After noting excessive axle endplay during my rear suspension tear down I decided to investigate further (thankfully). After hours of reading posts by @GTR1999 and those who have had the good fortune of his assistance I've developed the confidence to handle this myself having never torn into a diff previously.

Tear down and general observations:

1. The metal collar around the pinion is loose and freely rotates. Is this normal?
2. Passenger stub axle endplay .051
3. Passenger axle tip to c-clip .153
4. Driver stub axle endplay .032
5. Driver axle tip to c-clip .167
6. Gouges in the posi case! (catches a nail pretty good...salvageable assuming no other cracks?)
7. All teeth look great. All bolts still properly torqued.


A couple initial questions I'd love some assistance with:

1. Where to source quality, heat treated axles or would I be better off machining these for a 'button'? (bummer to see 1970 axles so worn...)
2. Does replacing my 10 18 spider gears necessitate new side gears? (I have to assume so but haven't come across that yet)
3. Part number for proper length ARP ring gear bolts (posts I've seen indicate they are too long)?


Plans for the build:

1. Polish posi case
2. Replace/repair stub axles
3. ARP ring gear bolts
4. Replace pinion seal
5. Replace side bearings
6. Replace side seals
7. Tune posi
8. Add drain plug
9. Grade 8 socket head cap screws


Important target measurements:

Axle endplay: .005-.007
Axle tip to c-clip: .185+
Ring and pinion lash:
Axle to cross pin:
Pinion rotational force:
Side gear backlash:
Axle face Rc: 50
Posi clutch plates (each):
RG bolt TQ:
Cap bolt TQ:
Cover bolt TQ:


Have to pull the clutches today and see what I've got. Any feedback so far?

 

What kind of milage do you think is on this rear end = just curious due to the wear

 

I have zero ideas on the mileage honestly. Car is a non original motor and in great shape from a rust perspective but certainly shows it age. Well north of 100k I'm sure.

 

That is a 69-71 posi case. The grooves I see in the first picture are machining marks not impact marks. I can't tell clearly if there are impact marks by the tear-drop window, but usually they are around the whole case. That is from someone changing out the pinion seal or rebuilding the diff and not getting the pinion set up correctly.

Your axles appear to be worn too far to reuse with a tuned posi. I would wait and see once the posi is done. I don't refer parts vendors and for good reason. With that said your options are new (imported), rebuilt (only done by 2 places), machine them if you have the machinery and install your own tips, (possibly better than the previous options), check and reuse them if in spec with a correctly tuned posi, in which case they have to be thru hardened and tempered. The new axles I inspected the past few years are hardened but the snap ring groove is inconsistent and the ring too thin. They are Chinese made. The rebuilt axles I have seen, in hand, are also widely inconsistent. If you get a good set, they're fine but QC is not being checked by some of these places. You may find it takes several returns to get what you need, and all the shipping is on you. Some out there core the axles, they work great rolling a car on and off a trailer. Bring it to a track night and launch it, you may find it became a 2-piece axle. I have changed what I use and have better results- what that is I am not disclosing.

Tuning a posi is more involved than leaving out the spring pack. Do it right and it will work better than the spring pack setup, do it wrong and you will have an open diff. I did 2 Posi's this week and both were original Eaton/GM. The machine work on them originally is not as good as the new Chinese Eaton cases. One of them was out 015" from one side to the other. Using a stock shim set will not give you the best results most times. Watch Tom's video, he has shims ground in 0025" increments, I own a corvette machine shop and grind them to 001" at times to get what I want. You can get a lot of info from the video and here, but the end result is often governed by experience doing this work. That is ole hands on for 100's of cases, and I still get oddball jobs that come in.

Polishing a posi is also involved depending on how you do it. No one does them like I do, that takes about 4 hours. Those few rebuilders who say they do the same level - do not. The pictures of their work tells the story if you know how to read it. Some guys have done very nice work at home, better than what they would get with an exchange. Anything you do will be better than what you will get from most rebuilders, as most are in competition and prices posted are not accurate- yet most don't get it. No one can tell you honestly what the cost of a diff or TA rebuild is unless they inspect it or just spec and quote all new parts. For some that works, I guess.

Spiders are replaced as a set typically. If you are not racing and the 18's are not damaged, you can reuse them. I just tuned a 66 posi and reused the 18's. They dialed in perfect, and I have over 800 rev's on them.

Check the case for cracks before you spend any money.

Get good parts, for example I don't buy from any vendor. I source my parts from various locations both wholesale and retail, again I don't list my resources anymore. Some kits I see that guys ship to me are ok, some are cheap. Look for differences in the parts- ring gear bolts, seals, axle bearings are all parts often replaced with cheaper ones. I can always tell how well a diff was previously worked on by the parts used and the typical mess made assembling them. These are diff's that failed, that is the only reason I see them. Some may be from flipped cars or owners too cheap to pay for quality work and think all are the same level and price is the only difference. However, it cost more doing it 2 or 3 times.

So, good luck to you. I may stop back and see your progress, but I am usually working in my shop.

 

SKF seals, Timken and Koyo bearings and a Ratech solid spacer have been ordered.

Still need to run down appropriate shims, quality axles and now a carrier....found the dreaded crack today.

Solid steel clutch plates look to be in good shape at least and the real bonus was having my helper in the garage this afternoon.

 

Unfortunately, that posi case is toast.

 

And now the 'fun' begins!

 

Measured the clutch plates today:

Passenger: .068, .065, .066, .066, .065, .066, .067, .066, .066, .031 shim, .018 shim

Driver: .065, .066, .067, .067, .068, .066, .068, .067, .067, .025 shim, .015 shim

I guess I'm down clutch plates as well in this build...