As for the rear end posi job you're about to undertake, IIRC you're using an 85 442 posi rear?
*cross shaft pinon backlash in the posi unit should be .001"-.006". Anything over .006" will need shimming of the side gears.
*Not sure if you're doing the pinion too, but new pinion bearings for bearing preload per the 1985 CSM is 20-25 inch-pounds. (used bearings is 10-15). Many places will tell you 14-19 inch-pounds for new bearings. Ring gear backlash is .005" - .009" for new gear set per CSM (it doesn't mention any used gears), although again, other places will tell you that .006"- .010" for any set is fine. You decide.
*Side bearing pre-load, from the CSM, says once you get pinion depth and backlash set right as per dial indicator and good pattern, remove gear side shim, then replace with a shim that's .004" thicker. Then do the same on the passenger side and tap it in for a total of .008" extra shimming for preload. Check backlash again and if it's out, get it right, and then button it up and call it a day.
*Plus, here's a spring tip... when banging out the "S" spring on the bench, place a couple of shop towels or equivalent over the carrier so when it does pop out, it doesn't fly out across the shop and hit something or someone you don't want it to hit.
I don't want to overtake the conversation/thread - if Donovan has any questions, then I'm sure he'll ask.
Don’t sweat it Jim, you guys weren’t overtaking the thread. I encourage any and all information and suggestions when they’re on point to whatever is being done. All good sir.
And Mike, thanks very much for all the info you provided above, it was very helpful and directly pertained to what we did today.
The Skunkworks is certainly worthy of the first part of its namesake today, it stinks like 90 weight gear oil. So you KNOW some good shjt went down today.Mike came over this morning, and in just over an hour we had the rearend completely out of the car. This was planned for all along as it was going to make the work that much easier, plus there would’ve been no way to completely remove the axles where the car sits.
In tearing into the original diff, we found almost everything to be in rather exceptional shape. Even the crosspin bolt came out without a fight. The only damage I could find was the crosspin itself had some odd wear on it on the one end, but that was it. The gears were all in excellent shape (even the side and spider gears), and it all came apart beautifully.
That is, until we got to removing the ring gear bolts. For whatever reason, we had a total collective brain fart and snapped two of the ring gear bolts and jacked up the threads on a third before we realized the bolts were LEFT HAND THREAD!!!
What a bunch of dummies.
We had even looked through the 4” thick 1980 Oldsmobile FSM I have and didn’t see anything about it until afterwards. (Of course)
Thankfully, the bolts had broken because the heads were bottoming out before the threads were pulling, so once we (easily) got the other 7 out, the broken remnants just threaded out by hand.
From there on everything else went smoothly again. Got the ring gear cleanly off and back on the new carrier, and seated it into place with the remaining 7 good bolts. When we dropped it back into the housing, we did the math and used the new shims I bought to get the carrier installed within the FSM spec. The FSM called for 8 thou of preload IIRC, and I think we ended up with 9 due to the thickness of the shims we had. Backlash is at around 4-5 thou, so it might be just a touch on the tight side, but again, still within spec according to the FSM. I don’t think an extra thou here or there is gonna make or break it.
Once we had the carrier reinstalled and the bearing caps torqued back down, we turned our attention to removing the drum brake assemblies from the axle flanges. Driver’s side came apart ok, but getting that big Stover nut off the brake spring kingpin was a pretty good workout. Passenger side fought us equally as hard, but here the two smaller M7 x 15mm x 1.0 bolts snapped off flush in the flange due to rust. After Mike left, I spent a few minutes drilling out the broken bolts and re-threading the holes, so they’re good to go now.
So today (it’s now after midnight here), I’ll have to track down at least 3 new ring gear bolts, (but probably have to buy a complete set) and two new backing plate bolts locally.
I still have to finish removing the old axle seals and bearings and install the new ones, reinstall the axles with new “C” clips, clean up and install the new diff cover, then clean and paint the housing. It should be a busy week of nights in the shop, but in a good way.
That’s all for now gents, I’m off to bed before I fall over. Back to work tomorrow.
D.
