How old is the posi or miles

 

isnt this a continuation of your other thread where it was advised by Willcox to change fluid and use Posi additive?
https://www.corvetteforum.com/forums...-may-help.html

 

 

I don't think that gear oil varnishes up the clutches. What I have seen when I open up differentials is black fine metal flake contaminated oil.


You have posi clutch material mixed with metal from our yoke ends waring away. It is a poor design putting weight on the yokes.


I just removed a diff from a 77 and the diff from my 79. The 77 had more than .040 ware on the end of the yokes. So they are trash. The gear oil was black with fine metal dust. I tapped the 77 for a drain plug, so I can change it periodically. My 79 diff had been rebuilt with new 3.55 gears and custom hardend yokes a couple of years ago. The oil looked pretty good.



I've had popping and snapping sounding posi units upon rebuilding. Because they are assembled tighter with extra frictions and steels. But and extra tube of posi lube quiets them down. This last 4.11 rear I put in I used Lucas gear oil with lube in it. It wasn't enough lube so it got a tube full from NAPA auto parts and cured it.

I am not an expert rear end guy like some of these guys here that do it for a living. I'm more of race motor hacker

 

 

I just tore down an original 75 diff today. It was out of the car, untouched since 1975. Here is what I found and why I recommend you remove yours for a good inspection since it too is virgin 1975 with 80k miles?

1- Posi case is cracked- junk now
2- All the ring gear bolts were loose, time bomb
3- Clutches were the junk snowflakes but not broken- stuck like glue
4- Axles worn out- but didn't hit the housing yet
5 Metal chips inside

This diff would not have lasted much longer in use, too bad the posi is now junk. I can rebuild it but the cost of all new internals makes it a wash for a 73-79 diff. There are plenty of cores out there and some think they have gold with them but they are still only cores needed work.

Now if your budget is tight, you can do a "roadside" repair that might get you some miles. Remove the diff, mount it on a stand if you have one or can borrow one, pull the cover, drain the oil, spray the posi with brake cleaner and lightly blow it off, if cracked you will see it stay wet. This one looked ok until I cleaned off the baked on gear oil as you can see.

If yours is ok and you want to save a lot of money, break it down, measure the axles, clean the parts, keep the shims marked for the correct sides, leave the pinion bearing in place with that shim, and wash everything. Personally going this far I would at least replace the bearings, the seals will have to be anyway, and I would break down the posi to check the clutches. I never use those snowflake type and yes I know vendors still sell them. If really tight for cash, wash each clutch and mic it, should be 068 +/- 001" you can reuse them if you like, as long as they are not broken. Again I would never do that but it's an option. This will cost you a master kit, approx. $140, axles $200-220, and some Loctite for the RG bolts.

Doing an oil change may solve the clutch chatter but if you did that already - who knows. Oil won't correct the other issues like I mentioned above, if those continue on the diff is going to lock up and break parts.

 

 

Gary is it a common thing for the ring bolts to come loose? they were loose on that 77 diff I rebuilt. I thought that maybe it had been worked on in the recent past.

This is how ARP said to do their bolts.

The tremendous shock loads generated at launch by most any drag racing vehicle equipped with today’s sticky tire compounds or the acceleration and deceleration of oval track cars put considerable strain on the ring gear. For this reason, the fastener experts at ARP Pro Series ring gear bolts are forged from premium grade 8740 chrome moly steel and are heat-treated to a nominal rating of 200,000 psi tensile strength. Specially hardened, precision-ground washers are included where required. TECH NOTE - It is critically important to properly tighten ring gear bolts and make sure they don’t loosen. This is especially important in drag cars with tire shake. It’s also a good idea to check bolt tightness on a routine basis. If you use a locking compound (like Loc-Tite), it is best to install the ring gear first without any compound, then remove the bolts one at a time, reinstalling them with the compound. Be sure and torque each bolt before going on to the next one, because the locking compound sets up fast. Install and torque the bolts in an alternating or crossing pattern to distribute the load evenly around the ring gear.

 

George,
GM used hardened shoulder bolts and lockwashers, without any type of locking compound, from 63 to 77. I found loose bolts on original diffs from 63-79. Most though are from the 77-79's when GM went to flanged head bolts, no lockwasher and they backed out a lot more. When ever I look at a used diff housing and see a groove cut into the LH side of the housing and/or the webs on the posi case I know it sheared bolts that backed out. Sometimes the posi case is still good other times it is wrecked.

The ARP method is the correct way to install RG bolts, I did one today in fact.

Now a little test for you- does anything look different in this picture?

 

After surfacing did it need the spacer installed? You see it in the hole. These are those bolts. 230-3001

 

Without hijacking this thread, yes those are the ARP RG bolt. The difference in this one compared to a stock one- you're very close- the case bores are bored larger to accept Tom's 30 spline KA Axles. You can also see the 30 spline clutch inside.

 

Are those bolts so high that you have to TQ them to 60 and then grind the edge for case clearance. Yes I was looking down the hole and forgot about 30 spline. I have never had a problem with those Mid America 20 year old custom hardened 17 spline. No idea who manufactured them.

 

 

I had to grind some years ago on an oddball diff, but not since. You would know once installed if they were going to hit. You do have to countersink the flange holes to clear the under head radius. Those might have been Tom's hardened 10-17 x 17 spline spiders.