1985 442 8.5" posi casing shimming question

[84hurstolds]

I'm not an experienced rear end builder, that's why I'm here. I plan on a rear-end restoration during the overhaul of my car hopefully if things go right in a few months. Researching what I'm going to need to do for shimming the case and I have a question about it.

If I'm reading the service manual correctly, it basically says get the ring gear where you want it, then for final preload you basically remove a shim from the left side, push in a .004" fatter shim then remove a shim from the right side and then tap in a .004" fatter shim, recheck backlash and if good, call it a day.

I'm thinking wouldn't it be more prudent to use the torque wrench and check total running torque? You get around 25 for the new bearings in the pinion, and then what, another 25 (calculated) using the gear ratio as a multiplier? Meaning you should probably see 32 inch pounds roughly for all new bearings on a 3.73? Or it this incorrect?

[monzaz]

Sounds like you are working too hard at this...
Follow the manual, as they have 90 years + of experience.
I have been doing this so long I do not even think about it any more. It is all by feel on the carrier preload. Once you have done 1000s of installs...you just get it.
We try to give a back yard shade tree mechanic a rule of thumb of carrier preload to having to pry out the carrier with a J bar ...if you can pull the carrier out with you grabbing the ring and pulling it out and it is removed it is not tight enough. IF you are destroying the shims when installing them...denting and bending them from a brass driver then you are too tight. I know this sounds Soooo extremely caveman like.... but it does keep you safe. You have to know what a proper preload feels like instead of shrugging your shoulders and going...'THAT IS WHAT THE MANUAL SAYS'... If you know what I mean.
Plenty of grey areas in a rear build and that is why many fear these builds.
will play with preloads as to the kind of driving a customer will be doing...drag racing, circle track, one mile blasts, off road, street etc.

So Yes your info can be correct BUT I always go by feel and if that preload seems too tight will not use the info.
Adding .004 to each side to what you think is zero preload could be a recipe for disaster...That is why apprentice ship is such a great lost way of teaching someone.
Books are great BUT if you can not apply it properly ...your in trouble.

So - you can try the manual way and see what you get. I can tell you the pattern is total key to making the rear last and then the preload of the pinion and carrier ...Backlash for the street will be in the .006-.008 (used .009 -.010 is acceptable) 5 cut gear. Lock tight those ring gear bolts (65 ft lbs) and light oil on the main cap bolt 60ft lbs.
Creep up on the crush sleeve so you do not go past your correct pinion preload. (again another area we just do by feel after so many rears. 15-20 inch pounds for new bearings (rated with out a carrier in the case) about 10 inch pounds for reused bearings.

Rear end building is just more than numbers it is a feel. ... Making them last really has a lot to do with who is building it.
All in all I know this is not exactly what you wanted to hear... But I think it will help you on the feel of a proper preload of the carrier. As long as you have the pinion preload correct of coarse.

Jim
JD Race

[84hurstolds]

That's good info to know. Hopefully I'll not get to do this 1000 times to get that feel. But I do understand what you mean about feel. I don't fear the rear gears. I just think that jamming .008" more for preload and calling it done is a bit too general. Just seems like there'd be a better spec.

[monzaz]

YEp, In a perfect factory assembly line that all works...BUT if you have a rear that is 50+ years old your dealing with a lot for stuff. Jim