits Through When You Pull On On The Yoke. What Is Considered To Be Within Specs And What Normally Causes This Much Play When It Is Not Caused By A Damaged Snap Ring Or Snap Ring End Of The Side Yokes. Both Side Yokes Appear To Be In Good Condtion With The Surfaces That Contact The Cross Shaft In Good Shape With The Original Radius At The End Of The Yoke Shafts Still Existing. I Have Seen New Ones That Look The Same And Several On The Forum That Appeared To Be Damaged, But Mine Appear Good. After Looking At The Yoke Diameter And Splindes I Determined That They Are The Same Diameter As The Trailing Arm Axel Shafts And Was Wondering If I Could Us A Milled Down Rear Bearing Spacer To Take Up This Space Between The Snap Ring And Face Of The Spider Gear To Eliminate This Movement. The Spider Gear Has A Raised Area That Appears To Be The Same Od And Id As The Rear Axel Spacer. This Is The Area On The Spider Gear Where The Snap Ring Makes Contact. I Would Like To Know What Is Causing The Problem And If My Fix Appears Would Work. Thanks!

 

It has been a couple years since I set mine up, but you are right that the amount of play you have is too much. The side yoke is one of the suspension links and this much slop will allow the wheel to move in and out. However, most Vettes on the road have at least the amount you are talking about.

I purchased a shim pack and shimmed the posi plates to take up this slop. I don't have the manual handy right now, and it should be confirmed before you set it up, but I recall he manual stating at least 50foot pounds or torque to turn one side against the other with the pinion secured on a new third member. At least 25-30 pounds on a decent used one. Check to see how much you have now, I'll wager it probably doesn't take much to turn one side against the other now. Once I had the shims packed, a real bear to reassemble, my differential measured at least 50 foot pounds to turn the posi against itself. I set it up, a multiple trial and error process, for .001 of an inch. You don't measure this with simple push and pull with your hand either. Think of the forces the car is putting on this when cornering hard on a rough road. I used a long bar bolted to the yoke and leveraged against the work bench/vise.

Something that saved me a great deal of time was not using the spring pack. Setting up the clutch's with only .001 really removes any need for the springs. I recall looking at some of the respected third member rebuilder's pictures of their heavy duty rear ends and noticed that they didn't use them either. I had no negative issues by not using them in mine. I would encourage you to check with other knowledgeable mechanics and confirm this.

Some of the yokes had very soft ends that quickly wore against the center shaft. As memory serves, I think this was a real problem around 1977. The supplier did not harden the ends as they were supposed to do. As a precaution, heating just the end cherry red with a torch. Then quenching the end in oil will harden the surface like it is supposed to be. The hotter the torch, the better to heat just the one area.

Hope this helps,

Chuck

 

I've got play in mine too, dont have a measuring device to get the specs for you, but the yokes are new and unworn, so my play is in the clutch packs. I'm gonna keep on driving it - already drained and cleaned it all out when I replaced the side yokes.

 

I had about .060 on both of mine. It was due to wear at the inside end of the yoke. Replaced them, now I'm under .010.
If they wear too much, they'll mushroom and be hard to get out.
Shimming the clutches can get this down even more.
Search for gtr1999, he's got a lot of good info on differentials.
Gary

 

If you're over .040 then the case hardening is probably gone and the yokes will wear quickly. I wouldn't try and shim them just get a good set of rebuilt ones with the hardened tips to solve the problem, Those are the ones I use on my jobs.

As Chuck mentioned setup the posi without the springs.If you correctly set them up with steel solid clutched and shims the end play will be under .010 MOST times. I find my jobs fall in about .002-.004" BUT you cannot tune a posi to set the endplay. You have to tune the posi to the application of the car not to what you want the endplay to be. Again most times it falls in line but I've had one carrier that I couldn't tune without the springs, I ended up replacing it with one I had here.

As Gary said if they wear down enough they will hit the housing and grind the face where the seal boss is.

 

I have become more knowledgable sense my post last night as I discovered that my 1973 factory truck overhaul manual has a section on rebuilding the corvette differential and corvette Eaton posi. I am however still unclear on a few things. Sound to me that some of the play might be taken up by putting in the correct amount of spacers behind the posi clutch plates and the outer case, The facory manual has spider gear backlash tooth clearance between the pinion spider gears and the side spider gear as the method of determing if the spacer amount is correst. I do have some of these spacers. The book has the spider gear lash set at .001-.008. This implies that if the backlash is correct that that would take up some of the room between the side gear and the yoke snap ring. Do these clutch packs get worn out to a point where you need to replace them? Can this be visually determened once there out of the case? Is there a minimal thickness of the pack. I still dont quite understand how you can eliminate the springs or exactly what their purpose is if they can be eliminated. I assumn the springs are designed to keep a constant presure on the side gears so that an equal presure is placed on the clutch pack, if this is correct will the minimal clearances suggested keep enough presure on the clutch pack so it will work. Does any centrifical forces come into play. Sound like new yokes maybe a nessesity, but I thought I would take it apart and examine the clutch packs conditions and see if there are any spacers in their before I order the yokes. As I mentioned in the first post, visually the yokes look ok based on all of the pictures I have seen on the forum of good and bad yoke ends. I actually have to diffs open on the bench, unfortunatly the second diff does not have side yokes, but it is interesting to note that one diff has springs in it that are a different diameter wire with less windings which are clearly stiffer when pryed on with a screw driver. Also what is the trick for getting the springs and plates out of the posi. There is a spacial tool listed in the factory manual, but I figure not everybody has this tool. Any suggestions? Sure appreciate the advise and input! Thanks!

 

The factory overhaul manuals cover both cars and trucks. A great resource - that's why I bought one.

 

The stock setup uses the springs and has since 63. You are correct that the backlash, unloaded, is .001-.008" This is similar to the rear bearing endplay spec too but if you set the endplay over .003" you'll have some issues to deal with. Keep in mind this units were not custom fit blueprinted units, they were meant for production cars to be driven daily. I've had low mileage posi's apart that had loose backlash with the 4 springs and it never hammered- never. It also was pretty poorly setup from day one. The constant force against the clutches will wear them faster and depending on the backlash set may hammer lightly or very hard. There were various springs used and were colored coded. I'm not use of the color codes, but I believe they were rated at 400 ft/lbs. I've seen blue,green, and yellow springs. The special tool I use is a screwdriver to reach in to the ID and lever it out. I store them in the trash can for the most part. If you plan on rebuilding yours with springs I would get new ones.
The clutch type has also changed over time. The 63-63 used a Dana unit with flats on the ends and are no longer available. The 65-70 used solid steel clutches and were a good setup, unfortunately the spiders were not too good and were the 10-18 type. In 71 they went to 10-17 spiders which are the ones you want and slot type clutches that I call "snowflakes" because that's what they look like to me. They are junk. They were meant to solve the hammer problem by getting more oil and additive in between the clutches but all they did was make them weak and break. I wouldn't use them with or without springs, they do make nice flying disc's though. You can use the new fiber clutches but they're junk too.
When I did my first posi tune I wasn't convinced it was better then the spring setup. I fully understood both principles but I could easily twist one yoke against the other by hand. With the stock setup you can not easily do that. I did compare the backlash with my final springless setting to the factory shim procedure and it was only about .002". I don't reference a backlashnumber though as each setup is different. I've used .025-.045" shims per side in them. You have to develope the "feel" for the setup you want. I set the solid clutches for a st car to slightly notchy feel. For a HP car where cornering isn't a concern they can be tighter. The proper street setup will lock up yet slip enough in a turn not to hammer.

I hope this helps you out. If you search my name gtr1999 you should find more pictures that I posted on this subject.

Good luck,
Gary